Vertical zonation and functional diversity of fish ... - Rodrigo Riera

Journal of Fish Biology (2017) doi:10.1111/jfb.13394, available online at wileyonlinelibrary.com

Vertical zonation and functional diversity of fish assemblages revealed by ROV videos at oil platforms in The Gulf F. Torquato*†, H. M. Jensen*, P. Range‡, S. S. Bach§, R. Ben-Hamadou‡, E. E. Sigsgaard*, P. F. Thomsen‖, P. R. Møller* and R. Riera¶ *Section for Evolutionary Genomics, Natural History Museum of Denmark, University of Copenhagen, Copenhagen, Denmark, ‡Department of Biological and Environmental Sciences, College of Arts and Sciences, Qatar University, Doha, Qatar, §Maersk Oil Research and Technology Centre, Doha, Qatar, ‖Centre for GeoGenetics, Natural History Museum of Denmark, University of Copenhagen, Copenhagen, Denmark and ¶Centro de Investigaciones Medioambientales del Atlántico (CIMA SL), Avda. de los Majuelos, 115. Santa Cruz de Tenerife (Canarias), Spain (Received 29 November 2016, Accepted 29 June 2017) An assessment of vertical distribution, diel migration, taxonomic and functional diversity of fishes was carried out at offshore platforms in The (Arabian–Iranian–Persian) Gulf. Video footage was recorded at the Al Shaheen oil field between 2007 and 2014 using a remotely operated vehicle (ROV). A total of 12 822 individual fishes, from 83 taxonomic groups were recorded around the platforms. All the species identified are considered native to The Gulf, although Cyclichthys orbicularis and Lutjanus indicus were recorded for the first time in Qatari waters. Several trends were uncovered in the vertical distribution of the fish community; most species were observed between 20 and 50 m depth and fish abundance decreased towards the bottom, with the highest abundances recorded in the upper layers, i.e. down to 40 m depth. Vertical variation in fish diversity, however, was generally not accompanied by differences in vertical movements. Carnivores and invertivores were the dominant trophic groups, being found at each depth range from surface to seabed. The functional indices showed no significant differences between water depths or diel cycles. The study demonstrates that oil platforms represent a hotspot of fish diversity and interesting sites for studying fish communities, abundance and behaviour. © 2017 The Fisheries Society of the British Isles

Key words: artificial reef; functional traits; Persian gulf; Qatar; ROPME Sea.

INTRODUCTION About one third of the oil and gas extracted worldwide comes from offshore sources (World Ocean Review, 2014). Currently, there are thousands of large-scale oil and gas platforms spread across the seas and coastal oceans, from the North Sea to the seas of south Asia (Chapman & Khanna, 2000). Although their primary purpose is not related to enrichment of biodiversity, gas and oil platforms can provide large and complex †Author to whom correspondence [email protected]

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1 © 2017 The Fisheries Society of the British Isles

addressed.

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F. T O R Q U AT O E T A L.

