The Ecology and Demography of the Invasive Ascidian Botrylloides violaceus in the Coos Estuary
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Marine fouling communities on docks and other man-made structures are highly susceptible to invasion by non-native ascidian species. Botrylloides violaceus, a colonial ascidian, is a cosmopolitan invader of fouling communities in bays and harbors including Oregon’s Coos Estuary. This study documents seasonal and spatial patterns of B. violaceus distribution, assesses the impact of abiotic factors on this distribution, and characterizes the demography of this population and its interactions with other fouling organisms. I surveyed five fouling communities on floating docks in the Coos Estuary, three near the mouth of the estuary and two near the upper sloughs, and observed B. violaceus at all sites except Isthmus Slough in the upper bay. In laboratory experiments B. violaceus survived temperatures up to 27°C and salinities down to 25 psu, conditions which would permit survival at the uninvaded Isthmus Slough. Furthermore, the species survived transplantation to both upper bay study sites, indicating that temperature and salinity do not limit its distribution to the lower bay as hypothesized. Botrylloides violaceus demonstrated continuous recruitment and settlement on plates deployed from August 2015 through May 2016, as well as lateral asexual growth which rapidly increased during the spring. Botrylloides violaceus consistently overgrew all fouling species it encountered on settlement plates except for Halichondria bowerbanki which overgrew B. violaceus. Understanding the interactions between B. violaceus and both its abiotic and biotic surroundings is critical for determining the effects of this invasion on native biodiversity and improving invasive species management in the Coos Estuary.