Abstract
We report a reef ecosystem where corals may have lost their role as major reef engineering species but fish biomass and assemblage structure is comparable to unfished reefs elsewhere around the world. This scenario is based on an extensive assessment of the coral reefs of Farquhar Atoll, the most southern of the Seychelles Islands. Coral cover and overall benthic community condition at Farquhar was poor, likely due to a combination of limited habitat, localized upwelling, past coral bleaching, and cyclones. Farquhar Atoll harbors a relatively intact reef fish assemblage with very large biomass (3.2 t ha−1) reflecting natural ecological processes that are not influenced by fishing or other local anthropogenic factors. The most striking feature of the reef fish assemblage is the dominance by large groupers, snappers, and jacks with large (>1 m) potato cod (Epinephelus tukula) and marbled grouper (E. polyphekadion), commonly observed at many locations. Napoleon wrasse (Cheilinus undulatus) and bumphead parrotfish (Bolbometopon muricatum) are listed as endangered and vulnerable, respectively, but were frequently encountered at Farquhar. The high abundance and large sizes of parrotfishes at Farquhar also appears to regulate macroalgal abundance and enhance the dominance of crustose corallines, which are a necessary condition for maintenance of healthy reef communities. Overall fish biomass and biomass of large predators at Farquhar are substantially higher than other areas within the Seychelles, and are some of the highest recorded in the Indian Ocean. Remote islands like Farquhar Atoll with low human populations and limited fishing pressure offer ideal opportunities for understanding whether reefs can be resilient from global threats if local threats are minimized.
Highlights
Preserving coral reefs under the threat of climate change presents the difficult challenge of determining how effective conservation efforts will be, when the prognosis for reefs seems so bleak [1,2,3]
We present a scenario for a reef ecosystem where corals may have lost their role as major reef engineers but where fish assemblages are relatively intact
General Oceanography and Geomorphology Based on survey results and knowledge of the region, we developed a conceptual model of the general oceanography and geomorphology of Farquhar Atoll (Fig. 8)
Summary
Preserving coral reefs under the threat of climate change presents the difficult challenge of determining how effective conservation efforts will be, when the prognosis for reefs seems so bleak [1,2,3]. Given the facts that most CO2 and temperature scenarios exceed current limits of survival of reef corals and many other reef and calcifying species, and adaptation options are essentially unknown and not yet predictable, reefs may disappear on a 50–100 year time scale [1,4]. This brings into question the utility of conserving reefs at the local scale. These functions and processes have value in and of themselves from a perspective of maintaining and conserving mature ecosystems under current circumstances, as well as from the provisioning of some of the ecosystem goods and services to society
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