Point Sampling for Eelgrass (Zostera marina) and Seaweeds in Duchikthluk and Shoal Bays of Nunivak Island, Alaska, 2010

Boat-based surveys were performed at Duckikthluk Bay from 21 to 25 July 2010 and in Shoal Bay on 19 and 28 July 2010. Survey points were distributed across each of these bays using a systematic random design and accessed by boat using a GPS unit. Sampled points were accessed by snorkeling in dry suits during high tide. At each point, water temperature and depth, salinity, substrate type and depth, and water clarity were measured. Percent cover of eelgrass and seaweeds/bluegreen algae, and presence and absence of selected invertebrates (mussels, gastropods, and epiphytes on eelgrass leaves, such as caprellid shrimp and amphipods) were determined within four, 0.25 m sq quadrats that were spaced approximately 5 m apart in cardinal directions around the point. To minimize among-observer differences in estimates of eelgrass and seaweed cover, a cover score was assigned between 0.0 and 5.0 based on the Braun-Blanquet (BB) visual estimation technique (Braun-Blanquet 1972).

Estimates of aboveground biomass of eelgrass in each bay were based on collections of eelgrass shoots taken from 25 calibration quadrats in Duchikthluk Bay. Percent cover (BB cover score) were estimated, and all live eelgrass shoots were collected within each quadrat at a point. Ten representative shoots from each quadrat were later measured for shoot length and shoot width. An Abundance Index (AI) was calculated for each calibration quadrat by multiplying the BB cover score times the average length of the eelgrass shoots. The entire sample was then dried to constant mass and weighed to determine biomass per quadrat, which was scaled to grams dry weight per meter squared (g/m sq). Linear regression was used to determine the relationship between AI and aboveground biomass for the calibration quadrats. This relationship was then applied to determine aboveground biomass of eelgrass for each quadrat at a point.