Scientists are already observing that many marine species have started shifting their distributional ranges with the changing environmental conditions as a consequence of global warming. However, understanding and projecting what marine biodiversity might look like in the future and how the extent of habitats might change is a difficult task due to many unknowns, Hodapp points out.
“Some species are only poorly studied and we don’t know exactly how the environmental conditions will look like in about in a few decades”, she says. Moreover, previous projections often considered temperature as the sole environmental factor driving future biodiversity changes.
To overcome these problems to a certain extent, the researchers based their modelling efforts on occurrence data of more than 33.500 marine species and seven environmental factors such as water depth, water temperature, salinity, and oxygen concentration. Based on this information and assuming three different CO2 emission scenarios the team estimated whether and where the species are likely to occur in the future.
The results indicate that species’ so-called core habitat ranges – that is the marine area in which chances are higher than 50 percent that a particular species occurs based on its preferred environmental conditions – may not only shift but may be halved in case of the high CO2 emission scenario.
In addition to habitat loss, the results give an idea about how the preferred habitat area of many species may be disrupted. “Especially along the equator, our model projections revealed areas which are ill-suited for most marine species, for instance because of high temperatures”, Roca explains. If such regions developed in the future this would disrupt currently continuous equatorial habitat ranges.
Fragmented habitats lead to smaller population sizes which can put species at higher risk to go extinct. However, in the long-run new species could also develop. Another problem is that species can only keep pace with changing environmental conditions to varying degrees, Hodapp explains. This can lead to a restructuring of food webs and changes in the interactions between habitat-forming species, such as corals, and their inhabitants.
“Even though our model does not account for such interspecific interactions, the results provide valuable clues on how differently marine environments and communities are likely to change depending on the future CO2 emission scenarios”, the marine ecologist stresses. Being aware of such a high risk of a fundamental reorganization of marine life will pose further challenges to conservation management, she adds. “We need to think ahead and work on effectively implementing the recent international agreements on biodiversity protection.”