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/A Diversity of Aquatic Life

Macro-Algae Use in Marine Aquariums

by Bob Fenner

Halimeda sp. in Tobago

New Print and eBook on Amazon

Marine Aquarium Algae Control

by Robert (Bob) Fenner

"Okay this will do". Here I go over the side again, looking for productive spots for collecting good numbers of "key" Caribbean fish species (i.e. angels, hogfishes, blue tangs...) in Belize. The last few years have seen my associates and hapless vacationing friends aiding other "not yet ready for prime time" collection and distribution sites in this part of the western Atlantic.

"No, not enough rock, or angels". (only one queen, Holacanthus ciliaris, and a couple of grays, Pomacanthus arcuatus). Hardly economical in terms of the time to "make a set" with the fence net, and drive the paltry catch into it. The Belizean coast, nestled twixt Mexico's Yucatan and Guatemala to the south, is about the best place in the world to be a marine collector. With the world's second largest barrier reef (to Australia's GBR), and thousands of square miles of calm, shallow, inner reef hunting grounds. Alas, there are but a few economically desired species hailing from these waters; so up into the boat I come, in search of more fertile spots.

"By the way, is there some reason why we're not collecting non-fishes?", I ask the crew. There are currently only three licensees involved in the trade in this small (8,867 square miles) sparsely populated (about 250,000) Central American country. All three are focused on the high dollar fishes found only in this part of the world in huge, can you say insatiable (?), demand in the U.S., Europe and the orient. With the advent of biotopic presentations, thematic assemblages that attempt to mimic the environment and biota of a given geographic setting, let alone the ever-growing "reef-craze", where is the demand (for here is supply in abundance) for the algae and invertebrates of the Caribbean?

Ah, as is all too often the case, Ofttimes the explanation as to what gets done (or who gets to go out with whom) is "they asked". My Belizean hosts are incredulous; "people will really pay for this stuff?" "Wow, it would be great to not hold up shipments to get to a minimum box count or freight weight break, using these other items to fill out an order."

Good indeed, for all concerned parties; several types of macro-algae are available in quantity from here that are useful to the marine aquarium hobby; for functional (filtration, food, water quality...) and decorative/habitat applications.

Here's a listing of the currently most popular/used species of macro-algae from the area between the Bahamas and Brazil, and how to select and care for them.

Classification: Taxonomy, Relation With Other Groups

A few fast words on algae altogether and their use to us as aquarists; they are definitely a wide assemblage. Most forms/species are microscopic, like the Diatoms and Dinoflagellates, as are many of the Greens, Golden-Browns, Euglenophytes, and Blue-Greens. These are termed "microalgae", an arbitrary descriptor signifying only size, though most are of nominal use to hobbyists. Further, you should know that most of these micro types and several of the "macros" are considered undesirable for aquarium applications. Some grow out of control, covering other more-desired stock, using up nutrients, even driving water quality parameters like Redox and pH haywire. To restate, our intention here is to cover the most commonly available and useful types of macro-algae from the tropical west Atlantic. Thus we'll confine ourselves to but a few of the genera and species of green, brown and red algae found and collected there.

So what are algae, or better still, how can the algae be characterized? They're considered the simplest oxygen-producing life; algae are autotrophic (self-feeding), have no complex organization (no leaves, roots, stems, xylem/phloem vascular network); but do contain chlorophyll and other photosynthetic pigments.

Algae are not, strictly speaking, true or vascular plants, by definition lacking seed embryos with their internal development and the structural complexity/division of labor of these "higher forms". Hence the Subkingdom of most algae (excluding the blue-greens which are actually more closely related to bacteria) is called Thallophyta, roughly meaning "all or about the same 'plant' body" in reference to the lack of specialized structures.

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

A Classification of Algae

Though all algae contain chlorophyll, the major Divisions can for the most part be distinguished on the basis of their predominant apparent color, due to other photosynthetic pigments that mask the chlorophyll green.

Kingdom Monera (lack a nuclear membrane, have "naked" DNA)

Division Schizophyta- the bacteria

Division Cyanophyta- the Blue Green Algae, aka Cyanobacteria (because that's what they are...); often slimy, slippery blackish smears or threads. Generally out-competed in well-maintained systems. A blue-green algae green, Scytonema ... Note that BGAs lack plasmids, organized nuclei, double-layered cell wall… more like the bacteria they really are than the true algae (Sub-kingdom Thallophyta)

Kingdom Protista (Beginning of Eukaryotes or "true cell-walled" life)

Division Euglenophyta- Euglenoids; freshwater, marine, mud.

Division Pyrrophyta- Dinoflagellates; unicellular, get around via 2 flagella. Marine, brackish, fresh, sand. Includes Amyloodinium the "rust disease" that infects marine fishes.

