Stoichiometry in a benthic invasive: Exploring how stoichiometric imbalances with algal resources affect zebra mussel (Dreissena polymorpha) growth and condition

Scope and Method of Study. Ecological Stoichiometry has become a new framework to describe interactions in many different habitats. In this research, I used stoichiometry to examine the effects of food quality and quantity on zebra mussel growth and condition. This study took place in 60, 1L microcosms under controlled laboratory conditions. Zebra mussels were fed Scenedesmus sp. at two food quantities (1mg C L -1 and 4mg C L-1) and two food qualities (C:P ratios 20 and 45). These food quality treatments were selected to represent very low C:P ratios to represent C:P ratios that are found in eutrophic systems across North America. Treatments were crossed to make 4 total treatments; 20-1, 20-4, 45-1, and 45-4.;Findings and Conclusions. Zebra mussel shell growth was not affected by algal quality or quantity. However, dry tissue mass and Tissue Condition Index (TCI) were significantly lower in the lower C:P ratio treatments (20-1, 20-4) when compared to the higher C:P ratio treatments (45-1, 45-4). Significantly more ammonia and soluble reactive phosphorus (SRP) were also excreted in the lower C:P ratio treatments than in the higher C:P ratio treatments. There were no food quantity effects on growth, TCI, or excretion, but there was a significant interaction between food quality and food quantity for TCI and excretion in the 45-4 treatment, with TCI being the greatest and excretion being the lowest between all treatments. Combined, these results show that despite enhanced excretion of excessive nutrients, there were significant growth and condition penalties at the lower C:P treatments, clearly indicating toxic effects of excess dietary P. Zebra mussels were also able to adjust their tissue stoichiometry based on food quality to a certain point, but were not able to benefit from the excess P in the food resources. Therefore, the response of consumers to stoichiometric imbalances is driven by not only when nutrients are limiting but also when nutrients are in excess, and should be considered especially under rapid cultural eutrophication. With respect to zebra mussel invasions, there may be stoichiometric limitations in eutrophic and hyper-eutrophic systems that do not allow zebra mussels to have the same effect as seen in other systems.