PARENT SESSION
Oral Session #26: Aquatic Ecology: Fish - Populations, life history, autecology. Presiding: M. Fox.
Tuesday, August 7, 2001. 8:00 AM to 12:00 PM. Hall of Ideas H.
Responses of juvenile southern flounder to environmental variability in estuarine ecosystems.
McClellan, Catherine1, Crowder, Larry1, 1
ABSTRACT- Estuaries are intrinsically dynamic and physiologically challenging environments due to widely varying hydrographic parameters such as temperature, salinity, and dissolved oxygen. Among eutrophic estuaries in the Southeastern U.S., intermittent hypoxia (dissolved oxygen concentrations < 2 mg/l) in bottom waters is a common problem. We hypothesize that juvenile southern flounder, Paralichthys lethostigma, respond to this variability, specifically changes in dissolved oxygen, with mesoscale changes in habitat use. We used controlled lab experiments and a novel field manipulation to examine how fish respond to the changing environment. We ran choice experiments with variable dissolved oxygen and salinity treatments. We also released individual southern flounder into dissolved oxygen and depth "treatments" in their natural environment. Using ultrasonic telemetry, we tracked flounder continuously for an average of 5 hours and then every other day for approximately three weeks while synoptically monitoring temperature, salinity, dissolved oxygen, and sediment type. Fish moved out of low oxygen areas quickly relative to well oxygenated areas and avoided the center of the river which remained hypoxic for most of the study duration. Only when hypoxia permeated the shallow inshore waters were flounder found in low oxygen. These fish had higher movement rates indicative of active avoidance response. Salinity did not appear to influence movement in our study. We conclude that hypoxia alters habitat use and lowers habitat quality by increasing energy expenditure.
KEY WORDS: flounder, habitat, hypoxia, estuary