Red Algae.

Black brush or "beard" algae (Audouinella and other species) are Red Algae, or Rhodophytes. Black brush algae is the frustrating bane of some well-managed long-running aquaria. It's slow to get started, but so tenacious it can't be removed from its favored sites along the edges of broad slow-growing leaves (Anubias is a favorite) without damaging the leaf. Bit by bit it can swamp a tank; it's so difficult to eliminate that it rates its own thread among algae notes at theKrib.com That's where you'll find Eric Olsen's photo illustrating black brush algae, if you're in any doubt about whether you've got it. And be sure to look at Neil Frank's rogue's gallery of red algae portraits.

The best single long article on red algae and how to avoid it and deal with it is by Neil Frank, once again. Frank, the editor of The Aquatic Gardener who first popularized Siamese Algae-Eaters, summarized several methods for "Control of red algae in the freshwater aquarium" in a 1996 article in T.A.G. and in another version published in F.A.M.A., Nov and Dec 1996, now archived for you in the Aquatic-Plants Digest. or at theKrib.com. What he has to say about red algae--— "beard" or "brush" algae--— often applies to other kinds of algae. In spite of his confusing lapse calling these algae "Rhytophyta," if you follow up only one algal link here, this is the one. But George Reclos successfully treated black brush algae with a syringe of hydrogen peroxide, at some cost to his plants. Read his detain led and excellently illustrated article.

The Rhodophytes do have chloroplasts that produce chlorophyll. It's the same chlorophyll a invented by cyanobacteria that other algae use, but the green is masked by a photosynthesizing auxiliary pigment, phycoerythrin, that is unique to the red algae. Phycoerythrin and other phycobilin pigments absorb blue light and reflect red, which gives many marine red algae a pronounced bronzy-red cast. Almost all the red algae have stayed in the sea, where they include reef-building "coralline" algae and the nori that wrap sushi. In the small group of freshwater red algae, which include Audouinella, phycoerythrin levels are reduced. So black brush algae is not always very black, sometimes more of a purplish-gray.

Few fish are willing to eat "red algae." ...but Siamese Algae-Eaters, Crossocheilus siamensis, are generally undeterred. You can bet that their track record on this score is closely followed: some aquarists are convinced that SAEs only crop the new growth and don't eradicate the basal growth. The solution is to introduce the Siamese Algae-Eaters before black brush algae overwhelms the tank. I'm inclined to prune out any leaf showing some Audouinella tufts along its edges. It's no problem! even slow-growing Anubias is more inclined to replace a leaf if you'll first remove one. Gravel showing tufts of black brush algae should be siphoned out and discarded. Sometimes I drag the edge of a credit card over the gravel to roll algal growth away from the light. A mulch of beech leaves discourages algae on the substrate in some of my tanks. Other ornaments can be boiled, bleached, rinsed and sun-dried... and the stuff might still come back: Lazarus algae.

It's been noticed that red algae are especially troubling in aerated soft waters with plentiful free CO₂. I can attest to that. Neil Frank noted that when a LFS buffered a display tank to neutral pH, red algae died back considerably, and he notes that they're never a problem in an alkaline Rift Lake aquarium. Brush algae are troublesome when aquarium waters are high in nitrate and phosphate, and free iron in the water encourages problem algae too: keeping your iron fertilizer in the substrate, not in the water, is part of the answer.

Green Algae.

Identifying green algae. Okay, now at last we're really talking about the real green algae. Aren't we? On the whole, we're all stumped when we try to be scientific about identifying the species of real green algae (Chlorophytes) that we find in the aquarium. It reassured me to read Diana Walstad telling how she gave up on algal taxonomy after she'd had a biologist examine some "green mat" algae.

"Under the microscope, the algae turned out to be a conglomerate of many separate species. The two dominant genera, identified by their filamentous branching pattern and characteristic spores, were Oedogonium and Pithophora... they appeared to be a mixture of several species."

Cyanobacteria types appeared in her mat as small blue-green bulbs attached to the green algae filaments, and additionally she found that there were small populations of diatoms. Thus, Diana Walstad decided to stick to common descriptive names to describe the dominant type of algae in the mixed biofilm. I'm sure that under higher magnification many fungi and bacteria would also have been found co-existing with Diana Walstad's algae, because this uncategorizable mix is characteristic of the biofilm.

