aldabra: monitoring the path to recovery

ALDABRA: MONITORING THE PATH TO RECOVERY Ben Stobart, Raymond Buckley, Larry LeClair, Kristian Teleki, Nigel Downing , David Souter and Martin Callow

Cover photo courtesy of Camerapix, Nairobi

ALDABRA: MONITORING THE PATH TO RECOVERY Phase II February 2001

Ben Stobart1, Raymond Buckley 1,2, 3, Larry LeClair 3, Kristian Teleki 1, Nigel Downing 1, David Souter4 and Martin Callow5

1 Cambridge Coastal Research Unit, Department of Geography University of Cambridge, Cambridge, CB2 3EN United Kingdom Email: [email protected], www.aldabra.org 2

University of Washington, College of Ocean and Fishery Sciences Fishery Science Building, Box 355020, Seattle WA 98195-5020 USA Email: [email protected] 3

Washington State Department of Fish and Wildlife, Fish Program Science Division, 600 Capitol Way N., Olympia, Washington 98501-1091 USA Email: [email protected], [email protected] 4

CORDIO, Department of Biology and Environmental Science, University of Kalmar, SE-391 82, Kalmar, Sweden Email: [email protected] 5

Shoals of Capricorn Programme, PO Box 1240, Victoria, Mahé, Seychelles, Email: [email protected]

Table of Contents Introduction Aldabra Atoll: A Natural Science Laboratory The 1998 El Niño Event in the Seychelles Results of the 1998 Southern Seychelles Atoll Research Programme The Aldabra Marine Programme The 1999 Aldabra Marine Programme Phase I The 2001 Aldabra Marine Programme Phase II

Methodology Coral and Fish Transects Coral Recruitment and Tagging Temperature Data Loggers

Results Re-location of the 1999 AMP Expedition sites New Survey Sites Established by the 2001 Descriptions of Permanent AMP Survey Sites Coral Transects and Benthic Habitats Coral Recruitment and Tagging Fish Transects Temperature Data Loggers

Discussion Coral Community Fish Community Temperature The Aldabra Marine Programme: Short Term and Long Term

1 1 4 6 6 7 9

11 11 13 15

17 17 17 17 24 31 35 54

59 59 60 61 61

Acknowledgements

63

References

65

List of Figures 1. 2. 3. 4.

5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16.

17.

18.

19. 20. 21. 22. 23. 24. 25. 26. 27.

Location of Aldabra Atoll, Seychelles in the Western Indian Ocean. Aldabra Atoll. Monthly sea surface temperature (SST) anomalies (i.e. when mean temperatures are above or below the long term mean) for Aldabra Atoll using 1961-1990 baseline. Note the 1997 anomaly (Teleki et al. 1999). Monthly mean maximum sea surface temperatures for Aldabra Atoll from September 1997 to July 1998, in comparison to the average monthly mean maximum sea surface temperatures for the period September to July 1961-1996 (Teleki et al. 1999). Diagram of transect layout. Aldabra Atoll with the 11 permanent Aldabra Marine Programme monitoring sites for coral and reef fish studies on the outer reef and within the lagoon. Site 1 reef profile with corresponding coral species composition. Site 2 reef profile with corresponding coral species composition. Site 3 reef profile with corresponding coral species composition. Site 4 reef profile with corresponding coral species composition. Site 5 reef profile with corresponding coral species composition. Site 6 reef profile with corresponding coral species composition. Site 7 reef profile with corresponding coral species composition. Site 8 reef profile with corresponding coral species composition. Site 10 channel profile with corresponding coral species composition. General substrate cover for outer reef shallow and deep transect sites (numbers in boxes) around Aldabra in November 1999. Shoreward coral graph = 10m depth, offshore = 20m. Coral branch length and numbers indicate percent cover of category. Colours represent: Sand, rock, rubble; Algae; Live coral; Dead coral. General substrate cover for outer reef shallow and deep transect sites (numbers in boxes) around Aldabra in February 2001. Shoreward coral graph = 10m depth, offshore = 20m. Coral branch length and numbers indicate percent cover of category. Colours represent: Sand, rock, rubble; Algae; Live coral; Dead coral. General substrate cover for lagoon transect sites (numbers in boxes) at Aldabra in February 2001. Coral branch length and numbers indicate percent cover of category. Colours represent: Sand, rock, rubble; Algae; Live coral; Dead coral. Size frequencies of three genera of coral recruits at Aldabra Atoll in February 2001. Percent of juvenile coral families in shallow (6m, n = 1409), intermediate (10m, n = 1579) and deep (20m, n = 819) water at Aldabra Atoll in February 2001. Percent of juvenile coral families at Aldabra Atoll outer reef sites (pooled depths, n = 3715) and lagoon sites (n = 881) in February 2001. The pattern of fish species distribution around the outer reef of the atoll in February 2001. The pattern of fish species distribution around the outer reef of the atoll in November 1999. Encrustation on a temperature logger deployed in this survey. Temperatures recorded at 30 minute intervals at Aldabra Marine Programme survey Site 1 at 10 m depth, from 18 February to 8 July 2001. Temperatures recorded at 30 minute intervals at Aldabra Marine Programme temperature monitoring site Passe Dubois at 3 m depth, from 19 February to 19 June 2001. Temperatures recorded at 30 minute intervals at Aldabra Marine Programme temperature monitoring site North Ile Esprit at 3 m depth, from 11 April to 10 July 2001.

List of Tables 1. 2.

3. 4. 5.

List of coral genera and species recorded at Aldabra during the November 1999 and February 2001 AMP surveys. Average numbers of recruits /m2 for three depths at sites around Aldabra Atoll. Note that at Site 7 the recruit estimate labelled 10 m was made at 15 m. s.e. mean = standard error of the mean, s = standard deviation, max nº = maximum number of recruits per quadrat and n = total number of recruits. Species of fish counted in the transects and sighted off the transects during the Aldabra Marine Programme surveys in February 2001 and November 1999. Number of fish counted, by transect depths and fish size groups, during the Aldabra Marine Programme surveys in February 2001. Temperatures (ºC) recorded, by monthly period, at Aldabra Atoll by the Optic StowAway temperature loggers deployed during the February 2001 AMP expedition (SD = standard deviation, n = number of 30 minute interval recordings). A. Site 1 at 10m depth, 18 February to 8 July; B. Passe Dubois at 3 m depth, 19 February to 20 June; and C. Île Esprit at 3 m depth 11 April – 10 June 2001.

Introduction Aldabra Atoll: A Natural Science Laboratory Aldabra Atoll (9°24' S, 46°20' E), Southern Seychelles Islands Group, is one of the world’s largest raised coral atolls (34 km long, maximum 14.5 km wide, area 155 km2). It is located 1150 km southwest of the capital of the Republic of Seychelles, Mahé, and 420 km north of Madagascar (Figures 1 and 2). Late Quaternary raised reef limestones, averaging two km in width and up to 8 m above sea level, rim a shallow, central lagoon (190 km2). The lagoon is on average 2 - 3 m deep at low tide. The coastline consists mainly of deeply undercut limestone cliffs and a broad intertidal reef flat (200 – 500 m). The lagoon is linked to the ocean by two major and one smaller channel and by several smaller reef passages (Stoddart 1984). Aldabra has monthly mean maximum (December) and minimum (August) air temperatures of 31°C and 22°C respectively (Stoddart and Mole 1977). The climate is semiarid, with an annual rainfall of 1100 mm (Stoddart 1983; Viles et al. 2000). Northwest monsoon winds from November to March bring the heaviest rainfall, with SE trades blowing throughout the remainder of the year. The tidal range is 2 - 3 m and results in large-scale hydrodynamic exchanges between the lagoon and the ocean through the channels. The main channel alone drains approximately 60% of the lagoon (Stoddart 1971). Aldabra Atoll has been characterised as “one of the wonders of the world” and “one of the world’s greatest surviving natural treasures” (Attenborough 1995). The isolation of Aldabra in a remote area of the Indian Ocean has helped preserve this large atoll in a relatively natural state. Although increasing levels of stress from human activities are contributing to the decline of the world’s coral reefs (Bryant et al. 1998; Hodgson 1999; Wilkinson 2000) the marine environment of Aldabra with its coastal reefs and expansive lagoon has remained untainted. Aldabra is surrounded by a region which has a number of coral reef systems at high risk from activities ranging from coastal development and destructive fishing practices, to the overexploitation of resources, marine pollution, and runoff from inland deforestation and farming (Bryant et al. 1998). Aldabra is an ideal natural laboratory for studying tropical marine ecosystems and related environments (i.e. seagrass and mangroves).

1

Figure 1. Location of Aldabra Atoll, Seychelles in the Western Indian Ocean.

Lagoon

Figure 2. Aldabra Atoll.

