Current hotspots of marine mammal diversity are concentrated in the temperate waters of the southern hemisphere, and the number of cetacean and pinniped species will likely remain highest in these areas in the coming 40 years, -- regardless of climate change. However, on the level of individual species the picture may be different: Whereas about half the species of marine mammals will experience some loss in their habitat, distributional ranges of the other half may increase by up to 40 percent.
This is the conclusion of a study recently published in the online scientific journal PLoS ONE and conducted by marine biologist Dr. Kristin Kaschner, research affiliate at the Institute of Biology I of the University of Freiburg, in collaboration with researchers from the USA, Canada, and Brazil.
The international team of ecologists produced predictions of patterns of global marine mammal biodiversity using a species distribution model which incorporated oceanographic data such as water depth, sea surface temperature, and sea ice concentration as well as information on marine mammal species occurrence. The researchers subsequently modeled and investigated the effects of global warming on individual species' distributions and biodiversity hotspots by the year 2050 based on an intermediate climate change scenario. They found current marine mammal biodiversity to be highest along the Pacific coasts of North America and Japan, north of New Zealand and in waters surrounding several Subantarctic islands.
Based on the simulation, overall the expected change in the distribution patterns of marine mammals by 2050 was relatively small, with the exception of Antarctic and Arctic waters where currently only relatively few species occur. In these polar regions, the model predicted local losses in native species of up to 80 percent while at the same time overall biodiversity could increase by more than an order of magnitude due to the invasion of temperate and subpolar species. Tropical waters will also be experience a loss in diversity, albeit one of less severity. However, the researchers stress that the results of the study probably underestimate impacts of climate change, since the model could not account for indirect effects such as changes in prey distribution or breeding habitat of polar species.
Cetaceans and pinnipeds play an important role in the marine food webs, and marine mammal biodiversity hotspots can thus be indicative of high levels of overall biodiversity. Prediction models such as the one used in this study may therefore help with the identification marine areas of high conservation concern.. One of the main targets of the international Convention on Biological Diversity (CBD) is to the establishment of a network of marine protected areas covering at least ten percent of the global ocean surface by the year 2020. With currently just over one percent being protected, however, the international community is still far from achieving this goal.
- Kristin Kaschner, Derek P. Tittensor, Jonathan Ready, Tim Gerrodette, Boris Worm. Current and Future Patterns of Global Marine Mammal Biodiversity. PLoS ONE, 2011; 6 (5): e19653 DOI: 10.1371/journal.pone.0019653
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