ENERGETIC COSTS OF SWARMING BEHAVIOR FOR THE COPEPOD DIOITHONA-OCULATA

The cyclopoid copepod Dioithona oculata forms dense swarms within shaf ts of sunlight that penetrate the mangrove prop-root habitat of island s off the coast of Belize. Previous studies, based on in situ video re cordings and laboratory studies, have shown that D. oculata is capable of maintaining fixed-position swarms in spite of currents of up to 2 cm s(-1) The purpose of this study was to examine the energetic costs of maintaining these swarms, in terms of increased metabolic costs of maintaining position in currents and in terms of reduced feeding rates in densely packed swarms during the day. Using a sealed, variable-spe ed flow-through chamber, the respiration rates of D. oculata were meas ured while swarms maintained position in different current speeds. The results indicate that active metabolism (swimming at maximum speed to maintain the swarm in a cut-rent) is approximately three times greate r than routine metabolism (normal swimming speeds in the absence of cu rrents), indicating a significant metabolic cost of maintaining swarms in the presence of currents. In addition, gut-pigment analysis indica ted that feeding rates of these copepods were often reduced in swarms during the day compared to when the copepods were dispersed at night. Given the high ''cost'' of swarming, the adaptive value of swarming in terms of reduced predation, increased opportunities for mating, and r educed dispersal, must be substantial.