DIJKSTRA, J.A.*; HARRIS, L.G.; University of New Hampshire; University of New Hampshire: Long-Term Shifts in Seasonal Patterns of Biodiversity in a Marine Fouling Community

The relationship between invasions and the long-term shifts in seasonal diversity remains poorly understood for most ecosystems. However, examining this relationship provides insight into the effects of invasive species on biodiversity. In the past 25 years, three invasive colonial ascidians (Botrylloides violaceus, Diplosoma listerianum and Didemnum sp.) have become dominant members of fouling and subtidal communities in the New England area. While it is clear these species have impacted communities, their effect on long-term shifts in seasonal diversity is less axiomatic. In this study, we link seasonal space occupancy of recent dominant invaders to long-term shifts in seasonal biodiversity by comparing the development of a marine fouling community at two temporal periods (1979-1982; 2003-2006). Long-term changes in seasonal diversity and spatial dominance of invasive colonial ascidians were determined through the analysis of 8 vertical and 8 horizontal 0.1m2 Plexiglas panels. Panels were deployed underneath a cement pier in Newcastle, N.H. in July 1979 and July 2003. Both panel sets were photographed on a monthly basis for a period of three years. Space occupancy of dominant invaders was recorded using point count analysis, while diversity was measured by counting all individuals and species found on each panel. Results from this study show a decline in the abundance of resident colonial ascidians. This decline coupled with an increase in invasive colonial ascidians has lead to a seasonal shift in the dominance of colonial ascidians that has in turn altered seasonal diversity.