Fish ecosystems hide their losses

08 July 2015 New mathematics shows that as the fish diversity of complex marine food webs declines, fish production resists the change, masking ultimate rapid loss.

Fishes are a main protein source for over a billion people worldwide and is one of the most traded food commodities, but many fisheries are declining. Using a realistically complex mathematical model of fish ecosystems, a team including Mr Tak FUNG from the Department of Biological Sciences in NUS has examined the role of species removal in this decline. It turned out that the remaining species resisted losses in production by compensating with increases until the losses became too much and a collapse ensued. As species were removed from model communities, production remained high until only about 1/3 of species remained, whereupon it sharply declined. Fish ecosystems maybe well down this path already.

This resistance of change in wild fish ecosystems maybe masking a more serious decline in production potential in situations where biodiversity loss is already reported, severely threatening food security. It is vital to understand that biodiversity losses do not lead to linear declines in production. The team’s results show that fisheries must be managed within the whole ecological context. Action to halt species loss may avert severe loss of production if, as has been reported, many fisheries systems are already significantly depleted of species. The danger is one of false reassurance generated by the systems’ capacity to compensate for losses.

This study results from a breakthrough in the mathematical modelling of complex ecological communities: the Population-Dynamical Matching Model (PDMM) that the team use is unique in being able to represent thousands of coexisting species, dynamically interacting as a complex food web with properties that are a good match with empirical observations. The model is part of the next generation in mathematical modelling of complex ecosystems, which run on high-performance computer platforms. With its huge capacity and detail, it will be used for further investigations of relationships between biodiversity and ecosystem functioning that are crucial for informed stewardship of natural ecosystems.

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This image shows a group of tuna at 22 m depth in the waters of Faviganna, Sicily. [Image credits: National Oceanic and Atmospheric Administration/Department of Commerce; Danilo Cedrone; United Nations Food and Agriculture Organization]

Reference

Fung T, Farnsworth KD, Reid DG, Rossberg AG. “Impact of biodiversity loss on production in complex marine food webs mitigated by prey-release”. Nature Communications 6 (2015) 6657.