Award: OCE-1131013

THE MUSSEL BED DISTURBANCE PARADIGM Natural communities rich in species, such as coral reefs and rainforests, posed a riddle to ecologists. How can so many potentially competing species coexist? Should not one or a few favored species eventually "win", gaining all the resources of the habitat and eliminating all the others? An explanation for the richness of the rocky shore community of the Pacific Northwest coalesced the mid- 1970s. The theory held that the intact cover of mussel beds is the final stage of a succession, at which the mussels eliminate all other competitors. Gaps, breaches in the continuous cover, occur randomly throughout the shore. Competitively subordinate species, barnacles and seaweeds mostly, colonize briefly until the gaps are reclaimed by the mussels, the entire bed presenting a shifting patchwork of different species. Under the theory, the degree of wave force was the only significant factor in gap formation, making it the sole agent of species diversity. Our findings diverge from this scenario. For six years on numerous shores in British Columbia, we recorded spatial patterns of gap formation, wave force, and details of structure within the beds. Gaps form in a thickened, layered region at the center of each bed. Deep layering and the resulting fragility of mussel cover are a simple consequence of crowding, which alters the strength and geometric arrangement of mussel attachment. Wave action plays an essential role, but it is the spatial pattern of bed structure, not the spatial patterns of wave force, that determine where gap forms. Disturbance is not random, but occurs in predictable landscape patterns. Severe competition among the mussels themselves is essential to gap formation and the patchwork of succeeding species, the basis of community richness. Peripheral areas of the beds are thinned by predation or physical stress, and consequently are maintained as stable monolayers, where the dominance of mussels never breaks. Remarkably, a species once thought to threaten all other species with competitive exclusion if not held in check, appears to assure their continuance in the system. ARCHIVED DATABASE: BASELINE OF A FOUNDATIONAL SPECIES Publically archived, the project database provides a medium to explore contemporary issues beyond the implications of disturbance theory. For example, one might expect that with global warming, a rise is sea surface temperature would depress ocean plankton productivity, upon which mussel productivity depends. Less productive beds could be expected to develop less layering, less frequent gap formation, and possibly show declines seashore diversity. The highly detailed database offers a clear baseline for measuring change. Still other issues can be explored. More than a century after their extirpation by Russian traders, sea otters (Enhydra lutris) are beginning to recolonize the study area. Solitary young males, whose appearance typically precedes the establishment of dense populations, have been spotted repeatedly near the study sites since 2015. Initial studies of the impact of otter re-introduction (Singh et al. 2013) suggest that they greatly reduce mussel bed thickness and maximum sizes. The project database presents a valuable resource with which to study the community effects of re-introducing a keystone predator. The complete data set provides a wealth of information about the condition of the mussel bed community over a 10 km2 area of Barkley Sound. Photo-mosaic images, topography, wave force estimates, mussel beds thickness, size-specific attachment strengths, and ratios of flesh to shell dry mass were stored in georeferenced layers of a GIS database. The photo-mosaics are noteworthy because although each may cover many square meters, their high resolution allows identification of species as small as 1 cm long. Over 5,300 component images have been taken, in which a point may be located to within a few centimeters in 3-D space relative to permanent georeferenced bench marks at each site. The data were taken on a total of 8 separate mussel beds surveyed annually for periods of 5 to 7 years, for a total of 53 site-years. We believe the database is unmatched in its detail and breadth of factors for sea mussel beds. Metadata descriptions have been submitted to the Biological and Chemical Oceanography Data Management Office (BCO-DMO project url: http://www.bco-dmo.org/project/541233). Last Modified: 10/23/2017 Submitted by: Carlos D Robles