Dive Dry with Dr. Bill

#535: The Good "Brother"

Ever since the winter of 2005-06 I've fumed and railed about the nasty invasive Asian seaweed Sargassum horneri. It is back in force this winter just like it was in the winter of 2007, which followed a period of warm summer and fall water temperature similar to this year.I'm still trying to get the invasive species division of the California Dept., of Fish & Wildlife (formery Fish & Game) to authorize attempts to control it in the Casino Point dive park. As I've written before, apparently the language for such marine protected areas (MPAs) does not distinguish between native and non-native species... a glaring omission!

This week I want to talk about that Sargassum's good "brother." I'm referring to Sargassum palmeri which is a native species in the same genus. Unlike its bad brother, it belongs right here in southern California waters.

During my tenure as Conservancy vice-president, I learned that plants are the Rodney Dangerfields of ecosystems... they don't get no respect. During the Community Awareness Programs we conducted about our ecological restoration programs, the public did not seem to understand why plants were important. Why were we so concerned about eliminating the feral pigs and goats that threatened them? Why was it so important to establish good conservation measures to ensure the survival of our endemic plants, the ones found only on Catalina?

This lack of understanding of the critical role of plants in any ecosystem is a glaring example of how science education has failed, at least in the field of biology. Plants are indeed critical because they are the base of most of an ecosystem's food webs! Without plants for the herbivores to munch on, there'd be no meat for the predators to chew. Without plants, there'd be no vegetarians or vegans... and those of us who like a nice barbecued steak would be up a creek. Let's not even raise the issue of how plants generate oxygen that some of us like to breathe!

The same is true in the marine world. Although scientists no longer consider kelp and other algae to be plants, they serve the same purpose in King Neptune's realm as the grasses, herbs, shrubs and trees do on land. Herbivorous fish like the opaleye need them to munch on. Carnivores like barracuda, moray and sharks need seaweed eaters and their other predators to sustain them. So anything that affects the primary producer level, the organisms that convert sunlight into carbohydrates and eventually protein, can have a serious impact on the rest of the marine ecosystem... and us!

Now in years like this, the Asian "devil weed" Sargassum horneri largely outcompetes our native seaweeds (including giant kelp) for substrate to attach to, light to photosynthesize with and the nutrients necessary to produce carbohydrates and protein. Today the dive park looks like a submarine wheat field due to the dense growth of this intruder. It forms a virtual monoculture that prevents our native species from growing and reproducing. Biodiversity in our waters plummets when it dominates. Our very own Sargassum palmeri has a tough time dealing with this.

The scientific genus Sargassum is very complex and contains more than 150 different species. Most readers are probably familiar with the Sargasso Sea, named by Portuguese explorers for a circular gyre in the Atlantic Ocean filled with floating Sargassum of another species. Surprisingly enough, I forgot to film it while diving in the Bahamas. We have four species here in SoCal. Sargassum palmeri is most common out here on Catalina while S. aghardianum is more prevalent on the mainland. S. muticum appeared in our waters after working its way south from Puget Sound where it was probably introduced on oysters imported from Japan in the early 1900s. It is therefore an exotic, but hasn't lived up to the invasive threat we thought it might be back in 1970 when it arrived here. For some reason it does not compete well against our native seaweeds. And then there's the "devil weed" which I've written plenty about already.

For you budding biologists who want to know how to identify it, Sargassum palmeri is distinguished from the species in having "blades on all orders of branches divided into several flattened filiform sections" in Abbot & Hollenberg's Marine Algae of California. Phycologists, scientists who study algae, may understand its description there as :Thalli perennial, 45-70 cm tall, arising from solid, rugose, more or less discoid holdfast; stipe terete, verrucose, to 1.2 m long..." Did I lose you? Me, too. See what it takes to be able to identify algal species? Do you still want to do that for a living? Thankfully, there are a few who do.

Sargassum palmeri has very fine blade structures, thin and elongated. Apparently these are the sterile blades that develop after the alga has released its gametes and the other blades have disintegrated. Sexes are separate. The structures containing the gametes are best developed during winter. The species is found in the shallow subtidal and occasionally in the intertidal from Santa Catalina down to Isla San Benito off Baja California. It was first described from specimens taken off Guadalupe Island. I wonder who dove to collect it there... I hope it was off-season for the great whites!

Now I'm about to depart for the tropics again. I've become a true "warm water wussie" after my stay in the Bahamas a few months ago. Besides, the darned exotic Sargassum makes it hard to find anything here to film. So I'm now in the Philippines diving in Anilao and Puerto Galera for several weeks. Hopefully by the time I get back, the waters here will be warmer! Oh, don't worry... I've written plenty of my columns to sustain you during my absence and help cure your insomnia. I always look out for my readers!

© 2013 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 29, 10:00 AM weekdays and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. You can also watch these episodes in iPod format on YouTube through my channel there (drbillbushing). 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!

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The exotics, "devil weed" Sargassum horneri and the less invasive Sargassum muticum; our own native Sargassum palmeri.

This document maintained by Dr. Bill Bushing.
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