Green Marine Algae: Friend or Foe?

Chaetomorpha Marine Algae

Hearing the words, “green hair algae,” “Bryopsis,” “bubble algae,” and some species of Caulerpa are enough to send some aquarists begging for mercy. Thankfully, in the algae world, not all is bad. There are the good, the bad, and the plain ol’ ugly. These are some of the green marine algae I’ve come across throughout my reefkeeping days.

Algae falls under three phyla with the red species as Rhodophyta, the green as Chlorophyta, and the brown under Chrysophyta. Some good species (and readily available in the hobby) of green algae are Chaetomorpha, Halimeda, and Ulva; some nuisance species are green hair algae, Valonia, and Bryopsis

Bornetella sphaerica: Not Reef Safe

Dictyospaeria cavernosa marine algae

Although this one small ball of Bornetella sphaerica green marine algae looks like a cluster of Valonia sp., it is just one singular mass. Thankfully, it is not very common in reef tanks.

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Bryopsis sp. Marine Algae: Not Reef Safe

Bryopsis Marine Algae

When I started in the reefkeeping hobby, Bryopsis algae was one of the worst plagues, especially of all the green marine algae. Practically nothing eats it in large quantities, it takes over everything, and it can grow in just about any aquarium, regardless of nutrient and light levels. Thankfully, there are now some very effective treatments.

Bryopsis looks like long feathery strands of green algae, and short clumps of it can sometimes be confused with green hair algae.

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Caulerpa Marine Algae:

For the most part, I really, *really*, don’t like Caulerpa in reef aquariums. While beautiful in species-specific tanks, it can wreak havoc on a beautiful, clean system. Many species of Caulerpa “go sexual” and can spread invasively throughout an aquarium. Manual removal is difficult due to strong hold-fasts (root-like structures that secure the algae from floating away) that can grow deep into rockwork, and manual removal usually ends in breakage (from which the algae can regrow).  Often, very few reef tank inhabitants eat these algae, as many are quite noxious.  While it’s a beautiful algae genus, I only recommend it for specialized aquariums only (such as macroalgae aquariums or “natural” reefs).

Caulerpa nummularia (“Mermaid’s Cup”): Reef Safe with Caution

Caulerpa nummularia marine algae

Caulerpa nummularia is no exception. Although it has very unique “mushroom-shaped” cups, I recommend this only for macroalgae aquariums or “natural” reef aquariums.

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Caulerpa brachypus: Not Reef Safe

Caulerpa brachypus marine algae

Since this algae was quite unhealthy, the distinguishing serrated edge is difficult to see. Caulerpa brachypus looks quite similar to Caulerpa prolifera with the addition of small points along the leafy frond edges. Once again, this species of Caulerpa follows the typical behavioral characteristics of its parent genus and is probably best kept out of a typical reef aquarium.

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Caulerpa serrulata: Reef Safe with Caution

Caulerpa serrulata marine algae

Caulerpa serrulata has blade-shaped fronds and is also known for “going sexual” in an aquarium. Again, the holdfasts can grow deep into rockwork, and manual removal usually ends in breakage.

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Caulerpa taxifolia or C. mexicana: Not Reef Safe

Caulerpa taxifolia or mexicana marine algae

Caulerpa taxifolia is a fern-like species on the Federal Noxious Weeds list and is nicknamed the “killer alga” due to its invasive and toxic nature. Use caution, as “No person may move a Federal noxious weed into or through the United States, or interstate….” (See the Federal Noxious Weed Act for full regulations.) This “weed” has outcompeted native seagrasses in the Mediterranean and off the coast of California. It is very tolerant of poor conditions and has few predators. Best method of eradication is manual removal. Caulerpa mexicana is very similar to Caulerpa taxifolia but has more tightly-segmented fronds.

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Caulerpa ashmeadii (“feather” Caulerpa): Not Reef Safe

Caulerpa ashmeadii marine algae

Although very similar to Caulerpa toxifolia, this may be Caulerpa ashmeadii or Caulerpa sertulariodes (this was a very unhealthy sample, so a proper identification is difficult). Due to its similarity in appearance and behavior, it is probably not an ideal reef tank macroalgae.

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Caulerpa prolifera: Not Reef Safe

Caulerpa prolifera marine algae

Similar to Caulerpa brachypus, Caulerpa prolifera (in the front right of the photo) has tall, leafy green fronds extending from a wandering root structure. However, Caulerpa prolifera is missing the hallmark characteristic of the serrated edges of Caulerpa brachypus.

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Caulerpa racemosa (“Grape Caulerpa”): Reef Safe with Caution

Despite growing Caulerpa racemosa for years, I do not have a photograph of it for some reason. Regardless, it is a vine-looking type of Caulerpa that resembles grape vines with small clusters hanging off the main stems. Although it shares characteristics with many other species of Caulerpa, it seems to “go sexual” less and has weaker hold-fasts than other species. To be honest, this species holds a small, special place in my heart, as I often traded bagful’s of it with my local fish store in exchange for my beginner-level corals.

Chaetomorpha sp. Marine Algae: Reef Safe

Chaetomorpha Marine Algae

Chaetomorpha is one of the most commonly encountered reef tank macroalgae. It grows in long spaghetti-like masses and readily utilizes nitrates and phosphates.

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Cladophora sp. Marine Algae: Not Reef Safe

Possibly Cladophora marine algae

I do not have a great identification on the algae in the photograph, but a species of Cladophora (maybe C. pellucida?) is currently my best guess. This algae is more wiry and less fern-like than Bryopsis, which made it easy to remove from the rockwork.