2

UNESCO World Heritage Site In the 1960’s Aldabra Atoll was under the threat of military development. Through the efforts of concerned scientists and the Royal Society this threat was staved off. Instead a unique and intensive research campaign was initiated to fully study this exceptional environment. Aldabra was eventually handed over to the Seychelles Island Foundation (SIF), established in 1979, for the management and protection of Aldabra in perpetuity to protect the atoll’s significance and importance to natural science. Aldabra Atoll was designated a UNESCO World Heritage Site in 1982 as further recognition of the atoll’s environmental importance. A recent global study by Conservation International has included Aldabra in one of the areas identified as a marine biodiversity hotspot (Roberts, et al., in press). High endemism and species richness are used to identify priority sites for marine conservation worldwide. The Conservation International study demonstrates the present critical importance of the marine environments of Aldabra for ecological studies that have global significance. Marine Research Studies of the marine environment of Aldabra have been conducted since the late 1800s, but the majority of the work on the atoll has been in the terrestrial environment. The paucity of marine research on Aldabra, and the dramatic decline of dedicated study in the last three decades, can largely be attributed to the logistical and financial constraints of undertaking a comprehensive marine monitoring programme at this remote location. To date, 23% of all published scientific works at Aldabra concern the marine environment (studies of corals and reef fishes amounting to 11%), and of these 5% have been published in the last decade (Teleki et al. 2000; Stoddart 1997). The majority of marine related research on Aldabra since the benchmark work of Barnes et al. (1971) has been a series of individual and unrelated studies, with the exception of the on going monitoring of turtle populations (i.e. Mortimer 1988; 1997). Coral Studies Barnes et al. (1971) and Drew (1977) conducted the first coral reef studies of Aldabra Atoll. The western reefs are characterised by a reef flat 460 m wide, a reef ridge margin and reef front slopes of 20 to 45°. The northern reefs support a narrower reef flat and reef front slopes of 30 to 45°, whose margin at approximately 25 m depth is characterised by massive, often vertically-sided, ‘reef bastions’ separated by sand-filled and rubble-filled channels. The east and southeast coasts are the most severely exposed and have neither a reef flat nor a reef ridge. No hermatypic corals are present. On the southern, less exposed shore the reef flat is present but is not delimited by a prominent ridge. The reef front itself is characterised by large areas of dead coral which vary greatly in extent. On the basis of a photo-transect (Drew 1977), western coasts are typified by branching and columnar corals at 0 – 6 m depth, followed by a dominance of soft corals (6 – 14 m), massive corals, particularly favids, and Halimeda (14 – 28 m), and finally encrusting corals and gorgonians (28 – 42 m). On the more exposed coasts, these zones are translated downwards, with branching and columnar corals reaching 20 m depth and massive corals in over 30 m. (Barnes et al. 1971). Fish Studies There is a long history of Aldabra reef fish studies extending back over 100 years (e.g. Jatzow and Lenz 1899; Regan 1912; Arnoult et al. 1958). The fishes of Aldabra were

3

included in a description of 820 marine fish of the Seychelles (Smith and Smith 1969). This list was expanded and revised by numerous studies during the period 1969-1979 to 883 species in the region (Polunin 1984). Specific studies of the fishes at Aldabra found a high diversity, with 185 species recorded in a 300 m2 section of reef habitat in 1973 (Polunin 1984). However, there were substantial variations in species and abundance between habitats (reef-slope – 228 species, back-reef – 146 species; Polunin 1984). Several site-specific and species-specific investigations in recent years (i.e. Potts 1973; Shapiro 1977; Robertson et al. 1979; Stevens 1984) provided valuable information on the behaviour, diversity, and ecology of several reef fishes and sharks.

The 1998 El Niño Event in the Seychelles The 1997-98 ENSO (El Niño Southern Oscillation) was described as the largest El Niño for the last 100 years (Slingo 1998; McPhaden 1999). This event increased the magnitude of ocean warming in the tropical Pacific, Atlantic and Indian Oceans. In the western Indian Ocean this led to extensive and pervasive coral bleaching in this region, including the southern Seychelles. In early 1998, the waters of the Seychelles experienced high sea temperatures ranging from 29 - 34°C, and exceptionally reaching 37°C in some lagoons (Teleki et al. 1998). High sea surface temperature (SST) excursions for the Seychelles were prolonged in early 1998. Temperatures in excess of 30°C persisted for approximately four months. Previous studies have shown that small temperature and short duration excursions above the mean monthly summer maximum result in partial and complete recovery of bleached coral colonies (Brown et al. 1996; Brown 1997; Davies et al. 1997). Larger temperature changes that were maintained for prolonged periods, as was the case in 1997-98, lead to the mass mortality of affected corals. SST archives for the southern Seychelles suggest that a bleaching event of this magnitude had not been witnessed within the last three decades (Spencer et al. 2000). Mortality was particularly high in the branching corals - Acropora spp., Pocillopora spp., Millepora spp. (fire coral) and Heliopora spp. (blue coral). Death in the massive or boulder corals such as Porites spp., Favia spp., Pavona spp. and Diploastrea spp. was in most cases partial and spatially patchy (Spencer et al. 2000). In Aldabra, bleaching was generally worse in shallower waters, 10 m or less (Teleki et al. 1998). Areas which were impacted least were those influenced by cooler currents and localised upwelling, and in lagoonal channels where water fluxes are high. Furthermore, corals subjected to frequent high temperatures, such as in the lagoon of Aldabra faired well suggesting local adaptation of corals to periodic high sea temperatures. Records for Aldabra also indicate that SSTs for 1998 were the highest of the previous three and a half decades (Figure 3). Anomalous temperatures began with a rapid increase in SSTs from November 1997 to a +1°C SST anomaly by January 1998. The peak SST of 30.7°C was reached in March, representing a +1.3°C anomaly above the long term monthly mean maximum SST. This +1°C anomaly persisted until April 1998, a duration of almost four months (Figure 4). All temperatures recorded for the period leading up to the bleaching event, and those following, ranged from +0.5ºC to + 1ºC higher than the long term average of the monthly mean maximum temperatures for 1961 to 1996 (Figure 4).

4

1.5

1

0.5

0

-0.5

-1

-1.5 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997

Figure 3. Monthly sea surface temperature (SST) anomalies (i.e. when mean temperatures are above or below the long term mean) for Aldabra Atoll using 1961-1990 baseline. Note the 1997 anomaly (Teleki et al. 1999).

31

30

29

ºC 1997-98

28

Mea n

27

26

25 Sep

Oct

Nov

Dec

Jan

Feb

Mar

Apr

May

Ju n

Jul

Figure 4. Monthly mean maximum sea surface temperatures for Aldabra Atoll from September 1997 to July 1998, in comparison to the average monthly mean maximum sea surface temperatures for the period September to July 1961-1996 (Teleki et al. 1999).

5

Results of the 1998 Southern Seychelles Atoll Research Programme In April 1998, at the peak of the coral bleaching event, a Cambridge Coastal Research Unit (CCRU) research team, the Southern Seychelles Atoll Research Programme (SSARP), found that widespread bleaching and mortality was common on the outer reef slopes (3 – 25 m) surveyed from the western to northeastern sides of Aldabra Atoll. Coral coverage was 37%, with 41% of those bleached or recently dead. The intensity of the coral bleaching in Aldabra was not as high as in other areas of the southern Seychelles because peak warming was 0.5ºC lower (Spencer et al. 2000). Bleaching and related mortality was primarily seen in the branching and tabular species of coral (e.g. Pocillopora spp. and Acropora spp.), and was partial to patchy in most massive species (e.g. Porites spp. and Pavona spp.). Bleaching was in some areas confined to a single side of the coral colony. A high proportion of the massive species of corals displayed signs of previous mortality indicated by a thick overgrowth of algae and the presence of encrusting and boring invertebrates. As in other areas, soft corals had high levels of bleaching and mortality. Although no quantitative data were gathered for the reef communities in the lagoon at Aldabra, extensive observations were made in all the channels and in the western half of the lagoon. Most coral species found in the channels, with the exception of isolated incidences of branching corals, were alive and displaying no obvious signs of stress. Normally deep water corals (e.g. Tubastrea micrantha) were found in the channels, most likely adapted to shallow waters because of channel hydrodynamic activity mimicking conditions of the deep water environment. This may also explain the high survivorship of massive and branching coral colonies in the channels. In the lagoon, patch reefs and individual colonies of massive coral species showed limited bleaching. Distinctive species such as Galaxea, Seriatopora, Acropora and Pocillopora were completely bleached, most often with increased distance from the flux of water from the channel. The CCRU expedition to Aldabra also conducted surveys of fish communities on the reefs at four locations along the western and northeastern shorelines. The species of fish were recorded by abundance categories that ranged from 10 m). Most of the live branching corals were dominated by Pocillopora spp. and Porites spp., which represented 20% of the coral cover. Massive species formed 63% of total live coral coverage on deep transects, compared to 45% on shallow transects. Physogyra spp. formed 65% of the live, massive coral coverage on the deep transects, but only 3% on the shallow transects. The foliose Echinopora spp., Pachyseris spp., and Turbinaria spp., and the encrusting Montipora spp., were common live corals at all sites, but the foliose genera were almost exclusively found on the deep transects. From west to east along the coastline of Aldabra there was a prominent gradient of decreased coral growth, related to levels of increasing hydrodynamic energy. There was evidence of widespread mortality in all coral growth forms with a high degree of spatial heterogeneity of tissue death within and between colonies. In massive corals it was most common to find surviving live tissue on the periphery and/or the underside of the colony. At locations where branching corals survived, often the colony had suffered only partial mortality. Plate and fine branching corals were not found at any of the locations surveyed, probably due to the relatively high hydrodynamic conditions at Aldabra. The onset of mortality in these growth forms would rapidly compromise their structural integrity. Overall, comparisons with coral coverage data collected in 1998 revealed that in shallow depths bleaching primarily led to mortality, while in deeper water bleached corals were more likely to recover. Fish Surveys The quantified fish surveys on the outer reefs at Aldabra found 165 species representing 27 families, and the qualitative (off-transect) surveys identified an additional 46 species and 6 families. The total of 211 species from 32 families found in November 1999 were generally in agreement with the 287 species from 35 families (Spalding 1998) reported by the CCRU expedition to Aldabra in April 1998. The densities of fishes on the transects were often dominated by large schools of a few species from the families Serranidae (groupers and basslets), Apogonidae (cardinalfishes), Pomacentridae (damselfishes), and Caesionidae (fusiliers). The abundance of fishes in the smallest size category was caused primarily by large numbers of small sized species, and secondarily by juvenile life stages. Although there was a prominent gradient of decreased coral growth from west to east along the coast line of Aldabra, there was no correlation between either the number of species, or the density of fishes, and the corresponding west to east locations of the transects. However, there were positive correlations between the amount of live coral habitat, and the number of species, and the density of Chaetodontidae (butterflyfishes), Labridae (wrasses), and Serranidae. These families each have several species that are commonly associated with live corals and habitat structure formed by erect dead corals (Crosby and Reese 1996).

