Oyster drills threaten mollusk populations

BILOXI, Miss. -- Coastal living is all the sweeter when you’re able to enjoy fresh seafood. Not everyone has the luxury of choosing between numerous seafood restaurants offering Southern classics year-round. One seafood staple Biloxi has a long history with is the oyster.

Long before Biloxi was known as the Seafood Capital of the World, the Gulf Coast was supplying people with a steady population of oysters. Before European settlement, indigenous harvesting of these mollusks sustained generation after generation of coastal living families.

Evidence of these once prolific oyster populations can be found in the heaps of oyster shells known as shell middens that dot the Mississippi and Alabama coastlines.

Whether it is charbroiled, stewed in a gumbo, crispy-fried or served raw, oyster eaters today still know how to enjoy these gifts from the sea. But who else is after this edible treasure?

Anyone who has spent time observing dock pilings or one of the many concrete bulkheads at low tide has probably seen an oyster drill. Oyster drills are a carnivorous marine snail that eats barnacles, mussels and oysters, often recognized as the most devastating oyster predator in the Gulf.

Ideal environmental conditions of oyster drills mirror our coast, where we have both native oyster reefs and oyster farms. In ideal conditions, one female oyster drill can produce more than 10 million eggs during her lifetime.

It is easy to see how this predator could quickly become a problem, especially with Mississippi oyster populations already struggling. Native oyster reefs aren’t only struggling with predators, but disease, hurricanes and sudden changes in salinity from massive freshwater inflows have all contributed to the state of oyster populations in the last few decades.

One way to maintain a supply of oysters here against these challenges has been through oyster farming. Farmers monitor diseases and fouling, secure cages before large storms and even reduce predation with different cage styles. However, a recent survey of Mississippi and Alabama farmers still shows oyster drills as the number one predator of concern.

While the thought of sharing our vital seafood bounty might not be the first thing oyster farmers and harvesters are thinking, there might be a way to reduce the number of oysters lost to this predator.

Our coast is made up of patches of different types of sediment, some having the nice sand we expect to see at beaches and other areas that have thin, muddy silt. Just like you, oyster drills seem to have a preference.

Oyster drills on our coast have been observed in higher numbers in areas with sandy bottom instead of the soft mud bottom. While the reasons why are still being investigated, understanding where oyster drills seem to populate gives us the advantage before constructing new restored oyster reefs or sites for oyster farms.

A simple decision made during site selection for an oyster farm or restored reef could lead to a big difference in the amount and type of predators drawn to that area. 

[EDITOR’S NOTE: Based at MSU’s Coastal Research and Extension Center in Biloxi, Dr. Cynthia Lupton is an MSU Extension associate with the Coastal Marine Extension Program. Extension Outdoors is a column authored by a rotation of MSU Extension specialists.]