California Sea Grant College Program

Copepods are the most important metazoan grazers of phytoplankton in the sea. In order to more fully understand the flow of energy from phytoplankton through copepods (and beyond), it is necessary to know what factors modify their feeding. Contrary to the classical paradigm of passive, mechanical feeding by copepods, copepods are quite selective in their preferred prey. Some of this selectivity appears to be mediated by chemicals produced by their phytoplankton prey. Knowing the time required for selectivity to occur and the persistence of that selectivity should give us a better understanding of copepod sensory and decision-making capabilities.

Some members of the marine phytoplankton, particularly some dinoflagellates, produce toxic (or noxious) chemicals. The biosynthesis, biochemical modes of action, and structures of some of these chemicals are known, but virtually nothing is known about the natural function of these toxins. One of the likely functions is chemical defense against herbivores. Chemically-defended dinoflagellates may be selectively avoided, and preferred cells selectively ingested. If true, then chemical defense may provide an ecological advantage over co-occurring undefended cells. Otherwise, all cells may be equally rejected or accepted, thus conferring no advantage on the defended cell.

The goal of my doctoral dissertation research was to investigate the physiological and behavioral aspects of the feeding biology of Calanus pacificus vis a vis the presence of noxious dinoflagellates. In addition, I studied the significance of chemical defense to the noxious dinoflagellate Gonyaulax grindleyi.