Division Chrysophyta- Golden Brown Algae.

Division Bacillariophyta- diatoms; silicate based exoskeletons, unicellular. Marine, freshwater and soil.

Live diatoms through a microscope and a prepared skeleton of Biddulphia sp. under a scanning electron microscope.

Division Xanthophyta- Yellow Green Algae, mostly non-marine.

Division Phaeophyta- Brown Algae/Kelp; marine, mostly littoral. About 1,500 species.

Division Rhodophyta- Red Algae/Kelp, including Corallines; mostly marine, about 4,000 species.

Division Chlorophyta- Green Algae; most freshwater, a few marine, some terrestrial.

Halimeda in Tobago, the joy of Bryopsis in an aquarium.

Family Caulerpaceae- Caulerpa Green Algae

Kingdom Metaphyta- the true plants; have leaves, roots, stems.

Varieties of Caribbean Algae of Primary Use to Aquarists:

Delimited here by two criteria; those of principal suitability to aquarium care, and secondly the species generally collected for such use.

Greens; the Chlorophyta are as a rule the most common and easily kept varieties. In part, this is probably due to our preference (otherwise read as bias) toward "greens" as many of the red algae are just as tough and ubiquitous in marine environments. Most commonly encountered genera and species include:

Acetabularia; Mermaid's Cups, are comprised of a long slender stalk capped with an inverted cup. These can be sensitive, getting easily beat up in collection/transport. These are about a quarter inch across the tops... in the Bahamas.

Caulerpa; with their distinctive horizontal creeping stolons and sand-penetrating rhizoids, come in many different shapes per species and growing conditions; some look like feathers, barb-wire, grapes and straps. Odd as it may seem, the biggest problem with this genus is that it's too vigorous in it's growth, using up nutrient, light and space you might want for other livestock, and possibly shifting water chemistry in its exuberance. Keep them trimmed back. Some favored species are Caulerpa prolifera, Caulerpa sertularioides, Caulerpa racemosa, Caulerpa mexicana. Caulerpas are non-calcareous and consequently sought out ahead of calcium encrusting forms by herbivores. Loss through the reproductive process is also a concern with these easily grown greens (See Sprung, 1989, Wilkens, 92). Some examples of the many Caulerpa species below.

Caulerpa cupressoides, Aquarium

Caulerpa racemosa, Cebu, Close-up

Caulerpa sertularioides, Belize

Halimeda; cactus algae, this genus was amongst the earliest cultured (1960's). It is one of the toughest mineralizing (calcified) genera available. Six species come into the trade of which H. incrassata, H. discoidea and H. opuntia are my favorites.

Here's a grouping of Halimeda in the Cook Islands.

Penicillus; "shaving brushes", named for their uprising tufts of filamentous "bristles" on the apex of a upright "handle". Sand-anchored specie, mainly Penicillus capitatus and Penicillus dumetosus. Shown: Penicillus dumetosus in Belize and an aquarium specimen.

Udotea are fan-shaped algae, 3-8" in height, they and the Pine Cone Algae of the genus Rhipocephalus have the same care requirements as Halimeda. Some young Udotea in the Bahamas shown.

Ulva growing prolifically on a waterfall at the original (San Diego, 1963) Sea World 2014.

Red Algae, the Rhodophyta. Spurious or incidental forms include the encrusting varieties such as Porolithon and filamentous forms (e.g. Centroceras, Wrangelia) that piggy back on live rock and sessile invertebrates.

    Articulated and encrusting forms of red algae are of extreme importance to shallow marine environments. To some large extent, they contribute mightily to reef building and nourishing of all life there. If you look close you will find rhodophytes in every near shore tropical to temperate setting and you may be "blessed" with some freebies on your live rock purchases. There are other, multi-branched forms; Galaxaura, Jania, Pterocladia, Laurencia and Amphiroa as well as plate shaped varieties that find their way into the trade from time to time.

Browns; the Phaeophyta, are the least used, and hardest group to culture in captivity. Members of the genus Dictyota can have exquisite highlights of green and blue. Keep your eye on iodine and iron levels in particular if you're trying them. Add Turbinaria.

Sargassums floating and attached make for endless possibilities in observing the many forms of life associated with the genus (Sargassum fish, crabs, shrimp...) .

Scroll-like algae of the genus Padina must be purchased attached to their natural base. Once acclimated they do quite well.

Angiosperms: Lastly a mention of the True, Flowering Plants, especially turtle grass, Thalassia testudinum. If you're looking for a real biotopic challenge do consider real vascular plants.


Most specimens offered are something in the range of 3-5 inches long/high. About what they are on the reef.

