In recent years interest has increased concerning the accuracy with which collections made with plankton samplers describe the size and species composition of zooplanktonic communities. The indications are that errors arising from the avoidance of sampling devices by zooplankton may be important, especially when precise data are required. A model is proposed to describe the processes by which zooplanktonic organisms escape or avoid a sampler in terms of the radius of the mouth of the sampler, the speed at which it is towed, the effective speed the organisms can attain in order to escape, and the distance at which the organisms can detect the sampler. The model is capable of being fitted to field data to provide a curve of percentage catch plotted against speed of towing. The results presented indicate that the model gives a good representation of the processes of biological escapement. Implications of the results are embodied in recommendations respecting the design of plankton samplers. / Science, Faculty of / Zoology, Department of / Graduate

The species composition, primary productivity and relative abundance of the plankton organisms in Marion Lake, British Columbia were recorded at biweekly intervals for two months following artificial enrichment with nitrate or phosphate or both, of six large wooden enclosures within the lake in four seasons during the year. Enrichment resulted initially in a decrease in diversity and an increase in the productivity of the phytoplankton and standing crop of the entire plankton community. These events were collectively termed a "regressive succession" because their "direction" of change was the reverse of that normally encountered in primary and secondary successions. The regressive succession terminated following algal bloom formation, and diversity began to increase slowly while the primary productivity and standing crop of the plankton dropped. This was indicative of the beginning of a secondary succession in which one group of dominant species was replaced by another and then others in turn replaced these. This successional pattern occurred regardless of season, prevailing physical, chemical, or climatological factors. Thus, such a pattern appeared to be a very general one and was disrupted only by the physical removal of the majority of the planktonic species from the lake resulting from persistent and heavy rains which "flushed" the lake. A statistical analysis of each of the 167 euplankton species observed in the lake was performed using the data from each of the four enrichment series to determine which species responded significantly to artificial enrichment. The individual response patterns were nearly as diverse as the species themselves, however, one of the most common responses was made by very rare species which "bloomed" two to three weeks after nutrient addition. Few primary producers responded to more than one type of nutrient enrichment in any one season which emphasized the importance of Liebig’s Law of the Minimum. The higher trophic levels, on the other hand, responded more to the increase in standing crop in the different enclosures than to any one particular type of nutrient enrichment. The Shannon-Weaver formula, H =nP, log P, was modified by changing the definition of Pi, that is, the individuals in the ith species divided by the total number in the sample. This index was insensitive to changes in the relative abundance of the planktonic species from the higher trophic levels. Pi was redefined so that it was less sensitive to number and more sensitive to both relative biomass and relative productivity. This new index of diversity (Hp ) did not act selectively on the different trophic levels represented in the plankton samples. An understanding of the principles governing community organization and biotic succession should be based on the life history of the individual species comprising the community and not on assumptions about supposed trophic changes. This study indicated that pertinent information about the changes in the structure of a planktonic community could be gained from an analysis of the changes in the relative abundance of each of the species without artificially isolating and culturing these species and without lumping all the organisms into vague trophic categories. / Science, Faculty of / Zoology, Department of / Graduate

Monthly samples of nutrients, phytoplankton and zooplankton were taken in the Columbia River estuary over a period of 16 months in order to determine distribution with season and salinity, and interrelationships between plankton and nutrients. Nitrate and phosphate levels in the river water entering the estuary are high in the winter and show depletion during the summer. Silicate levels are high in the river water at all seasons. Nitrate and phosphate levels are high in the entering ocean water during summer offshore upwelling. The nutrient levels in the estuary generally show a linear relationship with salinity, resulting from the levels of nutrients in the entering river and ocean water. Superimposed upon this linear relationship is a tendency for the nutrients to be enriched in the bottom waters of the central part of the estuary. The estuary phytoplankton are primarily composed of freshwater forms, and probably represent a downstream extension of the river flora. Regression analysis of phytoplankton levels vs. light, nutrients, and river flow indicates that light probably limits phytoplankton abundance on most dates. The zooplankton of the estuary are composed of three groups, preferring fresh, oligohaline, and polyhaline waters respectively. Regression analysis indicates a strong correlation between abundance of the freshwater group and river temperature. The factors controlling the abundance of the oligohaline and polyhaline groups are less obvious. The oligohaline group, principally Eurytemora affinis, reaches the greatest population density (100,000/m³ or more). Regression analysis indicates a close correlation between Eurytemora abundance and phosphate levels. This indicates a strong potential for zooplankton regeneration of phosphate necessary for phytoplankton growth. / Graduation date: 1970

Typescript. / Thesis (Ph. D.)--University of Hawaii. 1967. / Bibliography: leaves 211-218. / xi, 218 l illus., maps, tables