Scotian shelf (Eastern) - Environment

The temperature, salinity and movement of the waters of the ocean have profound impacts on the distribution, growth and survival of marine organisms. Each organism has a particular range of temperature and salinity, which is optimal for its success. Water transports their food and oxygen, removes their wastes and also conveys the less active organisms from place to place.
The hydrographic environment of the eastern Scotian Shelf is governed largely by its location, near the meeting place of three major currents of the Northwest Atlantic; and its complex topography. The shelf-bottom topography consists of a series of submarine banks and cross-shelf channels along the outer shelf and basins and troughs along the central shelf that limit and guide the near-bottom flow. The eastern end of the Scotian Shelf consists mostly of cold fresh water from the Gulf of St. Lawrence and the Newfoundland Shelf and overall there is transport of water and organisms from the northeast towards the southwest. The eastern Scotian Shelf responds to the conditions in the Gulf of St. Lawrence and the Newfoundland Shelf, which are thought to reflect processes at more northerly latitudes. The deep basins on the central shelf are directly connected to the slope water, where the water properties are determined by interactions between the Labrador Slope Water Current and the Gulf Stream.
This response to different forcings leads to variations in the temperature, salinity and currents of the Scotian Shelf on many time scales from interannual to decadal. The gradual cooling of the bottom waters of the eastern shelf from the mid-1980s through the 1990s is an example of such decadal length variation that had a measurable impact on the structure and function of eastern Scotian Shelf ecosystems. The eastern shelf cooled from the mid 1980s to the early 1990s. This cold period is associated with increased abundance of cold-water fish (capelin, turbot) and invertebrates (snow crab, shrimp) usually more prevalent in the colder waters of the Gulf of St. Lawrence and Newfoundland. Colder temperatures also lead to reductions in growth rates of demersal fish. Changes in growth rates of species in response to changes in oceanographic conditions affect productivity, and therefore we must temper our expectations of yield in fisheries. In addition these physical changes will have impacts on the overall productivity and trophic structure of the supporting ecosystem. Changes in growth and distributions of fish and invertebrates in response to changes in oceanographic conditions have significant implications for the overall trophic structure of the ecosystem.
The complex nature of the physical oceanographic features of the Scotian Shelf influences the patterns of abundance of phytoplankton. High-frequency spatial (kilometres) and temporal (days) variability in phytoplankton biomass is a common feature of the Scotian Shelf. Superimposed on this is a distinctive seasonal cycle of growth characterized by a conspicuous and widespread spring biomass peak, the spring “bloom”, and a more diffuse fall bloom. This annual growth cycle may be as important in linking phytoplankton to production at higher trophic levels as the bulk (annual) primary production. In addition to the general current structure, early spring mixing (or stratification) is a critical physical property of the eastern Scotian Shelf, since it likely determines the timing of the spring bloom. Decadal trends in the spring bloom on the Scotian Shelf indicate that blooms start earlier now than they did in the 1960s and 1970s, and that spring blooms are now more intense and last longer.