Dive Dry with Dr. Bill

#315: Eisenia... Dreaming of Palm Trees amd Sunny Beaches

Years ago when we were removing the feral goats and pigs from the island, several community meetings were held to explain the reasons for these actions. Of course the primary reason was that these mammals were not native to the island, in fact not even native to the North American continent. They had been introduced by early Europeans from their native range where they had been domesticated. But just being non-native wasn't the only reason, it was because they were seriously impacting the native plants (and therefore animals) of the island which the Conservancy was formed to preserve.

I was surprised at the response from several in the audience. "Who cares about plants?" It displayed a very disturbing lack of awareness about ecological systems. Almost all living things depend on plants which are the basis for most of the food chains and webs that keep ecosystems supplied with energy. They convert sunlight, nutrients and water into a usable source of stored chemical energy... which most of us, including the animals, call food! I wonder what our human food chains would do if we had no more wheat, rice, corn or barley. They serve as the basis for most of the foods we eat (other than fish)... and also for the beer that sustains us! To not care about plants is to not care about your own survival, or the survival of ecosystems in general.

In the marine world, plant-like species known as algae are very critical to those ecosystems. They include our own kelp forests, surfgrass meadows, algae embedded in tropical corals and the plant plankton that all provide the fundamental source for "munchies" in the underwater world. They capture sunlight using various chemical pigments, and use the energy to produce carbohydrates and other edible products through photosynthesis. Oh, I probably should mention that one of the by-products of that process is oxygen. Some scientists estimate that up to 70% of the oxygen in our atmosphere may be produced by "plants" underwater. I guess if you don't care about plants, you don't care about life itself.

I can't imagine an individual living on the island that isn't aware of our giant kelp forests. However Macrocystis is but one of a number of brown algal species called kelp... and there are many more types of algae other than kelp. The best scientific field guide lists some 669 species of benthic or bottom-dwelling algae in California alone. That doesn't even consider all the plant plankton suspended in our waters. Today I will focus on a species that is fairly common here off Catalina, the southern sea palm kelp.

This kelp, known scientifically as Eisenia arborea, was first described from a specimen taken in Catalina waters back in the 1870's. It was collected by Dr. Gustav Eisen, and named after him. This is the same person who first collected our own Catalina ironwood for science. The top marine botany field guide states the sea palm is also known as far north as Vancouver Island, British Columbia, and down to Isla Magdalena in Baja. However, some authors have stated it is only found south of Pt. Conception. There is also a northern sea palm kelp found from Vancouver Island to Morro Bay. Here in our waters, Eisenia forms dense thickets in shallow waters from just below the low tide zone to about 30 feet where the giant kelp canopy begins to overgrow it and shade it out. Too much competition for light for the poor "lowly" (depth-wise) southern sea palm.

Back in the early 70's I taught marine biology to a group of young ladies from the Kent School in Denver. One day some of them grabbed a few detached sea palms from the beach at Toyon and used them like a cheerleader's pom poms. That gives you some idea of this kelp's appearance. The sea palm has a small holdfast that attaches it directly to rocks and other hard substrates. It must grip the bottom tenaciously because this kelp is found in the shallows where it may be significantly impacted by surge and storms. There is a relatively short (up to about three feet), broad leathery stipe running from the holdfast to the cluster of strap-like blades that grow off a split at the top of the stipe. Because it is found in shallow waters, it does not need float bulbs (pneumatocysts) like giant kelp to buoy it up towards the light.

In researching this column, I discovered that southern sea palm kelp has two different blade types. In waters that are calm, it tends to have "bumpy" blades whereas in regions affected by strong currents or surge it usually has flat blades. The first type is believed to be an adaptation to increase the absorption of nutrients from the surrounding water by slowing down its flow over the blade; while the second is to reduce drag on the blades, thus preventing the plant from being "uprooted" by water motion.

Like our giant kelp, the southern sea palm has two separate generations that alternate in its reproductive process. The large plants we see are the sporophytes, producing spores. The spores develop into tiny, microscopic gametophytes that produce the equivalent of sperm and egg. Once they fertilize and attach to the substrate, the individual becomes the much larger sporophyte generation.

Back in my "hippy-dippy-trippy, it's organic" days (have I left them?), I used to make kelp muffins out of dried giant kelp blades. I've never tried eating southern sea palm, although I'm told it tastes great with fava beans (oops... that was something else). My research did reveal that this species is eaten in Japan where it is known as Arame, and grows there as well as Peru according to that source. It is also considered a folk medicine with anti-allergic properties, and is used in some cosmetics as a moisturizer. I guess if the current economic recession gets any worse, I can always make a seafood stew with it, or give it to my future girlfriend. Who says plants aren't important?

© 2008 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. Please help me climb out of self-imposed poverty... buy my DVD's (see this link). Yes, take Dr. Bill home with you... we'll both be glad you did!

Southern sea palm, its holdfast, the upper end of the stipe and base of the blades, and a whorl of blades.

This document maintained by Dr. Bill Bushing.
Material and images © 2008 Star Thrower Educational Multimedia