Meeting Abstract

P2.41  Wednesday, Jan. 5  Distribution of Calanoid Copepods: The Role of Myelin LENZ, P.H.*; HARTLINE, D.K.; University of Hawaii at Manoa; University of Hawaii at Manoa petra@pbrc.hawaii.edu

Calanoid copepods (Crustacea) are an important component of planktonic communities. Approximately half of the calanoid species possess myelinated nervous systems, that is their axons have a membranous ensheathment that saves energy, speeds the conduction of nerve impulses and shortens behavioral response times. Existing data on the distribution of calanoids suggest that both types are widely distributed and abundant in both coastal and oceanic environments. A more detailed analysis of these data suggests that myelinated and non-myelinated species were not distributed evenly across habitats. In the open ocean, non-migratory calanoids found in the upper 100 m were mostly myelinated. In contrast, the most abundant non-myelinated species were vertical migrators, which enter this region only at night. Estuaries are typically dominated by non-myelinated calanoids. However, myelinated species comprise 80% of the calanoid copepod population in many sub-tropical estuaries. Two advantages conferred by myelin, an enhanced escape response and savings in energy, may be key factors that promote the success of myelinated calanoids under oligotrophic conditions such as oceanic surface waters and sub-tropical estuaries. These habitats are characterized by low food resources, yet chronic high predation pressure. Conditions that offer temporary relief from predators — physical and/or temporal “refugia” — provide opportunities for non-myelinated calanoids.