Research Document - 2014/065
Inshore Scotian Shelf Ecosystem Overview Report: Status and Trends
By A. Bundy, D. Themelis, J. Sperl, and N. den Heyer
Abstract
The Inshore Scotian Shelf Ecosystem Overview Report (EOR) describes the geological, oceanographic and biological systems of the inshore region and their relationships at the habitat and ecosystem levels. Its objectives are to provide the ecological context for integrated management, a baseline for impact assessment and planning for sustainable use of the area.
The geographical scope of the Inshore Scotian Shelf EOR is the waters less than 100 m deep or less than 25 km offshore Nova Scotia between Cape North and Cape Sable Island. This definition is largely based on the inshore limit of the Fisheries and Oceans Canada (DFO) Research Vessel trawl surveys, and does not necessarily fully reflect either the functional role of the inshore region in the structuring and population dynamics of diadromous and marine species, or the distribution of species, habitats and ecological processes considered in this report. However, it does contain distinct habitat and species that do not occur in deeper waters. Information is also presented from outside of these boundaries when relevant to the ecological and biological processes of the larger Scotian Shelf ecosystem.
There is a long history of coastal marine research in Nova Scotia, although it is patchy in nature, focusing on specific areas, specific time periods, or both. As a result, the quantity of information is not equally distributed across species, habitats or ecological processes, meaning that information quantity is not necessarily related to relative importance. Information is drawn from primary literature; provincial, federal, municipal and environmental consultants’ reports; and preliminary analyses from the DFO Inshore Ecosystem Project. Although a historical perspective is provided, this report is largely based on information from the last 50 years.
Most of the inshore region is characterized by relatively rugged and hard bedrock outcrop terrain at or immediately below the seabed. Mapping along the Atlantic coast shows that sand and gravel are present over most of the inner shelf but in such a thin layer as to have little effect on the seabed morphology. Shoreline habitats include rocky shores and headlands, large bays and inlets, estuaries, salt marshes and sandy and rocky beaches.
The entire coastline is influenced by periodic forcing of large scale shelf processes, such as coastal upwelling and the Nova Scotia Current (NSC). The NSC is a longshore current bringing fresher water from the Gulf of St. Lawrence onto the shelf, resulting in an along-shore gradient of increasing salinity and decreasing stratification from east to west. However, many of the invertebrate and fish species of the inshore region are ubiquitous. Community composition and diversity vary at the habitat level, with the degree of exposure to the open ocean largely defining the inter-tidal and sub-tidal communities.
The inshore and offshore regions are linked through the export of production by macrophytes, larvae from sessile invertebrates, and anadromous fishes. There is also a net loss of production to migrating birds, reptiles, large pelagic fishes and marine mammals that seasonally visit and feed in the inshore region. Many species caught offshore in shelf-based commercial fisheries use the inshore region as a nursery area and also feed upon the anadromous fishes and larvae exported into the pelagic food chains of the offshore region. Human activities that have the largest influence on inshore ecosystems are fishing, aquaculture, coastal development and infilling, transportation, mining, and climate change. Four centuries of fishing have left the inshore region low in abundance of traditional fish species and depauperated of spawning areas for species such as cod and herring, while the abundance of invertebrates such as lobsters and crabs has increased. Macrophytes, the defining biological feature upon which inshore organisms depend for food and habitat, will be impacted by the effects of climate change on shoreline habitats. The nature and extent of these impacts are currently unknown, requiring urgent research.
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