Abstract
We present the first data on copepod feeding and production in the Rio de la Plata, and discuss their correlation to the physical and biological environment. Sampling was performed at a protected area on the Montevideo coast where temperature, salinity and size fractionated chlorophyll a and phaeopigments were monitored weekly from January through February 2003, plus two additional observations in March and April. Acartia tonsa ingestion was measured by gut fluorescence, and gut evacuation rates, egg production and egg hatching success were estimated using standard methods. Food availability was moderate/high, but quality appeared low as reflected by chlorophyll a:phaeopigment ratios <1. Ingestion correlated with both chl-a and pha, suggesting that A. tonsa fed also on detrital matter. Egg production rates were low (1.4-7.5 eggs female-1 d1) - except for one exceptional record of ca. 88 eggs female-1 d-1 - indicating low productivity rates. Egg hatching success ranged from 30-94% and tended to increase during the study period. Overall results suggest that at the study site A. tonsa fed on both phytoplankton and detritus, and that its production was limited by food quality.
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