Meeting Abstract

68.8  Jan. 7  Effects of salinity on mortality and heart rates of two introduced colonial ascidians, Botryllus schlosseri and Botrylloides violaceus DIJKSTRA, J.; University of New Hampshire dijkstra@cisunix.unh.edu

The role of abiotic factors in the establishment and success of invasive species remains difficult to determine for most ecosystems. However, examining this relationship is critical to predict the spread of invasive species. In this study we examine the mortality and physiological sensitivity of adult colonies of the colonial ascidians Botryllus schlosseri and Botrylloides violaceus using a combination of field and laboratory studies. Mortality and spatial dominance of colonial ascidians in the field were documented using 16 0.1m2 Plexiglas panels. Panels were deployed in July 2003 and photographed monthly at the mouth of Great Bay Estuarine Reserve in Newscastle, New Hampshire. Here annual salinity ranges from 33 ppt in the summer to 10 to 15 ppt in the spring. Adult colonies of each B. schlosseri and B. violaceus were exposed to abrupt salinity fluctuations (5, 10, 15, 20, 25, 30 ppt) in the laboratory. Heart rates were used to assess the condition of individual colonies and monitored daily for approximately two weeks. Results revealed that both B. schlosseri and B. violaceus experienced mortality after 1 day at 5 ppt and that their heart rates declined with decreasing salinity. Heart rates of B. schlosseri remained consistent between 15 ppt and 30 ppt and slowed at 10 ppt. Heart rates of B. violaceus were not significantly different between 20 ppt and 30 ppt but slowed at 15 ppt. The laboratory results corresponded to those in the field that showed a marked decline in spatial dominance of B. violaceus but not B. schlosseri during periods of low salinity. These results will help to explain dominance patterns of B. schlosseri and B. violaceus among coastal and estuarine sites.