Abstract
Parrotfishes are a group of herbivores that play an important functional role in structuring benthic communities on coral reefs. Increasingly, these fish are being targeted by fishermen, and resultant declines in biomass and abundance may have severe consequences for the dynamics and regeneration of coral reefs. However, the impact of overfishing extends beyond declining fish stocks. It can also lead to demographic changes within species populations where mean body size is reduced. The effect of reduced mean body size on population dynamics is well described in literature but virtually no information exists on how this may influence important ecological functions. The study investigated how one important function, scraping (i.e., the capacity to remove algae and open up bare substratum for coral larval settlement), by three common species of parrotfishes (Scarus niger, Chlorurus sordidus, and Chlorurus strongylocephalus) on coral reefs at Zanzibar (Tanzania) was influenced by the size of individual fishes. There was a non-linear relationship between body size and scraping function for all species examined, and impact through scraping was also found to increase markedly when fish reached a size of 15–20 cm. Thus, coral reefs which have a high abundance and biomass of parrotfish may nonetheless be functionally impaired if dominated by small-sized individuals. Reductions in mean body size within parrotfish populations could, therefore, have functional impacts on coral reefs that previously have been overlooked.
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Acknowledgments
We would like to thank DR Bellwood for valuable comments on the manuscript and N Jiddawi (MSI, University of Dar es Salaam), M Peterson, and H Peeks (CHICOP) for their kind support. The field work of J L was supported by L & E Kinanders foundation. The work of MN, MT, and CJ was supported by the Swedish International Development Cooperation Agency (Sida/Sarec).
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Lokrantz, J., Nyström, M., Thyresson, M. et al. The non-linear relationship between body size and function in parrotfishes. Coral Reefs 27, 967–974 (2008). https://doi.org/10.1007/s00338-008-0394-3
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DOI: https://doi.org/10.1007/s00338-008-0394-3