Shifting to subtidal sea squirts – marine community transformation under climate change
Dijkstra, Jennifer A., Erica L. Westerman, and Larry G. Harris. “The Effects of Climate Change on Species Composition, Succession and Phenology: A Case Study.” Global Change Biology 17, no. 7 (2011): 2360–69. https://doi.org/10.1111/j.1365-2486.2010.02371.x.
Summary
Climate change has altered the thermal and chemical marine environment in the Northeast and the arrival of new invasive organisms, such as sea squirts, have altered the marine community. However, it has been difficult to assess the joint effects of climate change and invasive species on marine communities over decadal time scales. To address this knowledge gap, the authors replicated an earlier 3-year study (1979 – 1981), beginning in 2003. Their study correlated changes in multiple environmental indicators with species composition changes under a pier in the Great Bay Estuary, Newcastle, NH. In the earlier time series, dissolved nitrogen and phosphate were important to the community (which consisted of perennial species), while in the 2003-2005 period temperature, pH, and chlorophyll a were most correlated to the community which had become dominated by annual species.
Take home points
Community shifted from perennial species and bivalves (barnacles and mussels) to annual native and invasive tunicates, a.k.a. sea squirts.
Temperatures were significantly higher in the 2003-2005 period than in the 1979-1981 period, while salinity and pH were significantly lower.
Long term ecological studies are rare, but extremely valuable to understand the interaction of climate change, and other biotic and abiotic factors affecting species phenology, associations, and community composition.
Sensitivities to environmental factors are important for understanding changes in community composition; determining physiological tolerances of invasive and native species to climate variables should be a priority.
Management implications
Increased temperatures and altered phenology mean new invasives will be moving into the Northeast from the south, which we should review and keep an eye out for.
Longer periods of warm water extend both the growing season and number of annual reproductive cycles of invasive species such as the colonial sea squirt Botrylloides violaceus.
Increasing abundance of invasive tunicates like B. violaceus may be an early indicator of additional climate change-mediated community changes.
Keywords
Shifting seasons, Range Shifts, Impact Study, Tunicates, Sea Squirts