By Cynthia Drummond | The Westerly Sun

NARRAGANSETT — It will come as no surprise to local anglers that different fish species are now found in Rhode Island waters. In some cases, these fish are displacing ones traditionally found here, and scientists are trying to understand which species pose the greatest threat to the native marine populations of Narragansett Bay.

Students presented some of the findings Thursday at the University of Rhode Island Graduate School of Oceanography. The talks on the bay’s marine food web were part of the monthly Bay Informed series sponsored by Rhode Island Sea Grant and open to the public.

“It gets more complicated when you start realizing that there’s a lot of different predators for any given species,” said Maggie Heinichen, a master’s degree candidate. They’re not just eaten by one thing. And it gets even more complicated when you look at an entire ecosystem.”

Scientists have looked at changes at both the bottom and the top of the food web, analyzing fluctuations in populations of organisms at the bottom, like plankton, and of fish at the top level such as striped bass.

The preferred approach now, however, is ecosystem-based management, in which researchers look at entire ecosystems, including humans, rather than at individual components.

“You can’t really look at what’s happening to a system as a whole unless you know how that system is connected to each other,” Heinichen said.

Mapping out the ecosystem using a qualitative “network” model provides data on species populations and water temperature. Quantitative models provide data.

“The next step is, add some numbers to it,” Heinichen said. “This is usually the step where we have to go out and collect some data, do a more thorough literature review. Sometimes, all these numbers don’t exist and the best you can do is a qualitative model, but the ideal is a quantitative model.”

Quantitative models calculate the population numbers of different organisms and measure the rates of change. In Narragansett Bay, one of the most significant changes in recent years has been an increase in the population of the striped sea robin, a fish that wasn’t found in Rhode Island waters in the 1960s and ’70s, but has spread northward as ocean temperatures have risen. Striped sea robins, not to be confused with the native northern sea robin, are remaining in Rhode Island waters for longer periods, too, from April to the end of October.

The Bay Informed Discussion Series is URI Graduate School of Oceanography School supported by Rhode Island Sea Grant. This series is held every third Thursday of the month at 7 p.m. at URI’s Graduate School of Oceanography’s Bay campus in Narragansett. These events are designed for the community to get involved and learn more about research at GSO.

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