Testing ecological theories in the anthropocene: alteration of succession by an invasive marine species.
Ecologists employ a diverse body of theory to help explain patterns and processes in ecological systems, with the consistency of ecological theories tested against an increasingly altered world. The global redistribution of species is a prominent impact of climate change and human-mediated biological invasions and often results in negative impacts to ecosystems. Recently, a species of colonial tunicate not previously present, Clavelina oblonga, has become prominent within the marine fouling community of Beaufort, North Carolina, USA. Fifty years ago, researchers tested theories of ecological succession developed in terrestrial systems and found that this marine community was characterized by a heterogeneous mixture of species that varied inter-annually (i.e., multiple community states) and increased in diversity over time. A recent follow-up study found that the fouling community is dominated by C. oblonga with patterns of community development and structure that led to the loss of alternative community states, domination by C. oblonga, and reduced species diversity. The present study addressed the question: Will patterns of community development identified over 50 yr ago still operate under reduced cover of invasive C. oblonga? This study also quantified the impacts of two large-scale environmental disturbances (extremely cold winter and hurricane) on the abundance of C. oblonga and the resulting fouling community. Clavelina oblonga remains a dominant component of the fouling community due to its rapid growth and strong seasonal recruitment. Under conditions of reduced percent cover of C. oblonga, the local fouling community displayed unique community states that became even more distinct over time, consistent with the pattern of multiple community states identified by researchers over 50 yr ago, and that were dependent upon date of disturbance. Natural disturbances in this study caused by a harsh winter and a hurricane greatly reduced the presence of C. oblonga. This experiment advanced our understanding of marine community ecology by testing whether the concept of multiple community states identified over 50 yr ago is still operable in the absence of invasive C. oblonga, and highlights how natural environment disturbances can potentially moderate the spread of this invasive tunicate.