artificial habitats for a wide range of marine organisms, including sessile invertebrates (Friedlander et al., 2014) and fishes (Claisse et al., 2014). These structures have been shown to enhance ecosystem functions, especially secondary fish production, relative to adjacent natural reefs (Love et al., 2012), besides being among the most productive marine fish habitats globally (Claisse et al., 2014). Oil and gas platforms are top-security areas with an exclusion zone of at least 500 m around the structures (Kashubsky & Morrison, 2013). Possible security threats around platforms are not restricted to terrorism or insider threats, i.e. employees, contractors, etc., but also include commercial shipping and fishing vessels, as well as recreational activities (CSCAP, 2011). Diving and snorkelling are strictly forbidden in the exclusion zone around offshore platforms, precluding conventional monitoring techniques such as underwater visual census and collection of sessile organisms. Routine inspection and maintenance surveys however, are conducted to monitor the state of underwater structures, i.e. pillars, pipes, etc. These surveys are mainly performed through video footage recorded using remotely operated vehicle (ROV), which is controlled by authorized personnel. ROV-based surveys enable researchers to cover wider and deeper areas than other approaches, such as conventional scuba diving. The method has previously been used for quantifying the distribution and abundance of sessile invertebrates in areas with logistic limitations (e.g. due to depth, intense currents) and remoteness (Thrush et al., 2001; Teixidó et al., 2011). In addition, the presence of ROVs seem to have less effect on the behaviour of most fish species (Patterson et al., 2009), compared with the effects of scuba diving, which, despite easier detection–identification of cryptic and small individuals (e.g. blennies, gobies, etc.), allows many species to escape detection (Dearden et al., 2010). Owing to such advantages, ROV videos have been shown to be effective for estimating both the community structure of fish and the spatial distribution of individuals (Patterson et al., 2009; Trenkel & Lorance, 2011; Ajemian et al., 2015). Recently, ROV videos have also been utilized for the calculation of functional diversity (De Juan et al., 2015). The underlying concept of functional diversity is based on functional traits, which are defined as biological and ecological attributes that influence the performance (e.g. swimming, foraging, reproduction aspects) of an organism (Villnäs et al., 2011). Previous studies have shown that functional diversity is a better predictor of many ecosystem processes than species richness (Lombarte et al., 2012) or taxonomic diversity (Mouillot et al., 2005). Offshore reefs in The (Arabian–Iranian–Persian) Gulf generally contain a more diverse coral-associated fish fauna because they occur in deeper waters and are less impacted by human disturbance. They also are less affected by extreme temperature and salinity fluctuations compared with nearshore reefs (Feary et al., 2010, 2011; Burt et al., 2014). Deep reefs (natural and artificial) however, are generally less studied in The Gulf than shallow nearshore reefs (Blegvad & Løppenthin, 1944; Buchanan et al., 2016). In Qatari waters, natural reefs are scattered within the exclusive economic zone (EEZ), whereas the main concentration of artificial reefs is found in the Al Shaheen oil field c. 100 km offshore (Fig. 1). The area is known to host a large aggregation of whale sharks Rhincodon typus Smith 1828, feeding on eggs from the mackerel tuna Euthynnus affinis (Cantor 1849) (Robinson et al., 2013, 2016; Sigsgaard et al., 2017), but the remaining fish fauna remains unstudied. The aim of the present study was to explore the taxonomic and functional diversity, vertical zonation and diel migrations of fish aggregations at the oil platforms in Al Shaheen oil field (north-eastern Qatar EEZ). The hypothesis was that environmental

© 2017 The Fisheries Society of the British Isles, Journal of Fish Biology 2017, doi:10.1111/jfb.13394

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V E RT I C A L Z O N AT I O N O F F I S H AT O I L P L AT F O R M S 30·0°

Iran 27·0°

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Qatar

50·5°

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51·5°

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Fig. 1. Map of the study area showing the location of the oil platforms (A–I) in Qatari waters of The Gulf.

gradients across the vertical profile of the pillars affect the distribution of fish species, causing functional groups to occupy layers where their respective realized niches are better fitted. Therefore, large abundances of browsing herbivorous fish were not expected at deeper layers, for instance, where algal growth is limited owing to the reduced penetration of sunlight. Data were opportunistically extracted from ROV inspection videos, recorded from 2007 to 2014, from which basic information about fish communities of these artificial habitats was obtained, including a list of species inhabiting the platforms and their relative abundance (hereafter referred to as abundance) and spatial differences in relation to depth, including diel cycles. In addition, the information generated was analysed to determine if these differences are noticeable at the level of functional traits.

MATERIALS AND METHODS S T U DY A R E A The Gulf (also known as the ROPME sea; Regional Organization for the Protection of the Marine Environment; www.ropme.org) is a relatively young and shallow sea that originated c. 15 000 years ago (Sheppard et al., 2010), currently c. 990 km long, with a maximum width of 370 km and a mean depth of 36 m. The Gulf is connected to The Gulf of Oman by the Strait of Hormuz through which it receives Indian Ocean surface water (IOSW). Otherwise, the major, but not significant, input of fresh water is provided through precipitation and river discharges from the Rivers Tigris and Euphrates in the north (Kämpf & Sadrinasab, 2006). The Gulf is located in the arid sub-tropics, between latitudes 24∘ and 30∘ N, surrounded by most of the


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Table I. Oil platforms in Qatari waters included in the study

Name AS-A-C AS-A-D AS-B-A AS-B-B AS-B-C AS-B-D AS-B-E AS-B-F AS-B-G AS-C-A AS-C-B AS-C-C AS-C-D AS-D-A AS-D-B AS-E-A AS-E-B AS-E-C AS-E-D AS-E-F AS-F-A AS-F-B AS-G-A AS-G-D AS-H-A AS-H-B AS-I-A AS-G-A

