'Ocean census' scientists taken aback by diversity

by Frank POPE

Oceanographers hoping to create a comprehensive census of marine life feel that their task is far bigger than imagined.

During some 300 voyages scientists of the 10-year Census of Marine Life have been sampling plankton, microbes and sediment-dwellers, but the rate at which they made new discoveries - including a bacterial community the size of Greece on the seabed near Chile - is forcing them to reappraise their estimates of how much they know.

Light micrograph of an assortment of radiolaria, a type of marine protozoa

"There are many more species than we thought there were," Dr Ann Bucklin, head of the University of Connecticut Marine Sciences Department, who headed up the team investigating zooplankton, told The Times. "It turns out the ocean food web is much more complex than we thought it was, in terms of the number of different species."

The team used DNA-sampling techniques to catalogue the life they found, but other techniques have not changed much since the first oceanographic expedition, conducted by HMS Challenger in 1872. Huge nets were dragged through the deep sea between one and five kilometres beneath the surface. Some samples were kept for taxonomic study, while others were probed for their DNA. Now, as then, new species and genera were found with every trawl.

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"We've already seen the North Sea become inhospitable to a northern species of zooplankton which is a critical part of the diet for commercial fish species, and it's been replaced by its southern cousin," Dr Bucklin said. Dr Paul Snelgrove, of Memorial University, Newfoundland, also worked on the census of "hard to see" marine organisms. "Historically we've often dealt with these plankton species in box models, where we don't really worry about species. Now we know that different species do very different things," he said.

Some species thought to be from different families were discovered to be the same. When larvae of tapetails, bignose fishes and whalefishes were recovered from five kilometres down, they were all found to simply be developmental stages of the same organism.

The team discovered that in the deep, rarity is common. "In many types of ocean systems there are a few things that are very abundant, but lots and lots of things that are extremely rare. This is true for microbes, plankton and benthos," Dr Snelgrove said.

"That raises the question what role they play. What we don't know is if these rare things are common somewhere else, or is it just their nature to be rare. Do they do anything? Or are they trivial players on the sidelines? We don't know."

Dr Snelgrove admits that the rarity may be because of how little sampling has been done in the deep. "Globally in the history of science we've probably sampled a few football fields' worth of the deep sea, and that's it. We're trying to extrapolate up from that," he said.

Life on the seabed is also profuse. "If you take a bottom photograph it looks like there's not much there, but if you actually collect the sediment and bring it up you find it's crawling with all sorts of things," said Dr Snelgrove.

"One study found 700 new species of crustaceans in an area the size of a small bathroom."

On the seabed off Chile, Dr Victor Gallardo of the Census team discovered thick mats of white, spaghetti-like bacteria that cover an area the size of Greece. The strands - reaching the length of a human finger - thrive by absorbing methane from the seabed. Similar mats have been found in human-caused oxygen-free "dead zones", such as those found beneath unregulated fish farms.

"These things may be tiny individually but altogether they are a huge fraction of the biomass of ocean life. Not only are they beautiful, but they're very important ecologically," said Anne Bucklin.

"How could we have missed so much? It's because we relied on our eyes, but these are tiny little things and they're difficult to discriminate.

"It wasn't until DNA sampling that we realised that, oh my goodness, we're farther down the discovery curve than we thought we were."