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Derbesia sp. (“Green Hair Algae (GHA)”): Reef Safe with Caution

Green Hair Algae

Green Hair Algae (“GHA”) is just what it sounds like…green algae that looks like a hairball. Hermit crabs, snails, etc. may eat it, as long as it doesn’t get out of control. Cleanup crews usually will not touch massive mats of GHA. I recommend manually removing as much GHA as possible to allow the cleanup crew to effectively remove the remnants. Limiting nutrients through reduced feeding, skimming, running granular ferric oxide (GFO) and activated carbon (AC) may help slow GHA’s growth. Adding a refugium with “good” macroalgae, such as Chaetomorpha, can help outcompete the GHA.

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Enteromorpha sp. Marine Algae: Reef Safe

Enteromorpha marine algae

This alga can be found in new, cycling aquariums, although I do occasionally find it growing in my tank whenever I know it’s time to replace my cleanup crew. Typically, it only grows to about two inches (about five centimeters) in length, although I have seen a few pieces grow to over 10 inches (about 25 centimeters). It is a cylindrical type of algae in the Ulva family (very palatable algae), and it is apparently quite delicious to my cleanup crew. Similar to the more leafy type of Ulva, it prefers cooler water (typically 77 degrees Fahrenheit or below) and higher nutrient water.

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Green Film Algae: Reef Safe with Caution

Green Film Algae

Although it’s not the most visually appealing algae, it’s a sign of good things to come in a new aquarium (and a sign of some issues in an established tank.) These microalgae films usually appear during the first couple of months of a new tank cycle, and they can cover the glass/ acrylic, rock, and sand. For a new aquarium, this is a critical part of the cycle: this algae feeds and helps establish a pod population! If it becomes a nuisance, it can be removed manually by scraping it or by utilizing a cleanup crew. It can also be reduced by limiting the nutrients in the aquarium.

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Halimeda sp. (“Money Plant”) Marine Algae: Reef Safe

Halimeda Marine Algae

As a calcareous type of marine algae, Halimeda grows slowly and does not become invasive. It requires a stable supply of calcium and seems to prefer lower nutrient levels. This algae can make a beautiful backdrop for macroalgae tanks, decorative refugiums, or even “natural-looking” reef tanks as it is not a target for most clean-up crews.

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Parvocaulis parvulus: Reef Safe

Acetabularia Marine Algae

Not to be confused with Brown Clove Polyps, this green marine algae grows green flower-like fronds supported by a calcified stem.  They do not appear to proliferate much in home aquaria; in fact, these only appeared for about a month on a shell, then vanished.  They are typically found in shallow, warm water (above 78 degrees Fahrenheit). The most crazy part about this alga is that it is unicellular; the nucleus is found at the base of the stalk.

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Ulva sp. (“Lettuce Algae”): Not Reef Safe

Ulva lettuce marine algae

Ulva grows in large, floating sheets, and in the wild it tends to grow nearer to the shore. Its natural habitat suggests it prefers higher (but gentle) flow, high light, and high nutrients. This makes it a difficult algae to cultivate in a reef aquarium as most aquarists place macroalgae in low flow, low light areas with competitive algae (such as Caulerpa and Chaetomopha.) Additionally, this algae is a great food source for…well…just about everything. Herbivorous fish love it, as do snails, pods, and even bristleworms up to a point. The algae shown was in a 10g aquarium with about 65gph turnover rate and a 150W metal halide lamp over it.

Update [6/6/2023]: As one of the readers shared in the comments below, if/when Ulva “goes sexual,” it turns into a nuisance, with growths nearly everywhere. Interestingly, according to various posts, nothing seems to eat it (or eat it fast enough) at this point. While I haven’t dealt with this personally, I would assume Fluconazole would take care of it.

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Valonia Marine Algae: Not Reef Safe

Valonia macrophysa (“Green Bubble Algae”): Not Reef Safe

Valonia Green Bubble Algae

Although green bubble algae won’t choke out a reef quite like Caulerpa, Valonia macrophysa is extremely invasive. Very few reef-safe inhabitants eat it, but some emerald crabs will (as always, just because some do, doesn’t mean all will.) The best prevention for this algae is a good quarantine system and manual removal outside the aquarium. There are some products available now that have varying degrees of success with eradicating it (although they come with their own risks of use).

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Valonia aegagropila (“Green Bubble Algae”): Not Reef Safe

Valonia aegagropila marine algae

Here is another example of green bubble algae, possibly Valonia aegagropila (although it is missing the characteristic branching segments, but this colony may be to small for branching yet). Fortunately for my aquarium, there wasn’t enough present for a good identification.

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Neomeris annulata (“Snake Polyps”): Reef Safe

Neomeris annulata marine alage

This calcium-based algae is always a treat for me to see.  It is not often found in home aquaria, and when it does appear, it seems to require a narrow set of parameters to thrive (I’ve only seen one case where these started to reach nuisance levels).

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Unidentified Green Marine Algae

Unknown Marine Algae

And then, there are the unidentified green marine algae, like this one shown in the foreground (note the Halimeda and Padina, along with some other species). With over 1500 known species of green marine algae, there’s no way this blog can cover them all. What neat species have you found? Post up in the comments!

Lobophyllia Rehabilitation

Lobophyllia Rehabilitation
Dying Lobophyllia

On 8 January 2012, I received this dying Lobophyllia coral. It was covered in several nuisance species of algae, and it had both old and new damage.

Dying Lobophyllia

Here it is overexposed for a better view of its condition.

Bubble Algae

As you can see, the bubble algae was quite severe.

Recovered Lobophyllia

By 13 May 2012, the coral was healed and regrowing.

Lobophyllia Rehabilitation

What a difference only four months can make!

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