03 August 2010

Census of Marine Life: It's a crabby ocean!

About a fifth of the world's marine species are crustaceans such as crabs, lobsters, krill and barnacles. Add in molluscs (including squid and octopus) and fish (including sharks) and that accounts for up to half of the number of species in the world's seas.

"When people think of the ocean, they think of fish and whales. But the big mammals are only two percent of diversity, and fish are 12 percent. We should think first of crustaceans and molluscs."

Yesterday, the Census of Marine Life released an inventory of species distribution and diversity in key global ocean areas. Here's more about their findings based on their press release (pdf) and media reports.

What does the Census cover?
"From coast to the open ocean, from the shallows to the deep, from little things like microbes to large things such as fish and whales" The study also covers crabs, plankton, birds, sponges, worms, squids, sharks and slugs.

What did the Census find?

The number of known, named species contained in the 25 areas ranged from 2,600 to 33,000 and averaged about 10,750, which fall into a dozen groups. On average, about one-fifth of all species were crustaceans which, with molluscs and fish, make up half of all known species on average across the regions. The full breakdown follows:
  • 19% Crustaceans (including crabs, lobsters, crayfish, shrimp, krill and barnacles)
  • 17% Mollusca (including squid, octopus, clams, snails and slugs)
  • 12% Pisces (fish, including sharks)
  • 10% Protozoa (unicellular micro-organisms)
  • 10% algae and other plant-like organisms
  • 7% Annelida (segmented worms)
  • 5% Cnidaria (including sea anemones, corals and jellyfish)
  • 3% Platyhelminthes (including flatworms)
  • 3% Echinodermata (including starfish, brittle stars, sea urchins, sand dollars and sea
  • cucumbers)
  • 3% Porifera (including sponges)
  • 2% Bryozoa (mat or ‘moss animals’)
  • 1% Tunicata (including sea squirts)
The rest are other invertebrates (5%) and other vertebrates (2%).

The scarce 2% of species in the “other vertebrates” category includes whales, sea lions, seals, sea birds, turtles and walruses. Thus some of the best-known marine animals comprise a tiny part of marine biodiversity.

How was the Census done?

"To create this baseline, the Census of Marine Life explored new areas and new ecosystems, discovering new species and records of species in new places. We reviewed what had been documented through the huge efforts of scientists in years past. However, most of this information was scattered or unavailable except at a very local level. The Census has made a tremendous contribution by bringing order to chaos. This previously scattered information is now all reviewed, analyzed and presented in a collection of papers at an open access journal."

"We must increase our knowledge of unknown biodiversity more quickly, lest much of it is lost without even being discovered. International sharing of data, expertise and resources, as has been accomplished through the Census of Marine Life, is the most cost-effective way of achieving this."

Do we know everything in the sea now?

For every marine species of all kinds known to science, Census scientists estimate that at least four have yet to be discovered. In a few taxonomic groups, like fish, scientists believe more than 70% of species have been discovered, but for most other groups likely less than one-third are known. Scientists believe that the tropics, deep-seas and southern hemisphere hold the most undiscovered marine species.

The proportion of species not yet described is estimated at 39 to 58% in Antarctica, 38% for South Africa, 70% for Japan, 75% for the Mediterranean deep-sea, and more than 80% for Australia. New Zealand has more than 4,100 undescribed species in its specimen collections, which would comprise 25% of the country’s known marine species.

The studies found that while the depth of knowledge varies across regions, knowledge in all regions is inadequate. Australia, China and all three European regions scored the highest index results while the Tropical West Atlantic, Tropical East Pacific and Canadian Arctic were well below average. But, even in regions with the highest index scores, knowledge of marine biodiversity is poor. In Australia it is estimated that only about 10% of marine life in its Exclusive Economic Zone is known.

Why do the Census?

“This inventory was urgently needed for two reasons,” says Dr. Costello, lead author of the summary. “First, dwindling expertise in taxonomy impairs society’s ability to discover and describe new species. And secondly, marine species have suffered major declines -- in some cases 90% losses -- due to human activities and may be heading for extinction, as happened to many species on land.”

What are the threats?

The surveys have highlighted major areas of concern for conservationists. "In every region, they've got the same story of a major collapse of what were usually very abundant fish stocks or crabs or crustaceans that are now only 5-10% of what they used to be. These are largely due to over-harvesting and poor management of those fisheries. That's probably the biggest and most consistent threat to marine biodiversity around the world."

The main threats to date include overfishing, degraded habitats, pollution and the arrival of invasive species. Other problems due to climate change are anticipated: rising water temperatures and acidification, the growth in areas of the ocean that are low in oxygen and, therefore, unable to support life.

Which are the 'best' oceans in the world?

Australian and Japanese waters, which each feature almost 33,000 species are by far the most biodiverse. The oceans off China, the Mediterranean Sea and the Gulf of Mexico round out the top five areas most diverse in known species.

How come there is no mention of our part of the world?

Major inventories continue in highly diverse areas such as Indonesia, Madagascar and the Arabian Sea, which have yet to report. There are Census reports on several more regions anticipated in years to come: An exploration currently underway in the species-rich Timor and Arafura Seas, facilitated by Dr. Antonio (Tonny) Wagey, leader of the Census’ National Committee in Indonesia, will enrich the Indonesian report.

A final report is expected in October.

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