Selection: General to Specific

1) Stiffness: I'm serious here. For the encrusting and calcareous types (most of them here), poor collection, handling and holding practices will show up in decalcification. Poor lighting, low pH, et al. result in flaccid specimens. Leave them.

2) Signs of growth... are the tips and base complete? Is the base intact with it's holdfast? Leave them be.

3) Earthy-Sea smell definitely not a rotting smell to the specimen or the water its in.

4) Source; If yours don't just "show up" on live rock or other hard invertebrate material, and you can't find them through a LFS (local fish store), consider ordering your macrophytes through one of the culture or collecting businesses to be found through the classifieds in hobby magazines.

Environmental: Conditions


The following generalizations are, of a necessity, just that. Much more specific information should be sought (and is available, see bibliography/further reading below) before plunking down your hard-earned dollars on this livestock.

As a rule the attached forms should be purchased attached, and more of similar solid material installed for spreading as well as chemical environment amelioration. Burrowing forms require anaerobic to oxygen-limited substrates; either blind potted in a chemically-inert pot, and/or without undergravel filter use. Fine crushed calcareous (coral sand, aragonite...) material is better; overlaying a live-sand bed or not. Two or more inches of depth are required for sand-anchoring types.


Higher pH's (8.0-8.3); stable temperatures in the low 70's to low 80's; ditto for specific gravity (1.023-1.025) as these organisms are stenohaline and appreciate constancy.

Marine macro-algae require the same 16 essential nutrients as aquatic and terrestrial plants; most are readily available in aquarium settings, but a few listed here may become rate limiting in crowded, poorly maintained settings.

Calcium concentrations are obviously a concern with most of these forms as many are metabolic calcium depositors. A concentration of 400 ppm plus should be strived for. For folks with "boosted" systems utilizing powerful metal halide lighting, a calcium reactor tied with CO2 infusion is ideal. For less-demanding applications periodic chemical addition is fine.

Iodine likewise is a valuable, often limiting element in culture of these algae. As with hermatypic corals supplementing and testing to 0.4ppm is desirable.

Iron can be of concern with folks utilizing natural seawater or promoting rapid and large algal growth. Synthetics purposely come oversupplied with high concentrations of iron; "real" seawater users should supplement theirs to 0.1 ppm with regular water changes.

Be wary of poor filtration or water changing practices that leave your system with too much organic source nutrient (or overzealous supplementation). You want your nitrates to be low (less than 10ppm) and little phosphorus content (less than 2ppm), not difficult as the algae should be taking up these dissolved nutrients.


Besides water quality, the quality, quantity and duration of useful wavelengths of light are most important in determining the health of captive algae. Variations of regular, high and very-high output fluorescents and metal halide lighting have been employed with good success. A good rule of thumb for those with light meters calls for ten to twelve hours per day of full-spectral lighting.

13,000-16,000 lux for green macro-algae

7,500 to 11,000 lux for brown macro-algae

2,000 to 8,500 lux for red macro-algae

An alternative guideline might be 2-5 watts per gallon, very roughly, depending on species, depth of tank, and much more.


Nutrient build-up and its consequent promotion of slime and filamentous algae growth should be avoided on several fronts. First and foremost by guarding against introduction... through foods, improper carbons, decor, etc.. By routine water changes/gravel vacuuming and filter media rotation/replacement. Through the use of an efficient skimmer and possible denitrating mechanism. And lastly, the encouragement of other, desirable, macro-algae!


May be done concurrent with live rock/sand placement, but as the saying goes in grading school papers, "when in doubt, count it out"; it's better to make sure the system is cycling before putting in marine algae.

Algal Control

Too much of a good thing? You betcha. You want to keep them going but not growing to the extent they take over, deprive other tankmates of room, light or food... how to keep them curtailed?

1) Elbow Grease: Gingerly wipe the viewing panel(s), keeping in mind that cleanliness is not sterility, and that other than seeing into the system, the other surfaces actually benefit from having growth on them. Purchase some fish-tank-dedicated full length gloves, tongs and other pruning gear and get into a regular routine of weekly inspection and trimming.

2) Less Food: Being careful to make especially major nutrients like nitrates and phosphates limited is important. Be on your guard against overstocking and overfeeding fishes and invertebrates, putting in too much in the way of chemical supplements for your macro-algae, and to a lesser extent, chemical food from your tapwater and synthetic salt mix.

3) Enhanced Filtration: Better foam fractionators utilizing ozone, preserving and increasing Redox potential will increase macro- and decrease undesirable micro- algae growth. If/where practical chemical filtration can be of service.

4) Biological Controls: Involves using suitable predators (dwarf angels, some snails and hermit crabs, tangs...) adding them one at a time until a happy balance is achieved.