8

The 2001 Aldabra Marine Programme Phase II Phase II of the Aldabra Marine Programme took place between 8th and 22nd February 2001. The main objectives were to: • • • • • •

Repeat the transects of corals and fishes at the seven permanent survey sites established in 1999; Establish additional permanent survey sites on the outer reef and conduct benchmark transects of corals and fishes at these sites; Establish permanent survey sites in the lagoon and conduct benchmark transects of corals at these sites; Conduct coral recruitment transects at selected locations on the outer reef and in the lagoon; Tag coral recruits at selected locations on the outer reef to monitor growth and survival; Deploy temperature data loggers at selected locations on the outer reef and in the lagoon.

The secondary objectives of this phase were to: • • • •

Improve the ease of location of each permanent transect site; Establish a checklist- of fishes in off-transect areas at the outer reef and lagoon survey sites; Assess the status of Echinometra spp. and Diadema sp. (black-spined urchins) at selected locations on the outer reef; Conduct training exercises for Aldabra Station staff in the methods of assessing coral recruitment, surveying urchins, and monitoring the physical marine environment.

9

Honeycomb Moray Eel (Gymnothorax favagineus)

10

Methodology Coral and Fish Transects The procedures used in the 2001 AMP survey to locate and mark permanent survey sites, and the methods used to quantify corals and fishes on the transects, replicated those used in AMP Phase I (Teleki et al. 1999). To establish new outer reef sites, a primary transect of varying length was extended from 20 m depth to the reef crest at 3 - 5 m depth, and two 50 m secondary transects were extended laterally from the primary transect along the 10 m and 20 m depth contours (Figure 5). Permanent survey sites in the lagoon were established in areas where there was abundant live coral habitat. At the lagoon sites a single 50 m transect extended along a depth contour appropriate to the habitat. All 50 m transects were permanently marked with steel stakes at the beginning and end, and each stake location was fixed using a Global Positioning System (GPS). Prior to each coral and fish survey, a tape or line was placed along the transects between the two stakes, following the appropriate depth contour. Digital underwater videography was used to record the benthic habitat on both sides of the 50 m secondary transect lines, first along the shoreward side and then back along the off-shore side, with a pause every 25 m. All video footage was acquired at a slow swimming speed to maintain image quality, with the diver positioning the camera 40 cm above the substrate. The imagery from the secondary transects was later analysed using the AIMS 5-dot method (Osborne and Oxley 1997). Four still pictures were also taken around each stake in a clockwise direction with the stake always in the corner of the picture: lower right corner for first picture, lower left for second, top left for third and top right for fourth. These pictures

11

were recorded approximately 1 m from the substrate. Below 20 m, reference footage was filmed to characterise the general habitat.

Primary transect from 20m to 3-5m depth

Secondary 50m transect laid out perpendicularly to the primary

10m

20m

A

B

D

C

Figure 5. Diagram of transect layout.

The 1999 primary transect videography was not repeated in 2001, although it was filmed for the newly established site 8. Fish transects were conducted using protocols developed for rapid visual assessments (Ginsberg et al. 1998; English et al. 1997). Two divers recorded the species, number, and sizes of fish in a 2 m corridor extending out from either side of the 50 m transect, and vertically to the surface. The sizes of the fish were recorded in six total length categories: 0 5 cm, 6 - 10 cm, 11 -20 cm, 21 - 30 cm, 31 - 40 cm, and > 40 cm. Transects were surveyed in 25 m sections, first for larger/conspicuous fishes, and then immediately re-surveyed for small/cryptic fishes. Only the first 25 m section of the transects at 20 m depth were surveyed. Thus, over 300 m2 of benthic habitat was surveyed for fishes at each site. The fish transect data was analysed using Analysis of Variance (ANOVA) and regression statistical procedures (Zar 1984). Qualitative surveys were conducted for species of fish off the transects on the outer reef, and at the lagoon survey sites, to develop a more complete inventory of fishes at Aldabra Atoll. On the outer reef, these surveys were done visually after a transect survey was completed, and concentrated on locating species not seen on the transect. In the lagoon, digital videography was used to record fishes near the permanent survey sites, and focussed on obtaining a video record of the many juvenile life-stages found in the shallow water. New methods were used in February 2001 to facilitate locating the survey sites in following years, and to improve the repeatability of the coral and fish surveys. To make the stakes visible underwater floats were attached to each one. To delineate the exact locations of the permanent transects for future surveys, the positions along the depth contour of five of the 50 m transect lines were marked by permanent leadcore line. This will allow the 50 m secondary transect tapes to be laid in exactly the same

12

position on subsequent surveys. If this is successful, lead-core line will be placed along all 50 m transects on future expeditions. Two underwater lasers were mounted on the video camera housing, and the beams set to cross each other (i.e. converge into a single spot of light) when the camera was 40 cm above the substrate. This provided the video camera operator with an accurate height reference above the substrate.

2

3 4

6

5 10 11 1

9

Lagoon

7

8 Figure 6. Aldabra Atoll with the 11 permanent Aldabra Marine Programme monitoring sites for coral and reef fish studies on the outer reef and within the lagoon.

Coral Recruitment and Tagging In February 2001 coral recruitment was assessed at all permanent survey sites on the outer reef and in the lagoon for the first time, using counts of recruits in 1 m2 quadrats, with up to nine randomly positioned 4 m x 1 m quadrats, at each of the 6 m1, 10 m, and 20 m survey depths. A maximum width of 5 cm was used as the upper limit for defining recruits (Engelhardt 2001). These criteria are based on in-situ coral growth rate observations of Wallace (1985), Wallace et al. (1986) and van Moorsel (1988). Fast growing Acropora corals have been shown to reach a maximum size, two years after settlement, of between 2 cm and 5 cm (Wallace 1985; Wallace 1999). At lagoon sites, counts were only made at the depth of the single transect. At most sites and depths 8 sets of 4 quadrats were surveyed to give a total area of 32 m2. The recruits were measured across their greatest width and the width at 90 degrees to this. Recruit size was calculated by averaging the two widths. Where possible, recruits were identified to genus level. When the first quadrat in a set was completed, the quadrat frame was flipped over to give the next quadrat location, and so on.

1

Heavy swell in some outer reef sites prevented the count at 6 m depth.

