Ichthyol Res (2009) 56:314–318 DOI 10.1007/s10228-009-0097-y
SHORT REPORT
How does shoreline development impact the recruitment patterns of coral reef fish juveniles (Moorea Island, French Polynesia)? David Lecchini Æ Julien Million Æ Yohei Nakamura Æ Rene´ Galzin
Received: 7 October 2008 / Revised: 10 January 2009 / Accepted: 14 January 2009 / Published online: 13 March 2009 Ó The Ichthyological Society of Japan 2009
Abstract The study examined the effects of coastal embankment building on fish recruitment in three habitat types (beach-rock, white sand and muddy sand) in the near shore and fringing reef habitats of Moorea lagoon (French Polynesia). The results showed a positive relationship between the presence of embankments and the density and species richness of juvenile fish along the shoreline (whatever the habitat types). However, embankments deteriorated adjacent fringing reefs (decrease of live coral), which led to a decrease of fish density on beach-rock and white sand sites, and a decrease of fish species richness on muddy sand sites. Keywords Coral reef fish Habitat selection Recruitment pattern
D. Lecchini (&) Centre IRD Noumea, Institut de Recherche pour le Developpement, UR 128 CoReUs, Anse Vata, BP A5, Noumea 98848, New Caledonia e-mail:
[email protected] J. Million R. Galzin UMS 2978 CNRS-EPHE, Centre de Recherches Insulaires et Observatoire de l’Environnement, Moorea, French Polynesia Y. Nakamura Department of Global Agricultural Sciences, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan Present Address: Y. Nakamura Department of Kuroshio Science, Graduate School of Integrated Arts and Sciences, Kochi University, 200 Monobe, Nankoku, Kochi 783-8502, Japan
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Introduction In coral reef ecosystems, habitat degradation is usually characterized by coral mortality from natural and anthropogenic stressors (e.g., hurricane damage, pollution, temperature-induced bleaching; Hughes et al. 2003). Coral areas experiencing degradation often exhibit declines in adult populations, leading to extirpation at a higher rate than in pristine habitats, and the persistence of species in the area becomes reliant on the ‘‘rescue’’ effect of recruitment (Hanski and Gilpin 1997). The potential of the area’s population to be supplemented by recruits, however, depends on whether pelagic larvae detect an appropriate habitat in that area and then settle and persist in that habitat (i.e., recruitment phase). For a number of marine species, reductions in the availability of live coral at recruitment may decrease their numerical abundance within degraded reef systems. Such changes in recruitment patterns with reef degradation may then lead to a shift in the community structure of marine communities, away from live coral specialists to degraded reef associates (Hughes et al. 2003). The present study aimed to examine how the presence of rock embankments may affect recruitment strength of larval reef fishes across three habitat types (beach-rock, white sand and muddy sand) and two spatial scales (shoreline and fringing reef) at Moorea Island (French Polynesia). Over the past 20 years, the main human degradation at Moorea has been the building of rock embankments (for roads, private houses or hotels) along the shoreline; these embankments have deteriorated both shoreline and adjacent fringing reefs (Aubanel et al. 1999). These shoreline and fringing reefs are nursery areas for many fish species (Lecchini and Galzin 2005; Lecchini and Tsuchiya 2008). Specifically, we addressed the following three questions: (1) Do embankments affect recruitment success of reef
Recruitment patterns of coral reef fish
fishes? (2) Does the strength of this effect change according to primary habitat type (i.e., beach-rock, white sand and muddy sand)? (3) Does the strength of this effect change with proximity to the embankment (i.e., shore versus fringing reef transects)?