Marine macro-algae of several types are readily available and arrive in good shape where wild collected and handled properly from Caribbean waters. Progress is being measured by their increase in species and volumes employed by aquarists.

Though I don't accept that "Mother Nature" uses only algae as a "filter" (let's face it "ma nature" is the filter), it is one of the fundamental means of concentrating inorganic and organic material into less noxious, more useful (ornament, habitat, food, oxygen) matter for wild and captive systems.

Given simple consideration of lighting, water quality, controlled predation, and the elusive initially healthy specimens, all marine systems can benefit from macro-algae use. For biotopic marine presentations of the western Atlantic they are a must.

Success with marine macrophytes is simply a matter of selecting the proper types from the proper places and maintaining them under proper conditions. Are you ready for the challenge?

Bibliography/Further Reading:

New Print and eBook on Amazon

Marine Aquarium Algae Control

by Robert (Bob) Fenner

Algaebase: http://www.algaebase.org/

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

Baugh, Thomas M. 1988. Caulerpa prolifera; an attractive species which does well in the marine (sic) aquaria. FAMA 5/88.

Black, Tom & Alex Bielawski. 1971 Algae culture. Marine Aquarist 2(2):71.

Blackburn, Wayne. 1989. Plants in the marine system. FAMA 7/89.

Bold, Harold C. & Michael J. Wynne. Introduction to the Algae. Prentice-Hall, NJ.

Brawer, Marc. 1971. So you want to keep marine plants. Marine Aquarist 2(2):71.

Brelig, Allen. 1993. Plants in the reef system. FAMA 6/93.

Caribaldi, Lou. 1973. Seaweeds are not weeds. Marine Aquarist 4/(4):73.

Colin, Patrick L. 1978. Caribbean Reef Invertebrates and Plants. T.F.H. Publications, NJ. 512pp.

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.

Dewey, Don. 1979. Marine algae; a key ingredient to the successful saltwater system. FAMA 8,9/79.

Emmens, C.W. 1991. Algae. FAMA 8/91.

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. The Conscientious Marine Aquarist. Microcosm, VT.

Gamble, Sam. 1995. Algae curse: a new view. FAMA 8/95.

Giovanetti, Thomas A. 1989. Caulerpa; enemy of the miniature reef aquarium? FAMA 10/89.

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

Glodek, Garrett. 1996. All you ever wanted to know about marine plants (selected bibliography). FAMA 1/96.

Graff, Rick. 1993. Getting control of microalgae; how to deal with this problem in reef tanks. AFM 1/93.

Hoff, Frank H. Marine algae of the genus Caulerpa. FAMA 10/83 & 4/84. 

Hoff, Frank. 1988. Coral reefs of Florida, part II, the algae. FAMA 1/88.

Humann, Paul. 1996 (93 third ed. revised). Reef Coral Identification (including algae): Florida, Caribbean, Bahamas. New World Publications, Inc. FL. 239pp.

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

Jacobs, William P. 1994. Caulerpa; this tropical alga is the world's largest single-celled organism. Yet it differentiates into a complex of structure of leaves, stems and roots. Scientific American 12/94.

Kraft, Herbert. 1959. Caulerpa prolifera; a plant for salt-water aquaria. TFH 5/59.

Mancini, Alessandro. 1995. Tropical algae of the genus Caulerpa Lamouroux, 1809. FAMA 6/95.

McGregor, Glenn. 1996. Cyanobacteria. FAMA 8/96.

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

Minor, K.I. 1995. What is that? Pt II: Valoniaceae Pt. 6: Calcareous algae. FAMA 6,10/95.

Paletta, Michael. 1990. Eliminating problem algae. SeaScope v. 7 Fall 90.

Prasek, Ed. 1995. Mirror & slime algae; are they driving you crazy too? TFH 7/95.

Smit, George. 1987. The ecological marine aquarium, part four The use and benefits of live rock and Caulerpa in marine aquariums. FAMA 8/87.

South, Robin G. & Alan Whittick. 1987. Introduction to Phycology. Blackwell Scientific Publications.

Sprung, Julian. 1989. Reef Notes (on reproductive loss of Caulerpa). FAMA 2/89.

Thiel, Albert J. 1988. Keeping and growing marine macro-algae. FAMA 8/88.

Tullock, John H. 1983. Growing marine "plants". FAMA 3/83.

Wecsler, Lawrence H. 1975. Algae in the marine aquarium. TFH 2/75.

Wilkens, Peter. 1992. Green water in the marine aquarium; the sexual reproduction of Caulerpa algae. TFH 2/92.

Wilkens, Peter. 1994. Red calcareous algae: Creator of coral reefs. Aquarium Frontiers Spr. 94.

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