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Distributional ecology of the calanoid copepod Pareuchaeta elongata esterly Evans, Marlene Sandra

Abstract

Many field and laboratory studies testing the growth of phytoplankton and the survival of the early developmental stages of zooplankton and benthic organisms have shown that sea waters that are alike in salinity and temperature are nevertheless different in other properties (qualities). These differences in quality may be associated with variations in the concentrations of dissolved trace elements and organics. The concentration of a trace element or organic may have beneficial or harmful effects on marine organisms. Bary (1963) suggested that, in certain areas, these variations in the properties of sea waters may be sufficiently great, and the tolerance, of zooplankton sufficiently small, .for species to be restricted to various waters. These waters, called water bodies, were described by their temperature and salinity characteristics and the distribution of species was described in relation to these water bodies. Many of the species Bary (1963) studied were at the northern' most or southern-most boundaries of their geographic ranges. It was the purpose of this study to investigate whether or not, within the geographic range of an organism, variations in water quality are an important environmental variable in determining a species’ abundance and distribution. The study organism was the calanoid copepod Pareuchaeta elongata. Lewis and Ramnarine (1969) had shown that, in the laboratory, the egg and the prefeeding naupliar stages were sensitive to variations in water quality. The biological portion of this study consists of three parts. The first part is the results of three survey cruises of the waters of the inlets of the British Columbia mainland, the west coast of Vancouver Island, the connecting passages, and the Pacific Ocean. Six groups of water were identified on the basis of the similarity in the temperature-salinity characteristics of their subsurface waters. The results indicate that P. elongata is capable of breeding in all the waters studied, thus suggesting that variations in the species' abundance are unrelated to variations in water quality. Variables which may affect the species' abundance were suggested as being associated with the primary production of that area, and the origin and the residence time of the water in that area. The one-year laboratory study, testing P. elongata egg clusters in various natural sea waters, .indicated that there were differences in the survival among egg clusters from various areas. It was also shown, by testing egg clusters from one area in a number of seawaters of similar salinities, that there were variations in the quality of these waters. Egg clusters were collected from G.S.-1(in the Strait of Georgia) and Indian Arm, and were tested in their home water once a month over a 12-month period. Field collections were made at these two stations over a 29-month period. The laboratory data were evaluated in terms of the field data.. The number of nauplii in the water was correlated with the number of eggs in the water, and was apparently not significantly affected by variations in the survival of the egg in its home water (as measured in the laboratory). This lack of any significant effect of variations in survival was probably due to the very large effect of variations in egg production. There was a high mortality from the hatched nauplius to the adult (approximately 97%), indicating that the mortality of the egg due to its interaction with the water had a small role in determining the final population size. The data suggested that variables, such as prey availability, and predation, are probably the most effective variables in regulating the abundance of the species in these two areas. In conclusion, while the data showed that the species was more abundant in some areas than others, these differences could be explained by considering the primary production of the area, and the origin and residence time of the water. Although seawaters within the study area may vary in quality, these variations probably do not significantly affect the abundance and distribution of the species.

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