NO MORE seafood by 2050. That was how the biggest-ever analysis of global marine biodiversity and fisheries, published last week, was widely reported. In fact, the study was not just another forecast of doom from fisheries scientists.
Instead, what it provided was confirmation, on a global scale, that life in the ocean is an enormously complex system. For its ecosystem “services” to work – for the ocean to absorb pollution and provide us with food – it needs all its parts intact.
Unlike their counterparts on land, marine scientists have never been able to prove that more biodiversity equals a more resilient, productive ecosystem. The new report has done just that.
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However, while it does indeed show that if we keep on as we are now all our fisheries are headed for collapse by 2048, “that is just where the trend is leading, not what is going to happen,” says the study’s lead author, Boris Worm of Dalhousie University in Halifax, Canada. “The main message is that we can still turn that around, but our options for doing so diminish with every species we lose from the ocean.”
We need them all, he says, from plankton to seabirds, not just for the sake of conservation, but because without them we could permanently lose the many concrete economic benefits people get from the ocean.
The key to reaching this conclusion was number-crunching on a scale rarely seen in wildlife biology. “People have shown before that individual marine communities recover better from stress if they are diverse,” says Worm. For example, seagrass beds in the Baltic sea that died off during Europe’s heatwave of 2003 recovered faster if they had more species to begin with. “But people couldn’t show that this applied to the whole ocean.”
To do that scientists from a dozen leading marine labs analysed a wide variety of data, including 32 small-scale controlled experiments; long-term biological surveys of 12 estuaries and coastal zones; and fisheries statistics from 64 large marine areas such as the North Sea (Science, vol 314, p 787). Crucially, the fisheries reports were checked for reliability by the same scientists who detected the over-reporting of Chinese catches five years ago (91av, 1 December 2001, p 18). The authors even looked at historical records of when certain seafood was commonly available to cooks, and sediment cores bearing plankton remains, says Worm.
Gerd Hubold, head of the International Council for the Exploration of the Sea in Copenhagen, Denmark, is not convinced such diverse records can be meaningfully combined. “The data are all of such different quality, I wouldn’t dare to make any predictions,” he says.
“If the data all showed different things, I would agree,” Worm responds. “But we found completely different data sources, from cookbooks to sediment cores, show the same thing across different scales of time and space.” In every system, recovery from perturbations, from storms to human exploitation, was faster and stronger the more biodiversity the system had to begin with. Fisheries were far more likely to collapse in seas with fewer species, and less likely to recover. Fisheries with more biodiversity also produce higher catches, possibly because the fish have more diverse food sources.
“In every system, recovery was faster and stronger the more biodiversity the system had to begin with”
This might explain the difference between cod in the North Sea, where stocks somehow survive despite years of over-fishing, and off Newfoundland, where stocks collapsed in 1992 and have yet to recover. The North Sea has higher biodiversity. “That is entirely consistent with our findings,” says Worm.
Importantly, the mechanism works both ways – data from 44 protected marine reserves and four fisheries closures showed biodiversity can recover, and that fish catches just outside the reserves increased at the same time. “This shows it is not too late,” says Worm. However, the study shows biodiversity is important for weathering all kinds of impacts. And the less biodiverse seas are, the more marine resources will struggle to survive the biggest upset yet: climate change.