Weight Depth Year of with (m) installation piles (t) Platform function 60·0 62·0 61·0 61·0 61·0 61·0 61·0 61·0 61·0 56·5 56·5 56·0 56·5 65·0 65·0 66·5 66·5 66·5 66·5 66·5 55·0 55·5 51·0 50·5 57·0 57·0 69·5 51·0

1997 1998 1998 1997 2004 2007 2009 2009 2009 1998 1997 2004 2007 2004 2004 2004 2004 2004 2009 2009 2004 2004 2007 2009 2007 2009 2007 2007

774 2078 3610 671 1098 3536 8131 916 7986 3590 659 1088 3322 4610 941 4474 958 1101 6061 913 4440 916 3129 7210 3407 NA 4139 3129

Flare platform Accommodation platform Wellhead platform Flare platform Accommodation platform Wellhead platform Process platform Accommodation platform Utility platform Wellhead platform Flare platform Accommodation platform Wellhead platform Wellhead platform Flare platform Wellhead platform Flare platform Accommodation platform Process platform Accommodation platform Wellhead platform Flare platform Wellhead platform Wellhead–Process platform Wellhead platform Flare platform Wellhead platform Wellhead platform

Sampling year 2007 2009 2010 2011 2012 2014

+

+

+

+ + + + + + + + +

+ + + +

+

+

+ +

+

+

+ + + +

+ +

+ + + +

+ + + +

+ + + + + + + + + + + + +

Earth’s deserts. It is one of the warmest (surface waters ≥36∘ C in summer) and most saline of waters (often >45) on Earth (Reynolds, 1993; Kämpf & Sadrinasab, 2006; Sheppard et al., 2010). Water temperature and salinity are mainly driven by the seasonal cycle of incident solar radiation and by the inflow of IOSW, respectively (Coles & Riegl, 2013). This study focused on the Al Shaheen oil field, located in the offshore area called Block 5, in the north-east of the EEZ of Qatar. Maersk Oil Qatar was operating in the oil field on behalf of Qatar Petroleum, with oil and gas production platforms installed at nine different locations (A–I) with mean ± s.d. spacing of 14·31 ± 7·2 km and at depths ranging from 50 to 70 m. In each location, platforms of different weights, ages and functions have been working for almost 18 years (Fig. 1 and Table I).

S U RV E Y M E T H O D S A N D D ATA A N A LY S I S A total of 4510 video files, containing 120 h of underwater video recordings, were provided by Maersk Oil Qatar A/S. These videos were recorded over 6 years (2007, 2009, 2010, 2011, 2012 and 2014), during day and night, at the nine platform locations (A–I) within the Al Shaheen oil field using a ROV (model SAAB Seaeye Surveyor Plus 229; www.seaeye.com). To assess the local fish community, a total of 242 videos amounting to 21 h of observation were selected randomly, but if no fish appear in a selected video a new video was randomly selected from the list. The total time of observation was spread out nearly equally over the 6 years. For 2012


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V E RT I C A L Z O N AT I O N O F F I S H AT O I L P L AT F O R M S

Table II. Total hours of observation time for selected videos for different years of the study period Year

Recording time

Number of videos

2007 2009 2010 2011 2012 2014

04 h 05 min 25 s 04 h 04 min 34 s 04 h 02 min 44 s 04 h 22 min 24 s 00 h 22 min 09 s 04 h 09 min 14 s

34 42 38 55 18 55

however, only 22 min of video recording were observed since this was the total recording time available for that year (Table II). During the video survey, the camera moved randomly, i.e. did not perform any survey protocol, at slow and constant speed. All fishes were counted, being careful to not count the same fish or group of fish twice and identified at least to family level following the approaches described by Allen (2009), Allen et al. (2003), Carpenter et al. (1997) and Sivasubramaniam & Ibrahim (1982). Unidentified fish were only included in overall abundance estimates. In order to standardize the effort employed, i.e. recording time, abundances of individual taxa were standardized to one minute (individuals min−1 ) of each video file.

