Intellectual Merit: The importance of fluxes across ecosystem boundaries is a characteristic of marine ecosystems that differentiates them from their terrestrial counterparts. From this viewpoint, any comparative analysis of marine ecosystems should address the patterns and degree of connectivity among ecosystems to be of highest utility. Here the investigators will conduct a suite of analyses that seek to quantify the sources, patterns and consequences of connectivity among 10 marine fishery ecosystems that together from the northwest Atlantic coastal shelf ecosystem. By conducting analyses in a hierarchical fashion with smaller ecosystems nested spatially within larger ecosystems they hope to identify scaling relationships in the ecological processes that characterize the dynamics of key species within these ecosystems. This work seeks to quantify the patterns and degree of connectivity among ecosystems in the Northwest Atlantic. Specifically, the investigators will conduct statistical analyses of empirical data from each ecosystem to quantify patterns in univariate, distribution and multivariate descriptors of their structure. They will also undertake time series analyses to describe relationships in the responses of different taxa and groups within each ecosystem. They will use the results of analyses conducted on the highly studied nearshore ecosystems as hypotheses to be tested on the somewhat sparser data of the offshore ecosystems. These analyses will delineate patterns of functional connectivity among ecosystems. They will also construct dynamic models of differing complexity to understand the principal consequences of the connectivity demonstrated in the first two objectives on ecosystem function. Models will include biomass dynamic and coupled predator-prey simulations that will consider the impacts of removals from the overall region globally and more specific patterns of localized spatial depletion.
Broader Impacts: Agencies, at all levels, are seeking to develop ecosystem-approaches to management (EAM) of fisheries in efforts to ensure long-term sustainability of the exploited marine resources and ecosystems. Central to EAM are Integrated Ecosystem Assessments (IEAs), which provide the societal, legal, and scientific basis to examine marine ecosystems at multiple scales -spatially, temporally, and jurisdictionally - and to coordinate the management of coastal ecosystem resources across multiple sectors. The open nature of marine ecosystems is a challenge for IEAs and EAM and particularly so for the Northwest Atlantic Coastal Shelf (NWACS) ecosystem. Key to management in this open ecosystem is assessment of the connectivity among key biota across space and time in the different regions. Here, the investigators will analyze ecosystem structure and function at a range of scales in a suite of interconnected regional ecosystems to support IEA development.
This research was conducted as part of CAMEO. In comparative analyses, marine ecosystems can be considered as experimental units that have been subjected to differing pressures from fishing and environmental drivers. Our project recognized that these experimental units are not independent—continental-shelf ecosystems are connected by common environmental drivers, by currents, and by migration. This collaborative research project included scientists from NOAA Fisheries, The College of William and Mary, The University of Maryland, and Stony Brook University. As Co-PI, I contributed to two of the project components, as described below. A. The first objective was to quantify the spatial and temporal patterns in fish communities in the northeast shelf large marine ecosystem (NESLME). We compiled fish population data from six coastal and four shelf ecosystems within the NESLME. Twenty-two species were selected that were sufficiently abundant in all the trawl surveys. Time-series analysis was used to identify common time trends among the surveys. Here, we report on two of the species with contrasting patterns: winter flounder and summer flounder. The best-fitting time series models for both species included the Atlantic Multidecadal Oscillation (AMO) as a covariate. The AMO is an index of large-scale temperature changes in the North Atlantic Ocean, which exhibited a general warming trend during the 1963-2010 time period of the trawl-survey data. Winter flounder had a generally declining trend with peaks in the 1960s, early and mid 1980s. The declines were most pronounced for the more southern stocks (Delaware and Mid-Atlantic Bight) and less severe for more northern stocks (Gulf of Maine). The dynamics of the offshore ecosystem were uncoupled from those in the estuaries. Winter flounder is an estuarine spawner with a rich sub-population structure. Warming temperatures reduce winter flounder productivity, such that harvest pressure will need to be reduced, especially in the more southern ecosystems, where the effects of warming are already apparent. Summer flounder abundance increased in most ecosystems, except Delaware. In contrast to winter flounder, the temporal patterns for summer flounder are coherent between the coastal and shelf ecosystems, with the exception of the Gulf of Maine. This coherence reflects the life history of summer flounder, which spawn offshore and use the estuaries as nursery areas. One management implication of these results is that catch allocation among the Atlantic states will need to be adjusted in response to a northward shift in summer flounder abundance. B. The second component of this research was to develop dynamic models of these fish communities, which include multiple areas of the NESLME: Southern New England, Georges Bank, and the Gulf of Maine. Biomass and catch data from 1979 to 2008 were compiled for 15 commercially and economically important species. We found significant shifts in the spatial distributions of six of these 15 species. Atlantic herring, spiny dogfish, silver hake, and white hake shifted to the north. By contrast, the spatial distributions of little skate and winter skate shifted toward Southern New England. The next step was to aggregate the 15 species into four functional groups: non-migrating benthivores (bottom feeders), non-migrating piscivores (fish eaters), migratory piscivores, and migratory planktivores (plankton feeders). Multispecies models were fit to these data; accounting for interactions among the functional groups significantly improved the fit to the observed data. Significant interactions occurred between migratory piscivores and benthivores and between benthivores and migratory planktivores (Figure 1). Interestingly, there was little support for trophic interactions with non-migratory piscivores (e.g.) cod, except in Southern New England, where the dominant piscivore is summer flounder. Overall, there were more negative than positive trophic interactions, which suggests top-down control of these fish communities by predators, especially in Southern New England. The interactions involving migratory fish species provide connectivity among the offshore regions and provide a mechanism for indirect trophic interactions. For example, the harvest of non-migrating benthivores on Georges Bank positively affects the equilibrium yield of benthivores in the Gulf of Maine via the migratory piscivores. One implication for Ecosystem Based Fisheries Management is that functional groups of species should be managed together, not in isolation. Fishery management plans need to account for the full spatial distributions of migratory species, as trophic interactions in one ecosystem can have indirect effects in another area.
