Energy densities and fatty acids demonstrate the low quality of dreissenid veligers

Abstract Dreissenid mussels represent two of the most problematic invasive species in the Laurentian Great Lakes yet little is known regarding the biochemical and nutritional composition of the veliger larval stage. Here, we quantified energy densities and fatty acids (FA) in veligers as metrics of nutritional quality relative to those determined for three size fractions of crustacean zooplankton collected from Lake Huron's Saginaw Bay. Veliger energy densities ranged from 1.14 to 1.72 kJ g −1 (wet wt.) and were significantly ( p < 0.001) lower than energy densities of 1.91 ± 0.23 kJ g −1 (64–150 μ m); 1.94 ± 0.10 kJ g −1 (150–250 μ m); and 1.85 ± 0.19 kJ g −1 (≥ 250 μ m) for size fractionated crustacean zooplankton. Nutritional quality indicators including the unsaturation index (UI) suggested veligers (238 ± 229) were similar to those for 64–150 (233 ± 21), 150–250 (206 ± 30) and ≥ 250 μ m (195 ± 49) zooplankton size fractions. However, veliger UIs were primarily driven by high docosahexaenoic acid content relative to zooplankton size fractions. For other essential compounds including arachidonic, α‐linolenic and eicosapentaenoic FAs, veligers consistently ranked the lowest. These results demonstrate veligers to be of lower caloric content relative to zooplankton, especially compared to similarly sized 64–150 μ m planktonic biomass and of lower overall nutritional quality with respect to fatty acid composition. This study provides benchmarks regarding the overall nutritional quality of veligers and furthers our understanding energy and nutrient availability among the lower trophic levels of food webs in invaded ecosystems.