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fishes. On the second pass, the diver swam slowly (\1 m min-1), recording more sedentary species. The recruitment size of coral reef fish species (to count the fish at juvenile and not adult stage) was determined by David Lecchini from February 2001 to June 2002, the period in which he conducted his PhD research at Moorea (see Table 1 in Lecchini and Galzin 2005). The fish juveniles
Materials and methods Moorea Island (17°300 S, 149°50 W) is surrounded by a coral reef 61 km long and 750 m mean wide. The shoreline is characterized by three main habitat types (beach-rock, white sand and muddy sand; Aubanel et al. 1999). We conducted recruitment surveys on 22 sites around Moorea according to habitat types (beach-rock, 3 sites; white sand, 3 sites; muddy sand, 5 sites) and the presence or absence of rock embankments. We selected paired sites (e.g., one beach-rock with embankments close to one beach-rock without embankment; always \100 m between two paired sites) to avoid the spatial variability in larval supply (Lecchini et al. 2004). On each site, the cover percentage of different substrate categories (i.e., live coral, dead coral, coral rubble, rock, white sand, muddy sand and macroalgae) was measured on four replicate 10 m line intersect transects (one record every 1 m; Fig. 1). On each site, diurnal underwater visual counting (0900– 1600 h) of fish juveniles was conducted along four belt transects (bands parallel to the shore), 10 m long and 1 m wide. One transect was located as near to the shoreline as possible, generally 1–2 m away. The three others were randomly positioned on fringing reef (\100 m from shoreline and water depth \1 m). Fishes were censused during two passes over each transect. On the first pass, the diver swam quickly ([5 m min-1) to record ‘transient’
Table 1 Summary of the three-factor ANOVA conducted on density and species richness in fish population recorded at Moorea df
F value
P value
ANOVA on density Habitat type
2
3.711
0.031
Embankment or not
1
3.702
0.062
Spatial scale (shoreline or fringe)
1
14.228
0.001
Habitat vs. embankment
2
4.791
0.010
Habitat vs. spatial scale
2
5.574
0.008
Embankment vs. spatial scale
1
14.566
0.001
Three-factor interaction
2
4.631
0.011
Residue
32
ANOVA on species richness Habitat type
2
53.602
\0.001
Embankment or not
1
171.803
\0.001
Spatial scale (shoreline or fringe)
1
253.038
\0.001
Habitat vs. embankment Habitat vs. spatial scale
2 2
41.261 93.991
\0.001 \0.001
Embankment vs. spatial scale
1
64.276
\0.001
Three-factor interaction
2
11.161
0.001
Residue
32
All pairwise comparisons (PLSD-Fisher’s test) on habitat factor were significant (P \ 0.05)
Fig. 1 Variation in cover percent of substrate composition (live coral, dead coral, coral rubble, coral slab, rock, white sand, muddy sand and macroalgae) among three habitat types (beach-rock, white sand and muddy sand) of fringing reef at Moorea Island (French Polynesia). Error bars represent 1 standard error (SE)
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D. Lecchini et al.
Fig. 2 Variation in density (a) and species richness (b) of coral reef fish juveniles across three habitat types (beach-rock, white sand and muddy sand) and two spatial scales (shoreline and fringing reef) at Moorea Island. Error bars represent 1 SE
were surveyed three times: 24 June (during the full moon), 10 July (new moon) and 24 July 2002 (full moon). The data (density and species richness) collected on fringing reef transects (mean density and total species richness of the three transects) and shoreline transect were analyzed using a three-factor ANOVA (embanked or not, shoreline or fringe, habitat type). A multivariate ordination (Canonical Correspondence Analysis, CCA) was also used to explore the variance explained by each factor, as each can be included sequentially as a covariate, and the unique variance of the assemblage explained by each factor can then be stated.
