Oyster population suffers due in part to this carnivorous species

Fewer wild oysters are being featured on Florida menus, due in part to drought in the state’s estuaries, which has spurred a rise in salt water levels. Moreover, a population outbreak of carnivorous conchs has overtaken the oyster reefs in the Matanzas River Estuary (MRE), according to new research from Northwestern University.

The high water salinity and influx in new neighbors have made it tough for oysters to thrive. But it’s not just the bivalves having trouble.

"Coastal ecosystems around the world depend greatly on the services provided by oysters," said David Kimbro, marine and environmental sciences professor. "They are important for the stabilization of shorelines, filtration of coastal water, protection of important economically valuable fishes and invertebrates, and the removal of excess nitrogen."

The research team, led by Kimbro and graduate student Hanna Garland, found that conchs tend to reproduce at a faster rate in waters with higher salinity. As freshwater was overpowered by salinity due to drought, conch larvae grew in abundance and eventually, oysters were being consumed by the conchs on the reef at an increased rate.

"Environmental change and consumer pressure--the conchs being the consumer--can impact foundation species like oysters on their own," Kimbro said. "But we have a case here where it is the interaction between the two stressors that is causing the greatest impact on the decline of the oysters."

The Nature Conservancy finds that the oyster reef habitat has declined by 85 percent as a result of degradation, overharvesting and human activity. Fortunately for the oyster fishery, efforts to restore these habitats are underway, said Kimbro.

“There are government and non-government led efforts that will begin to restore this habitat in 15 dif­ferent states," Kimbro said."But if an area to be restored contains or is likely to develop an outbreak of conchs like the one in Matanzas, then the restoration effort will fail, regardless of the expenditure of effort or expense, unless the salinity and conch problem is first solved."

There is hope that the reef and those that face similar circumstances can be returned to proper ecological order. Once the high salinization subsides, the conch population can normalize. Conchs can actually be good for oyster reproduction at large, concluded Kimbro: “After conchs pry open the oyster valves to consume the tissue inside, they leave behind a clean internal cavity, which oyster larvae can then use for its own development.”

The research was published in the latest edition of PLOS ONE


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