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Carnivorous conchs to blame for oyster decline

High water salinity, coupled with, a conch population outbreak is the cause of a sharp decrease in oyster populations on Florida reefs

August 14, 2015
Northeastern University
A marine and environmental science professor has solved the mystery of why reefs in Florida inlets were experiencing large numbers of oyster loss. Drought and subsequent high salt levels in water led to a population spike in one of the oysters' main predators: conchs.

What hap­pens when a drought in Florida estu­aries causes a rise in the salt levels in water? Fewer wild oys­ters appear on restau­rant menus, for starters.

New research from North­eastern Uni­ver­sity marine and envi­ron­mental sci­ences pro­fessor David Kimbro and grad­uate stu­dent Hanna Gar­land, pub­lished in PLOS ONE, links the dete­ri­o­ra­tion of oyster reefs in Florida's Matanzas River Estuary (MRE) to a pop­u­la­tion out­break of car­niv­o­rous conchs and high water salinity--or saltiness--caused by a pro­longed regional drought.

This isn't just bad news for oyster lovers.

"Coastal ecosys­tems around the world depend greatly on the ser­vices pro­vided by oys­ters," Kimbro said. "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."

As a result of degra­da­tion, over­har­vesting, and human activity, the global abun­dance of this habitat has declined by 85 per­cent, according to the Nature Con­ser­vancy. Today, most of the world's remaining reefs are con­cen­trated in only six eco-regions--four in the United States.

"Luckily, 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."

When one of these eco-regions expe­ri­ences an envi­ron­mental stress, like that seen in the Floridian estuary, the impact can be felt across industry and ecosystems.

"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 team found in this case that conchs repro­duce better in water with a high salinity. Because of the deficit of fresh­water and increase in salinity from the drought, conch larvae pro­lif­er­ated, resulting in an abun­dance of the conch, which then led to a greater con­sump­tion of oys­ters on the reef.

While the team deter­mined the conch pop­u­la­tion out­break to be the prox­imal cause of oyster loss, it is the salinity of the water spurred by the multi-year drought that is the ulti­mate cause, because that is what led to a spike in the car­niv­o­rous conch population.

Kimbro says there is opti­mism the reef could recover if the high salin­iza­tion sub­sides. And a nor­mal­ized conch pop­u­la­tion can actu­ally be ben­e­fi­cial to oyster reproduction--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.

This research, along with addi­tional studies on the conch-oyster dynamic in this eco-region could prove vital to oyster reef con­ser­va­tion efforts.

Story Source:

Materials provided by Northeastern University. Note: Content may be edited for style and length.

Journal Reference:

  1. Hanna G. Garland, David L. Kimbro. Drought Increases Consumer Pressure on Oyster Reefs in Florida, USA. PLOS ONE, 2015; 10 (8): e0125095 DOI: 10.1371/journal.pone.0125095

Cite This Page:

Northeastern University. "Carnivorous conchs to blame for oyster decline." ScienceDaily. ScienceDaily, 14 August 2015. <>.
Northeastern University. (2015, August 14). Carnivorous conchs to blame for oyster decline. ScienceDaily. Retrieved December 7, 2023 from
Northeastern University. "Carnivorous conchs to blame for oyster decline." ScienceDaily. (accessed December 7, 2023).

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