Deep channels and submarine canyons frequently have strong currents and usually contain coarse sediments. The bottom of the continental slope has thick surficial sediments of clay and sand. Plants Beds of kelp and other marine algae grow on the seabed close to shore, and microscopic phytoplankton occur both nearshore and in most other waters. The main attached species of the Nova Scotia coast are the kelps and rockweeds, but more than 300 species of seaweed occur around Nova Scotia coasts. Marine seaweed growth is most abundant on exposed rocky shores typical of the Atlantic coast, where there are sites for attachment and adequate water movements to supply nutrients.
Seaweeds generally grow less and their shapes change in sheltered environments.
In areas with ice cover through part of the year, profuse algal growth can develop only beneath the depth of winter ice scour, even on a suitable substrate. Irish Moss develops in the subtidal zone beneath the ice in western and northern P.E.I. Particularly in the Northumberland Strait but also in protected inlets and bays throughout Nova Scotia, soft bottoms, usually just below tide level, are populated by Eelgrass. This flowering plant grows the world over and is important in marine food chains. Eelgrass beds support a diverse invertebrate fauna as well as the young stages of a variety of fish and shellfish species. Phytoplankton, notably diatom growth, occurs throughout the offshore and creates the main food source for planktonic animals and bottom-dwelling filter feeders.