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Remember the song: "What's it all about, algae?" By the time this article's over you may feel like shouting out "Kelp, Kelp, call the carps. This piece considers marine algae as a whole, and brown algae in particular; for naturalists and aquarists. What they are, how they make their life, how to select and culture them.
History of Use:
Prior to World War I the study of marine plants was little more than an academic curiosity. With the German cutoff in World War I of potash (as a source of the element potassium) used to make fertilizer and gun powder, and Japanese agar (from red algae) in World War II research, processing and industrialization of seaweeds was expanded greatly.
Lay people, that is vulgar non-aquarists, experience with marine macrophytes is in accord with the implications of the word sea "weed"... noxious, useless, even bothersome; a bunch of stinky litter on the beach attracting flies, clogging their boat prop or fishing line. But these algae and plants fulfill nobler roles in the great circles of life, including useful human purposes; food, fodder, fertilizer, medicinal and pharmaceutical applications. Oh, and also as ornament and more for the marine aquarist!
Marine macro (versus micro) algae serve several important functions.
1) They stabilize the captive environment by introducing beneficial microbes, absorbing nutrients, and producing metabolites that mediate systems biologically.
2) Are good as bio-indicators, showing signs of degrading water quality, before your other livestock.
3) As controllers of undesirable algae growth, macro-algae utilize fertilizer and light that would otherwise be available to noisome forms.
4) Food; most all fishes and invertebrates augment their diets with algal material given the opportunity.
5) As habitat/ornament to break up the environment physically, providing hiding space and beauty.
In terms of biological taxonomy, the algae are grouped as photosynthetic organisms that are not quite plants. Some (the blue green algae, Phylum Chlorophyta) are more like bacteria than even other algae, in that they lack discrete nuclei and protoplasts.
In the grand scheme of things science-wise all algae are part of the Sub-Kingdom Thallophyta, meaning "all about the same plant body"; an allusion to their lack of organized tissues. Algae lack leaves, roots and the elaborate vascular structure (remember "xylem up and phloem down" from high school?) of "higher" plants. But don't weep for their apparent backwardness. As the noted astrophysicist Carl Sagan has quipped; "those cells are smart". Though individual cells are to some degree specialized as holdfasts (attachment organs), laminas, etc. each is capable of photosynthesis, respiration, excretion...
Another sure distinguishing characteristic between thallophytes and "true" plants is their form of reproduction. "Higher", "vascular" plants, Subphylum Embryophyta reproduce via sexual flowering. There are a few species of true, flowering marine plants, but their diversity, abundance and depth-range is limited.
Algae instead reproduce by way of a few variations on the theme of alternating between generations of sexual and asexual spore reproduction; they do not produce flowers. In most cases algae have complex life histories including an alternation of a tiny asexual gamete-producing generation with a sexual spore-producing generation. Please see the accompanying illustration.
Algae are divided into several phyla (or the botanical equivalent, Divisions) on the basis of several characteristics; some phylogenetic, others artificial. The three groups that include the macro-species of interest to us as aquarists, the can be distinguished on the basis of simple color! Green algae are in the Phylum Chlorophyta ("klor-oh-fight-ah"), red algae are the Phylum Rhodophyta ("road-oh-fight-ah"), and our group of brown algae, the Phylum Phaeophyta ("figh-oh-fight-ah"), which unless bleached out and dying are all some varying brownish hue.
The large size and conspicuous abundance of brown algae in Northern Atlantic and East Pacific shores have led them to be termed seaweeds. Though less numerous in species than red algae, browns dominate in bulk in nearly all temperate and high latitude coastal waters. There are several species of smaller brown algae adaptable to warm water systems. It's a shame these aren't offered as often as the various greens (e.g. Caulerpa, Penicillus, Codium) and reds.
More Commonly Encountered Phaeophytes: