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/A Diversity of Aquatic Life

The Red Algae, Division Rhodophyta

By Bob Fenner

Fauchea sp. 

At long last the red algae, particularly the coralline and encrusting calcareous forms, are receiving their due. These small, unassuming forms play a huge role in the real development of coral reefs, natural and aquarium; growing quickly, utilizing nutrients, packaging them into food-useful formats while generating oxygen... all under lower illumination than most co-photosynthetic animals or Caulerpas.

Though we often refer to coral in labeling tropical reefs, it is the algae, in particular the encrusting and branching reds that make up a good deal of the biomass and productivity of these important areas. Some estimates put the calcareous red algae at more than half of both; providing resistance to wave action, providing habitat and food for other living things.

Here we'll discuss what these "simple plants" are, their recruitment, control and culture.

Classification: Taxonomy, Relation With Other Groups

Talk about misidentified life-forms! Rarely are these organisms made out for what they are; algae. The larger red algae are kelp-like, with leaf-like fronds, attaching holdfasts et al.; the encrusting and branched varieties require closer inspection.

The simplest oxygen-producing life on this planet are the algae. They are for the most part autotrophic (self-feeding), have no complex organization (no leaves, roots, xylem/phloem vascular network); but do contain chlorophyll and other photosynthetic pigments.

The various Divisions (equivalent to the zoological taxonomic Phylum) of algae are classes on several criteria; pigments (by which we may generally identify them), storage foods, make-up of their cell walls and flagella where present.

Most aquarists are more interested in avoiding algae than knowing them better. Some algae are noxious, others indeed strange; all are worthwhile at least in terms of identification and control.

A Classification of Algae

Kingdom Monera (No nuclear membrane, "naked" DNA)

Division Cyanophyta- the blue green algae

Kingdom Protista (Beginning of eukaryotes)

Division Euglenophyta- Euglenoids

Division Pyrrophyta- Dinoflagellates

Division Chrysophyta- golden brown algae

Division Bacillariophyta- diatoms

Division Xanthophyta- yellow green algae

Division Phaeophyta- brown algae

Division Rhodophyta- red algae

Division Chlorophyta- green algae

The Blue-Greens (Division Cyanophyta) are closer kin to bacteria than other algal groups; they can make up slimy sheets or threads in nutrient laden conditions. Diatoms (Division Bacillariophyta) may make a brownish scum where silicate and other foods are available. The dinoflagellate (Division Pyrrophyta) Amyloodinium infects marine fishes... The algae are so diverse in their biology and use that we'll restrict our discussion here to the reds.

Red Algae: Rhodophyta on parade!

Actinotrichia fragilis (Forsskal) Borgeson 1932, Spikeweed. Close up and colony images, in the Red Sea. 

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Amphiroa foliacea.

This one in Tobago.

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Amphiroa tribulus  Small clumps of flattened randomly branched flexible joints. Whitish w/ pink highlights

Here in Key Largo, FLA.


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Bossiella, a common branched calcareous genus; note wing nut shape and reproductive conceptacles (bumps on the faces). This genus and Corallina are notably tolerant of human pollution, often growing luxuriously near outfall "boils".


Fauchea sp. 

Aquarium image.

Galaxaura sp. (maybe G. marginata, see: Galaxaura species in Hawaii) At right in Hawai'i and below, a bleached-out colony in the Red Sea, and a small piece off Cozumel. Distinct dichotomously branching species of pink to red color. 

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Gibsmithia hawaiiensis Doty 1963. S. Leyte 2013

Gracilaria/Ogo, a fabulous food genus for humans and fishes. Cultured for both uses. 

Verticals (Full/Cover Page Sizes Available)
Halymenia sp. Queensland, Australia. 

Jania, a tropical genus of jointed corallines; found in South Africa, South Australia and Southern California! This one in Belize. 

Jania adherens, Pink Segmented Alga. Appear as fine, tangled clumps. Widely separated dichotomous branching made up of tubular segments and flexible joints. Pink to red with white joints. 

Laurencia sp. Here in S. Sulawesi.

Lithophyllum the most widespread genera of marine algae are this and Lithothamnion, rock encrusting forms; all reefs, reef-tanks, both poles and everywhere in-between to 500 feet depths! Thin calcareous films to knobby, stony masses. 

Lithothamnion (prolifera?), encrusting Coralline Red Algae. Here off of Queensland, Australia. 

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Nemastoma sp. Class Rhodophyceae, Subclass Florideophycidae, Order Gigartinales, Family Nemastomataceae. Di.F close-up in the Red Sea and N. Sulawesi.

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Peyssonnelia sp. An encrusting Red. Class Rhodophyceae, Subclass Florideophycidae, Order Gigartinales, Family Peyssonneliaceae. Below, in an aquarium, Cozumel and the Red Sea. 
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Plocamium, a beautiful non-encrusting red, and a giant sea hare (Aplysia), off San Diego. Used to be made into greeting and post card "forests" ironed onto paper stock.

