Feeding of Flaccisagitta enflata (Chaetognatha) upon copepods in the southern Gulf of Mexico

For years, planktologists considered the chaetognaths as great predators of other zooplankters. In this study, we analyzed the feeding rates upon copepods of the chaetognath Flaccisagitta enflata. Additionally, we sought signs of predatory competition with gelatinous zooplankton for copepod prey. Zooplankton samples collected in a Bongo net (333 µm mesh) in the southern Gulf of Mexico were analyzed in the laboratory. Results indicated that on average, a F. enflata individual eats 0.8 copepod.day-1. We suggest that competition for prey between chaetognaths and gelatinous zooplankton does not occur or is negligible because the feeding activity in chaetognaths does not increase with prey abundance, no habitat partitioning was observed between the two predator types, and that predator species can turn to alternative food items. The low intake of copepods and the fact that feeding rates do not increase with food concentration led us to hypothesize that chaetognaths are not voracious predators as previously suggested.