Bundy, M. H. The Academy of Natural Sciences Estuarine Research Center, 410-598-9705
Sanders, J. G. The Academy of Natural Sciences Estuarine Research Center, jsanders@acnatsci.org
Paffenhofer, G. -A. Skidaway Institute of Oceanography, gus@skio.peachnet.org
Oppert, C. J. Kansas State University, cjo0413@ksu.edu

 
POPULATION RESPONSES OF THE CALANOID COPEPOD ACARTIA TONSA TO DIFFERENCES IN FOOD QUALITY: MESOCOSM AND LABORATORY EXPERIMENTS
 
Populations of the copepod Acartia tonsa were followed in mesocosm experiments containing natural estuarine assemblages with nutrient and trace metal additions. Direct counts of phytoplankton and microzooplankton revealed that species composition of prey communities changed in response to nutrient and trace metal additions. Particularly during spring, the large chain-forming diatom Rhizosolenia fragilissima bloomed in tanks with nutrient additions, but not in tanks with nutrients and trace metals. Densities of A. tonsa were lower in tanks with R. fragilissima blooms than in tanks where trace metals inhibited this diatom. Laboratory experiments were conducted to determine the influence of food quality on copepod egg production when A. tonsa is feeding on: monocultures of R. fragilissima, mixtures of R. fragilissima and the small diatom Thallasiosira weissflogii, and natural assemblages of microzooplankton and algae. Preliminary data suggest that R. fragilissima alone severely depresses egg production, while mixtures of R. fragilissima and T. weissflogii do not. Visual observations of individual feeding events show that A. tonsa adult females reject Rhizosolenia cells soon after capture. These results provide evidence that blooms of large chain-forming diatoms may interfere with copepod feeding and may cause decreased copepod population growth in natural systems, due to suppression of secondary production.
 
Day: Wednesday, Feb. 3
Time: 10:30 - 10:45am
Location: Hilton of Santa Fe
 
Code: SS21WE0945H