Description

Sampling Nearshore Communities in the Rhode River

Shallow nearshore zones in Chesapeake Bay provide refuge, food, and nursery grounds for crustaceans and small fish. With their shallow depths and variable habitats, these zones can play a vital role in the survival, nurturing and growth of its inhabitants and is a vital part of coastal ecosystems. Our research has shown that grass shrimp use the shallow depths as a refuge from larger predators, as nursery grounds and as a resource for food. We are interested in examining how this zone is utilized and how predator-prey dynamics change over time.

Our lab’s Nearshore Survey is a long-term research study (1991-present) examining the interactions between native grass shrimps (Palaemonetes pugio, P. intermedius and P. vulgaris) and their common predators in the nearshore zone (<1.0 meters deep) of the Rhode River. Each summer, surveys of the nearshore zone are conducted at two different sites throughout the Rhode River. Canning House Bay is an exposed half-moon shaped embayment near the mouth of the Rhode River, characterized by sandy beaches, marsh plants and ever-encroaching stands of non-native Phragmites grasses. Fox Point is a sheltered spit of land near the mouth of Muddy Creek characterized by forested shoreline, marsh plants and submerged coarse woody debris.

Within our sites, shoreline compositions vary and include sandy beach, submerged coarse wood debris, emergent vegetation, marsh, and forested shoreline.  The sediments within each site are also variable and may include mud, sand, marsh detritus, clay, or a mix of each.  Sampling is repeated at 6 different permanent transects or stations at each field site to capture population variability within a site and to sample a range of sediments and natural shoreline types. By sampling the same areas annually, we can determine spatial and temporal changes in species composition, population size structure, and abundance.

Each month, we conduct the following surveys:

Dip-net sweeps: Shrimp abundance, size and shallow water distribution

Grass shrimp distribution and relative abundance in the nearshore zone is monitored at permanent transects each month using dip net sweeps. Ten meter long transects are sampled at four depths (five at Canning House Bay) by pushing a long handled dip net along the river bottom. Shrimp are collected, identified, measured, examined for parasites and reproductive state, and returned to the river unharmed. These data allow us to quantify the fluctuations in grass shrimp parasite load and population dynamics.

Seines: Fish and crab presence, abundance and size

We use a 16 meter long seine net of 5 mm mesh for sampling.  Each seine samples 10 meters of shoreline with the net parallel to shore, stretched between two people standing  in one meter depth of water, then the net is pulled all the way in to shore. All fish, crabs and reptiles that are caught in the net are identified, measured (up to 100 individuals per species per seine), and released unharmed back into the water. 

Shrimp Tethers: Predation and mortality of grass shrimp

While grass shrimp often seek refuge from predatory fish and blue crabs in shallow waters, the presence of these crustaceans attracts predators hoping for a snack.  Every summer since 1991, our lab has studied predation on grass shrimp at two sites in the Rhode River. Tethers are only conducted at one fixed transect per site, but this survey is performed on 3 consecutive days each month in the summer. The data collected helps us to determine who the important predators are and how the risk of predation changes from year to year. 

The data collected from these three long-term surveys provide insight into how predator-prey relationships change over time in relation to changes in abundance. 

Contact:

Stacey Havard

havards@si.edu