ZOOPLANKTON-PHYTOPLANKTON INTERACTIONS IN THE SAN JOAQUIN RIVER, CA

Authors

Cyle R. Moon, University of the Pacific
Gary M. Litton, University of the Pacific
Mark S. Brunell, University of the Pacific
William T. Stringfellow, University of the PacificFollow

Introduction/Abstract

The dynamics of zooplankton and phytoplankton growth and interactions play a significant role in water quality (e.g., pH and dissolved oxygen) and the available food supply for higher order organisms in the San Joaquin River Delta. Numerical water quality models developed to simulate and predict dissolved oxygen in the San Joaquin River (SJR) rely on mathematical algorithms that link chemical and biological mechanisms. Due to the complexity of natural systems, calibrating these models is challenging and often requires independent investigations to estimate input parameters, such as zooplankton grazing and algal growth rates. This investigation explored the applicability of three methods to quantify the rates that zooplankton graze on algae populations in the SJR. The significance of these data were also interpreted with a predator-prey model.

Method

Zooplankton grazing studies were performed in the Deep Water Ship Channel of the San Joaquin River from June to October, 2012. Light and dark bottle microcosm studies using the dilution method (Landry and Hassett, 1982), the food-removal method (Gauld, 1951), and the grazer concentration method (Capriulo and Carpenter, 1980) were tested. A modified approach similar to the grazer concentration method provided the most reliable results. Microcosms contained zooplankton concentrations that were up to 30 times higher than natural, background levels. Zooplankton was removed from control microcosms with a plankton net. Measurements of chlorophyll a before and after river incubation were sufficient to separate zooplankton grazing from algal growth and respiration.

Results

Phytoplankton and zooplankton populations before concentrating ranged from 4.24-14.23 μgL-1 and 10.74-53.80 μgL-1, respectively. Grazing rates were determined by fitting observed changes in chlorophyll a to coupled predator-prey equations developed by Chapra (1997). Measured grazing rates ranged from 0.5 to 3 with most values between 1 and 2 m3gC-1d-1; observations that are consistent with literature values. Results revealed algae productivity rates of 0.60-0.86-d-1 for daytime experiments, and 0.10-0.14-d-1 for day/night experiments.

Significance

Algae have been shown to significantly impact dissolved oxygen (DO) in the Deep Water Ship Channel of the San Joaquin River. Zooplankton grazing is one of the important mechanisms that influence the fate and spatial distribution of algae, and therefore, may contribute to DO deficits that adversely impact aquatic habitat and salmonid migration. These results, when utilized with comprehensive water quality models, facilitate the development of a management tool useful for assessing the benefits of improving habitat or reducing pollutant loads upstream.

Location

DeRosa University Center, Stockton campus, University of the Pacific

Format

Poster Presentation