Award: OCE-1458150

This project explored (1) whether regional differences in community-level processes on the rocky intertidal shores of the Gulf of Maine (GoM) are driven by very different patterns of population connectivity and recruitment in a few key species, and (2) whether these differences are ultimately caused by regional variation in temperature and food availability that are mediated by physical larval transport processes. We tested the following hypotheses with manipulative field experiments, field sampling, connectivity estimates, and integrative modeling: (1) Locally-dispersing species dominate dynamics in regions with a net export of planktonic larvae (Northern GoM), while species with planktonic larvae dominate the dynamics in regions with high settlement and extensive connectivity among populations (Southern GoM); (2) Settlement density of species with planktonic larvae increases from northern to southern regions in accord with regional variation in food availability; (3) Population connectivity varies greatly among regions, with regions differing in the degree to which they are self-seeded or serve as larval sources vs. sinks; self-seeding leads to relatively localized population dynamics in the middle portion of the GoM; and (4) Patterns of population connectivity are driven by physical transport processes and can be represented by coupling basic larval behavior models with circulation models. At 20 different sites in the GoM across ~ 600 km, surveys evaluated variation in recruitment, food availability and secondary productivity and experiments assessed community processes in wave-exposed and sheltered habitats. We used hydrographic, current profile, and larval vertical distribution surveys to collect data for coupled larval/circulation models. Population connectivity was both modeled and empirically evaluated (for one species) using elemental fingerprinting. Finally, a spatially explicit metacommunity model will integrate across all project components and test the relative importance of regional and local processes in controlling community organization and dynamics. Although we continue to process our voluminous data sets, some general trends have begun to emerge and patterns of community recovery align well with our predictions. In the northern GoM recovery is dominated by algae and barnacle and mussel recruitment is negligible. In contrast, in the southern GoM, barnacles and mussels, along with algae, participate in community recovery with invertebrate recruitment being most important on wave-exposed shores where larval supply is higher. Our data also suggest that the central Gulf of Maine is a transition zone and the goal of our more refined analyses will be to pinpoint where this transition occurs. The description above applies most consistently to sheltered shores throughout the Gulf, with community recovery being slower and specific to each region. On wave-exposed shores, however, we see important geographic differences. In the northern GoM, algae dominate recovery and thus far the impacts of winter disturbance have not reset the community. This resilience in the face of disturbance and lower overall consumer pressure may ultimately explain the similar community states of sheltered and wave-exposed shores in the northern Gulf. In contrast, on wave-exposed shores it appears that communities are largely resetting each year, particularly in the southern Gulf and less so in the central Gulf. Notably, there is considerable variation in the impacts of winter resets in the central Gulf. When it does occur, resetting is partly driven by consumer pressure and the impacts of winter disturbance on sessile invertebrates and algae. The equilibrium state of these communities is one of high turnover and such turnover may explain why sheltered and wave-exposed shores are so different from one another in the southern Gulf and in some parts of the central Gulf. Although more analysis is required, the general pattern emerging is that geographic variation, particularly at a regional scale, in consumer pressure is driving short term community recovery. By contrast, the recruitment of key community players rather than consumer pressure is driving longer term patterns of community recovery. Hence, while these geographically separated communities are quite similar in terms of species composition different factors shape short and long term recovery. We will more fully explore the issue of how local scale processes can be upscaled to explain community variation at a regional scale once our data sets are ready for integration into our metacommunity models. In terms of broader impacts, this project provided research training and professional development for three undergraduate students, three postgraduate students, two PhD students, and one postdoctoral scholar. To date, this award has also generated 14 peer reviewed publications and four presentations at scientific meetings. We anticipate at least additional five publications and presentations at scientific meetings to result from this research. Finally, the coordinates for our benthic research sites throughout the Gulf of Maine are available on our BCO-DMO project page (http://www.bco-dmo.org/project/542407). Data on barnacle and mussel recruitment, consumer surveys, and community recovery data will be placed on our BCO-DMO page once field samples and digital images of experimental plots have been fully processed and analyzed. Last Modified: 03/26/2020 Submitted by: Geoffrey C Trussell