Biodiversity of the tunicate fauna at Nantucket and Muskeget Islands

Report submitted in fulfillment of a 2016 Nantucket Biodiversity Initiative grant. Tunicates (Ascidiacea) are common benthic marine invertebrates that occur in New England and elsewhere from the intertidal zone to the deep sea. In the near shore, they are often the dominant fouling organism on anthropogenic and natural surfaces and are known to cause problems for shellfish aquaculturists. The tunicate fauna of Nantucket has not been previously documented. Our goal was to survey Nantucket and the nearby island of Muskeget for tunicates and to determine the biodiversity of the population for future comparisons. In July 2016, we surveyed Muskeget and found no tunicates. We also surveyed Nantucket in July 2016, and found 7 species of tunicates attached to anthropogenic substrates including boat hulls, floating dock sides, and ropes hanging off docks, and attached to natural substrates including bivalves, sponges, and eelgrass. When present, tunicate abundance or percent coverage ranged up to 50-75%. Of the 7 species observed on Nantucket, 5 are considered non-native species and 2 are considered native species. The Nantucket faunal composition, abundance, and substrates utilized are similar to other tunicate populations in New England