Results and discussion A total of 2,102 juveniles belonging to 43 species were recorded at Moorea. The density and species richness were always higher on shoreline transects with embankments
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than without embankments, regardless of the habitat types (Fig. 2). In contrast, two opposite recruitment patterns were highlighted on fringing reef transects according to the habitat types: a decrease of density and increase of species richness on beach-rock and white sand sites with embankments, and an increase of density and decrease of species richness on muddy sand sites with embankments (Fig. 2). The three-factor ANOVA showed that the only non-significant difference was the factor ‘‘embanked’’ (Table 1). Nevertheless, the interaction between factor ‘‘embanked’’ and spatial and/or habitat factor was significant (Table 1). Correlations between spatial patterns of juvenile fish communities and environmental factors (embanked or not, shoreline or fringe, habitat type) were assessed using CCA (Table 2). The CCA revealed that the most significant factor explaining variation in community structure was the spatial factor (shoreline or fringe, explained 19.2% of variance in the species matrix), then the habitat type (beach-rock, white sand and muddy sand,
Recruitment patterns of coral reef fish
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Table 2 Summary of the CCA performed on community structure of juvenile fishes Axis f1
Axis f2
Axis f3
-0.916
0.394
-0.068
2. Habitat type
0.613
0.780
0.121
3. Presence or not of embankment
0.612
0.028
-0.790
Eigenvalues
0.292
0.252
0.152
Species–environment correlations
0.893
0.647
0.665
Correlations of environmental variables with ordination axes 1. Spatial variable (shoreline vs. fringe)
Summary statistics for ordination axes
Cumulative percentage variance Species data
19.2
27.2
Species–environment relation
41.9
78.2
Sum of all unconstrained eigenvalues Sum of all canonical eigenvalues
32.0 100
3.166 0.696
Monte Carlo probability for significance of all eigenvalues: 0.001 Significant factors were selected using backward elimination permutation tests (number of permutations = 199) The robustness of the analysis was tested using a Monte Carlo test
8.0%) and lastly the presence or not of embankment (4.8%). Overall, the results showed a positive relationship between the presence of embankments and the density and species richness of fish juveniles on shoreline (whatever the habitat types). Many juveniles were often found around the rock embankments as the embankments may provide refuges or living space for juveniles (for review, see Doherty 2002). Moreover, muddy and sand sites are low quality habitats for most settling fish at Moorea (Lecchini and Galzin 2005). The embankments may increase habitat quality by providing additional refuges for recruits. However, the comparison of live coral percentage on sampling sites with embankments vs. without embankments showed a significant difference (e.g., 17% of live coral on muddy sand sites without embankment vs. 0% of live coral on muddy sand sites with embankments; chi-square test, P = 0.04; Fig. 1). Yet, Aubanel et al. (1999) have shown that the fringing reefs were dominated by living corals before embankment around Moorea. Other studies confirmed that the building of embankments was often associated with the death of corals and the overgrowth of macro-algae through water pollution (e.g., Feary et al. 2007; Garpe and Ohman 2007). However, our results did not support a reduction in the number of fish individuals on fringing reefs. The impact of embankment on juvenile fish communities of fringing reefs is rather ambivalent: a decrease of density and an increase of species richness on beach-rock and white sand sites with embankments, and an increase of density and decrease of species richness on muddy sand sites with embankments (Fig. 2). These results could be explained by the specialization level of habitat selection at recruitment in each species (Lecchini and
Galzin 2005). Indeed, as living coral cover declines within an area, some fish species may recruit on alternative habitats (e.g., macro-algal bed), whereas others do not do so (for review, see Doherty 2002). To conclude, our results show that it becomes important to ascertain the spatial scale being examined when describing embankment effects. In areas close to the embankment, effects may be beneficial due to increasing habitat availability; further from embankments, effects may be less noticeable because embankments are not directly increasing habitat area. Thus, while understanding where species occur at recruitment is a fundamental ecological requirement, prediction of occurrence is essential for much conservation and population management. In a time of increasing use of marine protected areas, this is important information. Moreover, this study provides important baseline data that will enable subsequent investigation of temporal changes in fish communities, as coral reefs in French Polynesia are subject to considerable pressure from anthropogenic impacts and natural disturbances (Adjeroud et al. 2005).
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