Partially dead massive coral and grazing sea urchins on reef outside Zanzibar. Photo: J. Lokrantz/Azote

Little can be too much

Small-scale fishing can have significant impacts on coral reefs.

The world´s coral reefs are threatened by a range of human-induced pressures, including climate change, coastal development, pollution and overfishing.

The implications are staggering, not only for the biodiversity but also for tourism, fisheries and coastal protection.
                               
No wonder then that managers and researchers around the world got interested when centre researchers developed early warning signals or operational indicators of resilience to predict whether or not reefs can absorb disturbances and rebuild itself.

However, little is still known about how fishing intensity can compromise coral reef resilience.

One thing leading to another
In a new study, centre researchers Albert Norström, Magnus Nyström, and Carl Folke have together with reseachers from Sweden and Australia showed how small-scale artisanal fishing can have significant impacts on herbivorous reef fishes and their coral habitats.
 
- Small-scale artisanal fisheries can have significant impacts on coral reefs because herbivores such as fish and sea urchins are not only important for suppressing algae, but also for removing them once they have become abundant. Herbivores are susceptible to artisanal fishing gear and if you remove the herbivores, you risk altering ecosystem processes to the point that its impossible turning back from the brink, says co-author Albert Norström.  
 
Knowing when to stop
Norström and his colleagues assessed the vulnerability of herbivory on five coral-dominated reefs on the western side of Zanzibar Island but examples elsewhere also show that things can go terribly awry if the fishing turns unsustainable.
 
Across several Caribbean island nations, abundances of important herbivorous fish families have become substantially lower due to increased artisanal fishing pressure. Similarly, in Fiji, a cascading effect of the coral-eating crown-of-thorns starfish has been attributed to the removal of predatory reef fish caused by overfishing.
 
- Knowing when key ecosystem processes such as herbivory are approaching critically low levels is important because it could provide resource managers with an opportunity to avoid unforeseen and potentially persistent ecosystem changes, says Norström.
 
He recommends the use of routine monitoring measures such as species richness, biomass and size class distribution of key functional groups provide important information regarding potential vulnerability of coral reefs.
 
- These methods should be used widely as significant indicators for managers to avoid undesirable ecosystem changes, Norström says.

Source: Lokrantz J, Nyström M, Norström AV, Folke C, Cinner JE (2010) Impacts of artisanal fishing on key functional groups and the potential vulnerability of coral reefs. Environmental Conservation. doi: 10.1017/S0376892910000147

See seminar video with Professor Nancy Knowlton on how human wellbeing and coral health can co-exist (read more about the seminar here):

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Reference

Citation

Lokrantz J, Nyström M, Norström AV, Folke C, Cinner JE (2010) Impacts of artisanal fishing on key functional groups and the potential vulnerability of coral reefs. Environmental Conservation. doi: 10.1017/S0376892910000147

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