Intertidal zone - Oceana Canada

Marine Ecosystems

Intertidal zone


Coastal zones in all oceans


Rocky, sandy or mudflats; covered with water at high tide and exposed to air at low tide


Sea anemones, star fish, crabs, barnacles, snails, mussels, algae


Nursery grounds, erosion prevention, storm surge prevention, carbon capture, ecosystem indicator


The intertidal zone is a marine ecosystem that exists in coastal regions between the highest high tide and the lowest low tide. In each tidal cycle, this region sees full water coverage at high tide and complete sun exposure at low tide. Marine life that calls the intertidal zone home are well adapted to these extremes, able to survive intense heat and sun exposure as the tide falls or pounding waves on the shoreline as the tide rises. The world’s highest tides occur in the Bay of Fundy off the east coast of Canada, where marine species can see twenty metre differences between high and low tide.

There are a variety of different types of intertidal zones, which differ by their physical characteristics and the species that call them home. Rocky intertidal zones host species such as sea stars, snails, anemones, algae and crabs. Barnacles and mussels fasten themselves to the rocky shoreline and hold seawater in their closed shells to keep from drying out during low tide. Intertidal zones with mudflats and sand can be home to a variety of species of clams, sand dollars and worms. The intertidal zone can take many other diverse forms including tidal marshes and mangrove forests.

Species that can be found in the intertidal zone often form communities along the coastal, elevation gradient. This gradient is divided into three main zones; high, middle and low tide. The high tide is only submerged at the highest tide and is hotter and drier than the other zones. The middle zone is submerged and exposed for equal amounts of time during the tide cycle. The low tide zone is only exposed in low tide and has the most water coverage and biodiversity of the three zones. Further, the ‘spray zone’ is a fourth zone above the high tide that is impacted by sea spray and occasional storm surges. Different species can typically be found within each of three zones, making the intertidal zone a fascinating marine ecosystem to explore at different times during the tidal cycle!



  • The highest tides in the world can be found in Canada in the Bay of Fundy, between New Brunswick and Nova Scotia
  • Another name for intertidal zone ecosystems is “tide pool”
  • The temperature of the water in intertidal zone tide pools can range from scorching hot to below freezing or can match the temperature of surrounding ocean waters
  • Water salinity is much higher in the intertidal zone because saltwater gets trapped in rocks and when the water evaporates, it leaves behind many salt deposits



National Geographic

Nature Conservancy Canada

NOAA National Ocean Service

World Wildlife Fund