a1 Natural Resource Management, Department of Systems Ecology, Stockholm University, SE-106 91 Stockholm, Sweden
a2 Stockholm Resilience Centre, Stockholm University, SE-106 91 Stockholm, Sweden
a3 Beijer Institute of Ecological Economics, Royal Swedish Academy of Sciences, PO Box 50005, SE-104 05 Stockholm, Sweden
a4 ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, Queensland 4811, Australia
Fishing can have major impacts on the structure of coral reef ecosystems. Overfishing of herbivores is particularly detrimental, as it makes the coral system more likely to undergo shifts to macroalgal dominance in the event of coral mass mortality. Knowing when important processes, such as herbivory, are becoming brittle is important because it can provide an opportunity for managers to avoid undesirable ecosystem-level changes. This study investigates the impact of artisanal fishing on three important functional groups of herbivores (grazers, scrapers and excavators) on five coral-dominated reefs outside Zanzibar (Tanzania). There was a negative correlation between fishing pressure and fish biomass, abundance, diversity and species richness. Moreover, fishing had a negative influence on the demographic structure of functional groups, particularly excavators, manifesting itself as a skewness towards smaller individuals within populations. Artisanal fishing can have significant impacts on key functional groups of herbivorous reef fishes which may increase the vulnerability of coral reefs to undesirable ecosystem shifts.
(Received August 01 2008)
(Accepted December 22 2009)
(Online publication March 30 2010)