Regulation of macroalgal abundance on Western Indian Ocean coralreefs – Fishery closure induced phase shifts an indication of successfulmanagement?
(English)Manuscript (preprint) (Other academic)
Grazing by herbivores is an important mechanism governing macroalgal distribution andbiomass on coral reefs. However, as feeding efficiency, preferences, mechanisms andeffects differs between grazers, the composition of the herbivore community determinesthe rates and impact of algal removal. Furthermore, environmental conditions such assubstrate availability can further affect the effects of herbivory, suggesting great spatialvariation in removal potential. Variation also occurs on a temporal scale as the herbivorecommunity and live coral cover are altered with recovering coral and fish populations.Thus, if the herbivore community changes across a recovery period, a phase shift mayoccur due to changing feedings rates and impacts. This study, therefore, investigated therelative importance of herbivorous fish and sea urchins, two groups with different feedingmethods and impacts, over different spatial and temporal scales in western Indian Oceanreefs that are mostly degraded through fishing. Overall, our results suggest that herbivoryby sea urchins is more important in controlling algal abundance than fish in the studiedregion. Sea urchins seem to be able to influence cover and community composition ofmacroalgae even though substrate available for macroalgal colonization is generally high.This same pattern was found at all investigated scales (the region as a whole, withinKenya and over time in Mombasa Marine Park). Furthermore, our results indicate thatincreasing macroalgal abundance may occur following the establishment of a fisheriesclosure, with declining sea urchin and recovering fish abundance. This may be a result ofweak recovery of herbivorous fishes in a seascape of heavy fishing but suggests thateliminating fishing of herbivores in small areas may not be able to recover intensegrazing and reduce macroalgal abundance.
Ecosystem change; Macroalgae; Herbivory; Fish; Sea Urchins; Coral Reefs; Scale
IdentifiersURN: urn:nbn:se:su:diva-48280OAI: oai:DiVA.org:su-48280DiVA: diva2:374820