Poriteria hortemannii. Common on low intertidal to subtidal Hawaiian reefs. To 12 cm. Widespread in tropical and subtropical Pacific and Indian Oceans. Two-Step, HI pic.
Porolithon pachydermum, Reef Cement. The actual credit for holding reefs together, cementing sand and living bits together... and holding them there through storms and eons should go to this species. Here in Cozumel. 

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Rhodymenia sp.

Cebu, Philippines.

Wrangelia penicillata Cozumel 2011. 

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Natural and Introduced Range

The Red Algae comprise the Division Rhodophyta, Greek for "red plant". The more than four thousand described species are found worldwide tropical to temperate; more in number than the greens and browns that dominate cooler waters (the reds are predominant in the tropics). The reds are mostly marine with a few being freshwater and brackish.

Coldwater too! A nice encrusting red algae photo from San Diego, California with a Yellow Sponge and Seastar Pisaster ochraceus.

Being photosynthetic rhodophytes occur only where sufficient light reaches; and yet often in less opportune settings than green (D. Chlorophyta) and brown (D. Phaeophyta) algae; often in deeper, darker environs, or in surgy, intertidal zones.

Intertidal corallines. Here is a patch of Corallina left high and dry during a minus-tide off of San Diego, California, USA. Note the white parts, calcium carbonate skeletons that readily dissolve in dilute hydrochloric acid. 

The Encrusting Red Algae of marine aquariums are mainly of the non-jointed calcareous Subfamily Melobesioideae ("Mellow-beas-ee-dfpoy-day-ee"), in the Family Corallinacae (Order Cryptonemiales); they appear as thin crusts or nodular ridges. On close observation these films of cells are composed of calcite shells. Commonly seen are Lithophyllum, Porolithon (a major component of many algal reefs), Melobesia and Lithothamnion.

Encrusting coralline algae... common on the reefs of the world, natural and aquarium! Need both high and consistent biomineral content (Ca, Mg) and alkalinity... Lose easily to other groups/Divisions of algae given circumstances that favour them.

The major reef builders, Porolithon, a shot from Moorea, French Polynesia. Closely related to Lithothamnion, Lithophyllum. Amazingly important biologically and geologically in role as reef builders. Porolithon is the principal component of a majority of reefs, cementing and binding all other material/life together; providing for growth and control of reef margin. Drill holes thousands of feet reveal that fossil calcareous algal material continue all the way to bedrock!

The branched forms of calcareous red algae are mainly members of the Corallinaceae as well; but in a different Subfamily, the Corallinoideae, comprising the jointed (or articulated) corallines. Both groups are worldwide and common in tropical to sub-tropical seas. Most often seen are the genera Corallina & Bossiella.

Other forms of red algae are more typically soft and string-like or flat sheets in body (thallus) shape and flexible in texture.

For the completeness sake let's mention that there are other living groups of calcareous marine algae in the green (e.g. Halimeda, Penicillus, Udotea, Acetabularia) brown and red Divisions. These forms are much less common on the reef and aquariums.


Almost all red algae live attached to rock, or epiphytic on other algae, shells, marine plants; none free floating like Sargassum. Some are almost microscopic, a few we call kelps get to 8-10 feet, but most are 2-10 inches.

Selection: General to Specific

What? Actually buy them? Well yes, either intentionally (as in mail order culture businesses), or as "ride along" accidental introductions with live rock. Describing what to look for is kind of hard. Hmmm; signs of growth... not a bad smell to the specimen or water its in... See below re introduction for more notes important than actual selection of healthy specimens.

Collecting Your Own

May be done in almost every marine locale on the planet. For intended live specimens, do try to gather the attached substrate; and take only what you can use. A two week quarantine is encouraged to determine hardiness and eliminate/weaken unwanted "hitchhikers". The usual admonition here concerning checking with the local powers-that-be regarding permits, conservation...

Dead "artifact" collecting is a tougher matter than for other algae; crustose and calcified articulated types of algae aren't given to easy pressing and mounting.

Environmental: Conditions


These reds will grow on almost any hard surface, rock, substrates or aquarium walls; some under intense illumination, others with very dim lighting. They are most prolific in settings where high calcium levels allow rapid asexual growth.


Higher pH's (8.3), stable temperature, ready calcium concentrations (400ppm plus), generally low metabolite loads are conducive to growing calcareous marine algae.


Besides water quality, the quality, quantity and duration of useful wavelengths of light determine the well-being of captive algae. Different variations of fluorescent and metal halide lighting have been employed with good success. For the scope and extent of our topic here, suffice it to say that proper spectral mix (i.e. broad visible spectrum and upper UV), of adequate brightness and regular light cycle are necessary.


