Authors:
Alison Tamsett, Kari B. Heinonen, Peter J. Auster Department of Marine Sciences and Northeast Undersea Research Technology & Education Center University of Connecticut
J. Linholm California State University Monterey Bay
The dynamics of gravel and boulder reef invertebrate community structure in areas inside and outside a closed fisheries habitat that overlaps Stellwagen Bank National Marine Sanctuary were analyzed based on time-series photographic transects from 1998-2005. The effectiveness of this protected area was evaluated based on three common predictions that emerge from previous studies of fishing impacts and the performance of temperate marine protected areas. We determined if: (1) gravel and boulder habitats have similar community composition, (2) community structure diverged between fished and unfished sites attributable to chronic fishing impacts, (3) structure forming invertebrates increased in abundance within the protected area, and (4) diversity increased within the protected area. Overall our results demonstrate that community structure over the seven years since closure in 1998 has been dynamic across both habitat types as well as within and outside the Western Gulf of Maine Closure (WGOMC) despite a high degree of similarity between paired habitat stations at the time of closure.
Comparisons of each habitat type inside and outside the closure across years in regards to community structure, populations of component taxa, and patterns of diversity all demonstrated a response to the closure but not in ways that are normally predicted from previous closed areas studies. Despite the presence of hard substratum resources in both boulder and gravel habitats, community structure was different between habitat types across all years. Community structure changed across time both inside and outside the WGOMC suggesting, at least to-date, recovery without resilience. While community composition tended to be more similar within each station than between each year, the pattern of similarity from 2005 transects suggest a greater degree of difference in composition between replicates from inside gravel and boulder stations than those paired stations outside. This pattern suggests the dominance of local processes, such as predation and competition, may be driving community composition inside the closed areas (i.e., contributing to greater variation in the distributions of taxa within stations). This is in contrast to larger spatial scale disturbance processes, produced either by natural events or by fishing activities that dominate at outside stations. Species populations and community structure within the closed area have yet to reach any stable configuration.
Interestingly, structural guilds and population trajectories of component taxa changed over time in unpredictable ways. We predicted that structure forming invertebrates would increase in abundance over time within the protected area due to elimination of fishing gear disturbance and a recovery of erect and emergent fauna. However, only encrusting forms at the boulder stations outside the closed area increased significantly from 1998 to 2005. Finally, the expected increase in species diversity at stations within the WGOMC was not observed by the end of the study period at either gravel or boulder stations. Overall the findings indicate that the WGOMC is having a significant impact on invertebrate community structure and that the community inside the closure area on both boulder and gravel habitats is recovering from chronic fishing gear impacts. However, community structure is dynamic and that "recovery" of the seafloor community does not necessarily lead to a climax community.
Key Words:
Marine protected area, resilience, recovery, disturbance, benthic, fishing, photography