V E RT I C A L D I S T R I B U T I O N Differences in fish abundance with depth were evaluated using one-way ANOVA. Data were log transformed to meet the assumptions of normality, which was evaluated by means of quantile-quantile plot of residuals and Shapiro–Wilk test, while homogeneity was assessed through residual v. predicted values plot. Tukey’s multiple comparison post hoc test was used to identify differences among each depth range (each spanning 10 m) when an overall effect was detected (P < 0·05). All these analyses were performed in R software (www.r-project.org). The association of the most prominent species to each 10 m layer was assessed by the indicator value index (IndVal; Dufrêne & Legendre, 1997) and its posterior statistical significance (P < 0·05) was obtained by a randomization procedure (1000 permutations). The IndVal quantifies the fidelity and specificity of species in relation to groups of sites. This analysis was performed with the labdsv package in R. D I E L V E RT I C A L M O V E M E N T Daily variation in the depth distribution of species with broad vertical distributions (≥ 50 m) and frequencies of occurrence higher than 10%, were represented by the index of vertical displacement of the mean centre of mass (Z CM ), as in Fortier & Leggett (1983) and Stephenson & x ∑ Power (1988): Z CM = 𝜌i zi , where, 𝜌i is the proportion of fish occurring at depth i and zi is the i=1

average depth of the ith stratum. For example, a value of 5 m was used for individuals observed in the stratum from 0 to 10 m depth. Similarly, a value of 35 m was used for fishes located in the stratum from 30 to 40 m depth.

F U N C T I O NA L T R A I T S The functional strategy of each species or taxon was described using seven categorical traits (body shape, swimming, mobility, diet, size, habitat and burying ability) based on locomotion and feeding of species that are important for determining their role in marine and


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freshwater assemblages (Webb, 1984; Fulton et al., 2001; Dumay et al., 2004; Bellwood et al., 2006; Villéger et al., 2011) (Appendix S1, Supporting Information).

M E A S U R I N G C H A N G E S I N F U N C T I O NA L D I V E R S I T Y Functional diversity was estimated with a multidimensional approach using three diversity indices, based on either the abundance of species (I FDis , functional dispersion; I FDiv , functional divergence) or on presence/absence data (I FR , functional richness) (Mason et al., 2003; Villéger et al., 2008). Functional richness was assessed through the functional dispersion index (I FDis ) (Laliberté & Legendre, 2010), which corresponds to the mean distance of a species to the centroid of the community in the community trait space. I FDis accounts for not only the trait space filled by a community (convex hull volume), but also dispersion and species relative abundance (Laliberté & Legendre, 2010; Koech et al., 2014). I FDiv describes how far high species abundances are from the centre of the functional space. High functional divergence indicates a high degree of niche differentiation and thus low resource competition (Mason et al., 2003; Mouchet et al., 2010). Rao’s Q (quadratic entropy) represents the average of the species differences when some measurement of pair-wise differences between species and relative frequency data are available. Rao’s Q is derived from entropy theory and is expressed as a quadratic form using the relative abundance of species (Casanoves et al., 2008). The equivalent number of species was used for Rao’s Q, in order to maintain the connection with the context of Rao’s quadratic entropy (Ricotta & Szeidl, 2009). Prior to estimating these functional indices, pair-wise functional distances between functional traits were computed using the Gower distance, which allows for mixing different types of variables while giving them equal weight. These multidimensional FD indices were calculated for each sample (video) of the dataset using the fd package in R (Laliberté & Legendre, 2010). Two-way ANOVA was used to assess diversity indices considering factors such as depth (shallow–mid–deep) and light (day–night). A similarity matrix based on the Euclidean distance of FD indices was generated for the analyses. The Euclidean distance was applied to the matrix of functional traits because it has been previously considered as appropriate for homogeneous and complete trait matrices (Petchey & Gaston, 2002). For each term of the model, P values were obtained with 9999 permutations of residuals under a reduced model and Type III sums of squares. All procedures were carried out with the PAST software (Hammer et al., 2001).

