910 Inner Shelf
| Geology & Seabed Morphology
| Sediments | Plants | Animals Oceanography | Cultural Environment | Topics & Habitats |
The Inner Shelf District comprises a large geographic area extending from the Northumberland strait to the Bay of Fundy. The District has been divided into the following Units:
911 Atlantic
912 Outer Bay of Fundy
913 Inner Bay of Fundy
914 Northumberland Strait
915 Sydney Bight
916 Bras d'Or Lake
Geology and Seabed Morphology
The Inner Shelf District borders the landmass of Nova Scotia, extending seaward from the coastline to a depth of 100-120 m. In most places the bottom gradually slopes offshore and is generally covered by reworked glacial till containing sand, gravel, and larger material, including boulders. Exposed bedrock occurs in places. Topography follows the ancient bedrock surface, but in some cases ancient features eroded in the bedrock (e.g., the valley of the ancient Sackville River on the continental shelf) have been infilled by later deposits. Inner Shelf banks occur in several areas (German Bank and Lurcher Shoals off southwestern Nova Scotia; St. Anns Bank in Sydney Bight).
On the Atlantic Coast (Region 800), the Inner Shelf is part of the Atlantic Uplands, a geomorphic division of the Appalachian Region. Here the bottom slopes steadily offshore to a distance of about 25 km and has much of its glacial deposits removed by the sea level advance, leaving significant exposures of bedrock.
In the Bay of Fundy and eastern Gulf of Maine, the Inner Shelf falls in the Fundian Lowlands, a part of the Carboniferous-Triassic lowlands of the Appalachian Region. The bottom contours largely follow the coastline and reflect its origin as a former drainage system originating in the Minas Basin-Truro area.
In Sydney Bight the Inner Shelf is largely underlain by Carboniferous rocks of the Sydney Basin. The topography is relatively flat and slopes gradually out to sea, forming an Inner Shelf bank. Bedrock exposures occur throughout this area.
West of Cape Breton in the southeastern Gulf of St. Lawrence, Ordovician to Middle Carboniferous rocks of the Antigonish and Cape Breton highlands extend under St. Georges Bay to approximately 16 km offshore. The west and central parts of the Northumberland Strait are underlain by horizontal or gently folded Upper Carboniferous and Permian sedimentary rocks.
Oceanography
Tides, winds, buoyancy, and remote forcing are important oceanographic factors on the continental shelf (see T6.1). The large ocean currents include the extension of the Gaspé Current in Northumberland Strait, and the Nova Scotia Current along the continental shelf. The Gulf Stream comes closest to the Canadian continental shelf off East Georges Bank (sub-Unit 931a). Other oceanographic features include coastal upwelling, estuarine circulation, tidal fronts, tidal gyres, shelf-break fronts, and warm-core rings.
Temperature and salinity are important components of oceanic climate and influence biological productivity. In February, upper layer temperatures in some areas are at or near freezing, while temperatures on the South Shore of Nova Scotia and in the Bay of Fundy are considerably warmer. August temperatures are highest in Northumberland Strait and become cooler southwestwards from Cape Breton along the Atlantic Coast (Region 800). At the sea surface on the Scotian Shelf, temperature and salinity increase as one moves southeastwards from land.
Sediments
Coarse sand and gravel mixtures predominate in the Inner Shelf District, though there are significant local variations. Often the sediments vary locally in composition based on the kinds of marterial derived from local erosion and their degree of exposure to waves and currents. Depressions in the Inner Shelf, as found in Chedabucto Bay and deeper areas of Northumberland Strait, have clay deposits.
Plants
Seaweeds grow in a band extending down to 30 m along the coast. Growth is patchy, reflecting the availability of suitable rock substrate and other factors, such as the activity of grazing animals and exposure to sea ice. Stunted and encrusting marine algae can be found attached to rocks throughout most of the Inner Shelf, but growth is most dense near mean low water. Kelps are commonly the most conspicuous species below mean low water along exposed coasts. Rockweed frequently occurs in the intertidal zone in coastal areas. Introduced species occasionally occur. Dead Man's Fingers has been found in dense stands in Prospect and Mahone bays (Unit 911); this species is believed to have been introduced from Japan to Europe, to New England, and then to Nova Scotia.
