Impacts of changing water temperatures on the life histories of two invasive ascidians in the Gulf of Maine: Botryllus schlosseri and Botrylloides violaceus

The impact of temperature on organism life cycles has received great attention due to heightened awareness of global warming. Relative growth and reproductive development were monitored in two dominant ascidians from the Gulf of Maine to compare effects of rising temperatures on established ( Botryllus schlosseri) versus recently arrived (Botrylloides violaceus) species. Settlement panels were deployed at three sites with different temperature regimes (Damariscotta, ME, Newcastle, NH, and Salem, MA) during two growing seasons June 2005 to December 2006, and a recruitment study conducted May to December 2006. Both species had elongated breeding seasons in Salem, MA relative to the other sites. Botryllus schlosseri settled two weeks earlier than Botrylloides violaceus at all sites, however this delay in settlement can be attributed to the longer brooding period of Botrylloides violaceus. Timing of initial settlement may not be as indicative of temperature tolerances as timing of initial egg production in brooding animals