RESULTS F I S H FAU N A C O M P O S I T I O N

A total of 12 822 fishes were recorded and 9298 identified, belonging to 83 identified species or taxonomic groups in 31 families (Table III). Among these, two species were recorded in Qatari waters for the first time: Cyclichthys orbicularis (Bloch 1785) and Lutjanus indicus Allen, White & Erdmann, 2013. In addition, two Chondrichthyes, one endangered, Stegostoma fasciatum (Hermann 1783) and one vulnerable species, Taeniurops meyeni (Müller & Henle 1841), were also observed across the platforms. Carangidae was the most diverse family (10 species) followed by Labridae (5) and Epinephelidae (5). The most abundant species were pennant coralfish Heniochus acuminatus (L. 1758), yellowbar angelfish Pomacanthus maculosus (Forsskål 1775), Indo-Pacific sergeant Abudefduf vaigiensis (Quoy & Gaimard 1825) and two-bar seabream Acanthopagrus bifasciatus (Forsskål 1775), respectively (Table III). Of the 23 coral-dependent species in The Gulf listed by Buchanan et al. (2016), six [A. vaigiensis, Acanthurus sohal (Forsskål 1775), Chaetodon nigropunctatus Sauvage 1880, H. acuminatus, Scarus ghobban Forsskål 1775 and Scarus persicus Randall & Bruce 1983] were found in the present study (Table III).


Species

Abudefduf vaigiensis Acanthopagrus bifasciatus Acanthurus sohal Aetobatus narinari Alectis ciliaris Aluterus monoceros Arothron stellatus Blenniidae sp. Caesio sp. Caesionidae sp. Carangidae sp. Carangoides bajad Carangoides ferdau Carangoides gymnostethus Caranx ignobilis Caranx sexfasciatus Caranx sp. Carcharhinidae sp. Carcharhinus amblyrhynchoides Cephalopholis hemistiktos Cephalopholis sp. Chaetodon nigropunctatus Cheilio sp. Cyclichthys orbicularis+ Cyclichthys sp. Diodontidae sp. Echeneis naucrates Epinephelus coeruleopunctatus

Family

Pomacentridae Sparidae Acanthuridae Myliobatidae Carangidae Monacanthidae Tetraodontidae Blenniidae Caesionidae Caesionidae Carangidae Carangidae Carangidae Carangidae Carangidae Carangidae Carangidae Carcharhinidae Carcharhinidae Serranidae Serranidae Chaetedonthidae Labridae Diodontidae Diodontidae Diodontidae Echeneidae Epinephilidae

861 390 19 5 1 1 1 1 570 6 645 5 6 2 5 379 70 1 2 90 6 37 1 12 15 20 13 26

12·4 31·8 4·1 1·7 0·4 0·4 0·4 0·4 2·9 0·8 12·8 1·2 0·4 0·4 1·2 5·4 1·2 0·4 0·8 21·1 2·1 7·0 0·4 4·1 4·1 6·6 1·2 7·0

Omnivore Invertivore Herbivore Carnivore Carnivore Invertivore Omnivore Omnivore Planktivore Planktivore Carnivore Carnivore Carnivore Piscivore Carnivore Carnivore Carnivore Carnivore Carnivore Piscivore Piscivore Invertivore Invertivore Invertivore Invertivore Invertivore Piscivore Carnivore

Number of Frequency Trophic individuals (%) group Ov Ob Ov SY Fu Ov Ov El Fu Fu Fu Fu Fu Fu Fu Fu Fu Fu Fu Ob Ob Ov El Ov Ov Ov El Ov

Lab Suc Lab Raj Cac Bal Tet Suc Cac Cac Cac Cac Cac Car Cac Cac Cac Cac Cac Suc Suc Bal Lab Tet Tet Tet Cac Suc

R R S H H R S S H H H H H H H H H H H R R S R S S S H R

No No N N N N N Y N N N N N N N N N N N N N N N N N N N N

MALG MINV SCRP MAC PIS MINV MINV OMNI DPLA DPLA PIS PIS PIS PIS PIS PIS PIS MAC MAC MAC MAC SINV MINV MINV MINV MINV MINV MAC

Body Type Burying shape swimming Motility ability Diet S M M L ML ML L S M M ML ML ML L L L L L L M M S ML SM SM SM L M

BP BP BP BP P BP BP B P P P P P P P P P P P BP BP BP BP BP BP BP P BP

Vertical Fish size distribution

Table III. List of species observed around oil installations in Qatari waters and their categories within the selected functional traits. Coral-dependent species are in bold



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Species

Epinephelus coioides Epinephelus sp. Gerres sp. Gnathanodon speciosus Gymnothorax undulatus Heniochus acuminatus Himantura bleekeri Himantura imbricata Kyphosus sp. Labridae sp. Labroides dimidiatus Lactoria sp. Lethrinus borbonicus Lutjanidae sp. Lutjanus fulviflamma Lutjanus indicus+ Lutjanus malabaricus Lutjanus sp. Monacanthidae sp. Myliobatidae sp. Ostraciidae sp. Ostracion cubicus Ostracion cyanurus Parapercis alboguttata Pinjalo pinjalo Platax sp. Platax teira Plectorhinchus gaterinus Pomacanthus maculosus Pomacentridae sp.

