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We are no longer completely at sea when it comes to the creatures that thrive beneath the ocean's surface, thanks to a decadelong effort to document marine diversity. The Census of Marine Life, an ambitious project to catalogue sea life, was prompted by estimates that science had sampled marine biota in only 0.1 percent of the volume of the world's oceans. The results compiled from this global collaboration of more than 2,700 scientists from 80 nations will be released in October, although some findings have been published in advance in a series of 12 papers available online August 2 in PLoS One.
The latest findings profile the diversity and distribution of known species in 25 important marine areas, including temperate, tropical and polar oceanic waters such as the Caribbean, Baltic and Mediterranean Seas as well as the Gulf of Mexico. The data provide a baseline for marine diversity that will be useful when assessing the future impacts of humans and nature on pelagic life.
Globally, the total number of marine species is estimated to be approximately 230,000, although the researchers suggest that a million or more aquatic species remain to be discovered. In waters near Japan and Australia the scientists documented nearly 33,000 species in each region, making these two of the most diverse aquatic areas on the planet.
On average, nearly 20 percent of all the identified species are crustaceans, including crabs, lobsters, shrimp and krill. The second most commonly documented are mollusks (including squids, octopuses, clams and snails), followed by fishes and sharks. The scientists note that some of the best-known marine animals, including whales, seals, turtles, sea lions and walruses, make up only two percent of the biodiversity of sea life. The current work simply sought to determine which species were present in the studied areas, however, and, as such, does not provide information about species abundance or the fraction of the total biomass each represents.
The survey revealed that waters surrounding Australia, New Zealand, South Africa and Australia have the greatest number of unique indigenous species. Meanwhile, the Mediterranean Sea contains some of the fewest unique species, albeit it hosts the largest number of invasive species. These findings confirm that biodiversity varies tremendously from region to region.
The researchers emphasize overfishing as the top threat to marine life worldwide. It impacts diversity and alters food webs in the sea by depleting the targeted, exploited species as well as reducing other animals commonly found in bycatch. Other threats of chief concern highlighted in the report are habitat destruction, pollution, invasive species and warmer waters due to climate change.