He swarming behavior of the copepod Dioithona oculata: In situ and laboratory studies

Abstract

The behavior of the swarm‐forming copepod Dioithona oculata was studied both in situ and in the laboratory using a video‐computer system for motion analysis. In nature, swarms form in light shafts between the prop roots of red mangroves. Swarms maintain their position within these light shafts despite currents of up to 2 cm s−1. In the laboratory, swimming speeds and turning rates of swarming copepods in still water were lower than those observed in the field. Copepods studied in a flowthrough chamber in the laboratory had swimming behaviors similar to those observed in nature; the stimulation from water movement caused increases in both swimming speed and rate of change of direction. Increased current speeds also caused the swarms to become more tightly packed within the center of a vertical light shaft. Nonswarming copepods were unable to maintain their position in a current in darkness. In laboratory experiments, the presence of actively feeding planktivorous fish caused swarms to temporarily disperse due to escape responses of the copepods. However, planktivorous fish were rarely observed feeding on swarms in nature, perhaps due to the presence of predatory fish hiding among the prop roots.