Perspective review of the impacts of overfishing on coral reef food web linkages

Abstract

Overfishing is increasingly understood to result in indi-rect alterations of habitat structure and function(McClanahan et al. 1995; Bowen 1997; Jackson 2001;Jackson et al. 2001; Gardner et al. 2003). The intenseharvesting of sea otters from kelp forests, for example,created ‘‘low- predation refuges’’ for their sea urchinprey. Following otter removal, sea urchin grazing ex-ploded resulting in large regional losses of kelp (Estesand Palmisano 1974; Duggins 1980). Further supportfor the impacts of large consumers was found in Alaskanembayments where inshore migration of killer whaleschanged the strength of interactions between sea ottersand their herbivorous sea urchin prey, again resulting inlocal losses of kelp forests (Estes et al. 1998). Similarly,McClanahan et al. (1995) found that intense harvestingof predatory trigger fishes promoted large-scale habitatchanges as their sea urchin prey, once released frompredation, increased. More urchins subsequently led tomore coral reef erosion and the eventual replacement ofcorals by seagrasses (McClanahan and Kurtis 1991).Moreover, the intense harvesting of both large piscivo-rous and herbivorous fishes, coupled with the die-off ofherbivorous sea urchins, is thought to be responsible forwidespread macroalgal overgrowth of coral reefs inJamaica (Hughes 1994 but see Aronson and Precht2001).Given that the dramatic impacts of fishing on marinefood webs preceded the development of most theory inmarine ecology, it is understandable that managementagencies have predominantly focused their efforts on therole of bottom-up processes (nutrient concentration) inregulating the productivity of coastal ecosystems. Butgiven the increasing evidence that food web alterationshave figured prominently in the collapse of marineecosystems, it seems clear that new studies are urgentlyneeded to assess the degree to which large-scale foodweb alterations have changed the structure and functionof marine ecosystems (Estes and Peterson 2000; Jackson2001; Pandolfi et al. 2003).