Mysid shrimp and zooplankton collection

Neomysis americana (LSID urn:lsid:marinespecies.org:taxname:157807) were collected in the Damariscotta River Estuary every 2 weeks beginning in May 2023 and ending in October 2023, giving approximately 12 sample dates for their growing season. Additionally, we conducted high-frequency sampling over three days in August 2023 alongside the optical equipment, giving a total of 20 sampling dates with 2-3 replicates for each sample. Starting in November 2023, we began sampling monthly and will continue this monthly survey until May of 2024 to capture seasonal patterns. During each sampling trip, we collected samples from the muddy bottom near the pedestrian dock at the Darling Marine Center dock, at a depth of 1.5 - 4 m, depending on the tidal cycle. A 45 cm x 25 cm rectangular 1000 μm net equipped with a flowmeter was deployed from the dock down to the substrate and hand towed along the bottom. The contents of the cod end were emptied into a container on the dock and all mysids were immediately preserved in 4% neutral buffered formalin for later analysis. The same net was then deployed vertically, resting just off the bottom for 2 minutes, to capture mysids in the water column.

To capture smaller zooplankton that might serve as prey for mysids, we lowered an 80 μm mesh ring net with a 0.5 m diameter opening into the water at mid-depth from the dock and let water flow through for 10 minutes. An attached flow meter was used to estimate the volume of water sampled by the net. Zooplankton were immediately preserved in 15% EtOH and taken to the lab for drying and identification. After splitting the sample with a plankton wheel (Wildco), one half was filtered through a pre-weighed, cone coffee filter and dried in an oven at a temperature of 60°C for 24-48 hours, or until constant weight was achieved. Zooplankton biomass is expressed as mg/m³ according to the formula B = W / V, where B is the zooplankton biomass (mg), W is the weight of the sample, and V is the filtered water volume (m³). The other half of the sample was cold preserved at 4°C in 50% EtOH/seawater until visual analysis, when the organisms were identified to the genus level. Subsample aliquots of organisms 100 individuals were measured to the nearest μm using a dissecting microscope with an attached camera and measuring software (CellSense, Olympus).

Phytoplankton collection and processing :

To capture phytoplankton that might serve as food for mysid shrimp, we towed a 20 μm plankton net just below the surface along the end of the dock 10 times (approx. 20m). On deck, we rinsed the net with 1L of seawater, washing the sample into a bucket. We then collected a 125ml subsample and preserved with 10ml Lugol’s iodine solution in a dark bottle and stored at 4°C for further analysis. To determine which phytoplankton species were present, a subsample was identified to genus level using a compound microscope.

Environmental parameters:

We conducted vertical profiles of environmental variables using a YSI-EXO multi parameter sonde. Dock samples were collected from the dock at the Darling Marine Center and all other estuarine samples were collected from the R/V Ira C. To begin a profile, the sonde was lowered by hand at a rate of app. 0.3 ms-1 until the sonde reached the bottom and then slowly raised to the surface. The sonde recorded temperature, salinity, turbidity, and fluorescence throughout the water column. What is reported here in this file are the bottom-water values because these values are most relevant to our target species, Neomysis americana which resides just above the substrate. We are currently working on processing files for the entire water column and those data are forthcoming (when submitted to BCO-DMO these will be discoverable from the project page).

Location: Measurements were made from the pedestrian dock at the Darling Marine Center, Walpole, Maine, USA (43.934 N, 69.579 W). Damariscotta River estuary, Walpole, Maine, USA.