A Day in the Field: Collecting Zooplanton along the Mystic

By: Kate Lamberti and Dani Davidoff, interns for the Mystic River Watershed Association

Tuesday was an extremely sunny day. In the morning, we arrived at the office to grab everything we needed, for our traditional cyanobacteria samples that we take at five spots along the Mystic, as well as zooplankton tests (a new thing for the Mystic River Watershed Association).

Horn Pond, where we collected zooplankton, was our fourth stop out of five. A large group of runners in matching T-shirts obscured our path through the parking lot, but eventually, we parked and loaded the canoe with equipment. We paddled to three different randomly chosen locations, anchored our canoe, and took turbidity measurements with the Secchi disk, measuring how far down the disk reached before the water made it appear unclear. To take zooplankton samples, we lowered an approximately six foot tall net into the water. At one location, when we pulled the net back out of the water, the jar attached to the bottom of the net was filled with black sludge. We waited for the water to filter through the slots on the side of the jar, until we were left with an amount small enough to re-bottle and bring back for analysis. In the other two locations, the water filtered through much more quickly.

The samples are being collected for Meghna Marjadi, a PhD student at University of Massachusetts Amherst, who is researching river herring conservation in freshwater. The research takes place in various water bodies in the eastern New England region. The Mystic River Watershed Association samples weekly at two sites - Horn Pond and Upper Mystic Lake - both impacted by dams. At these locations, the number of river herring entering the lake are monitored by numerous volunteers whose counts feed a model that estimates total herring populations each year. Herring are considered a threatened species, affected by habitat loss and degradation, by-catch, water pollution, poaching, lack of access to spawning habitat, and natural predators. Meghna helped to start the monitoring program at MyRWA to track the recovery of herring populations, and will be evaluating the educational value of citizen science as part of her research.

From our data collection, the density of zooplankton is determined, based on the estimated volume of water filtered through the net and the quantity of plankton in the sample. Zooplankton is a vital part of the food web as the primary food source for river herring, making these tiny organisms an important indicator of herring populations. Their density is potentially another mechanism for monitoring the herring migration temporally and spatially, not only in the Mystic River Watershed, but all along the east coast!