CALANOID COPEPOD THORACIC LEGS-SURFACE AREA VS. BODY SIZE AND POTENTIAL SWIMMING ABILITY, A COMPARISON OF EIGHT SPECIES

In considering the role of the thoracic legs in escape or predation, where rapid starts and quick movement are important, species differences in leg architecture and surface area should be expected. With this in mind, eight species of calanoid copepods were examined to test the hypotheses that thoracic leg surface area was related to organism size and that the amount and/or distribution of leg surface area was related to life strategies of the species. The eight species included herbivores, omnivores, a carnivore, and a detritivore; they also provided a range of body length and volume as well as life styles. All copepods were in the region of Reynolds numbers where drag decreases as Reynolds number increases. Total leg area was significantly correlated to body length and body length squared. While the relationship between total leg area and body length was significant when all species were included, the detritrivore Eucalanus bungii was a clear outlier and the correlation was stronger when it was excluded. The linear relationship between total leg area and body length squared was especially strong for the smaller species. The areas of leg components (protopodite, exopodite, and endopodite) also showed significant correlations with body length squared, with E. bungii again being an outlier. The relative areas of individual leg pairs also showed trends across taxa with the third and fourth legs being larger than the first and second legs in all species except E. bungii. Both body drag and leg propulsion were found to increase with copepod body length. Leg propulsion compared to body drag was high in several species, particularly in Metridia lucens (s.l.), was intermediate in the two smallest species, and was low in E. bungii.