On June 25, 2025, during peak eelgrass reproduction in southern New England, a Boston University research team, with help from the Center for Coastal Studies, attempted to collect reproductive shoots for seed-based restoration from an eelgrass meadow near Pah Wah Point Conservation area in Little Pleasant Bay (LPB).
Although the site has historically been suitable for seed collection at this time of the summer, efforts were abandoned due to the extensive fouling of reproductive shoots by invasive colonial tunicates, primarily the orange sheath tunicate, Botrylloides violaceus, and the golden star tunicate Botryllus schlosseri. Tunicates were observed covering the seed-containing spathes, which may block seed release and/or inhibit dispersal by weighing down the reproductive shoots.
The severity and timing of the fouling (occurring during peak eelgrass reproduction) raises concern about possible shifts in tunicate phenology, as their seasonal growth and reproduction are correlated with water temperature. Tunicate abundance typically peaks in late summer/early fall. Such shifts may be driven by warming water temperatures. Long term temperature data from the LPB seagrass monitoring site (seagrassnet.org) indicates that waters have warmed 0.3°C between 2004-2023 (temperature data provided by the National Park Service Inventory and Monitoring Program). If earlier seasonal peaks in tunicate abundance become more frequent, they may significantly impair eelgrass reproductive output and compromise the success of seed-based restoration efforts (Scavo Lord et al. In Prep).
By Karina Scavo Lord, PhD, Lecturer in Biology and Marine Biology, Boston University Marine Program & Department of Biology, Boston University
Photos by Morgan Bennett-Smith
