Distribution of coral reef fishes along a coral reef-seagrass gradient: edge effects and habitat segregation

Abstract

Coral reefs and seagrass beds are often located adjacent to one another, but little is known about the degree to which their fish communities are interlinked. To determine whether coral reef fishes on the coral reef are interlinked with or segregated from fishes on adjacent seagrass beds, a 60 m coral reef -seagrass gradient was studied on the island of Zanzibar in the western Indian Ocean. Using underwater visual census, coral reef fishes were surveyed in 4 habitat zones: (1) a coral patch reef, (2) seagrass beds bordering the coral reef, (3) seagrass beds at a 30 m distance from the coral reef edge and (4) seagrass beds at a 60 m distance from the coral reef edge. Based on the densities of juveniles and adults in the 4 zones, the 48 species that were observed were classified into reef-associated species, seagrass-associated species, nursery species, generalists and rare species. Reef-associated species occurred almost exclusively on the coral reef and at the reef -seagrass edge, while seagrass-associated species occurred almost exclusively on the seagrass beds. Generalists and seagrass-associated species occurred in all 3 seagrass zones, but densities of generalists on seagrass beds decreased with increasing distance from the reef, whereas that of seagrass-associated species increased. Reef-associated and generalist species showed an edge effect, where densities on the seagrass beds near the reef edge were higher than on the seagrass beds further away. Juvenile densities of nursery species on seagrass beds also increased with the distance from the reef, whereas their adults showed the highest densities on the coral reef, suggesting a possible ontogenetic shift from the seagrass beds to the reef. The results of the present study show that this seagrass-coral reef landscape features habitat segregation between species and life stages and shows an edge effect, possibly driven by competition mechanisms between species or life stages. KEY WORDS: Coral reef fish · Seagrass beds · Habitat connectivity · Species interaction · Migrations · Edge effect Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 299: [277][278][279][280][281][282][283][284][285][286][287][288] 2005 The few studies that have examined interlinkages between multiple fish species on seagrass beds and coral reefs were carried out in situations where the 2 habitat types were located at some distance (i.e. hundreds of metres) from each other. This distance may be too large to result in species interactions between these habitats, because species associated with 1 habitat may only migrate across short distances (metres) to adjacent habitats. No published studies seem to have investigated fish species distribution patterns in a continuous reef -seagrass gradient.Where coral reefs and seagrass beds meet, interactions between fish communities associated with 1 of these habitats are very likely to occur in the edge zone: reef-associated fish may partly migrate into the seagrass beds, whereas seagrass-...

Seascape ecology of coastal biogenic habitats: advances, gaps, and challenges

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Mapping Submerged Habitats and Mangroves of Lampi Island Marine National Park (Myanmar) from in Situ and Satellite Observations

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Preference of early juveniles of a coral reef fish for ­distinct lagoonal microhabitats is not related to common measures of structural complexity

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