The Intertidal Zone: a reef platform

The intertidal zone, also known as the littoral zone, is that area between high tide and low tide. It can be divided the following subzones – spray zone, upper intertidal zone, mid intertidal zone and the lower intertidal zone. It is an area that is constantly changing as the water moves in and out with the tides. Thus organisms inhabiting this area have a variety of adaptations that allow them to survive.

Conditions to Cope With… Temperature Light Moisture/Desiccation Wave Shock/Energy Dissolved Oxygen Food Supply Images from google images

Tidal Zones Intertidal Zone Tidal habitats are divided into zones based on relative beach location and how often they are covered by water Splash Zone Intertidal Zone High, Mid and Low High Tide Zone Zones affected daily by changing tides Most adaptation required Middle Tide Zone Low Tide Zone Subtidal Zone

The spray zone, or supra-littoral zone is the highest zone of true marine life. It is usually only kept damp through wave splash. Organisms surviving this environment include barnacles, limpets and periwinkles (pictured).

The upper intertidal zone is only covered by water at high tide The upper intertidal zone is only covered by water at high tide. Any algal growth is green, and the zone is characterised by barnacles, limpets, chitons, crabs, mussels, sea stars and periwinkles.

Sandy Beach Organisms and Adaptations On sandy shores, there exists the option to burrow into the sand to avoid drying out. Bivalve mollusks Soft body, hard shell Example: clams and mussels Greatest number in low tide regions Annelid worms

Sandy Beach Organisms and Adaptations Another option when living in the tidal zones is to move with the tides. Crustaceans Segmented body, hard exoskeleton, paired jointed limbs Example: crabs, lobsters

1) Crabs: Have a hard shell that protects them and allows them to squeeze into tight places. They can survive for extended periods of time out of the water. During low tide they scavenge for bits of plants and animals.

The middle intertidal zone is regularly covered by water The middle intertidal zone is regularly covered by water. Seaweed is more prominent. Organisms in this zone include anemones (pictured), barnacles, crabs, mussels, sea stars, gastropods and sponges.

The lower intertidal zone is usually submerged, only being exposed at very low tides. The zone is characterised by brown algae (funnel weed pictured – top), encrusting sponges, abalone, sea stars, crabs, sea cucumbers, gastropods and sea urchins (pictured). Small fish may also inhabit the area.

Organisms exposed to air must be able to prevent (or tolerate) desiccation (drying out). Many organisms have a protective covering such as a shell.

© Department of Fisheries, Michael Burgess Intertidal zones can be high energy environments, as waves pound the area with force. Algae (seaweed) possess a root-like structure called a holdfast that they use to anchor themselves to the substrate.

Others, like this sea anemone, Anthopleura xanthogrammica, grow tall in light tidal action, yet grown short and wider when in the rough seas. This limits the forces they must endure. Keeping your feet is a matter of using hold fast (seaweeds) and byssal threads (mussels).

Barnacles (pictured) attach themselves to the substrate with a strong ‘glue’ and mussels with their byssal threads. Mobile animals such as limpets and chitons use their muscular foot to cling on to the reef during heavy wave action.

Animals in more exposed locations tend to have thicker shells (e. g Animals in more exposed locations tend to have thicker shells (e.g. turban snails – pictured) than those in sheltered locations (e.g. pipis). Likewise, many intertidal organisms, such as barnacles, limpets and chitons have low profiles, close to the rocks.

Being flexible is an option as well.

Salinity in the intertidal zone can be quite variable depending on the amount of rainfall, and the rate of evaporation of the water. Organisms inhabiting this area, particularly rock pools, can usually withstand changes in salinity, and also temperature. Some animals in rock pools will take shelter from direct sunlight under algae.

Animals inhabiting the intertidal zone may be restricted as to when they can feed. Many sessile animals are filter feeders (feed on planktonic material in the water) and thus are unable to feed when the tide is out. Those animals that are not filter feeders may also be restricted as they seek shelter from the elements and predators at low tide.

Tide Pools Tide pools are rocky areas on the edge of an ocean that are filled with sea water. They are created when the tide goes out, and each is unique based on the depth and width of the pool.

Lets not forget that even in the midst of chaos is…more chaos!! Food webs, prey and predation still apply when your fighting for your life.

In an intertidal zone, keystone species are very important to community structure.

© Department of Fisheries, Alicia Edwards In addition to the environmental challenges that organisms inhabiting the intertidal zone face, one of their greatest threats is humans. We cause damage to this environment as we step on organisms and their habitats, and remove organisms altogether.