AbstractsBiology & Animal Science

Typescript. Theses for the degree of Master of Science (University of Hawaii at Manoa) – University of Hawaii, 1973. Bibliography: leaves 87-90. Data on primary productivity, chlorophyll a, nitrate, and phosphate in surface waters were collected on a 14-month (March, 1970 to April, 1971) series of approximately biweekly cruises in Kaneohe Bay, Oahu, Hawaii. During the latter part of the survey data ammonium ion concentrations and light penetration through the water column were also collected. The year is divided into two seasons on the basis of rainfall, and the effects on the dynamics of the phytoplankton community of terrestrial runoff and sewage effluents entering the bay are separated on the basis of differences between wet season and dry season productivity indices (productivity/Chl. a). The bay is divided into three sectors; South, Transition, and North. The most important nutrient sources are; the Kaneohe Municipal Sewage Treatment Plant effluent to the South Sector, terrestrial runoff to the Transition Sector, and a persistent, but unidentified nitrate input to the North Sector. The Municipal Treatment Plant effluent is shown to be toxic to phytoplankton in the immediate area. Phosphate concentration is not correlated with rainfall, and is present in non-limiting concentrations in all sectors. Nitrate concentration is strongly correlated with rainfall in the Transition Sector, and low dry season (summer) concentrations may limit phytoplankton growth. Wet season (winter) nitrate concentrations in the other two sectors are also higher than summer values, but the differences are not significant. Fluctuations in phytoplankton population size seem to be primarily a function of variable grazing pressure by herbivorous zooplankton. Phytoplankton growth rates peak in summer and winter, and may be related to the availability of light. Light penetration itself is directly related to phytoplankton density in the water column, and the winter growth rate peak may result from increasing light penetration due to extensive grazing on the phytoplankton population. The present data are compared with similar data collected 10 years earlier. Based on a hyperbolic relationship between substrate concentration and growth rate, the South Sector is shown to have been eutrophic for at least the past decade, while in the Transition and North Sectors symptoms of eutrophication have appeared during this decade.