13

Divers measuring coral recruits in a quadrat

AMP Phase II initiated the first study of coral growth and survivorship at Aldabra. At four permanent survey sites (Sites 1, 3, 6, and 7) 20 coral recruits (20 cm, by transect depth. At the shallow and deep transects, the largest percentage of fish was in the 1 to 10 cm category (82% and 70%, respectively), and the smallest percentage in the 11 - 20 cm category (4% and 5%, respectively). The abundance of fishes in the 1 to 10 cm category at both transect depths was primarily due to large numbers of fish from families with numerous small-sized species (Serranidae (fairybasslets), Apogonidae, and Pomacentridae), and secondarily because of the number of juvenile life-stages (e.g. Serranidae). Table 4. Number of fish counted, by transect depths and fish size groups, during the Aldabra Marine Programme surveys in February 2001. Total Survey Area - 2325 m2

Family/Genus species

10 m Transects (Site 7 - 5m)

20 m Transects (Site 7 - 15m)

Area Surveyed: 1500 m2

Area Surveyed: 825 m2

Size (cm)

Size (cm)

1 to 10

11 to 20

Size (cm) Size (cm) >20

1 to 10

Size (cm)

Size (cm)

11 to 20

>20

Total

MURAENIDAE Gymnothorax flavimarginatus

1

1

1

1

BELONIDAE Tylosurus crocodilus

HOLOCENTRIDAE Myripristis adusta

1

Myripristis berndti

40

Myripristis murdjan

22

Neoniphon sammara

6

Sargocentron caudimaculatum

31

1 17

9

1

12

226

14

297

14

36 1 3

Sargocentron diadema

58

7 92

13

13

Sargocentron spiniferum

2

2

550

552

4

21

12

20

SERRANIDAE Aethaloperca rogaa

2

Cephalopholis argus Cephalopholis leoparda

1 2

Cephalopholis miniata

11

1

1

1

5 9

Cephalopholis spiloparaea

1

16

Cephalopholis urodeta

1

10

1

12

5

2 1

27

5

16

Dermatolepis striolatus Epinephelus fasciatus

4

1 3

Epinephelus fuscoguttatus

11 1

Epinephelus polyphekadion

1 27 1

2

2

4

Epinephelus spilotoceps

1

2

1

4

Gracilia albomarginata

1

5

4

10

1

1

Plectropomus laevis

45

Table 4 (continued)

Total Survey Area - 2325 m2

Family/Genus species

10 m Transects (Site 7 - 5m)

20 m Transects (Site 7 - 15m)

Area Surveyed: 1500 m2

Area Surveyed: 825 m2

Size (cm)

Size (cm)

1 to 10

11 to 20

Size (cm) Size (cm) >20

Variola louti

1 to 10

>20

Total

2

3

1

Pseudanthias cooperi

3

8

Pseudanthias evansi

281

100

Pseudanthias squamipinnis

928

Plectropomus areolatus 10

1

1 6

17 381

1098

1

2

37

2

2027 3

Pseudanthias ignitis Anyperodon leucogrammicus

Size (cm)

11 to 20

1

Nemanthias carberryi

Cephalopholis nigripinnis

Size (cm)

6

15

64

6

6

1

1

APOGONIDAE Apogon apogonoides

400

2

1835

Cheilodipterus macrodon

2237 1

1

HAEMULIDAE Plectorhinchus gaterinus Plectorhinchus obscurus

4

Plectorhinchus orientalis

7

7

3

7

4

4

LUTJANIDAE Aphareus furca

1

11

1

4

17

3

3

2

15

43

4

711

715

5

1

8

14

69

15

10

94

60

15

2400

1

800

3201

Aprion virescens Lutjanus bengalensis Lutjanus bohar

1 1

6

18

Lutjanus gibbus

1

1

6

6

Lutjanus kasmira Lutjanus monostigma

CAESIONIDAE Caesio xanthonota Pterocaesio lativittata Pterocaesio tile

75

MULLIDAE Parupeneus barbarensis Parupeneus bifasciatus

1 1

10

4

3

4

148

31

3

Parupeneus cyclostomus Parupeneus macronema Parupeneus pleurostigma

1

29 1

Mulloidichthys vanicolensis Parupeneus rubescens

3

1

7

1

2

2

20

3

10

1

219

2

4

550

550 1

46

Table 4 (continued)

Total Survey Area - 2325 m2

10 m Transects (Site 7 - 5m)

20 m Transects (Site 7 - 15m)

Area Surveyed: 1500 m2

Area Surveyed: 825 m2

Size (cm)

Size (cm)

1 to 10

11 to 20

Chaetodon auriga

4

11

Chaetodon bennetti

1

Family/Genus species

Size (cm) Size (cm) >20

Size (cm)

Size (cm)

1 to 10

11 to 20

>20

9

6

Total

CHAETODONTIDAE

Chaetodon falcula Chaetodon guttatissimus

2 19

3

30

2

3

6

2

10

14

14

3

1

40

15

1

4

20

6

2

2

2

1

Chaetodon kleinii Chaetodon lineolatus

2

Chaetodon lunula Chaetodon meyeri

3

1

Chaetodon trifasciatus

8

4

Chaetodon xanthocephalus

2

5

7 12

2

9

Chaetodon zanzibariensis

5

Forcipiger flavissimus

9

Hemitaurichthys zoster

12

Heniochus acuminatus

4

7

16

5

6

42

7

19

1

1

Heniochus monoceros Chaetodon interruptus

1

Chaetodon madagaskariensis

3

Chaetodon vagabundus

2

2 10

3

1

1

1

2

2

8 2

Heniochus singularius

2

2

LETHRINIDAE Lethrinus nebulosus Monotaxis grandoculis

5

21

5

8

18

3

3

2

59

3

8

EPHIPPIDAE Platax orbicularis

5

MALACANTHIDAE Malacanthus latovittatus

1

1

PINGUIPEDIDAE Parapercis hexophthalama

3

Parapercis millipunctata

5

4

1

8 5

Parapercis signata

6

6

POMACANTHIDAE Apolemichthys trimaculatus

1

Centropyge acanthops

17

Centropyge multispinis

59

Pygoplites diacanthus Centropyge bispinosa

7

4

4 1

28

45

37

100

2

1

Centropyge debelius

47

12

2

2

7

3

4

6

6

Table 4 (continued) 10 m Transects (Site 7 - 5m)

20 m Transects (Site 7 - 15m)

Area Surveyed: 1500 m2

Area Surveyed: 825 m2

Total Survey Area - 2325 m2

Family/Genus species

Size (cm)

Size (cm)

1 to 10

11 to 20

Size (cm) Size (cm) >20

1 to 10

Size (cm)

Size (cm)

11 to 20

>20

Total

POMACENTRIDAE Amphiprion chrysogaster

2

Amphiprion clarkii

1

1

705

1710

267

36

303

565

164

729

Chromis dimidiata

1005

Chromis nigrura Chromis ternatensis Chromis weberi

374

Dascyllus aruanus

36

431

2

21

10

12

63

63

1

14

15

4290

15985

5

24

Dascyllus carneus Dascyllus trimaculatus Lepidozygus tapeinosoma

11695

Plectroglyphidodon dickii

14

Plectroglyphidodon johnstonianus

49

Plectroglyphidodon lacrymatus

91

Pomacentrus caeruleus

58

Pomacentrus sulfureus

1

5

8

4

53

5

104

11

69 1

Chromis xutha Abudefduf sexfasciatus

2

107

107

2

2

Amphiprion allardi

2

Chromis atripectoralis

1

Pomacentrus chrysurus

1

3

5 1 1

Pomacentrus philippinus

1

1

LABRIDAE Anampses meleagrides

4

2

Bodianus axillaris

5

1

1

Bodianus bilunulatus 5 604

Coris cuvieri

16

5

14

1

12

3

1

1

3

8

3

20

138

754

2

Coris frerei Epibulus insidiator

6

2

1

Bodianus diana Cirrhilabrus exquisitus

4

2

4

1

2

1

7 1

Gomphosus caeruleus

25

16

8

5

54

Halichoeres cosmetus

134

9

49

6

198

Halichoeres hortulanus

2

8

1

8

19

Halichoeres vrolikii

3

3

Hemigymnus fasciatus

1

Hologymnosus doliatus

2

Labroides bicolor Labroides dimidiatus

9

6 1

3

5

104

Labrobsis xanthonata

1

Macropharingodon bipartitus

11

2 1

3 1

110 6 2

18 214

1

8 13

Pseudocheilinus evanidus

61

94

155

Pseudocheilinus hexataenia

174

47

221

48

Table 4 (continued)

Total Survey Area - 2325 m2

Family/Genus species Pseudocheilinus octotaenia

20 m Transects (Site 7 - 15m)

Area Surveyed: 1500 m2

Area Surveyed: 825 m2

Size (cm)

Size (cm)

1 to 10

11 to 20

31

7

Pseudodax molucanus Thalassoma amblycephalum

10 m Transects (Site 7 - 5m)

Size (cm) Size (cm) >20

Size (cm)

11 to 20

>20

3

1

15

2

2

1

2

Thalassoma herbraicum

14

33

Thalassoma lunare

6

1

20

3

41

2 4

Anampses caeruleopunctatus

1

Bodianus anthioides

1

Bodianus mesothorax

4

4

9

1

18

2

9

Hologymnosus annulatus

1

Novaculichthys taeniourus

66 26 1

3

4

2

37

1

Coris batuensis

Total 42

2

Thalassoma hardwicke

1

9

1

1

2

1

8

1

16

1

Pseudojuloides kaleidas Stethojulis albovittata

Size (cm)