A common lack of understanding concerning algal culture is the role of filtration and circulation in promoting growth; at night algae (and other photosynthetic life) require adequate oxygen much the same as terrestrial plants. Other anomalies (e.g. pH, ORP) may be concurrent with lowered dissolved oxygen. Under crowding, aeration, complete circulation, good general maintenance are requisite for avoiding the ill-effects of dark-hour respiration.

Nutrient build-up and its consequent promotion of slime and filamentous algal growth can be avoided on several fronts. First and foremost by guarding against introduction... through foods, improper carbons, decor, etc.. By routine gravel vacuuming and filter media rotation/replacement. Through the use of an efficient skimmer and possible denitrating mechanism. And lastly for our purposes, the encouragement of other desirable macro-algae! For "goosing" the growth of encrusting reds, the periodic addition of Kalkwasser or similar product to supply needed assimilable calcium; boosting calcareous deprivation of other materials. While incorporating calcium carbonate as new growth, the encrusting red algae have the added benefit of sealing out other undesirable algae from the substrate.


Showing and growing reds is no problem; they're profuse under minimal "reef" conditions, often "popping-up" on their own and crowding your other specimens. Keeping them in check is done by assiduous scrubbing, scraping, making nutrient less available, and via biological control. Let's expand on these modes:

1) Elbow Grease: CAREFULLY inserting a blade or scrubber between the glass (not acrylic) may be your best route for removing encrusting reds from one or more panels of your system. Rocks, et alia decor and empty, dry aquaria can be mildly "acid-washed" with a dilute, weak acid (like vinegar) to dissolve away calcite skeletons.

2) Less Food: Obviously not adding calcium as a chemical supplement will limit your red algal growth. If you find you've become a red-algae farmer with or without supplementation; and you want to culture other photosynthetic calcium-using life, go to step 3)

3) Biological Controls: Chiefly involves using a suitable sea urchin or two, as most other critters find reds unappetizing. I advise adding them one at a time.

4) Limiting Biominerals and/or Alkalinity. If you have no other purposeful photosynthetic organisms that require these materials, or you can move them to another system...

Other Biology of Interest

Though red algae are, well, red in color, they do contain green chlorophyll. This pigment is usually masked by other pigments, in particular the groups definitive phycoerythrin. Depending on growing conditions a given species might appear pink, dark-pigmented red, purplish, live, brownish or blackish in color. The red pigment of the rhodophytes ("row-dough-fights") has allowed them to exploit greater depths (to 600') than other algal groups.

Reproduction, Sexual Differentiation/Growing Your Own:

The majority of red algae have a complex life history that includes three distinct plants per species. Now, follow along with me here. In addition to a sporophyte generation (one that reproduces by way of asexual spores) there is a male and female of similar size and appearance. Their differentiating characters are typically minute sex-cell generating structures. Reds are peculiar among algae in that their male and female gametes are non-flagellated, and get together passively through water movement.

Reproductive structures, sori (same word as for the ferns) in sporophytes, and conceptacles (in sexual phases) may be seen as raised bumps.


The pertinent facts concerning encrusting and other calcified red algae in the wild should not be lost on marine aquarists interested in "balanced" approaches in aquarium care. They are principal components of many, if not most tropical reefs, aiding in wave shock "control", cementing other media and life, converting nutrients into biomass under a wide range of conditions. To a large extent, it is the calcareous rhodophytes that make reefs hospitable to stony coral exploitation.

Could they, should they be encouraged in your set-up?

Bibliography/Further Reading:

Abbott, I.A. & G.J. Hollenberg 1976. Marine Algae of California. Stanford Univ. Press, CA. 827 pp.

Dawson, E. Yale 1966. Marine Botany; An Introduction. Holt, Rinehart, Winston. NY.

Dawson, E. Yale 1966. Seashore Plants of Southern California. U. of Ca. Press.

Delbeek, J.C. & J. Sprung 1994. The Reef Aquarium. Ricordea Publ., Coconut Grove, FLA. pp 544.

Fenner, Bob 1989. Some notes on algae and their control. FAMA 6/89.

Fenner, Bob 1990. Macroalgae for marine aquaria. Pet Dealer 2/90.

Fenner, Robert 1997. Red Algae; Branching its way into the aquarium. TFH 9/97.

Fenner, Robert 1998. The Conscientious Marine Aquarist. Microcosm, VT. 432pp.

Glodek, Garrett 1993. A lesson in plant taxonomy and systematics. FAMA 11/93.

Hunt, Philip 1996. Marine algae: friends and foes. Parts 1 & 2. TFH 9,10/96.

Kornobis, Stefan 1996. An attractive red alga, Hildenbranchia rivularis. TFH 10/96.

Michael, Scott 1995. All that algae; If it makes you feel any better, this is a common problem. AFM 8/95.

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