Is seaweed a type of plant???

The jury is out on seaweeds; some people probably hear the word and think about sushi, some think about beautiful underwater seaweed forests floating up toward the sun, gently swaying with the currents, and some think about seaweed entangling rudders or mucking up beaches.

Another samples from the wrack line; that line of seaweed (wrack is another word for seaweed) deposited high up on the beach by the latest high tide. More often than not students are amazed by the sheer number and diversity of seaweeds present in the wrack line. I certainly am.

The wrack line isn't just one amorphous mass of rotting kelp, there are red and green and brown seaweeds with evocative names like sea lettuce, Irish moss, knotted wrack, rockweed, bladder wrack, sea colander, horsetail kelp, brown pom-pom, maiden's hair, dead man's fingers; the list is endless.

While there are some plants that grow in the ocean, the majority of the big ocean photosynthesizers are the seaweeds (or macroalgae), which are not plants at all but are currently housed in the kingdom Protista. This is the kingdom that contains all those single-celled organisms that we glimpsed under microscopes in pond water samples back in elementary school.

Because seaweeds live in the ocean, surrounded by water, they need and have none of the structures that plants use to obtain water and nutrients from the soil. Seaweeds lack the vascular system and roots of a plant; they can absorb the water and nutrients they need directly from the ocean surrounding them. Their blades (leaf-like structures) are not technically leaves since they lack veins.

Seaweeds have a spectacular range of form, adapted to the various conditions in which they live. Short and sturdy seaweeds able to take the pounding of waves attach to rocky shorelines with their root-like holdfasts; giant kelp form offshore forests; smaller, more delicate seaweeds grow on larger ones; and the coralline algae, a red algae that contains calcium carbonate, join with the corals to build reefs.

All of these seaweeds can be found in the wrack line, especially after a storm has torn them loose. As long as seaweed can float it will stay alive, but deposited on a beach above the tide line seaweed will start to die, and decay, which can be a problem for beach-goers.

However, the sometimes-smelly wrack line provides an irresistible array of delicacies for foraging shore birds, a smorgasbord of decaying bits of seaweed, numerous beach fleas and sand hoppers that eat the seaweed, small crabs and other crustaceans that were stranded with the wrack.