Carnivorous conchs to blame for oyster decline
What hapÂpens when a drought in Florida estuÂaries causes a rise in the salt levels in water? Fewer wild oysÂters appear on restauÂrant menus, for starters.
New research from NorthÂeastern UniÂverÂsity marine and enviÂronÂmental sciÂences proÂfessor David Kimbro and gradÂuate stuÂdent Hanna GarÂland, pubÂlished in PLOS ONE, links the deteÂriÂoÂraÂtion of oyster reefs in Florida’s Matanzas River Estuary (MRE) to a popÂuÂlaÂtion outÂbreak of carÂnivÂoÂrous conchs and high water salinity–or saltiness–caused by a proÂlonged regional drought.
This isn’t just bad news for oyster lovers.
“Coastal ecosysÂtems around the world depend greatly on the serÂvices proÂvided by oysÂters,†Kimbro said. “They are imporÂtant for the staÂbiÂlizaÂtion of shoreÂlines, filÂtraÂtion of coastal water, proÂtecÂtion of imporÂtant ecoÂnomÂiÂcally valuÂable fishes and inverÂteÂbrates, and the removal of excess nitrogen.â€
As a result of degraÂdaÂtion, overÂharÂvesting, and human activity, the global abunÂdance of this habitat has declined by 85 perÂcent, according to the Nature ConÂserÂvancy. Today, most of the world’s remaining reefs are conÂcenÂtrated in only six eco-regions–four in the United States.
“Luckily, there are govÂernÂment and non-government-led efforts that will begin to restore this habitat in 15 difÂferent states,†Kimbro said. “But if an area to be restored conÂtains or is likely to develop an outÂbreak of conchs like the one in Matanzas, then the restoraÂtion effort will fail, regardÂless of the expenÂdiÂture of effort or expense, unless the salinity and conch problem is first solved.â€
When one of these eco-regions expeÂriÂences an enviÂronÂmental stress, like that seen in the Floridian estuary, the impact can be felt across industry and ecosystems.
“EnviÂronÂmental change and conÂsumer pressure–the conchs being the consumer–can impact founÂdaÂtion species like oysÂters on their own,†Kimbro said. “But we have a case here where it is the interÂacÂtion between the two stresÂsors that is causing the greatest impact on the decline of the oysters.â€
The team found in this case that conchs reproÂduce better in water with a high salinity. Because of the deficit of freshÂwater and increase in salinity from the drought, conch larvae proÂlifÂerÂated, resulting in an abunÂdance of the conch, which then led to a greater conÂsumpÂtion of oysÂters on the reef.
While the team deterÂmined the conch popÂuÂlaÂtion outÂbreak to be the proxÂimal cause of oyster loss, it is the salinity of the water spurred by the multi-year drought that is the ultiÂmate cause, because that is what led to a spike in the carÂnivÂoÂrous conch population.
Kimbro says there is optiÂmism the reef could recover if the high salinÂizaÂtion subÂsides. And a norÂmalÂized conch popÂuÂlaÂtion can actuÂally be benÂeÂfiÂcial to oyster reproduction–after conchs pry open the oyster valves to conÂsume the tissue inside, they leave behind a clean internal cavity, which oyster larvae can then use for its own development.
This research, along with addiÂtional studies on the conch-oyster dynamic in this eco-region could prove vital to oyster reef conÂserÂvaÂtion efforts.
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