As filter feeders, oysters and other shellfish depend on microscopic organisms including plankton, algae and bacteria found naturally in the water column for food. On average, an adult oyster can filter over 50 gallons of water per day and are known to selectively sort potential food particles, expelling less desirable food items and sediment as pseudo-feces. Across estuaries in the northern Gulf of Mexico, the quantity and quality of food available may vary as many of these plankton, particularly phytoplankton (photosynthesizing plankton), have short generation times, responding to changing environmental conditions in estuaries. In addition, some phytoplankton species produce phycotoxins which may cause negative effects in organisms — directly to those feeding on the phytoplankton, but also indirectly, by species consuming these filter feeders. Yet, we have limited data on these food resources and potential phycotoxin exposure across the northern Gulf estuaries.

In 2022, Drs. Megan La Peyre, RNR professor and U.S. Geological Survey Louisiana Coop Unit, and Melissa Baustian, USGS Wetlands and Aquatic Research Center, initiated work across several northern Gulf estuaries to document baseline levels of filter feeder phycotoxin concentrations, and, with a larger team, to explore the spatiotemporal presence of phytoplankton species of interest identified by the National Oceanographic and Atmospheric Administration’s National Centers for Coastal Ocean Science Phytoplankton Monitoring Network. This work has expanded to support the research of RNR graduate student Megan Humphrey. One of Humphrey’s research chapters is focused on measuring potential phycotoxin tissue levels of common filter feeding organisms within Gulf Coast estuaries.

This work has resulted in larger collaboration with researchers in the Chesapeake Bay and across the Gulf. Humphreys also spent the summer assisting academic and government project collaborators in collecting samples to measure phytoplankton and phycotoxin presence in the water column across multiple estuaries of the northern Gulf to help develop a baseline database, relating findings to local environmental conditions. This ongoing work is critical to develop a baseline for understanding how changing environmental conditions may affect phytoplankton availability and identity for the organisms that rely directly and indirectly on these food resources.

Postdoctoral researcher Theresa Davenport, left, and graduate student Megan Humphrey seine to collect nekton for assessment of phycotoxin tissue levels during spring 2024 at the Louisiana Universities Marine Consortium in Cocodrie, Louisiana.