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FYI: Manitoba's jellyfish (and why they matter)

By: Bartley Kives

Posted: 11/21/2009 1:00 AM | Comments: 0 (including replies)

Graham Young (TREVOR HAGAN / WINNIPEG FREE PRESS)

THE proliferation of jellyfish blooms around the world has ocean scientists worried, as massive numbers of very simple creatures are floating around what used to be more complex ecosystems.

But a discovery in northern Manitoba suggests jellyfish blooms may not be just a recent phenomenon. A team of paleontologists has found the fossil remains of large numbers of jellies at a dig site that date back 445 million years, to a time when a shallow sea known as the Williston Basin covered what's now boreal forest north of Grand Rapids.

For the past eight years, Manitoba Museum geography and paleontology curator Graham Young, James W. Hagadorn of Amherst College in Massachusetts, and 10 other researchers, have been working at an Ordovician Period site where they've found all manner of ancient creatures, ranging from common fossils such as crinoids and corals to much more rare animals such as sea scorpions and sea spiders.

When the dig began, Young and his colleagues kept tossing away grey dolomite rocks with reddish-brown smudges, mistaking them for ordinary rust.

"We were just throwing these red blobs away," he said.

But Young and his co-workers soon realized they had discovered something very rare in the fossil record: Medusa jellyfish, whose soft bodies typically decompose before they can be preserved in stone or rock.

"It's an extremely weird place," said Young of the dig site, declining to reveal its precise location because his team still has three more years of excavations to conduct.

The site in question turned out to be several sites in one, with the branch-like crinoids -- also known as sea lilies -- on the bottom and the unusual sea spiders and sea scorpions on top.

Young figures the jellyfish were preserved by an unusual confluence of events: They were blown into a shallow bay where they were killed very quickly by too much salt and too little oxygen. A storm then buried the creatures in oxygen-free mud.

"This was a very nasty place," he said. "They were buried in what must have been anoxic mud. Otherwise, they would have broken down."

After excavating dozens of organisms, Young and his co-workers realized they had discovered one of the largest collections of fossil jellyfish in the world. Older sites exist in Wisconsin, Quebec and New York, while a younger, more spectacular site has been found in Illinois, he said.

Jellyfish fossils from even more recent rocks are uncommon because after life evolved on land, their dead bodies would have been scavenged by creatures that patrolled the shores. Oxygen-rich coastal sediments that promote decay also grew thicker as time went on.

As it stands, there are only nine known medusa-jellyfish fossil sites in the world, Young said, making the northern Manitoba discovery very important.

Finding ancient jellyfish demonstrates there were creatures inhabiting ancient seas other than the trilobites, cephalopods and other hard-bodied animals that dominate the fossil record. Evolutionary biologists tend to underestimate the variety and abundance of soft-bodied creatures that used to inhabit the planet, simply because they were so rarely preserved.

"A site like this changes ideas about the diversity of life on Earth at the time," Young said.

But the discovery also has implications for oceans today. Earlier this month, Young made a presentation about fossil jellyfish to coastal scientists at a Portland conference where other topics included modern jellyfish blooms.

As fish and seafood species continue to disappear from the oceans at the hands of overfishing, human beings may be returning the oceans to a state that existed before the evolution of bony fishes: a world where simple creatures like jellyfish dominate the seas.

"We're getting rid of the top of the food chain," Young said. "We're making conditions better for jellyfish."

bartley.kives@freepress.mb.ca

Republished from the Winnipeg Free Press print edition November 21, 2009 H16

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