Scientists have investigated the species diversity and functional uniqueness of the marine megafauna, and also determined the consequences of its partial extinction in the coming century. It turned out that the extinction of already endangered species will lead to the loss of half of the functions carried out within the ecosystems of the oceans. In a study published in the journal Science Advances, the authors proposed a new FUSE index that will better capture the ecological functions of marine species and prioritize their conservation.
The marine megafauna includes organisms weighing more than 45 kilograms. These species play a critical role in oceanic ecosystems: they consume huge masses of smaller organisms, transport nutrients through excretion, and create links between distant ecosystems through long-range migration.
Despite the comprehensive value of the marine megafauna, it is threatened with extinction due to uncontrolled human exploitation, habitat loss, ocean pollution and rising water temperatures. According to the International Union for Conservation of Nature (IUCN), a third of these species are already on the verge of extinction due to small populations and their fragmentation. Previously, scientists did not give clear predictions about how global marine ecosystems will change as a result of the loss of megafauna. In addition, many scientific studies focus on species diversity, ignoring functional diversity and the concept of ecological guilds. The functions of a megafauna in the ocean are unique, and less mobile small species of living organisms will not be able to perform them.
Scientists led by Catalina Pimiento of Swansea University have developed a special index called FUSE (functionally unique, specialized and endangered), which allows you to quantify the contribution of a particular species to ecosystem functioning and prioritize conservation.
The authors of the study created an extensive database that included all the living representatives of the marine megafauna (334 species). Scientists then modeled two extinction scenarios on a global and regional scale. The first one (IUCN 100) is based on the estimated probability of extinction of each species over the next 100 years, given their IUCN conservation status. The second scenario (IUCN AT) assumes the extinction of all endangered species.
Projected changes in global diversity for the IUCN 100 and IUCN AT extinction scenarios. A and B show the loss of specific and functional uniqueness; С - change in the number of unique ecological functions. Violin charts show values resulting from the loss of random views. P-values for all paired comparisons (empirical data in boxes compared to randomized data in violin charts)
Sharks are estimated to have the worst impact, with the IUCN 100 losing 19 percent of their species diversity, while the IUCN AT has a 62 percent chance of extinction. In such a case, an estimated 87 percent damage to their function as top predators is expected.
Further, the scientists combined the indicators of the uniqueness of species and the uniqueness of functions into one index - FUSE. The highest FUSE scores are gained by species with the most unique functions, and populations can be easily damaged due to fragmentation, a small number of suitable habitats, or their destruction.
Contribution of megafauna to functional diversity and their current conservation status. The columns represent the average for each species over all changes. A - functional uniqueness, (B) - species uniqueness, (C) - points according to the FUSE index.
The five highest indices are for the green sea turtle (Chelonia mydas), the golden Julien carp (Probarbus jullieni), the dugong (Dugong dugong), the sea otter (Enhydra lutris) and the giant clam (Tridacna gigas). Not all of these species are on the brink of extinction right now, but they definitely deserve the highest priority of protection.
The authors of the study demonstrated the advantages of a functional approach to marine megafauna compared to the classical assessment of species diversity. Their proposed FUSE index will help experts in the use of natural resources and environmental protection. Researchers believe that so far not so many representatives of the megafauna have disappeared, and there is still time to establish processes for monitoring ecosystems and preserving their functional structure.