Abstract
Red drum early larval stages migrate through coastal inlets and settle into shallow seagrass meadows within estuaries. This study describes environmental rhythms (ER) in red drum nursery habitats and evaluates their role in larval growth. Well-defined dial ER were observed in temperature (amplitude: 2 to 4.5°C) and dissolved oxygen (DO) (range: 2.9-7.5mg O2 L-1), and sporadic cooling caused by cold fronts. We exposed groups of settlement sized larvae (4.9mm standard length) to two oscillating temperature treatments (amplitudes: 3 and 6°C; daily mean 27°C), an oscillating DO treatment (range: 2.4-6.1mg O2 L-1; daily mean 4.2mg O2 L-1 ) and a control (no cycles; daily mean 27°C, 6.4mg O2 L-1). Relative to controls, growth was significantly reduced in the DO treatment but not in the temperature treatments. Survival was similar in all treatments. Fish previously exposed to temperature cycles maintained faster growth rates and higher food intake than control fish when exposed to a simulated cold front. These results suggest that (1) ER may impart a physiological advantage to fish, (2) acclimation to oscillating DO environments is unlikely, and (3) field estimates of environmental characteristics based upon averaged daily point samples are inadequate for predicting fish growth.
