ON THE ECOLOGY OF MARINE CYCLOPOID COPEPODS (CRUSTACEA, COPEPODA)

The goal of these studies was to improve our understanding of how Oithonidae and Oncaeidae can exist in nearly every part of the ocean. In particular, it was intended to obtain quantitative information on reproduction rates and the longevity of adult females, and on feeding and growth rates of Oncaeidae. When feeding at relatively high food levels, early copepodids of Oncaea mediterranea ingested approximately 100% of their body weight daily and had an exponential growth rate of r = 0.26. Average reproduction rates of field-collected O. mediterranea females ranged from 5.3 to 13.3 nauplii day-1 and those of females of Oithona plumifera were 3.8 nauplii day-1. However, females of the latter reproduced for longer periods than those of the former. Average longevity of females of O. mediterranea ranged from 29 to 41 days, and that of O. plumifera was 71 days on average. Their reproductive output per lifetime was similar to those of small calanoid species like Paracalanus parvus, for example, which reproduce at higher rates, but over a shorter adult female lifespan. It is assumed that predator avoidance, especially of early juveniles, extended egg production and female longevity, and relatively low metabolic expenditures contribute to the nearly ubiquitous occurrence of the two genera. The limited specialization of the two genera, when compared to calanoids, could be seen as an advantage to survival over an extended range of environmental conditions. It is hypothesized that the relatively low rates of food consumption, growth, reproduction and, possibly, mortality contribute to stabilizing planktonic communities in the ocean.