Warming ocean waters, coupled with direct human actions such as pollution and overfishing, may threaten the rich diversity of life under the sea, a new U.S.-Canadian study suggests.
Researchers looked at how various factors have influenced the distribution of a spectrum of species - from seagrass to squid to sharks. Their findings help fill in the moving map of biodiversity across the world's oceans, knowledge that long has lagged behind that of diversity patterns on land.
"We wanted to find out which species were where, and why some places were greater hotspots of diversity than others," said lead researcher Derek Tittensor of Canada's Dalhousie University, in Halifax, Nova Scotia. "We were also interested in how these newly mapped hot spots related to human impacts on the oceans."
Species patterns
With the help of a public database created by the international network of researchers who conducted the Census of Marine Life, Tittensor and his colleagues identified the home waters of more than 11,000 species across 13 major groups. Then they began to uncover patterns.
Among coastal creatures, including corals and mangroves, the greatest area of diversity for most species groups was around the tropics of Southeast Asia. This was expected, given that terrestrial biodiversity is known to be highest around the equator and lowest at the poles.
Whales and other open-ocean species, on the other hand, were found in greatest concentrations along strips of sea at subtropical latitudes - those latitudes to the north and south of the tropical zone embracing the equator.
In addition to this "surprising pattern," Tittensor said, his team discovered a "worrying sign": These same hot spots of marine life overlapped areas with the largest human footprints, which raises the threat of severe species losses from pollution and other human action. Meanwhile, the combined effects of pollution, exploitation and habitat destruction put at risk the benefits humans gain from diverse ecosystems, such as water filtration and fish protein.
Warmer oceans
Another potentially devastating trend emerged when the team looked at environmental effects. Sea-surface temperature stood out as the only factor that consistently influenced all species groups, which suggests climate change could rearrange the distribution of oceanic life. Warmer parts of the ocean, for example, tended to sustain greater species diversity. But at the extremes of the temperature scale, Tittensor said, biodiversity may no longer be increasing. Instead it may be reaching a plateau or declining.
"In temperate regions, you may see more southern species coming in, due to warming, whereas in polar regions you tend to see a decline in diversity," he explained.
Still, the present picture is far from clear, leaving the future of the oceans unpredictable. Climate change affects more than just water temperature - ocean acidification and the bleaching of coral reefs are also global-warming-related problems. And these environmental effects probably interact with the array of other human actions.
The researchers hope their new map of diversity will provide a baseline that can be used to monitor future changes as the waters continue to warm, eventually eliciting a more complete understanding of what is going on. The map also could guide marine conservation by identifying areas where a large number of species could be protected at one time.
"There is amazing diversity in the oceans, and I'd like to see that continue," Tittensor said. "I think limiting warming and other human impacts is an important step."
The study is detailed in the July 28 edition of the journal Nature.
Warming of Oceans Will Reduce and Rearrange Marine Life
Jess McNally Wired Science 28 Jul 10;
The warmth of the ocean is the critical factor that determines how much productivity and biodiversity there is in the ocean, and where.
In two separate studies, researchers found that warming oceans have led to a massive decline in the amount of plant life in the sea over the last century, and that temperature is tightly linked to global patterns of marine biodiversity.
“We are just now understanding how deeply temperature affects ocean life,” said biologist Boris Worm of Dalhousie University, a co-author on both papers appearing July 28 in Nature. “It is not necessarily that increased temperature is destroying biodiversity, but we do know that a warmer ocean will look very different.”
In one study that looks at historical records of algae abundance over the last hundred years, Worm and his co-authors found that warming ocean temperatures are correlated to a massive decline in the amount of marine algae, or phytoplankton. Marine algae are the base of the entire ocean food chain, and were also responsible for originally creating oxygen on the planet.
The study estimates the decline in marine algae has been approximately 40 percent since 1950.
“I think that if this study holds up, it will be one of the biggest biological changes in recent times simply because of its scale,” said Worm. “The ocean is two-thirds of the earth’s surface area, and because of the depth dimension it is probably 80 to 90 percent of the biosphere. Even the deep sea depends on phytoplankton production that rains down. On land, by contrast, there is only a very thin layer of production.”
The study on marine phytoplankton is the first to look at changes over the last century at a global scale with data from as far back as 1899. Similar models have been made using satellite data, but that data only extends back to 1979.
“One of the most important aspects of the new paper is that they’ve come up with the same answer but from a different approach than we saw from space,” said marine botanist Michael Behrenfeld of Oregon State University. “I think that we should be concerned that this convergence of multiple approaches sees a reduction in the phytoplankton pigments as the ocean warms. If we continue to warm the climate we will probably see further reductions.”
Biodiversity map of coastal and oceanic marine creatures, red boxes mark hotspots/ Tittensor.In a study of general marine biodiversity, scientists have made the first global map of the biodiversity of the oceans for more than 11,000 marine species, from tiny shrimp-like creatures to whales, building on 6.5 million records from the Census for Marine Life and other databases. Of all the factors they looked at to explain why some regions had more or fewer types of creatures, the only factor that consistently explained the patterns for the 13 groups of marine life they studied was temperature.
“It was surprising that we found such a strong correlation to marine biodiversity and temperature,” said biologist Derek Tittensor of the University of Dalhousie, lead author of the marine biodiversity map study. “You might expect a different response to temperature from cold and warm-blooded animals, for example.”