1 to 10

2

6

14 1

14 1

11

CIRRHITIDAE Cirrhitichthys oxycephalus

10

Paracirrhites arcatus

28

Paracirrhites forsteri

7

1

11

21

10

39

10

1

4

14

18

SCARIDAE Scarus sordidus

10

63

23

Scarus rubroviolatus

3

117

1

1

2

1

3

2

5

8

Caranx ignobilis

22

3

25

Caranx melampygus

32

Scarus frenatus Scarus strongylocephalus

1

CARANGIDAE

18

50

Caranx sexfasciatus

515

515

Elagatis bipinnulata

2

2

BLENNIIDAE Aspidontus taeniatus

6

8

15

Ecsenius midas

4

4

Plagiotremus rhinorhynchos

1

1

Plagiotremus tapeinosoma

6

Cirripectes castaneus

16

1

3 1

9 17

GOBIIDAE Valenciennea helsdingeni

2

2

Valenciennea strigata

4

4

49

Table 4 (continued) 10 m Transects (Site 7 - 5m) Total Survey Area - 2325 m2

Family/Genus species

20 m Transects (Site 7 - 15m)

2

Area Surveyed: 825 m2

Area Surveyed: 1500 m Size (cm)

Size (cm)

1 to 10

11 to 20

Size (cm) Size (cm) >20

1 to 10

Size (cm)

Size (cm)

11 to 20

>20

Total

ACANTHURIDAE Acanthurus auranticavus

2

Acanthurus leucocheilus Acanthurus leucosternon

2

6

9

6

21

11

76

1

1

4

5

5

11

67

Ctenochaetus striatus

75

30

7

11

3

Ctenochaetus strigosus

156

147

48

22

373

2

57

Acanthurus thompsoni

Naso brevirostris

55

Naso lituratus Zebrasoma scopas

3 32

Acanthurus lineatus

4 4

Acanthurus tennenti

88 2

1 15

Acanthusus nigricauda

93

4

4 55

1

5

4

4

1

1

Naso vlamingii

14

Zebrasoma desjardinii

128

14

1

1

2

6

4

11

ZANCLIDAE Zanclus cornutus

1

BALISTIDAE Balistapus undulatus

2

3

Balistoides viridescens Melichthys indicus

15

48

Odonus niger

3

7

Sufflamen bursa Sufflamen chrysopterus

5

1

1 3

5

72 10

3 5

6

3

1

4

1

14

OSTRACIIDAE Ostracion meleagris

1

1

2

TETRAODONTIDAE Arothron meleagris

1

Arothron nigropunctatus

2 2

1

2

1

3 6

Canthigaster valentini

7

7

Canthigaster coronata

1

1

SCORPAENIDAE Scorpaenopsis diabola

1

1

SIGANIDAE Siganus stellatus

2

50

2

Table 4 (continued) 10 m Transects (Site 7 - 5m) 2

Total Survey Area - 2325 m

Family/Genus species

20 m Transects (Site 7 - 15m)

2

Area Surveyed: 825 m2

Area Surveyed: 1500 m Size (cm)

Size (cm)

1 to 10

11 to 20

Size (cm) Size (cm) >20

1 to 10

Size (cm)

Size (cm)

11 to 20

>20

Total

1

1

MOBULIDAE Manta briostris

MICRODESMIDAE Nemateleotris magnifica

46

Ptereleotris evides.

2

22

68

3

5

MONACANTHIDAE Amanses scopas

2

Cantherinus pardalis

1

2

4 1

Total Fish Counted 17702

863

2901

9418

689

3328 34901

Number of Species

86

92

62

84

74

57

191

Fish/100m2

12

0.6

2

11

0.8

4

1501

Fish Species Distribution The pattern of fish species distribution around the outer reef of the atoll in February 2001 (Figure 22), followed the same general pattern as in November 1999 (Figure 23). Sites 5, 3, 1, and 4 on the eastern portion of the atoll ranked 1st, 2nd, 3rd and 4th, respectively, for the least number of species in both years. Sites 2, 6, 7, and 8 (2001 only) on the western portion of the atoll accounted for the most number of species of fish on the transects in both years. The difference in the species numbers from one end of the atoll to the other is striking. Thirty species were counted at Site 5 compared to a range of 62 to 115 species at the other sites. Furthermore, there were significant correlations between the number of species of fish surveyed on both the 10 m depth transects(R2 = 0.41, F.05,1 = 4.16, P = 0.087) and the 20 m depth transects (R2 = 0.47, F.05,1 = 5.23, P = 0.062) at Sites 1-8, and their relative positions from east to west along the shoreline of Aldabra Atoll (Figure 22). Fish Numbers Distribution In February 2001, the number of fish per 100 m2, combining shallow and deep transects ranged from 299 fish (62 species) at Site 3, to 3,867 fish (89 species) at Site 6 (Figure 22). The 550 fish per 100 m2 at Site 5 is unusually high for the low number of species at this site and was due to a school of 800 large fusilier, Pterocaesio tile (Caesionidae) crossing the transect line. The numbers of the fish counted in both shallow and deep transects combined, at Sites 1, 2, 3, 4, 6, and 7 were greatest in the 1 to 10 cm category. This ranged from 70% at Site 1 to 97% at Site 7. At site 8, 66% of the fish were in the >20 cm category. This was due to an extremely large school of >30 cm Aethaloperca rogaa (Serranidae) aggregated on a coral outcrop at 20 m depth.

51

Figure 22. The pattern of fish species distribution around the outer reef of the atoll in February 2001. 52

Figure 23. The pattern of fish species distribution around the outer reef of the atoll in November 1999. 53

There were no significant correlations between the densities of fishes at Sites 1-8, and the east to west positions along the outer reef.3 Relationship with Coral Habitat There was no significant correlation between the number of species of fish, nor the density of fishes, surveyed at both depths at Sites 1-8, and the amounts of live coral habitat, and live coral and dead coral habitat combined, at each site. The families Pomacentridae, Chaetodontidae, Labridae, and Serranidae each have several species that are commonly associated with live coral habitat, and habitat structure formed by erect dead corals. These selected fishes were examined for any associations with these measures of habitat structural complexity. a) Fish Density Only the density of Labrids at 10 m depth (R2 = 0.78, F.05,1 = 21.33, P = 0.004) and at 20 m depth (R2 = 0.54, F.05,1 = 7.02, P = 0.038), and the number of species of Pomacentrids at 20 m depth (R2 = 0.67, F.05,1 = 12.18, P = 0.013), were significantly correlated with the amount of live coral habitat at each site. In comparison, both the density of Chaetodontids at 10 m depth (R2 = 0.50, F.05,1 = 6.01, P = 0.050) and 20 m depth (R2 = 0.60, F.05,1 = 9.08, P = 0.024), and the density of Labrids at 10 m depth (R2 = 0.70, F.05,1 = 14.21, P = 0.009) and 20 m depth (R2 = 0.52, F.05,1 = 6.61, P = 0.042), were significantly correlated with the amount of combined live and dead coral habitat at each site. b) Fish Species For the number of species of fish, only the Chaetodontids (R2 = 0.52, F.05,1 = 6.53, P = 0.043) and Pomacentrids (R2 = 0.64, F.05,1 = 10.73, P = 0.017) were significantly correlated with the amount of combined live and dead coral habitat at each site.

Temperature Data Loggers Since the February 2001 deployment of the 10 water temperature data loggers, three have been regularly monitored by Aldabra station staff, and appear to be functioning as anticipated. Although they are developing encrusting growths (Figure 24), it is unlikely that these would interfere with the operation and accuracy of the loggers4. The temperature data from Site 1 (19 February to 20 June 2001) at 10 m depth on the outer reef had a maximum of 29.7 ºC (April), a minimum of 21.4 ºC (February) and a mean of 27.4 ºC for this period (Table 5). There was a significantly decreasing trend in the temperatures at this outer reef site for this period (R2 = 0.59, F.05,1 = 9818.18, P = 0.0; Figure 25).

3

The number of species of fish, and the fish per 100 m2, given in Figure 21 correct for errors in some of these numbers for Sites 1, 5, 6, and 7 in Figure 10 in Teleki et al. (1999). 4 OnSet Computer Corp was consulted about the effect which the encrustations would have on the temperature. Given that the electronics, including the sensor, are enclosed in a waterproof plastic housing, their engineering staff do not believe that external growth would cause changes in the accuracy of the logger's sensor or electronics. The growths will add thermal mass to the housing, which could affect time response. However, the housing is thick, so the expectation is that a fairly substantial amount of growth would be required to affect the response time of the logger. 54

Figure 24. Encrustation on a temperature logger deployed in this survey.

34

Temperature (ºC)

32 30 28 26 24 22 20

Feb

March

April

May

June

July

Figure 25. Temperatures recorded at 30 minute intervals at Aldabra Marine Programme survey Site 1 at 10 m depth, from 18 February to 8 July 2001.

55

34

Temperature(ºC)

32 30 28 26 24 22 20

Feb March

April

May

June

Figure 26. Temperatures recorded at 30 minute intervals at Aldabra Marine Programme temperature monitoring site Passe Dubois at 3 m depth, from 19 February to 19 June 2001.

34

Temperature (ºC)

32 30 28 26 24 22 20 April

May

Jun

July

Figure 27. Temperatures recorded at 30 minute intervals at Aldabra Marine Programme temperature monitoring site North Ile Esprit at 3 m depth, from 11 April 2001 to 10 July 2001.

