Intertidal Zone Invertebrates
Barnacle, Mussel, Snail, Sea Anemone, Star Fish, Sea Urchins, Crab
Feb 20, 2007
It’s vacation time. Daddy wants to go to the Rocky Mountains. Mother wants to go to Paris. Son and Daughter want to go to Disneyworld. So, it’s decided—let’s go to the beach which can be enjoyable for all of us. And, what living things will we see there? Well, besides the birds and an occasional fish, the area between the high tide and low tide, the Intertidal zone, is teeming with invertebrate life. Let’s take a look at some of this life.
Barnacles: Barnacles are small, but there can be at least a hundred per square foot on rock or wood or even other living creatures, if they have a hard surface. They are usually gray, about dime to quarter size with a hole in the top and are volcano shaped. They are filter feeders on the millions of plankton in the water around them.
Mussels: Mussels are shellfish (mollusks) with two wing-shaped shells hinged together, with the clam being the prototype. Most mussels can be eaten and they make very good chowder. They are filter feeders straining their food, mostly small algae plants, from the water. The stream of water also supplies them with oxygen which all living organisms need to live.
Snails: Snails are in the same family as mussels with a shell composed of calcium carbonate, but they are not hinged. Most species of snails have a spiral shell. Their primary food consists of algae rasped off of rock or sand, but a few species are scavengers. A few species even are predators boring a hole in other mollusks shells and sucking the juices out. Their major form of locomotion is slowly crawling around on a large, flat foot.
Sea Anemone: Anemones have no shell at all. They can be compared with a flower as they are built with a “trunk” with “flowers” on top. Actually the trunk is the body and the flower is tentacles. The tentacles are sticky and poisonous, and any animal, from zooplankton to fish or crab, coming into contact with them becomes a meal. There are some fish though that can live right in the tentacles without being harmed.
Starfish (sea star): Starfish (and brittle stars) are common on rocky shores in the water just below the tide lines. They have 5 arms (or multiples of five arms) that radiate out from a central disc that houses the mouth. Some species have arms that are strong enough to force open a clam, push their stomach out their mouth, and digest the meat of the clam. They move about by pulling themselves forward with hundreds of tube feet.
Sea Urchin: Sea urchins are one of the most abundant animals in the ocean. In the Intertidal zone, they are always found in the water and sometimes in great numbers. They are a round, puffed up, hard shelled creature with rigid spines. They slowly move along the bottom ingesting anything organic they come to—dead fish, crabs, and other decaying matter; algae; sponges, mussels, and barnacles.
Crab: Crabs are hard-shelled animals with ten jointed legs, two of which are equipped with pinchers or claws used for protection and holding food. They can move with great speed, usually sideways, on their walking legs, and often dig a hole into which they can quickly dive when danger approaches. Others live under rocks in pools.
Hermit crab: Hermit crabs have a specialized life style; they live inside snail shells. They have no shell of their but find an appropriate shell and sliding their abdomen into it, they live until they molt and then find another larger shell as their abode.
These are the major invertebrates that you will find when you visit the beach. You might want to make a checklist and look for each of them the next time you visit the ocean.