Ocean temperature had different effects on the number of different creatures in coastal habitats versus open-ocean habitats. The biodiversity hotspots for coastal marine ecosystems were mostly near the equator where ocean temperatures are warmest, much like on land.
But for open ocean ecosystems, which included many deep-sea creatures, whales and big fish like tuna, the hotspots for diversity were at the mid-latitudes, where temperatures were slightly cooler.
“What we can draw from this study is that it is very likely that we will see a reorganization of biodiversity in the ocean from a warming ocean, but right now it’s very hard to predict exactly what that reorganization will be,” said Tittensor.
The hotspots in biodiversity are also the areas that have attracted the most human impacts, such as fishing and habitat destruction, meaning that we are harming the areas that we should be trying to conserve.
By mapping where the biodiversity of marine life is today, scientists now have a baseline for comparing species distributions in the future. Understanding these changes will help them understand how marine biodiversity is being affected by changes in the amount of marine algae, for example.
“In order to understand life in the ocean, we need to understand where it is,” said Worm. “It’s a basis for understanding and also managing ocean life.”
“The ocean is something that we’re not very good at thinking about,” Worm added. “It is one of those things that is so big to see that it has been hard to see it until now.”
Citations
1) Daniel Boyce, Marlon Lewis and Boris Worm. “Global phytoplankton decline over the past century.” Nature, July 28.
2) Derek Tittensor, Camilo Mora, Walter Jetz, Heike Lotze, Daniel Ricard, Edward Vanden Berghe, and Boris Worm. “Global patterns and predictors of marine biodiversity across taxa.” Nature, July 28.
Marine Biodiversity Strongly Linked to Ocean Temperature
ScienceDaily 29 Jul 10;
In an unprecedented effort that will be published online on the 28th of July by the international journal Nature, a team of scientists mapped and analyzed global biodiversity patterns for over 11,000 marine species ranging from tiny zooplankton to sharks and whales. The researchers found striking similarities among the distribution patterns, with temperature strongly linked to biodiversity for all thirteen groups studied. These results imply that future changes in ocean temperature, such as those due to climate change, may greatly affect the distribution of life in the sea.
The scientists also found a high overlap between areas of high human impact and hotspots of marine diversity.
Much research has been conducted on diversity patterns on land, but our knowledge of the distribution of marine life has been more limited. This has changed through the decade-long efforts of the Census of Marine Life, upon which the current paper builds. The authors synthesized global diversity patterns for major species groups including corals, fishes, whales, seals, sharks, mangroves, seagrasses, and zooplankton. In the process, the global diversity of all coastal fish species has been mapped for the first time.
The researchers were interested in whether there are consistent "biodiversity hotspots" -- areas of especially high numbers of species for many different types of marine organisms simultaneously. They found that the distribution of marine life showed two fundamental patterns: coastal species such as corals and coastal fishes tended to peak in diversity around Southeast Asia, whereas open-ocean creatures such as tunas and whales showed much broader hotspots across the mid-latitude oceans.
The scientists also tested whether these global patterns could be consistently explained by one or more environmental factors. Temperature was the only factor found to be linked with the distribution of all species groups, with the availability of habitat also playing a role.
Says lead author Derek Tittensor of Dalhousie University, "it was striking how consistently temperature was linked with marine diversity. This relationship suggests that ocean warming, such as that due to climate change, may rearrange the distribution of oceanic life." Co-author Walter Jetz of Yale University notes "while we are increasingly aware of global gradients in diversity and their associated environmental factors, our knowledge of patterns in the ocean has lagged behind that of patterns on land. Our study attempts to help overcome this disparity."
The study also assessed the overlap between hotspots of marine diversity and human impacts, i.e. the combined effects of fishing, habitat alteration, climate change and pollution. Human impacts were found to be particularly concentrated in areas of high diversity, suggesting the potential for severe species losses in these regions. Says co-author Camilo Mora of Dalhousie University, "the combined effects of exploitation, habitat alteration, pollution and climate change are threatening the diversity of life in the global ocean. Our research provides further evidence that limiting ocean warming and other human impacts will be particularly important in securing these hotspots of marine biodiversity into the future."
Co-author Boris Worm of Dalhousie University also highlights the need to maintain biodiversity in the face of these impacts: "biodiversity and the functioning of ecosystems are often tightly coupled, with highly diverse ecosystems providing more goods and services that benefit human beings, as well as being more resilient in the face of disturbance, than less diverse ecosystems. The observed concentration of human impacts in our richest marine areas is a worrying indication of our growing footprint in the oceans."
Many of the data used for this study come from the Ocean Biogeographic Information System, (OBIS) a public database created by the Census of Marine Life. Says Edward Vanden Berghe of Rutgers University, co-author of the paper and executive director of OBIS: "with OBIS we've created a framework for sharing and re-using data, which makes this type of global, all-encompassing science possible."
Derek P. Tittensor, Camilo Mora, Walter Jetz, Heike K. Lotze, Daniel Ricard, Edward Vanden Berghe & Boris Worm. Global patterns and predictors of marine biodiversity across taxa. Nature, July 28, 2010 DOI: 10.1038/nature09329