56

The temperature data for Passe Dubois (19 February to 20 June 2001) at 3 m depth had a maximum of 32.7 Cº (March and April), a minimum of 23.6 Cº (June) and a mean of 28.0 Cº for this period (Table 5). There was a steadily decreasing trend in maximum and minimum values towards June. Despite the wide fluctuations in temperature on most days, there was a significantly decreasing trend in the temperatures at 3 m in this passage to the lagoon for this period (R2 = 0.33, F.05,1 = 2883.62, P = 0.0; Figure 26). The temperature data for Ile Esprit (11 April to 10 July 200) at 3 m depth had a maximum of 31.2 Cº (April), a minimum of 21.8 Cº (June) and a mean of 26.8 Cº for this period (Table 5). There was a steadily decreasing trend in maximum and minimum values towards July. There was a significantly decreasing trend in the temperatures at 3 m in area of the lagoon for this period (R2 = 0.80, F.05,1 = 17315.99, P = 0.0; Figure 27).5 Table 5. Temperatures (ºC) recorded, by monthly period, at Aldabra Atoll by the Optic StowAway temperature loggers deployed during the February 2001 AMP expedition (SD = standard deviation, n = number of 30 minute interval recordings). A. Site 1 at 10m depth, 18 February to 8 July; B. Passe Dubois at 3 m depth, 19 February to 20 June; and C. Île Esprit at 3 m depth 11 April – 10 June 2001. A. Site 1 at 10m depth Date Mean 28.3 Feb 28.6 March 28.5 April 27.8 May 26.0 June 25.3 July 27.4 Overall

Max 29.3 29.3 29.7 28.9 27.5 25.7 29.7

Min 26.0 25.7 25.7 23.5 23.5 21.4 21.4

SD 0.6 0.6 0.7 0.6 0.6 0.4 1.3

n 507 1488 1440 1488 1439 364 6725

B. Passe Dubois at 3 m Date Mean Feb 28.7 29.1 March 28.8 April 27.8 May 26.3 June 28.0 Overall

Max 32.3 32.7 32.7 30.8 29.7 32.7

Min 26.8 26.8 26.4 23.9 23.6 23.6

SD 0.9 1.0 1.1 1.0 0.9 1.4

n 462 1488 1440 1488 936 5814

C. Île Esprit at 3 m depth Date Mean 28.9 April 27.6 May 25.3 June 24.6 July 26.8 April-July

Max 31.2 30.8 28.2 26.1 31.2

Min 25.4 25.4 21.8 22.5 21.8

SD 0.9 0.9 0.9 0.6 1.8

n 940 1488 1440 450 4318

5

The temperature logger data was provided by the following Seychelles Islands Foundation personnel at Aldabra Station: Anna Liljevik, Research Officer, Tina Dubel, Ranger, Conrad Savy, Volunteer, and Allen Cedras, Logistics Manager.

57

Fish of Aldabra – Acanthurus lineatus (top), Epinephelus sp. (middle), Platax orbicularis (bottom) 58

Discussion Coral Community The 1999 survey results showed that coral bleaching in 1998 had had a pronounced effect on the reefs around Aldabra Atoll, particularly in shallow water (Teleki et al. 1999). Between 1999 and 2001 there has been little change in the outer reefs, with some suggestion of coral recovery at both the depths studied. There is no evidence of high macro algal growth since 1999, with the exception of site 7 and, to a lesser extent, Site 6. These sites had high coral mortality in 1999 providing a new niche for algae, particularly at Site 7 which appears to have provided suitable conditions for abundant coralline algae growth. By 2001 the dead corals still visible in 1999 had been mostly broken down to rubble and sand, or were covered by other organisms. The shapes of dead massive colonies were still visible in 2001, and some showed evidence of tissue regeneration from surviving areas around the side and base of the colonies. Many are now covered with coralline algae that are known to provide a good substrate for settlement of coral larvae. The detected natural variation in live coral cover around Aldabra Atoll can be attributed to the prevailing weather and current patterns. The area encompassing Sites 1, 2 and 6 is the most sheltered and has the highest live coral cover. Live coral cover at depth was good around most of the atoll, with the exception of Site 5 that appears to be a rubble zone. The new sites established in the lagoon have shown that coral cover is high in the vicinity of the drainage channels. Live coral cover at Sites 9 and 10 was estimated to be double that of most outer reef sites, though species diversity appears lower. There is also less evidence of old dead coral colonies in the lagoon, suggesting that the effect of the 1998 bleaching may not have been as great here, a theory supported by observations made by Teleki et al. (1998) just after the 1998 bleaching. Lagoon species may be acclimatised to extreme temperature changes, and new tides may bring in deep cooler water through the channels on every tide change reducing the time lagoon corals are exposed to extreme temperatures.

59

The temperature data recorded by the three loggers during April through June/July 2001 supports the suspected normally wider range in temperatures in the lagoon. During this period the temperature variation at the two lagoon sites was 9.1 and 9.4 oC respectively and at the outer reef site 6.1 0C. Coral recruitment at Aldabra appears to be good, with most occurring at around 10 m. This would be expected as corals in shallower than 10 m depth have to cope with higher exposure to swell and a mobile substrate making settlement difficult, while corals in deeper water have less available light and reduced available settlement space due to the higher proportion of live coral. Levels of recruitment at Aldabra are in line with those found at other locations, though direct comparison is not always possible due to differing sampling methods (Miller et al. 2000). The diversity of coral families recruiting to Aldabra is high and to be expected in view of the high coral diversity on reefs around the atoll. Size frequencies of recruits measured in 2001 suggests that there may have been several cohorts recruited since the coral bleaching of 1998. It appears that the fast colonisers such as Acropora and Pocillopora have had the best chance to produce several cohorts due to their high rate of growth and reproduction. The presence of so many recruits and evidence of several cohorts suggests that the atoll may be primarily self-seeding, though it is conceivable that the predominant southeasterly current may be carrying recruits from Assumption, Astove, Cosmoledo and potentially sites at much greater distances afar.

Fish Community Unlike sessile coral colonies, fish populations are notoriously variable, even when surveyed at short time intervals. The following conclusions are therefore made within the limitations of two surveys having been undertaken some 16 months apart. Comparing the 1999 and 2001 fish species lists there is generally good agreement between the two surveys even though the total numbers identified vary somewhat: in 1999, 35 families and 211 species and in 2001, 40 families and 205 species. Using a different survey method, Spalding identified 35 families and 287 species in 1998, prior to the bleaching episode. Given the broadly similar diversity it is therefore of note that a comparison of the actual counts of fishes and species at each site in 1999 and 2001 appear to be very different (Figures 22 and 23). At this stage it is not known whether this difference is attributable to the different seasons in which the surveys were conducted, some structural change in the fish community, or a survey error. It is nevertheless concluded that surveys should, if possible, be conducted at similar times of the year, ideally in November and February. If one compares the findings of the 1999 and 2001 surveys, the following conclusions emerge: 1. In 1999 the lowest fish density was at Site 5, and the highest at Site 6. In 2001 the highest count was still at Site 6, but the lowest at Site 3. This may be due to an anomaly at Site 5 where a large school of fusiliers crossed the survey area. If this number is excluded, Site 5 yields the lowest count in 2001. 2. In both years most of the fish counted were in the 0 – 10 cm length category. This was due to large numbers of fish from families with numerous small-sized species (Serranidae (fairybasslets), Apogonidae, and Pomacentridae), and because of juvenile

60

life stages (e.g. Serranidae). Exceptionally at Site 8 most fish were in the >20 cm category. 3. In both years there was no correlation between the densities of fishes counted and the relative positions of the survey sites east to west along the atoll. 4. In 1999 there was also no correlation between the number of species counted and the east/west position of the survey sites, but in 2001 a significant correlation did appear, both at the 10 m (R2 = 0.41) and 20 m depths (R2 = 0.47). 5. On coral reefs, fish diversity and habitat complexity are often linked (Ebeling and Hixon 1991; Sebens 1991; Turner et al. 1999; Williams 1991). In both 1999 and 2001 a distinction was made between benthic habitat whose structural integrity was still evident (live or dead coral), and habitat without such structural integrity (sand, rock and rubble). In 1999 no correlation was found between the density of fish, nor the number of species, and either the live or dead coral cover. In 2001 the analysis was slightly different, but a similar conclusion was drawn. 6. However, in 1999 an analysis of fish families that have species commonly associated with structurally complex habitat concluded that there were positive correlations amongst the Chaetodontidae, Labridae and Serranidae and live or dead coral. Although this association was not found amongst the Serranidae in 2001, it remained within the Chaetodontidae and Labridae, and was evident amongst the Pomacentridae at 20 m depth. Although it is too early to establish any significant trends in Aldabra’s fish populations, the nature of any long term study means that these will emerge in time. In particular, close attention should continue to be paid to the relationship between coral reef related species and reef structure. For example, the numbers of specific corallivorous Chaetodontids may prove to be an effective indicator of reef health (Crosby and Reese 1996).

