One of the most common examples of marine red algae is also one of the most complex. A genus called Polysiphonia is often seen attached to small rocks, shells, and other algae species in the intertidal zone. This attractive seaweed is easily identified using a hand lens. The alga appears to have bands along its central branch. These are actually groups of pericentral cells and are seen on all branches. Polysiphonia does have chlorophyll for photosynthesis, but also contains the red pigment phycobilin which gives the alga its characteristic color.
The life cycle of Polysiphonia is amazingly complicated for such a small, ancient organism. The plant collected in the field is likely the tetrasporophyte stage which releases a series of tetraspores. These germinate into either a male or female gametophyte plant. The male produces the spermatangia and the female forms a structure called a cystocarp that is fertilized by a single spermatium. After this occurs another kind of spore, the carpospore, forms and develops into the tetrasporophyte again.
There are hundreds of species of Polysiphonia world wide, and around a dozen in the Cape Cod region. Some of these are epiphytes, or plants that are attached to other plants. One of the most interesting Polysiphonia epiphytes is P. lanosa which grows exclusively on the brown knotted wrack Ascophyllum nodosum. P. lanosa is a small bushy alga growing in clumps on the branches of Ascophyllum. Possibly it’s more resistant to desiccation than other species, or maybe it is able to increase its rate of photosynthesis by floating to the surface because of Ascophyllum’s large air bladders. It can be spotted and identified with a good hand lens.
Locating smaller seaweeds such as Polysiphonia requires patience and close examination of shallow waters. There are many tiny, almost obscure, plants and animals which remain hidden under shells or larger seaweeds. I sometimes carry a bucket with me, collect a clump of macroalgae, and take it back to the lab. I then spread the collection into large trays where it can be more closely examined.
It’s often surprising what can be found floating, hidden, or attached to other plants. For example, another tiny red alga, Ceramium rubrum, with its definitive claw-like tips, is frequently seen attached to Codium fragile. Having access to a microscope makes it much easier for an accurate identification.
So the next time you go beachcombing take a closer look at this miniature world. You may encounter a variety of living things awaiting your discovery.
Copyright Gil Newton 2009 Thanks to Chris Dumas for logo image.