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. 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. Phytoplankton productivity is high as a result of oceanographic processes which enhance nutrient supply in the coastal zone. 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.