Variations in the Distribution and Biomass of Submerged Macrophytes in Five Coastal Lagoons in Rhode Island, U.S.A.

Publisher Website
Google Scholar
Abstract
The distribution and maximum biomass of angiosperms and dominant macroalgae were determined for 5 coastal lagoons within an 18 km strip of coastline [Rhode Islands, USA]. The primary variant among these basins was the exchange with oceanic waters for Rhode Island Sound. Distribution was assessed from aerial photographs combined with in situ observations, and summer biomass data from sampling stations within specific plant associations. In 1 lagoon (Ninigret Pond) biomass was measured throughout the year at stations selected on a distance gradient from the breachway. Total plant biomass averaged over an entire lagoon ranged from 61 .+-. 21 g dry wt m-2 (Green Hill Pond) to 288 .+-. 76 g dry wt m-2 (Ninigret Pond). The lagoons with the greatest exchange with outside water (Ninigret Pond, Point Judith Pond) were dominated by Zostera marina with a maximum biomass of 1120 g dry wt m-2 and 228 .+-. 75 dry wt m-2 averaged over the entire lagoon. Biomass of Z. marina correlated most closely with leaf length which in turn related positively to proximity to the breachway. In a closed lagoon (Trustom Pond) Potamogeton pectinatus was the dominant species (77 .+-. 58 g dry wt m-2 averaged over entire lagoon) followed by Ruppia maritima and P. perfoliatus. The values for angiosperms are generally within the range reported for other parts of the world. The algal components varied from 13 to 46% of the total plant biomass in any lagoon and reached 100% within certain areas. Dominant species with maximum biomass include Ulva lactuca (370 g dry wt m-2), Enteromorpha plumosa (400 g dry wt m-2) and Gracilaria tikvahiae (250 g dry wt m-2). These values were somewhat higher than those reported for other seagrass systems. These quantitative comparisons of the macrophytes in 5 neighboring lagoons may be used to predict some of the impact of future breachways upon the submerged plants.