By Environmental News Network staff

As the Isthmus of Panama formed, the exchange of water and marine life between the Caribbean and the Pacific was cut off.

After researching roughly 23 million years of the evolution of marine animals in the Caribbean, a Louisiana State University researcher has concluded that the formation of the Isthmus of Panama around 3.5 million years ago dramatically changed the shape of marine animals for years to come.

Laurie Anderson, an associate professor of geology and geophysics, says the Isthmus, which when it formed, connected Central and South America, changed the flow of ocean currents. Her ongoing research is to determine how the isthmus has affected a group of marine organisms that inhabit the Caribbean and the eastern Pacific.

After the emergence of the isthmus, the size of the corbulid bivalve mollusks, a type of clams, in the Caribbean and Atlantic was an indication that something was changing. The corbulid clams in the Caribbean and western Atlantic are half the size of those in the eastern Pacific.

The size difference, said Anderson, could be directly related to the loss of nutrient-rich water flowing from the eastern Pacific into the Caribbean as the isthmus rose.

"When you think of the Caribbean today, you think of clear blue warm water," Anderson said. "Probably about 12 million years ago, it was more like the eastern Pacific; it was a bit cooler. There was greater seasonal change in temperatures, and there were more nutrients around."

Higher nutrient levels relate to greater amounts of plankton for the filter feeders, she said.

Strong, deep circulation in the eastern Pacific carried those nutrients east before the time of the isthmus.

"So, if you go back to about 20 million years ago, you have big corbulid clams on both sides of the isthmus. As the barrier goes up, you lose the nutrient supply in the Caribbean because of changing ocean circulation," Anderson said.

"When that connection was cut off, the big mollusks slowly disappeared from the Caribbean side of the isthmus. But they were able to survive over on the Pacific side," she said.

Anderson said she hopes to use the data collected and tie that in to what other groups of animals are doing over time.

"There are good reconstructions of ocean circulation, climate change and changing configuration of land masses," Anderson said. "What it all boils down to is I can look at evolutionary patterns in my group and tie them very well to a changing environment.

"I see that it has huge benefits for us understanding how and why diversity changes over time and how that might be applied to evaluate potential effects of future environment and climate changes," Anderson said.

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