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Sessile marine invertebrate (biofouling) communities have served as an important model in ecology for evaluating fundamental patterns and processes, including invasion dynamics, which vary at broad spatial and temporal scales. Here, we tested for differences in biofouling community development among three biogeographically distinct bays in North America (Chesapeake Bay, Tampa Bay, and San Francisco Bay), exploring possible explanations for differential non-native species success. In particular, we aimed to examine if San Francisco Bay (a global hotspot for non-native species richness) differed in composition and space occupation, especially since open space can facilitate colonization. Additionally, we explored how biogeography, assembly and succession dynamics over the short and long term, and space availability affect marine communities across broad spatial scales. Patterns of community assembly differed among bays, with more bare space and less secondary cover (species settling on species) in San Francisco Bay. San Francisco Bay was also distinguished by a higher percent cover of Tunicata (almost all of which are non-native and historically absent) over multiple time scales. Cirripedia recruited on bare panels in all three Bays but cover increased only in Tampa Bay, as soak time increased. Tube-dwelling Polychaeta distinguished Chesapeake Bay from Tampa Bay and San Francisco Bay. Low-salinity events temporarily restructured the communities in all three bays. Whether differences among bays reflect coastal versus bay-specific patterns remains to be tested.

Citizen science is an important and useful approach to research that broadens public science engagement and expands the scale at which science can be conducted. Monitoring for marine non-native species has been repeatedly identified as a venue for citizen scientists to make substantial contributions. In this study, we evaluated the accuracy of identifications made by volunteers of marine invertebrates on the project Invader ID, hosted on the online citizen science portal Zooniverse. We tested the efficiency and accuracy of invertebrate identifications made through consensus, where more than one volunteer must agree on a final identification before it is added to the database. Using the Matthew’s Correlation Coefficient, we found that four volunteers in consensus balanced efficiency and accuracy when compared to gold standard scientist identifications. Common, large taxa were identified most accurately; Branching Bryozoa identifications made by four volunteers were 85% accurate, Solitary Tunicates 91% accurate, and Colonial Tunicates 64%. In community-based comparisons, the identity of the taxonomist (volunteer or scientist) had a small impact on overall community composition, while site and salinity gradients had a strong impact on composition. We suggest that citizen science monitoring programs focused on highly recognizable taxonomic groups, or on a few species within those groups that can provide crucial information for managers aiming to quickly identify new invasions. Moreover, long-term assessments of composition could be successfully monitored by volunteers from photographs, helping to bolster understanding of ongoing impacts of invasive species or climate change.

Community development of ascidians was monitored weekly in Mission Bay (San Diego, California, USA) from September 2011 through November 2012 to assess how ascidian communities might be structured by spatial differences in environmental conditions. We repeatedly photographed PVC plates that were deployed on floating docks at four sampling locations: Seaforth Landing, Mission Bay Yacht Club, South Shores, and Hilton. Environmental variables (temperature, salinity, visibility, flow and dissolved oxygen) were measured during each sampling period. Eleven of the fifteen ascidian species observed on plates were invasive, three were native, and one was cryptogenic. Ascidian community composition varied significantly by time and sampling location within Mission Bay. Spatial differences in community dissimilarity were correlated to visibility, salinity, and temperature. Ascidian communities established in the warm, hypersaline waters furthest from the mouth of Mission Bay were typically most different from those near the mouth. Comparisons of % dissimilarity at the beginning and end of sampling indicated that ascidian communities were more dissimilar at the end of sampling. Ascidians persisted year round, and invasive and cryptogenic species were generally more abundant in winter months than native species. Below average rainfall, and the consequent relatively warm sea surface temperature and high salinity in a relatively mild climate region like San Diego, probably prevented the winter ascidian die-offs that typically occur in this area. Such environmental changes may be advantageous to invasive ascidians, not only with regard to mediating their persistence, but also in terms of facilitating the establishment, spread, and dominance of future invaders.