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Algae: Green

Algae isn’t just for the ocean anymore.  It’s all around us, and its use in daily life is growing more frequently.  Even as I’m sitting here writing this, my husband brought home a fruit drink for me – Naked’s “Green Machine” that contains spirulina and blue green algae.  Cool coincidence!

Reef aquarium macroalgae amaze me for their beauty, diversity, and…let’s face it…most of us thought when we started this hobby that the concept of growing algae in a refugium to keep algae out of the display tank was just plain nuts.  These are some of the green algaes I’ve come across throughout my reefkeeping days.

Caulerpa nummularia: Not Reef Safe
For the most part, I really, *really*, don’t like Caulerpa in reef aquariums. While beautiful in species-specific tanks, it just wrecks havoc on a beautiful, clean system in my opinion. Many species of Caulerpa “go sexual” and spread invasively throughout an aquarium. Manual removal is difficult due to their strong hold-fasts, and very few reef tank inhabitants eat these algae as many are quite noxious. Caulerpa nummularia is no exception.  Although it has very unique “mushroom-shaped” cups, I recommend this only for macroalgae aquariums or “natural” reef aquariums.

Caulerpa prolifera:  Not Reef Safe
This is an invasive species of caulerpa with leafy fronds that can “go sexual” in an aquarium. The holdfasts (root-like structures that secure the algae from floating away) can grow deep into rockwork, and manual removal usually ends in breakage (from which the algae can regrow.) When it goes sexual, it can spread throughout the entire system. While it’s a beautiful algae, it is recommended for specialized aquariums only (such as macroalgae aquariums).

Caulerpa serrulata: Not Reef Safe
Caulerpa serrulatahas 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.  It is recommended for specialized aquariums only (such as macroalgae aquariums).

Caulerpa Taxifolia or Mexicana: Not Reef Safe

Caulerpa taxifolia is a fern-like species on the Federal Noxious Weeds list and is nicknamed the “killer algae” on the U.S. National Archives website 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 website 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.

Enteromorpha: Reef Safe
I found this algae in a new aquarium I’m currently cycling. I had never seen anything like it before, so thanks to some great people over at ReefCentral for the help identifying it! The tallest it has grown in my aquarium is only 2″, it’s cylindrical, and is apparently quite delicious to my cleanup crew. I initially thought it was bryopsis, but luckily it was not. Instead, it’s an Ulva algae (very palatable algae). It’s a cooler water algae, and I run my aquarium at 77 degrees, which is at the upper end of its preferential range. It also prefers high nutrient aquariums.

Green Film Algae:  Reef Safe

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.)  This microalgae film usually appears during the first couple of months of a new tank cycle, and it 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.

Green Hair Algae (GHA): Reef Safe with Caution
GHA is just what it sounds like…green algae that looks like a hairball. Hermit crabs, snails, etc. will 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 remants. Limiting nutrients through reduced feeding, skimming, running granular ferric oxide (GFO) and activated carbon (AC) will help slow GHA’s growth. Adding a refugium with “good” macroalgae, such as chaetomorpha, can help outcompete the GHA.

Ulva (Lettuce Algae):  Reef Safe
Ulva grows in large, floating sheets, and in the wild 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…so do snails, pods, and I’ve even found bristleworms eating it.  The algae below was in a 10g aquarium with about 65gph turnover rate and a 150W metal halide lamp over it.

Valonia (Green Bubble Algae):  Reef Safe with Caution
Although green bubble algae won’t choke out a reef like caulerpa, it is extremely invasive.  Manual removal should be attempted only outside the aquarium as bursting a bubble inside the aquarium may release spores.  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.

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