U. FLORIDA (US) — There are about 226,000 described marine species in the world but two to three times as many that remain undescribed, research suggests.
More than 100 taxonomists and biologists summarized the magnitude of all marine life, both known and unknown. Based on knowledge of described and estimated unknown species and the rate of new discoveries, researchers predict there may be fewer than 1 million eukaryotic marine species worldwide. Eukaryotes are all living things other than bacteria and viruses.
Published in the journal Current Biology, the conclusion differs from past estimates that exceeded 1 million, but unlike previous efforts, is based on a global inventory. The findings provide a reference point for conservation efforts and may be used as a baseline for understanding environmental changes such as global warming.
“There are issues with any estimate like this, but it’s the first time that we really have a solid background at least on what we know, rather than having to speculate about that,” says co-author Gustav Paulay, invertebrate curator at the Florida Museum of Natural History at the University of Florida. “The ocean is a large chunk of the world, so it’s useful for biologists to know how diverse the world is—before this, we didn’t have this information in one place.”
All of the study co-authors are contributors to a global marine life inventory known as WoRMS, or the World Register of Marine Species, a database that lists more than 90 percent of marine species used by researchers to create tables to show how diversity is distributed among different types of organisms.
Each co-author, an expert on a different group, compiled its known diversity and estimated the number of collected species that remain undescribed in museum collections, how many may be cryptic or unrecognizably different, and how many remain undiscovered in the wild.
More than 20,000 species have been discovered during the last decade and if trends continue, most species will be discovered this century, according to the study. There are also about 65,000 undescribed species already in collections.
“The entire ocean contains less than 300,000 species described to date and that includes everything from dolphins to worms to single-celled algae,” Paulay says. “Because it’s so connected, there’s less diversity in the ocean than on land. There’s still a lot more to be discovered, but it’s a manageable number so we can go after it and really understand the magnitude of marine biodiversity.”
Paulay is an expert on sea cucumbers, which are grouped together with sea stars, sea lilies, and sea urchins in the phylum Echinodermata. Sea cucumbers are bizarre among echinoderms because their skeleton is reduced to microscopic bits so the animals have secondarily become worms.
They occur worldwide in the deep sea and range from less than ¼-inch to about 10-feet long. For the study, Paulay organized the more than 2,400 named sea cucumber species and determined about 1,700 are valid, with the remainder being duplicate names proposed for the same species.
“The most abundant, conspicuous large organisms you see on the ocean floor—which is most of the planet—are echinoderms, especially sea cucumbers,” Paulay says. “They are very important down there, recycling sediment from the ocean bottom or eating suspended particles floating around in the ocean, and they are obviously food sources for other animals.”
Nancy Knowlton, a marine scientist at the Smithsonian Institution’s National Museum of Natural History, says the study is interesting because it differs from conclusions published in a 2011 PLOS Biology study co-authored by Camilo Mora that estimates there are about 2.2 million eukaryotic marine species, with about 91 percent still undescribed.
“It’s really nice to see a very carefully documented analysis that points to these lower numbers, but I think the jury is still out,” Knowlton says. “Until different methods start giving us the same answer, it’s going to be difficult to know where the truth really lies.”
Bill Eschmeyer, an associate researcher at the Florida Museum and California Academy of Sciences, is also a study co-author.
Source: University of Florida