Temperature The temperature data for the marine environment at Aldabra being recorded by the loggers deployed during the February 2001 AMP expedition has a great potential to yield a valuable long-term data base for the atoll. This is based on the assessment of the temperature data provided by the Aldabra Station monitoring of three of the loggers, and by the seemingly flawless performance of these three loggers. The temperatures recorded at Site 1 at 10 m depth (Figure 25) show February through June 2001 monthly averages (Table 5) that track favourably with the monthly mean temperatures for these months for the period 1961-1996 (Figure 4). The potential for the encrusting growths developing on the loggers to affect the temperature readings, while suspected not to be a problem, will be tested on the next AMP expedition to Aldabra.

The Aldabra Marine Programme: Short Term and Long Term The Aldabra Marine Programme has now established eleven permanent monitoring sites around Aldabra, seven of which have now been surveyed twice. These sites provide baseline data and will generate increasingly more important data as they are resurveyed on a yearly 61

basis. Furthermore, as the information is gathered and analysed more questions about the atoll are generated, and therefore the scope to amplify the study. After completing the 1999 survey, the AMP set out a list of five goals for the future. All of these goals have been achieved with the exception of the initiation of a study of mangrove ecosystem dynamics. AMP has therefore increased its research base in 2001 by: •

Continuing the fish and coral monitoring of permanent sites, and establishing one new long term site on the highly exposed southern shoreline;

•

Establishing permanent monitoring sites in the lagoon and Passe Houareau channel;

•

Initiating a coral recruitment study in the lagoon and outer reef slopes, and tagging corals to follow their survival and growth;

•

Deploying temperature data loggers;

There was also the opportunity to train Aldabra staff in survey techniques for coral recruitment and echinoderm population assessment, and to discuss suitable monitoring programmes for the station staff. AMP remains committed to training Seychellois rangers in marine survey techniques and hopes to continue doing so in the future. A long term marine science programme for Aldabra has now been established by AMP. Future surveys will continue to monitor the permanent sites and it is hoped that another site will be set up on the southern coastline along with further lagoon sites. The team also aims to improve the scope of the physical marine monitoring and expand the lagoon work, hopefully by appointing a PhD student.

62

Acknowledgements We would like to thank the following individuals and organisations for their invaluable support and advice. Phase II of the Aldabra Marine Programme trip would not have been possible without the generous support from the following organisations and individuals: Coral Reef Degradation in the Indian Ocean (CORDIO) Programme (Olof Lindén), The Global Environment Facility, The Shoals of Capricorn Programme, The Royal Geographical Society, The Royal Society, and British Airways Assisting Conservation. Guillermo Cryns continues to provide us with unwavering support and steadfast dedication to the long term success of the Aldabra Marine Programme. The following individuals gave AMP generous financial support: Maya Moltzer, Mallorca, Spain; Frank Smith, Pinney Allen, Robyn Ice, T. McCarthy and S. Train (Alston & Bird LLP, Atlanta, USA) The following people and groups are thanked for their advice, support in the field and assistance to the Aldabra Marine Programme: Etienne Quilindo who was part of the AMP Phase II research team provided dedicated support and field assistance which allowed AMP to achieve all of its objectives. Rolph Payet, Seychelles Ministry of Environment and Transport; David Rowat and the Indian Ocean Explorer; Patrick Lablache, Ministry of Land Use and Habitat; Seychelles Island Foundation: Executive Director Lindsay Chong-Seng and Executive Officer Angela Valente-Libanotis; Aldabra Station: Guy Esparon - Manager, Anna Liljevik - Research Officer, Tina Dubel - Ranger, Conrad Savy - Volunteer, Allen Cedras - Logistics Manager, Ross Wanless - Researcher and Brian Betsy – Ranger; David Boullet, Edwin Grancourt and the Seychelles Fishing Authority. Maurice Loustau-Lalanne SIF Chairman and Principal Secretary, Seychelles Ministry of Environment and Transport; Patrick Lablache, Seychelles Ministry of Land Use and Habitat; Sue Wells, IUCN East Africa Region Office; Stephen Blackmore, Royal Botanic Gardens, Edinburgh UK; and Claude Pavard, Photographer. Other participants of the Aldabra Scientific Workshop (December 2000) whose advice, suggestions and support for AMP have been and continue to be invaluable: Katy Beaver, Roger Bour, David Bourn, Joseph Francois, Justin Gerlach, Jeanne Mortimer, Robert Prys-Jones, Selby Remie and Richard White Jeanne Mortimer continues to be a wealth of support and assistance both scientifically and with the logistics of conducting marine research on Aldabra. The Shoals of Capricorn Seychelles based team (Martin Callow, Jan Robinson and Caroline Lawton) provided us with invaluable support and hospitality on Ste. Anne. John Collie and the staff of the Marine Parks Authority were very accommodating in transporting us to and from Victoria, helping us shift equipment, and allowing us to have access to the facilities of Ste. Anne. Tom Spencer, Shoals of Capricorn Science Plan Co-ordinator, provided us with valuable advice on both the logistics and the science plan of the research programme. His comments on the final report proved insightful and invaluable. Juliet Burnett and Jessica Kavanagh of the Shoals of Capricorn, RGS London Office were outstanding in coordinating the overall logistics in the UK and providing valuable contacts in the Seychelles.

63

David Stoddart, Peter Sale, Callum Roberts and Barbara Brown were generous with their time in reviewing funding proposals and providing comments on the AMP science plan. Clare Bradshaw, Mark Spalding, Tom Spencer and Kristian Teleki made important contributions as members of the original Southern Seychelles Atoll Research Programme (SSARP) who first visited Aldabra in 1998 at the peak of the coral bleaching event. The Cambridge Coastal Research Unit (CCRU) has provided immense support financially and logistically, and by allowing their personnel to participate in the expedition. Fabrice Meziani, Eureka Design Ltd., kindly helped with some of the artwork in this report. Camera Pix, Nairobi generously donated an aerial photograph of Aldabra which was used on both the cover of this report and on the AMP brochure. Alan Downing also kindly donated his time to edit the text of the AMP brochure. The enthusiasm, encouragement and support from Professor David Stoddart, who is the reason why any scientific research can be conducted on Aldabra, were deeply appreciated.

64

References Arnoult, J., M.L. Bauchot-Boutin and R. Roux-Estève. 1958. Les poissons de l’Ile Aldabra. Annales de l'Institut Océanographique 34:47-90. Attenborough, D. 1995. Foreword. In M. Amin, D. Willetts, and A. Skerrett, (eds) Aldabra World Heritage Site. Camerapix Publishers International, Nirobi, Kenya. p 7. Barnes, J., D.J. Bellamy, D.J. Jones, B. Whitton, E. Drew, L. Kenyon, J.N. Lythgoe and B.R. Rosen. 1971. Morphology and ecology of the reef front of Aldabra. Symposium Zoological Society London 28: 87-114. Beaver, K. and R. Gerlach. 1997. Aldabra Management Plan: a management plan for Aldabra Atoll, Seychelles Natural World Heritage Site 1998-2005. Seychelles Island Foundation and the GEF/World Bank. p 61. Birkeland, C. 1997. Symbiosis, fisheries and economic development on coral reefs. Trends in Ecology and Evolution 12:364-366. Bohnsack, J.A. 1995. Maintenance and recovery of reef fish productivity. In N.V.C. Polunin and C.M. Roberts (eds), Management of Reef Fisheries. Chapman & Hall, London. p 283-313. Bohnsack, J.A. and J.S. Ault. 1996. Management strategies to conserve marine biodiversity. Oceanography 9(1):73-82. Brown, B.E. 1997. Coral bleaching: causes and consequences. Coral Reefs 16:S129-S138. Brown, B.E., R.P. Dunne, and H. Chansang. 1996. Coral bleaching relative to elevated seawater temperature in the Andaman Sea (Indian Ocean) over the last 50 years. Coral Reefs 15:151-152. Bryant, D., L. Burke, J. McManus and M. Spalding. 1998. Reefs at risk: a map-based indicator of threats to the world’s coral reefs. World Resources Institute, Washington, D.C. p. 56. Chadwick, D.H. 1999. Coral in peril. National Geographic 195(1):30-37. Crosby, M.P. and E.S. Reese. 1996. A manual for monitoring coral reefs with indicator species: butterflyfishes as indicators of change on Indo Pacific reefs. Office of Ocean and Coastal Resource Management, National Oceanic and Atmospheric Administration, Silver Spring, MD. p. 45 Davies, J.M., R.P. Dunne and B.E. Brown. 1997. Coral bleaching and elevated seawater temperature in Milne Bay Province, Papua New Guinea, 1996. Marine and Freshwater Research 48: 513-516. Doubilet, D. 1999. Coral eden. National Geographic 195(1):2-29. Drew, E.A. 1977. A photographic survey down the seaward reef-front of Aldabra Atoll. Atoll Research Bulletin 193. Ebeling, A.W. and M.A. Hixon. 1991. Tropical and temperate reef fishes: comparisons of community structures. In P.F. Sale (ed) The Ecology of Coral Reef Fishes. Academic Press, San Diego, California. p 509-563. Engelhardt, U. 2001. Ecological characteristics of scleractinian coral communities around the inner granitic islands of the Seychelles 2 1/2 years after the 1998 mass coral bleaching event. Reefcare International Pty Ltd, Townsville, Australia. p. 86. English, S., C. Wilkinson and V. Baker. 1997. The survey manual for tropical marine resources. 2nd ed. Australian Institute of Marine Science. P. 390. Ginsburg, R.N., P. Kramer, J. Lang, P. Sale and R. Steneck. 1998. Revised rapid assessment protocol (RAP). Atlantic and Gulf Reef Assessment (AGRA). http://coral.amol.noaa.gov/agra/rap-revised.html. Glynn, P.W. and W.H. Deweerdt. 1991. Elimination of two reef building hydrocorals following the 1982-83 El Niño warming event. Science 253:69-71. Hodgson, G. 1999. A global assessment of human effects on coral reefs. Marine Pollution Bulletin 38(5):345-355. Jatzow, R. and H. Lenz. 1899. Fische von Ost-Afrika, Madagaskar und Aldabra. Abhandlungen der Senckenbergischen naturforschenden Gesellschaft 21:497-531.

