Temperature, space availability, and species assemblages impact competition in global fouling communities.
Competition drives community composition in many ecosystems and can influence the spread of invasive species. Marine fouling communities are excellent study systems for competition because of space limitation and the abundance of invasive species. While many studies have examined individual or site-specific responses to changes in temperature or presence of invasive species, it is difficult to predict ecological impacts without assessing interspecific interactions over a wide geographic range. This study compared interactions between several globally distributed invasive fouling species over a broad geographic range. Weekly examination of photographs of settlement panels in marinas at 18 sites around the world allowed for the quantification of competitive outcomes. In the north Atlantic, experimental panels became covered with fouling organisms exponentially faster at warmer temperatures, while northeast and south Pacific sites did not. An invasive ascidian (Diplosoma listerianum) and bryozoan (Bugula neritina) were strong competitors, but most species displayed a negative response in high competition settings where there was little available space. Two species (Botryllus schlosseri and Botrylloides violaceus) had better competitive outcomes at cooler temperatures, possibly due to fewer strong competitors at these sites. Thus, warmer sites with little open space and multiple strong competitors are likely most resistant to future invasions, while colder sites with more open space and weaker competitors would be more susceptible to invasive species. These results suggest that the establishment and spread of invasive fouling species is likely to be influence by seawater temperature, available space, and the competitive abilities of community members.