Glossary:Intertidal zone
- The zone between the mean higher high water and mean lower low water lines.
Where is the Intertidal Zone?
On the shore between high and low tide lies the intertidal zone, where land and sea meet. It is underwater during high tide and exposed to air during low tide. The animals and plants that live in this zone must cope with being submerged in water and exposed to the air during different times of day. Many species of worms, snails, clams, oysters, mussels and seastars make the intertidal zone their home. The motion of high tide and low tide creates four zones within the intertidal zone where different animals and plants live.[1]
Spray Zone
The spray zone is the upper part of the beach that occasionally gets splashed, but never gets covered by the ocean. This zone is more a part of the land than the ocean. Plants and animals in the spray zone have adapted to living exposed to the air, sun, rain and even frost.
High Intertidal Zone
The high intertidal zone is flooded during the peaks of the once or twice daily high tides, and out of the water for long stretches of time in between. Here plants and animals are used to living above the water surface.
Mid Intertidal Zone
The middle intertidal zone is generally submerged, except for a period during the turn of low tide. More plants and animals live here because they are not exposed to drying conditions for too long.
Low Intertidal Zone
The lower intertidal zone is exposed to air for only a short period of time at low tide. Life here is adapted to conditions underwater.
Intertidal Zone Biota
Rocky Shoreline
The rocky shore habitat is a hard place to live. Plants and animals here are adapted to the frequent changes in water chemistry, temperature and oxygen and pounding of waves on the rocks. Organisms must cling to the rocks or wash away on the tides. This adaption prevents some animals from becoming a meal to predators when they are exposed at low tide.
As the tide moves out, water is trapped between rocks forming tide pools. Tide pools help those organisms that have not adapted to being exposed to air for long periods of time. During low tide you might see sea stars, mussels, barnacles, sea cucumbers, crabs, octupuses, and even fish in tide pools.
Sandy Shoreline
The same beach where you might build sand castles or lay your beach towel is actually a very active ocean habitat. At low tide, organisms hide in the sand for protection from waves and to stay moist. When water comes back at high tide, these animals may come out to feed.
Ocean life benefits from increased oxygen levels and food sources brought in from deeper areas during high tides. High tides also bring fish searching for their prey as invertebrates emerge from the sand. Intertidal beaches supply food and habitat for both ocean and land animals. Prolific shorebirds can be seen nesting and feeding here.
Human Impacts
As the human population increases along coastline in the U.S., more people have access to the intertidal zone. This impacts many of the plants and animals that live and rely on this type of habitat. Here are some ways you can help save intertidal zones.
- Do not collect sea shells. Instead of taking shells, take photos of shells. Many of the shells that you see on the beach can still be a home to a snail or hermit crab.
- Step safely. With our for yourself and be sure not to step on a tide pool animal. The best way to view a tide pool is to approach and then quietly wait next to the pool.
- Do not trash. Properly dispose of trash when you visit the beach. Trash can easily be washed into the intertidal habitat.
- Volunteer. Participate in a beach clean up to prevent trash from polluting coastal and ocean habitats.
- Reduce, reuse and recycle. Recycling can reduce power usage and also reduce the use of fossil fuel.