65

Johannes, R.E. 1981. Words of the Lagoon. University of California Press, Berkeley, p. 320. McPhaden, M.J. 1999. The child prodigy of 1997 - 98. Nature 398: 559-562. Miller, M.W., Weil, E., and Szmant, A.M. 2000. Coral recruitment and juvenile mortality as structuring factors for reef benthic communities in Biscayne National Park, USA. Coral Reefs 19: 115-123. Mortimer, J.A. 1988. Green turtle nesting at Aldabra Atoll - population estimates and trends. Bulletin of the Biological Society of Washington 8:116-128. Mortimer, J.A. 1997 Turtle monitoring at Aldabra (1997 Version). Global Environmental Facility (EMPS Project J1: Turtle and Tortoise Conservation) and the Government of the Seychelles. P. 47. Osborne, K. and W.G. Oxley. 1997. Sampling benthic communities using video transects. In S. English, C. Wilkinson and V. Baker (eds) Survey Manual for Tropical Marine Resources, 2nd Edition. Australian Institute of Marine Science, Cape Ferguson. p. 363-376. Polunin, N.V.C. 1984. Marine fishes of the Seychelles. In D.R. Stoddart (ed) Biogeography and ecology of the Seychelles Islands. W. Junk Publishers, Netherlands. p 171-191. Potts, G.W. 1973. The ethology of Labroides dimidiatus (Cuv. & Val.) (Labridae, Pisces) on Aldabra. Animal Behaviour 21:250-291. Regan, C.T. 1912. New fishes from Aldabra and Assumption collected by Mr. J.C.F. Fryer. Percy Sladen Expedition Reports 4. Transactions of the Linnean Society, London Ser. 2, Zoology 15:301-302. Roberts, C.M., J.P. Hawkins, D.E. McAllister and F.W. Schueler. In press. Hotspots, endemism and the conservation of coral reef fish biodiversity. Coral Reefs. Roberts, C.M., J.P. Hawkins, N. Chapman, V. Clarke, A.V. Morris, R. Miller and A.Richards. 1999. The threatened status of marine species. Center for Marine Conservation/IUCN, Washington, D.C. Robertson, D.R., N.C.V. Polunin and K. Leighton. 1979. The behavioral ecology of three Indian Ocean surgeonfishes (Acanthurus lineatus, A. leucosternon and Zebrasoma scopas): their feeding strategies, and social and mating systems. Environmental Biology of Fishes 4(2):125-170. Russ, G.R. 1991. Coral reef fisheries: effects and yields. In P.F. Sale (ed.) The Ecology of Coral Reef Fishes. Academic Press, San Diego, California. Chapter 20, p. 601-635. Sale, P.F. 1991. Introduction. In P.F. Sale (ed) The Ecology of Coral Reef Fishes. Academic Press, San Diego, California, p. 3-15. Sebens, K.P. 1991. Habitat structure and community dynamics in marine benthic systems. In S.S. Bell, E.D. McCoy and H.R. Mushinsky (eds) Habitat Structure – The Physical Arrangement of Objects in Space. Chapman and Hall, London. p. 211-234 Shapiro, D.Y. 1977. Social organization and sex reversal of the coral reef fish Anthias squamipinnis (Peters). University of Cambridge Ph.D. Thesis. p. 386. Skerrett, J. and L. Mole. 1995. Somewhere in an empty ocean. In M. Amin, D. Willetts, and A. Skerrett, (eds.) Aldabra World Heritage Site. Camerapix Publishers International, Nairobi, Kenya. p. 23-48. Slingo, J. (1998). The 1997/1998 El Niño. Weather 53: 274-281. Smith, J.L.B. and M.M. Smith. 1969. Fishes of the Seychelles (2nd edition). Rhodes University Institute of Ichthyology , Grahamstown. p. 215. Spencer T., K.A.Teleki, C.Bradshaw and M.D. Spalding. 2000. Coral bleaching in the Southern Seychelles during the 19971998 Indian Ocean warming event. Marine Pollution Bulletin 40(7): 569-586. Steneck, R.S. 1998. Human influences on coastal ecosystems: does overfishing create trophic cascades? Theoretical Ecology 13(11):429-430. Stevens, J.D. 1984. Life-history and ecology of sharks at Aldabra Atoll. Proceedings Royal Society of London B 222:79106.

66

Stoddart, D.J. 1984. Coral reefs of the Seychelles and adjacent islands. In D.R. Stoddart, (ed) Biogeography and ecology of the Seychelles Islands. W. Junk Publishers, Netherlands. pp 31-68 Stoddart, D.J. and L.U. Mole. 1977. Climate of Aldabra Atoll. Atoll Research Bulletin 202. Stoddart, D.R. 1971. Scientific studies of Aldabra and neighbouring islands. Philosophical Transactions of the Royal Society of London B. 260:5-29. Stoddart, D.R. 1983. Spatial and temporal variability of rainfall on Aldabra Atoll. Atoll Research Bulletin 273. Stoddart, D.R. 1997. Bibliography of Aldabra Atoll, 3rd Edition. Seychelles Island Foundation, London and Mahe. p. 89. Teleki, K.A., N. Downing, B. Stobart and R. Buckley. 2000. Aldabra: Marine monitoring and management into the 21st century. Cambridge Coastal Research Unit, Department of Geography, University of Cambridge. p. 23. Teleki, K.A., N. Downing, B. Stobart and R. Buckley. 1999. Aldabra Marine Programme. Cambridge Coastal Research Unit, Department of Geography, University of Cambridge. p. 31. Teleki, K.A., T. Spencer, C. Bradshaw and M.D. Spalding. 1998. Coral Bleaching in the Western Indian Ocean – a sign of the times? International Society for Reef Studies – European Meeting, 1-4 September, Ecole Pratique des Hautes Etudes, Universite de Perpignan. Turner, J.S., S.F. Thrush, J.E. Hewitt, V.J. Cummings and G. Funnell. 1999. Fishing impacts and the degradation or loss of habitat structure. Fisheries Management and Ecology 6:401-420. Van Moorsel, G.N.M. (1988) Early maximum growth of stony corals (Scleractinia) after settlement on artificial substrata on a Caribbean reef. Marine Ecology Progress Series 50: 1008-1009. Viles, H., T. Spencer, K. Teleki and C. Cox. 2000. 16 years of microfloral recolonisation data from limestone surfaces, Aldabra Atoll, Indian Ocean: Implications for biological weathering. Earth Surface Processes and Landforms. 25(12): 13551370. Wallace C.C. 1985. Reproduction, recruitment and fragmentation in nine sympatric species of the coral genus Acropora. Marine Biology 88: 217-233. Wallace, C.C., A. Watt and G.D. Bull. 1986. Recruitment of juvenile corals onto coral tables preyed upon by Acanthaster planci. Marine Ecology Progress Series 32: 299-306. Wilkinson, C.R. 1998. The 1997-1998 mass bleaching event around the world. In C.R. Wilkinson (ed.) Status of Coral Reefs of the World: 1998. Australian Institute of Marine Science, Cape Ferguson. p. 15-38. Wilkinson, C.R. 2000. Status of coral reefs of the world:2000. Australian Institute of Marine Science, Cape Ferguson. p. 363. Wilkinson, C.R. and R.W. Buddemeier. 1994. Global climate change and coral reefs: implications for people and reefs. Report of the UNEP-IOC-ASPEI-IUCN Global Task Team on the Implications of Climate Change on Coral Reefs. IUCN, Gland Switzerland. p. 124. Williams, D.McB. 1991. Patterns and processes in the distribution of coral reef fishes. In P.F. Sale (ed) The Ecology of Coral Reef Fishes. Academic Press, San Diego, California. p. 437-474. Zar, J.H. 1984. Biostatistical analysis, 2nd edition. Prentice-Hall, Inc., New Jersey.

67