New threat of mass extinction, 'marine wipeout'

Wednesday, May 25, 2011

WE ARE living through a massive species extinction event that rivals the one that wiped out the dinosaurs 65 million years ago. But while an asteroid collision likely did in the dinos, today’s extinctions are a direct consequence of human activity, writes DICK AHLSTROM , Science Editor

Whatever the cause, the result could be a complete collapse of the marine ecosystem, according to new research from the US. Far from being no more than a theory, they warn that two marine wipe-outs have occurred in the past and we may be triggering a third.

Researchers from Brown University and the University of Washington catalogued the results of the two earlier extinction events by searching the fossil record. Their study of an extinct distant relative of today’s squid and cuttlefish showed just what can happen if you start messing with the marine food web, publishing the details in the journal Geology .

“It is definitely a cautionary tale because we know it has happened at least twice before,” states the paper’s lead author, Prof Jessica Whiteside, an assistant professor of geological sciences at Brown.

The research also showed that once you knock the marine ecosystem out of sync, it can take millions of years to put it right again.

The Permian geologic period came to an end in a massive extinction event about 250 million years ago, giving way to the Triassic period. The Triassic drew to a close about 200 million years ago due to a second major extinction event that heralded the start of the Jurassic period, authors say. The Permian-Triassic event was likely brought on by huge volcanic events that sent greenhouse gases into the atmosphere, knocking out land species and about 90 per cent of all marine species.

The Triassic-Jurassic event was also probably the result of powerful volcanism, something that threw the atmospheric and oceanic carbon cycle out of kilter to cause “chaotic carbon episodes” and trigger the extinction of 72 per cent of marine species.

The research team studied carbon isotopes from these periods, available today in rocks dug out of western Canada. The rocks also yielded up fossils that showed what was going on with the mix of marine life over a 50 million year period across these geologic periods.

The focus was on ammonoids, now extinct predatory squid-like organisms that either floated along waiting for a passing meal or actively moving about in pursuit of prey. Both of these predators were substantially knocked out during the mass extinctions, the authors say, leaving a significant gap in the overall predator/prey food web.

Most links in the marine food chain then and now are occupied by multiple species who predate whatever becomes available in their particular niche. This provides what biologists refer to as “ecological redundancy”. That ecological redundancy at the ammonoid level was lost, the authors argue. And this in turn triggered the marine ecosystem collapse seen in the two extinction events. The authors say theirs is the first research paper to make a direct link between lost ecological redundancy and ecosystem collapse.

Now fast-forward to today, to when the world’s oceans are effectively under siege, the researchers argue. A whole range of top predators are in sharp decline including cod, bluefin tuna, swordfish and sharks. They believe such a major disturbance of ecological redundancy at this level could precipitate species collapse and bring on a new extinction event.

Five years ago a UN report warned of the dangers of biodiversity loss. “In effect we are currently responsible for the sixth major extinction event in the history of the Earth, and the greatest since the dinosaurs disappeared 65 million years ago,” the report claims.

The research team only links two of the past five mass extinctions to ecological redundancy, and possibly the current event, assuming the marine ecosystem does go sharply into decline.

They warn that once lost, ecological diversity can take a long time to recover with a 10 million year wait before it was re-established after the Permian and Triassic events, they say.

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