Family

Epinephilidae Epinephilidae Gerreidae Carangidae Muraenidae Chaetodontidae Dasyatidae Dasyatidae Kyphosidae Labridae Labridae Ostraciidae Lethrinidae Lutjantidae Lutjantidae Lutjantidae Lutjantidae Lutjantidae Monacanthidae Myliobatidae Ostraciidae Ostraciidae Ostraciidae Pinguipedidae Lutjantidae Ephippidae Ephippidae Haemulidae Pomacanthidae Pomacentridae

18 51 5 2 1 1598 1 2 200 1 2 1 1 500 29 6 10 290 2 2 2 2 1 1 3 171 118 185 1562 102

Number of individuals 4·5 10·7 0·4 0·4 0·4 66·1 0·4 0·8 0·4 0·4 0·4 0·4 0·4 0·4 2·1 0·4 2·5 16·1 0·8 0·8 0·8 0·4 0·4 0·4 0·4 10·7 11·6 26 66·9 0·8

Frequency (%) Carnivore Carnivore Carnivore Carnivore Carnivore Omnivore Carnivore Carnivore Omnivore Omnivore Omnivore Carnivore Carnivore Carnivore Carnivore Carnivore Carnivore Carnivore Omnivore Omnivore Omnivore Omnivore Carnivore Carnivore Carnivore Carnivore Carnivore Carnivore Omnivore Herbivore

Trophic group Ov Ov Ov Fu El Ov Sy Sy Fu Fu Fu Ob Ob Ob Ob Ob Ob Ob Ov Sy Ob Ob Ob Fu Ob Ov Ov Ob Ov Fu

Body shape

Table III. Continued

Suc Suc Suc Cac Ang Suc Raj Raj Suc Lab Lab Ost Suc Suc Suc Suc Suc Suc Tet Raj Ost Ost Ost Suc Suc Suc Suc Suc Suc Suc

Type swimming R H H H S H S S H H H R H H H H H H R H R R R H H R R H R R

Motility N N N N N N Y Y N N N N N N N N N N N N N N N N N N N N N N

Burying ability MAC MAC MINV MAC MAC OMNI MINV MINV OMNI OMNI SCRP MINV MINV MAC MAC MAC MAC MAC MINV OMNI OMNI OMNI MINV MAC MAC MAC MAC MAC SINV MALG

Diet M ML SM L L SM L SM ML M S ML M M M SM ML ML S ML M M S SM ML ML ML ML ML S

Fish size

BP BP P P B P B B P P P BP P P P P P P P P BP BP BP B B P P P BP BP

Vertical distribution

8 F. T O R Q U AT O E T A L.



Pomacentrus sp. Pseudanthias sp. Pseudanthias townsendi Pterois miles Pterois sp. Rhinobatidae sp. Sargocentron sp. Scarus ghobban Scarus persicus Scarus sp. Scomberoides commersonnianus Scorpaenidae sp. Scorpaenopsis sp. Seriola dumerili Serranidae sp. Siganus canaliculatus Siganus sp. Sphyraena jello Sphyraena putnamae Sphyraena sp. Stegostoma fasciatum Taeniurops meyeni Thalassoma lunare Thalassoma sp. Trachinotus blochii

Pomacentridae Serranidae Serranidae Scorpaenidae Scorpaenidae Rhinobatidae Holocentridae Labridae Labridae Labridae Carangidae Scorpaenidae Scorpaenidae Carangidae Serranidae Siganidae Siganidae Sphyraenidae Sphyraenidae Sphyraenidae Stegostomastidae Dasyatidae Labridae Labridae Carangidae

20 105 13 26 96 1 1 1 1 85 1 2 3 5 15 4 13 2 475 298 1 4 35 23 9

0·4 0·8 0·8 7·4 16·9 0·4 0·4 0·4 0·4 12·0 0·4 0·8 0·8 1·2 3·3 0·8 2·9 0·8 3·3 7·4 0·4 1·7 1·2 1·2 1·7

