Paleontologists investigating the sea bed off the coast of southern California have discovered a lost ecosystem that for thousands of years had nurtured communities of scallops and shelled marine organisms called brachiopods.
(From Science Daily / by Steve Koppes) — These brachiopods and scallops had thrived along a section of coast stretching approximately 250 miles from San Diego to Santa Barbara for at least 4,000 years. But they had died off by the early 20th century, replaced by the mud-dwellling burrowing clams that inhabit this seabed today. Paleontologists Adam Tomašových of the Slovak Academy of Sciences and Susan Kidwell of the University of Chicago examine the lost ecosystem in a study published online June 7 in the Royal Society Proceedings B.
Evidence indicates that the brachiopod and scallop die-off occurred in less than a century. Because this community disappeared before biologists started sampling the seafloor, its existence was unknown and unsuspected. Only dead shells remain, permitting analysis by paleontologists.
“This loss unfolded during the 19th century, thus well before urbanization and climate warming,” said Kidwell, the William Rainey Harper Professor in Geophysical Sciences. “The disappearance of these abundant filter-feeding animals coincided with the rise of lifestock and cultivation in coastal lands, which increased silt deposition on the continental shelf, far beyond the lake and nearshore settings where we would expect this stress to have an impact.”
Continental shelves, the submerged shoulders of the continents, are a worldwide phenomenon. They form a distinct environment separated by a steep slope from the much deeper and vaster expanse of ocean floor beyond, and provide key habitats for biodiversity and fisheries.
The seabed off southern California is one of the most thoroughly studied in the world, but in applying geologic methods to modern biological samples of the sea floor, Kidwell and Tomašových encountered unsuspected results. Today that seabed consists of soft sediments, where creatures such as segmented worms, crustaceans, molluscs, crabs and urchins feed on organic matter.
This is a fundamentally different ecosystem than the one that preceded it not so long ago, said Tomašových, who heads the Department of Paleoecology and Organismal Evolution at the Slovak Academy.
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