The effects of climate change on species composition, succession and phenology: a case study

Climate change and its role in altering biological interactions and the likelihood of invasion by introduced species in marine systems have received increased attention in recent years. It is difficult to forecast how climate change will influence community function or the probability of invasion as it alters multiple marine environmental parameters including rising water temperature, lower salinity and pH. In the present study, we correlate changes in environmental parameters to shifts in species composition in a subtidal community in Newcastle, NH through comparison of two, 3-year periods separated by 23 years (1979-1981 and 2003-2005). We observed concurrent shifts in climate related factors and in groups of organisms that dominate the marine community when comparing 1979-1981 to 2003-2005. The 1979-1981 community was dominated by perennial species (mussels and barnacles). In contrast, the 2003-2005 community was dominated by annual native and invasive tunicates (sea-squirts). We also observed a shift in the environmental factors that characterized both communities. Dissolved inorganic nitrogen and phosphate characterized the 1979-1981 community while sea surface temperature, pH, and chlorophyll a characterized the 2003-2005 community. Elongated warmer water temperatures, through the fall and early winter months of the 2000s, extended the growing season of native organisms and facilitated local dominance of invasive species. Additionally, beta-diversity was greater between 2003-2005 than 1979-1981 and driven by larger numbers of annual species whose life-history characteristics (e.g., timing and magnitude of recruitment, growth and mortality) are driven by environmental parameters, particularly temperature.