Algal cover in the Northumberland Strait and the Inner Bay of Fundy tends to be less dense in exposed areas because of the abrasive action of ice. The intertidal zone is scraped clean of algae every year to a depth of several metres below low tide marks and results in the development of a "lawn" of short developing plants in the scraped areas. Ice also lifts off large patches of Eelgrass in some areas, creating many underwater "potholes" and bare areas.
Phytoplankton productivity is high as a result of oceanographic processes which enhance nutrient supply in the coastal zone. Algal "blooms" of dinoflagellates and diatoms occur at peak productive times of the year - the spring and early fall. Dense concentrations of dinoflagellates can create luminescent displays in coastal inlets and add a glow to the wake of passing ships, and they can also cause shellfish poisoning.
Animals
Most of the major offshore marine animal groups can be found in the Inner Shelf. Species that rely on filtering phytoplankton from the water, and estuarine species concentrate in this District. Suspension feeders include mussels, oysters, and scallops on appropriate substrates.
Many species of fish and invertebrates such as lobster live on the Inner Shelf because of its favourable temperatures and feeding conditions. The young of many fish species find food and protection in the algal beds and rocky surface features. Many fish species live in coastal waters and nearby freshwater environments during part of the year.
Migratory fish species such as herring and mackerel move seasonally into these areas; herring frequently spawn in shallows and on some offshore banks, attaching their eggs to the seabed. Large schools of adult Mackerel approach the Atlantic coast in late May and leave again in the fall, accompanied by young-of-the-year. Coastal populations of Sand Lance and Atlantic Silverside shoal in nearshore waters. Cod move inshore as the water warms in the summer. The shelter provided by algal beds, rocks, and boulders - and an ample food supply - provide ideal habitat for lobster. Large clam species, particularly the Ocean Quahog, occur in the sediments.
Seals and whales use the Inner Shelf as both a seasonal and year-round food source. Whales, including the Humpback and Northern Right, move into the area from more southerly areas to feed on summer populations of plankton and fish. Many North Atlantic whale species also move through Nova Scotia inshore and offshore waters en route to summering areas further to the north. The small Harbour Porpoise is characteristic of the coastal zone.
The Inner Shelf supports Harbour and Grey seals which feed on fish and invertebrates in the nearshore zone for at least part of the year. Grey Seals from most Atlantic coastal areas migrate to Sable Island, where they give birth in the spring.
The Inner Shelf is also home to a host of North Atlantic seabirds, many of which nest on shore and feed on the rich animal life just offshore; included are gulls, terns, cormorants, and Storm-petrels. Isolated colonies of seabirds such as Atlantic Puffin, Razorbill, Black-legged Kittiwake, and gannets also occur along the coasts.
Oceanography
Oceanographic features of the Inner Shelf include coastal upwelling, tidal fronts, tidal gyres, and a residual drift current eastwards through Northumberland Strait, around Cape Breton Island, and southwestwards to Cape Sable. Waters in the Inner Shelf tend to have higher turbidity owing to suspended sediments and increased phytoplankton growth at certain times of the year.
In general, the seasonal range of average water temperatures is higher in the upper layers than in the deeper layers, and is higher off Cape Breton than off Yarmouth. This reflects the reduced stratification and increased tidal mixing off Yarmouth.
Cultural Environment
The Inner Shelf District provides the most accessible marine resources for Nova Scotians, and several fisheries of high economic importance are found here. The relative importance of fisheries varies around the coast depending upon species, seasons, and environmental factors. Included are seaweeds, molluscs (clams, oysters, mussels, scallops, periwinkles, and squid), crustaceans (crabs, lobsters, and shrimp), demersal (bottom) fish (cod, pollock, and flounders), and pelagic fish (mackerel, herring, and tuna). Coastal waters offer the potential for the culture of various other species that can thrive on the phytoplankton found there. The inshore fishery for lobster occurs exclusively in this District. Anadromous fish that enter rivers and estuaries (e.g., Gaspereau and Atlantic Salmon) are also important. A wide range of gear, techniques, and vessels are used in these fisheries and often have local variations. The coast is divided into management districts, each of which has particular regulations regarding season, catch limit, and gear to be used. These resources have been greatly affected in recent years by pollution and sediment runoff from activities on land, red tides, and overexploitation. Aquaculture, particularly for mussels and salmonids, is becoming important. Other uses of the District include mining of placer deposits for sand and gravel, coastal recreation, marine transportation, and communications (submarine cables).
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