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Over-fishing blamed for Urchin outbreak

News item submitted by Flora O'Brien
News item dated 17 Jan 2011

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A newly published report of an 18 year long study conducted by the Wildlife Conservation Society and the University of California demonstrates the indirect dangers of over-fishing. The study compared two areas off the coast near Mombasa, Kenya; one site was a fishery closure and the other, a fished reef. The results of the study showed that sea urchins were more abundant in the fished site, and consequently there was a reduced abundance of crustose coralline algae.

Sea urchins are grazers, feeding predominantly on algae including crustose coralline. Since their main predators are reef fish, including triggerfish and wrasses, sea urchin populations expand in heavily fished areas. This concurs with Frontier’s research in Fiji, where it was found that a higher abundance of fish correlated with a reduced presence of urchins. Furthermore, the absence of herbivorous fish, such as parrot fish and surgeonfish, may also impact the coralline algae since these fish consume other fleshy algae, which compete with crustose coralline.

Crustose coralline algae is an important reef-building organism, which produces calcium carbonate, a compound which is ecologically very important in marine systems, particularly in shallow waters, as it help to bind and stabilise reef structures and also promote the recruitment of small corals by providing a surface for their larvae to settle on. Thus reefs with less crustose coralline algae will grow at a slower rate compared to those where the algae is abundant.

Evidently, it is paramount that fishery management is implicated and enforced globally, particularly in areas where there are coral reefs, in order to prevent further declines in crustose coralline. If the reef-building algae continue to decline, it will surely lead to further coral reef ecosystems collapsing. Needless to say, such events would not only negatively impact marine life overall, but would also deprive many human communities of their livelihoods. The creation of marine protected areas (MPAs), such as that of Mafia Island, Tanzania which Frontier helped establish, are essential in safeguarding oceanic biodiversity.

 

Find out more about Frontier Tanzania Marine Conservation & Diving project