WESTERMAN, E.L.*; HARRIS, L.G.; University of New Hampshire; University of New Hampshire: Environmentally caused changes in asexual reproduction rates in two invasive sea squirts: Botryllus schlosseri and Botrylloides violaceus

An increase in global ocean temperatures over the last century has coincided with an increase in invasive species. Ascidians have been particularly successful as invaders and are now dominant space holders in benthic communities throughout the world. A potential cause of this dominance may be increasing water temperatures in coastal areas leading to greater asexual and sexual reproductive rates. Two species of interest in the Gulf of Maine are Botryllus schlosseri, a non-native established ascidian, and Botrylloides violaceus, an invasive species first noticed in the 1980�s. In order to assess the relationship between increasing water temperatures and invasive ascidian success, we examined the impact of various temperatures on reproductive rates in B. schlosseri and B. violaceus. Settlement panels were deployed in Salem Harbor Massachusetts, Portsmouth Harbor New Hampshire, and Damariscotta River Maine, three sites of differing annual temperature ranges. We reared colonies of both species in the laboratory at 5�C, 10�C, 20�C, and 25�C while documenting both the growth rates of colonies and time of initial larval recruitment in the field. Asexual reproductive rates were quantified as the duration of the asexual zooid replacement cycle and the increase in number of zooids per replacement cycle. Initial recruitment was first noted in Salem Harbor and subsequently in Portsmouth and Damariscotta. Botryllus schlosseri had greater asexual reproductive rates than B. violaceus at 10�C, while the reverse was true at 20�C. This variation in asexual reproduction of colonial tunicate colonies suggests that environmental factors may play a large role in determining species success.