Herbivore Planktivore Planktivore Carnivore Carnivore Carnivore Carnivore Herbivore Herbivore Herbivore Carnivore Piscivore Piscivore Piscivore Piscivore Herbivore Herbivore Piscivore Piscivore Piscivore Invertivore Carnivore Invertivore Invertivore Invertivore

Number of Frequency Trophic individuals (%) group Fu Fu Fu Ov Ov Sy Fu Fu Fu Fu Fu Ov Ov Fu Fu Fu Fu El El El Sy Sy Fu Fu Ov

Suc Suc Suc Suc Suc Raj Suc Lab Lab Lab Car Suc Suc Car Car Suc Suc Car Car Car Raj Raj Lab Lab Car

R S S S S R R R R R H R R H R R R H H H R R R R H

N N N N N N N N N N N N N N N N N N N N N N N N N

MALG DPLA DPLA MAC MAC MINV MINV MALG MALG MALG MAC PIS PIS PIS PIS MALG MALG PIS PIS PIS MAC MAC MINV MINV MINV

Body Type Burying shape swimming Motility ability Diet S S S M M L M ML ML ML L M M L ML SM SM L L L L L ML ML L

BP BP BP BP BP B BP BP BP BP BP B B P BP BP BP P P P B B BP BP BP

Vertical Fish size distribution

+, First record in Qatari waters. Body shape: Fu, Fusiform; El, elongated; Ob, oblong; Ov, oval; Sy, symetrical flatfish; As, assymetrical flatfish. Swimming type: Ang, anguiliform; Raj, rajiform; Suc, subcarangiform; Cac, carangiform; Ost, ostraciform; Bal, balistiform; Lab, labriform; Tet, tetraodontiform; Motility: S, sedentary or territorial; R, roving; H, highly mobile or migratory. Diet: Mac, macrocarnivores; Pis, obligate piscivores; Minv, mobile benthic invertivores; Sand, sand invertivores; Sinv, colonial sessile invertivores; Dpla, diurnal planktivores; Npla, nocturnal planktivores; Scpr, scrapers; Malg, macroalgae browser; Omni, general omnivores. Vertical distribution: P, pelagic; BP, benthopelagic; B, benthic.

Species

Family

Table III. Continued


9

10


a

0 – 10 a,b

11 – 20

a

Depth (m)

21 – 30 a,c

31 – 40 b,c

41 – 50 b

51 – 60

b,c

61 – 70 0

2

4

6

8

10

12

14

16

18

20

Relative abundance (n min–1) Fig. 2. Mean + s.d. relative abundance by 10 m depth strata of fish aggregated along the vertical profile of oil installations. Different lower-case letters indicate significant differences (Tukey’s HSD, P < 0·05).

V E RT I C A L D I S T R I B U T I O N O F S P E C I E S A N D T R O P H I C G RO U P S

The abundance of fishes on the platform was higher in the upper layers, down to 40 m depth and decreased with depth (Fig. 2). Most species were observed between 20 and 50 m depth, though many showed high amplitude in vertical distribution. Heniochus acuminatus and Cephalopholis hemistiktos (Rüppell 1830) showed the largest vertical amplitude distribution, from 2 m to 71 m and 4 m to 71 m, respectively (Fig. 3). According to the IndVal index, the most prominent species in the first 10 m depth were A. vaigiensis, A. bifasciatus and A. sohal; in middle layers H. acuminatus, P. maculosus (20–30 m) and Cyclichthys sp. (40–50 m); and in deeper layers C. hemistiktos, Pterois miles (Bennett 1828) (50–60 m) and Pterois sp. and Diodontidae (60–70 m) (Table IV). Table IV. Numerical summary of Indicator Value index (IndVal) Species Abudefduf vaigiensis Acanthopagrus bifasciatus Acanthurus sohal Heniochus acuminatus Pomacanthus maculosus Cyclichthys sp. Cephalopholis hemistiktos Pterois miles Pterois sp. Diodontidae

Depth range

IndVal index

P

Frequency

0–10 0–10 0–10 21–30 21–30 41–50 51–60 51–60 61–70 61–70

0·3757 0·2657 0·1020 0·3042 0·2354 0·1400 0·1421 0·1091 0·2936 0·1782