The effects of the freshwater mussel Hyridella menziesi on the phytoplankton of a shallow Otago lake
Ogilvie, Shaun Craig
Summary 1. Biomass, filtration rate and rhythmic activity data for Hyridella menziesi in Lake Tuakitoto were combined to calculate the filtration capability of this population. It was calculated that this population filters a volume of water equal to that of the lake every 32 hours at 19-21 o C. These results strongly suggest that phytoplankton in Lake Tuakitoto will be suppressed by mussel grazing. 2. Experimental manipulations of mussels in situ using artificial enclosures showed that mussel filter feeding controls phytoplankton to below potential concentrations. 3. It was found in the enclosure experiments that mussels cause a shift in algal composition from phytoplankton to periphyton on the walls of the enclosures. 4. Phytoplankton growth was not generally limited by a lack of available nitrogen or phosphorus. This result lends further support to the hypothesis that mussels control phytoplankton biomass. Intermittent high chlorophyll ~ concentrations in this lake may be due to sediment resuspension by wind. 5. The mean mussel density in Lake Tuakitoto was 5.5 m-2 which corresponded to a mean biomass of 12.3 g m-2. The population had a mean age of 15 years. 6. The mean filtration rate of 32 mussels was 1.9 L hr-1 g-1 tested in the laboratory at 19-21 o C. Nine mussels filtered Gymnodinium sp. cells in water from a bloom at Tomahawk Lagoon, at a rate of 0.66 L hr-1 g-1. 7. Eighteen mussels tested in the laboratory showed no obvious pattern of activity over a 24 hour period. Ninety-three percent of the 610 observations made in 2 experiments were of mussels undergoing filtration. 8. These results suggest that Hyridella menziesi may be of considerable value as a biomanipulation tool.
Advisor: Mitchell, Stuart; Williams, Barbara
Degree Name: Master of Science
Degree Discipline: Zoology
Publisher: University of Otago
Research Type: Thesis