Towards and Understanding of the Existence of Small Oceanic Planktonic Copepods

Skidaway Institute Of Oceanography, Savannah GA

Investigators

Abstract

Large areas of our planet are covered by subtropical and tropical oceans which contain in excess of 200 species of copepods of which the most abundant are small. Attempts to conduct in-depth studies to understand the function of epileptic communities in these waters have been limited. The largest effort to date was conducted by Soviet scientists in 1974 in the equatorial Pacific, but yielded limited rate quantifications due to methodological shortcomings. Process studies of epipelagic environments included quantifications of major groups such as microzooplankton (collected by 20 to 200 mm mesh), mesozooplankton (200 to 2,000 mm mesh), and macrozooplankton (> 2,000 mm mesh). The microzooplankton, which is usually not collected quantitatively by traditional zooplankton sampling, includes juveniles of larger copepods and the vast majority of all stages of small copepods, as well as numerous protozoa. To understand the true contribution of microzooplankton to processes in the ocean requires a separation of proto- and metazooplankton. Numerous studies have quantified consumption and growth rates of various groups of protozooplankton, but direct quantifications of some of the rates of the metazooplankton component of the microplankton have been rare. The overall goal of this proposed work is to increase our understanding of the mechanisms governing persistence and existence of highly abundant species of subtropical-tropical oceanic planktonic copepods. We propose to conduct field and laboratory studies of three abundant species of oceanic copepods (Oithona plumifera, Clausocalanusfurcalus, Paracalanus aculeatus) which occur circumglobally, with the general objective of enhancing our understanding of the existence and persistence of small copepod species in environments of extraordinarily low abundances of potential food organisms. Specifically, field studies are expected to provide information on (1) vertical distribution of juveniles and adults of these three species; (2) their potential food organisms and major hydrographic variables; and (3) quantifications of feeding and reproduction rates plus estimates of mortality rates. Experimental studies will provide information on feeding and growth of juveniles, respiration and reproduction of adult females, motion of juveniles and adults, and sensor distribution on these copepods' sensory structures. The latter information will contribute to understanding the physiological constraints on feeding that are imposed by the functional morphology of the copepods' sensory structures. We hypothesize that differences in each species' energy budget, estimated mortality rate and perceptive ability will explain mechanisms contributing to these species' abundance in tropical/subtropical oceans. The significance of the proposed research is to obtain, through concerted field and laboratory studies, an understanding how these three abundant circumglobally occurring copepod species can persist, and through that improve our understanding of the functioning of an epiplanktonic oceanic community under the present climatic conditions. Combining information from field and laboratory data, we expect to reveal mechanisms by or through which each of the 3 species can persist in their environment. Once we understand how organisms are adapted to their respective environment, and know their requirements for living and reproduction, then we should be in a good position to be predictive about the way pelagic ecosystems might respond to climate variability and change.