Invaders Eat Their Greens: The Crustacean Hemimysis Anomala Grazes Not Only on Zooplankton but Also on Algae

Berges, John, Biological Sciences, College of Community Engagement & Professions, College of Letters & Science, Huelsbeck, Kristin, Mentor, Poster Presentation, School and College, Student

Kristin Huelsbeck, “Invaders Eat Their Greens: The Crustacean Hemimysis anomala Grazes Not Only on Zooplankton but Also on Algae”
Mentor: John Berges, Biological Sciences
Poster #100

The mysid Hemimysis anomala (the ‘bloody red shrimp’) is a native of the Ponto-Caspian region that was first reported in the Great Lakes in 2006. We know it eats zooplankton; however, little is known about feeding rates or preferences for phytoplanktonic algae. Our goal was to determine feeding kinetics on two different phytoplankton species and also natural Lake Michigan communities of phytoplankton. Animals were collected from Lake Michigan and either: kept in aquaria for experiments, or immediately frozen to determine phytoplankton pigment in the gut. To determine grazing rates, animals were held in beakers and fed various concentrations of either the green alga Chlamydomonas reinhardtii, the diatom Navicula sp., or concentrated Lake Michigan phytoplankton samples. Grazing rates were calculated from removal of cells (flow cytometry counts before and after) and ingestion of algae was estimated by measuring presence of alga pigments in the gut (extraction in solvent and fluorescence measurement). Hemimysis consumed C. reinhardtii at a maximum rate of about 12,000 cell ml-1h-1animal-1, which half-saturated at a concentration of 130,000 cell ml-1, and Navicula sp. was consumed at lower rates (925 cell ml-1h-1animal-1, which half saturated at 40,000 cell ml-1), with evidence of inhibition at high concentrations. When fed natural phytoplankton samples, it was difficult to accurately estimate cells consumed, but gut pigments were much higher (325 µg chl a and phaeopigment h-1animal-1) than for the cultures (50-70 µg chl a and phaeopigment h-1animal-1). Samples collected directly from the field had gut pigment comparable to those fed natural phytoplankton assemblages. There was little evidence for differences in grazing rates among adults and juveniles. Hemimysis are not necessarily carnivorous but feed significantly on algal cells, which could change predictions of their effects on Lake Michigan food webs.