Bryopsis: A Common Pest in Aquaria
An unsightly, green alga that herbivores dislike to eat.
Information and tips for eradication of the nuisance algae Bryopsis, indicating high levels of dissolved nutrients in the aquarium.
Bryopsis - What Is It?
Bryopsis is a common nuisance alga that can overgrow corals and other desirable algae by outcompeting with them for nutrients. It is generally dark green, coming from the Chlorophyta division, and can be either spiky or filamentous. It is a sure sign of high levels of nitrates, though often, the nitrates are not detectable because they are being uptaken by the Bryopsis itself. Therefore, if you do have detectable levels, think how much more would be released should the alga go sexual, that is, to re-release the nutrients into the tank. To the inexperienced eye, Bryopsis can even resemble some kind of urchin. It is not generally known to produce allelopathogens, but this is up for debate amongst some experts. In any case, it is not recommended to increase your bio-load at this point for obvious reasons.
Little Palm Trees in the Reef
The most common characteristic of this alga is the fernlike fronds resembling feathers, and it is therefore hard to distinguish it from some species of Caulerpa or Derbesia. However, in either case, the treatment for eradication is the same. The easiest way to tell it apart from other algae is testing to see how difficult it is to physically remove. Bryopsis tends to burrow deeply into a rock crevice where it can feed off nutrient-rich detritus, and so, it will take a little strength to pluck out.
What's Eating You?
Most herbivores will not eat this alga. In a mature tank, Bryopsis can take over, smothering all stationary life forms. Some tangs, such as those from the Zebrasoma and Ctenochaetus families may keep it in control, but because the pest can be embedded in the rock quite deeply, it can come right back. If you have a large tank, a Naso tang would also enjoy eating it. Other fish known to be willing to try this alga are: the lawnmower or algae blenny and the bi-colour blenny. However, the aquarist’s preferred method of natural removal seems to be with Diadema urchins, Elysia Nudibranches, and even common pincushion urchins. Emerald Mithrax and some hermit crabs can also help do battle, but depending on the size of your outbreak, you may need many of them. For example, the Tridachia Crispa (Sea Lettuce Slug) is a specialist feeder of Bryopsis but it will most assuredly die once the outbreak has been contained. Therefore, you have a responsibility to these animals to ensure them a new home with enough to eat.
Trendy Magnesium Solution
Some reports of a Bryopsis bloom mysteriously correct themselves over time and in fact, may disappear altogether where water quality is kept in good standing. This may go a ways in understanding why some people are insisting in the latest trend of elevating the levels of magnesium from the normal range (1,280 ppm) to 1,500 – 1,600 ppm. Most aquarists who have tried this method feel it is the fastest and least detrimental way to correct the dilemma. The theory behind this is that the magnesium stops the photosynthetic processes in the Bryopsis, but does this without affecting other desirable macros and life in the reef. There are some, though, that suspect the elevated levels of magnesium can kill desirable invertebrates, so as with most things in reef keeping, slow is best. Also, ask yourself, would you rather chance losing some snails or some corals?
The pH Solution
A similar method to try is while aggressively protein skimming, elevate your pH to a steady 8.5 for three weeks. It would seem that low ph/alkalinity ratios seem to aggravate an outbreak.
Freeze Them Off
Finally, there is the simple method of removing affected rocks from the tank and placing them in the freezer for forty-eight hours or more. This is an understandable nuisance and may not even be possible if aqua-structure or coral life will not allow. The process will burst the cellular structure of the alga, thereby killing it. At this point, it would be advisable to brush off/manually remove any remaining visible pieces before returning the piece to the display.
