Sarnelle, O., A. E. Wilson, S. K. Hamilton, L. B. Knoll, and D. F. Raikow. 2005. Complex interactions between the zebra mussel, Dreissena polymorpha, and the harmful phytoplankter, Microcystis aeruginosa. Limnology and Oceanography 50(3):896-904.
We report a reversal in the sign of the herbivore-phytoplankton interaction between the zebra mussel (Dreissena polymorpha) and Microcystis aeruginosa, a harmful planktonic cyanobacterium. A pair of large-scale manipulations of mussel density in the same lake in consecutive years showed that when phosphorus concentrations were very low (mean total phosphorus [TP] ~ 3 µg L−1), the effect of Dreissena on the biomass of M. aeruginosa was monotonically negative across the full range of sustainable mussel densities. When the enclosures were fertilized with phosphorus (mean TP ~ 9 µg L−1), there was a monotonically positive effect of Dreissena on M. aeruginosa across the same mussel gradient. These contrasting results indicate that D. polymorpha feeds on M. aeruginosa, as shown in previous laboratory feeding experiments, but that the positive effects of D. polymorpha on M. aeruginosa can be larger than the negative effects of consumption. A sign reversal in the interaction between these two species is congruent with highly variable patterns in the response of M. aeruginosa to D. polymorpha invasion across lake and river systems in North America.
Raikow, D. F., O. Sarnelle, A. E. Wilson, and S. K. Hamilton. 2004. Dominance of the noxious cyanobacterium Microcystis aeruginosa in low-nutrient lakes is associated with exotic zebra mussels. Limnology and Oceanography 49(2):482-487.
To examine the hypothesis that invasion by zebra mussels (Dreissena polymorpha) promotes phytoplankton dominance by the noxious cyanobacterium Microcystis aeruginosa, 61 Michigan lakes of varying nutrient levels that contain or lack zebra mussels were surveyed during late summer. After accounting for variation in total phosphorus (TP) concentrations, lakes with Dreissena had lower total phytoplankton biomass, as measured by chlorophyll a and algal cell biovolume. Phytoplankton biomass increased with TP in both sets of lakes, although the elevations of the relationship differed. The percentage of the total phytoplankton comprised by cyanobacteria increased with TP in lakes without Dreissena (R2 = 0.21, P = 0.025) but not in lakes with Dreissena (P = 0.79). Surprisingly, there was a positive influence of Dreissena invasion on Microcystis dominance in lakes with TP ≪ 25 µg L−1 (P 5 0.0018) but not in lakes with TP ≫ 25 µg L−1 (P = 0.86). The finding that Microcystis, a relatively grazing-resistant component of the phytoplankton, was favored by Dreissena in low- but not in high-nutrient lakes is somewhat counterintuitive, but predator-prey models make this prediction in certain cases when the cost for the prey of being consumption resistant is a low maximum population growth rate. This Dreissena-cyanobacteria interaction contradicts well-established patterns of increasing cyanobacteria with nutrient enrichment in north-temperate lakes and suggests that the monitoring and abatement of nutrient inputs to lakes may not be sufficient to predict and control cyanobacterial dominance of Dreissena-invaded lakes.
Wilson, A. E. 2003. Effects of zebra mussels on phytoplankton and ciliates: A field mesocosm experiment. Journal of Plankton Research 25(8):905-915.
Many observational studies in North American lakes have documented decreases in phytoplankton abundance after the invasion of the zebra mussel (Dreissena polymorpha). However, few field experiments have examined in detail the effect of zebra mussels on phytoplankton abundance and species composition over an extended period. Replicated in situ mesocosms were used to evaluate the impact of natural densities of zebra mussels on phytoplankton and ciliate biovolume, and algal species composition over a 5-week period in a habitat that lacked extant mussel populations. Mussel biomass used in the experiment was determined using a regression model based on a data analysis that predicts zebra mussel biomass from total phosphorus concentration. Within 1 week, zebra mussels decreased phytoplankton biovolume by 53% and ciliate biovolume by 71%. The effect of zebra mussels on ciliate biovolume was sustained throughout the study. However, the effect of zebra mussels on phytoplankton abundance gradually waned over the remaining 4 weeks of the experiment, such that the declining effect of zebra mussels could not be explained by a shift towards less edible and/or faster growing algal species. The mussels’ declining condition could help to explain the effect observed over the course of the experiment.
Wilson, A. E. and O. Sarnelle. 2002. Relationship between zebra mussel biomass and total phosphorus in European and North American lakes. Archiv für Hydrobiologie 153(2):339-351.