913 Inner Bay of Fundy
Geology and Seabed Morphology
The Inner Bay of Fundy comprises Cobequid Bay and Minas Basin (sub-Unit 913a) and Chignecto Bay (sub-Unit 913b). This Unit differs in many ways from the Outer Bay, particularly because of the effects of the high tides and the more sheltered environments there. Minas Basin and Cobequid Bay have extensive areas of intertidal mud flats, owing to the high tidal range, coastal erosion, and sediments brought in
from several of the major rivers of Nova Scotia - the Salmon, Shubenacadie, Kennetcook, Avon, and Cornwallis rivers which flow into Cobequid Bay or Minas Basin, and the Petitcodiac River of New Brunswick which flows into Chignecto Bay. The coastlines of these basins have extensive salt marshes or dykelands. Beyond the mud flats in the subtidal zone, the bottom is variable in character, consisting in places of exposed bedrock, sand, and gravel and mud. The strong tidal currents create sea-bottom sand waves several metres in height and hundreds of metres in length.
In the intertidal zone of the Minas Basin is a complex series of sand waves, megaripples, and sand bars that reflect the locally strong tidal flows. These occur at Economy Point, Five Islands, and the Avon River estuary, and over wide areas subtidally.
Glacially derived sediments comprise much of the seabed of the Inner Bay, but sediment derived from coastal erosion is important in some cases and accounts for local differences in bottom sediments, especially between Minas Basin and Chignecto Bay. Sediments in Minas Basin are principally sands and gravels, but intertidal and sheltered environments have muddy bottoms. The sand comes from the wave erosion of sandstone cliffs along the shoreline and from glacial outwash deposits. Chignecto Bay has extensive mud flats and the bottom is muddy, derived largely from shales on the nearby coasts.
The tidal force is predominant and, because of resonance, establishes a macro-tidal environment. Tidal mixing tends to minimize seasonal variations in temperature and salinity. Ice occurs in the upper reaches from December to April.
The Inner Bay of Fundy is estuarine in character and generally warmer than the Outer Bay, because of the pronounced warming of water as it moves over the mud flat, restricted circulation, and high turbidity. Suspended sediment levels in the Inner Bay of Fundy are high and significantly higher in Chignecto Bay than in Minas Basin. Phytoplankton productivity may be limited because suspended sediments make the water opaque.
Seaweeds are not generally abundant and occur in isolated patches where suitable hard bottom is present.
Fucus species and Ascophyllum
nodosum occur in the upper intertidal, and seaweeds of various kinds occur below extreme low water. A significant bed of the kelp Laminaria saccharina containing various seaweeds, including the dulse
Palmaria palmata and coralline algae Corallina
officinalis, has been found between Cape Blomidon and Medford Beach in western Minas Basin, and a dulse bed occurs near Parrsboro.
Phytoplankton populations are not generally as productive as in other Inner Shelf areas because light levels are reduced by high sediment loads in the Minas and Cumberland basins. The majority of plant production comes from microscopic algae growing on the surface of mud flats and from salt marsh grasses.
The Inner Bay of Fundy supports large populations of various coastal fish species. Some migrate into the bay for feeding and reproduction, and others are resident in the area throughout the year. Most of the American Shad from east coast waters spend the summer in the basins of the Inner Bay of Fundy. More than 40 species of fish can be considered regular residents, some of the more common being Atlantic
Herring, alewife, Blueback Herring, American Shad, smelt, Atlantic Tomcod, Atlantic Silverside, Windowpane, Smooth and Winter Flounder, Striped Bass, Atlantic Salmon, and American Eel. Waters are productive despite high turbidity and reduced phytoplankton production, because of the high abundance of zooplankton, which feed on detritus from salt-marsh grasses in suspension in the water. The mud flats are home to
invertebrates, including numerous species of polychaete worms; softshell clams; intertidal snails; and crustaceans, including the tube-dwelling amphipod
Corophium volutator (a small shrimp which is food for migratory shorebirds). Several species of flatfish, which live in the deeper water, come into the tidal flats and streams to reproduce and feed. Inshore concentrations of Atlantic Halibut at one time occurred in Minas Basin. Various seabirds occur, including gulls and cormorants, as well as various birds of prey (Ospreys and Bald Eagles) which use the coastal bluffs and nearby inland areas for nesting. Shorebirds in large numbers visit the mud flats on their passage north in spring and then return late in summer from Arctic breeding areas.
Both Minas Basin (sub-Unit 913a) and Cumberland Basin (in sub-Unit 913b) have muddy waters with generally poor fisheries, but the extensive tidal marshes are of great economic and cultural significance. Salt marshes are highly productive systems that support the fisheries of the Outer Bay of Fundy. These once-extensive marshes have been progressively dyked and drained since the seventeenth century to provide some of the finest agricultural land in the province. The dykes that protect the marshland from the sea must be constantly maintained, a task of increasing importance as the sea level continues to rise. There are some traditional fisheries of shad, shellfish (clams), and bait (bloodworms). Projects to generate electricity from the tides have been proposed for both Cumberland Basin and Cobequid Bay.
Sites of Special Interest
- Most major rivers entering the Inner Bay of Fundy - tidal "bores"; extensive areas of mud flats and beaches extend out from shore
- Minas Channel between Cape Split and Rams Head near Parrsboro - significant tidal currents flow into the outer reaches of Chignecto Bay; shifting sea ice is a significant winter feature
- Coastal areas - extensive dykelands and salt marsh; concentrations of shorebirds, chiefly Semipalmated Plover, can be observed on mud flats in the spring and late summer
- Grand Pré - extinct oyster bed at extreme low water mark reflects the progressively changing environment of Minas Basin, though several warm-water species, including Lady Crab and Angel Wing Clam, remain as disjunct populations in the area
|T3.5 Offshore Bottom Characteristics|
|T6.1 Ocean Currents|
|T6.2 Oceanic Environments|
|T114 Birds of Prey|
|T11.7 Seabirds and Birds of
|T11.12 Marine Mammals|
|T11.14 Marine Fishes|
|T11.17 Marine Invertebrates|
|T12.10 Plants and Resources||
|Associated Coastal Districts and Units|
|523 Tantramar Marshes|
|532 Chignecto Plains|
|540 Clay Plain|
|620 Tidal Bay|
|710 Basalt Headlands|
|720 Basalt Ridge|