Algal meadows. Each species in this mixed community has its particular requirements and its characteristic range of tolerances. And when resources are constrained to a limiting-point, various types of algae can be assumed to have varying competitive abilities. If you watch a freshwater pond in the temperate zones through the season, you'll usually see a progression of algal types. Conditions like warmth and daylight hours are changing, which tip the balance in favor of one type of algae over another. You've probably noticed during the lifespan of your own aquaria that at first one species of algae is prominent enough to rate as a problem, but then it takes a minor role, as a different species succeeds it. Not only are conditions of light spectrum and nutrients evolving in the aquarium, but the algae are also carrying on chemical warfare in their competition for resources.

Algal succession and allelochemicals. Many species of algae produce allelochemicals, which suppress the growth of other algae. Investigators found that allelopathic chemicals released by the filamentous alga Pithophora tended to suppress other algae, especially the single-celled pelagic algae responsible for "green water." In Ecology of the Planted Aquarium, Diana Walstad reported a 1969 study, in which aquaria with 24-hour lighting turned green in a week, but not identical tanks containing active Pithophora. Though the toxins of a successful alga may help suppress its competitors, directly or indirectly they may also be encouraging the species that will take that alga's place. Dying algae can release phytotoxins, an effect recognized in drinking water by unappealing tastes produced by otherwise acceptable algae after chlorination. This is a minor problem in water treatment systems, but it can be a major problem in the narrow confines of an aquarium. After you've done some successful algae killing, water changes are in order.

So, algal species tend to ebb and flow in whatever niches aquaria offer. Algal species follow one another in sequences of blooms, all responding to the resources you make available to them and to their own interactions, such as competition for a space in the light, or chemical warfare ("allelopathy"). The niches change too, as plantings and bacterial communities mature, and the bioload changes. And resources for algae also shift under the pressure of grazing patterns that are established by the particular group of algae-eaters you've set loose upon them. Each algae-eater has a characteristic repertory of algae it favors. Young fresh growths, even of preferred algae, seem to be favored over older mature growths. Some algae being faster and better adapted than others to re-colonize a cleaned surface, the result of all these effects taken together is an algal meadow, a mosaic patchwork of algae that develops on undisturbed surfaces, such the rear glass of the tank. Once in a while it's worth scraping the algae off a side wall to watch this process unfold again from the start. You'll see that the first growth is normally a quite uniform blanket of one pioneering species, probably the familiar one on the front glass where you clean every couple of weeks.

If you are curious to see the most diverse growth of algae on your side glass pane, try this: take a plastic pocket comb and snap off the end guards. Now scrape a set of closely parallel "furrows" down the algal meadow on the glass, in a single pass. Leave the rest undisturbed. You'll need a magnifier to watch the developments along these linear "edges." There's a parallel here with some experimental sustainable logging techniques in tropical forests ...but that would be taking us a long way from tropical fish.

"Succession" is the ecological term for these phenomena. For non-aquarists, familiar examples of succession occur when unplowed pasture reverts in stages to woodland, then forest.

"Good" filamentous algae. A non-invasive (in the aquarium, though perhaps not in a pond) filamentous algae (I'm calling it Pithophora but is it Cladophora ægropila?) that was given to me a year ago seems to help clear green water and to compete with more noxious algae, maybe by scavenging the available phosphate that algae require in an uninterrupted supply, or maybe by subtler allelopathic chemistry. This algae has elongated narrow cells linked into branching chains that are wool-like and coarse (not slimy) to the touch, characteristics that give it common names like "Cottonball Algae" and "Green Wool Algae." At theKrib it's referred to as Hair or Thread Algae. Baensch's translators are alone in dubbing it "Green Bunch Algae. Usually it grows on the bottom, attached at a few points to rock or gravel, but trapped oxygen bubbles may make it buoyant. In ponds it may form dense surface mats. Its color may vary from lime green to dark olive greenish brown. Similar algae-balls (Marimo) from Lake Akan in Japan are treated with a curiosity and respect that algae seldom inspire. Now something very like them is coming onto the aquarium market.

Links. A good portal to algae on the web is hosted at Southwest Missouri State University's biology site.

"Welcome to the world of algae" is the self-explanatory site run by the University of South Africa. Most of their algal interest focuses on marine algae, but look up the links under "alga groups."