Date of Award
Environmental and Forest Biology
John M. Farrell
The near shore invertebrate assemblages of four bays along the St. Lawrence River were surveyed as an extension of a juvenile muskellunge survival study to better understand the potential prey base. Zooplankton and macroinvertebrates were collected using light trap and zooplankton grab sampling methods. Since larval muskellunge are visual predators and are dependent on invertebrate consumption prior to their complete conversion to piscivory during ontogeny, there is a need to understand the potential prey community composition. Two gears were compared to determine the optimal approach to represent invertebrate community structure within critical Muskellunge nursery habitats in bays. The light traps were set at night simultaneously for thirty minutes at each of four bays. In the laboratory, samples were scanned under a dissection microscope for rare organisms and subsampled to a minimum of 200 organisms counted in milliliter increments. The zooplankton grabs were performed during daytime by taking three 2L samples sieved through 60μ mesh within a 1 meter square plot, and were subsampled underneath a dissecting microscope in full milliliter increments to a minimum of 100 organisms. The two sampling methods produced similar species composition, but with very different community structure. The light traps had greater overall abundance and greater richness; however they likely selected for photopositive organisms. The zooplankton grabs do not discriminate among organisms in the water column, but may be missing organisms which exhibit patchy distributions or are diurnally benthic. The differences observed with each method highlight the importance of using multiple sampling methods, and indicated that a selection bias may exist for surveys that employ a single gear and time.
Shaw, Amy, "A comparison of light traps and zooplankton grabs for assessing invertebrate assemblages in muskellunge nursery bays" (2014). Honors Theses. 46.