Brown jelly disease in corals: what it is and how to treat it

What brown jelly disease is

James Fatherree describes it as "an attack on any injured flesh by an assortment of microorganisms", in which "The coral's tissues basically turn into a light brown glob of slime". Researchers call it brown jelly syndrome (BJS) and count it among the aquarium coral diseases that have "no reported parallels in nature", although, as the next section explains, the organisms in it have close relatives in wild coral diseases.

It is best known on Euphyllia. The Maidenhead Aquatics care sheet says the hammer coral "does seem to be a little prone to 'brown jelly' infections", and Fatherree's article on the genus, which covers frogspawn and torch too, treats it as the most common result of injury. It isn't limited to LPS: all three brown-jelly corals sampled in the main microbiology study were Acropora. Manta Systems, a retailer, says it mostly hits LPS such as torch, hammer, frogspawn and bubble corals, and only rarely softies and SPS.

What causes it: the ciliates

Brown jelly is full of ciliates, single-celled organisms that swim with hair-like cilia, and they are the main suspect. The naming is a mess, which is why sources disagree:

• Helicostoma. In aquarium corals, BJS "has been strongly linked to a ciliate, commonly referred to as Helicostoma nonatum". In their 2012 review, Sweet, Jones and Bythell wrote: "We propose that Helicostoma is actually a misnomer".
• Philaster. The same group notes that the brown-jelly ciliate "has only recently been assigned to the same genus as that of two ciliates in WS and BrB, Philaster", meaning white syndrome and brown band disease, two diseases of wild corals.
• Porpostoma. Brown band disease on wild Acropora in Guam is linked to a ciliate described in 2011 as Porpostoma guamensis, which forms "an advancing brown band with a jelly-like consistency adjacent to clinically healthy tissue"; "Both zooxanthellae and nematocysts from coral occurred in the ciliates." The describing authors note that one taxonomist has treated Porpostoma as the same genus as Helicostoma, which is part of why the names overlap.

The best direct evidence comes from a 2013 study of diseased corals from public aquariums (Sweet, Craggs, Robson and Bythell). One ciliate type "was observed to burrow into and underneath the coral tissues at the disease lesion" in both white syndrome and brown jelly samples, "and contained algal endosymbionts indicative of coral tissue ingestion." It was more numerous in brown jelly, and its DNA differed by 1 base pair in 549 from a ciliate found in wild white syndrome and brown band disease. No single bacterium turned up consistently.

Cause or clean-up crew? That is still open. The 2013 authors say the ciliates may drive the disease, "or alternatively they are simply associated with the necrotic tissue of the disease." Bulk Reef Supply: "It is unknown if the ciliates play a direct role in the infection." A 2015 MacEwan University conference abstract (not a peer-reviewed paper) reported that inoculating corals with the ciliates produced no change in fluorescence, "suggesting the ciliates are opportunistic invaders", and said its authors were looking at viruses instead.

Triggers. Injury comes first in every hobby source we read. Fatherree ties brown jelly to flesh torn by cutting, breaking, or handling and shipping against the coral's sharp skeleton. The Maidenhead Aquatics care sheet suggests hermit crabs, saying infections may happen "possibly as a result of hermit crabs lumbering over them in their ongoing search for food items." Manta Systems adds poor water quality and sudden temperature or salinity changes as stresses that weaken corals.

Brown jelly vs RTN, STN and bleaching

The test that matters: is tissue coming off, and is there a brown mass? Bleached tissue is alive. NOAA notes that "Corals can survive a bleaching event and recruit new algae", so don't cut or dip a coral just because it's gone pale; work through the coral bleaching causes instead. Brown jelly and RTN, on the other hand, call for the same urgent response below, and BRS covers both in one article.

How fast it spreads

Fast. Fatherree: "Brown jelly infestations can spread very rapidly", and an infection "can spread quickly and destroy an entire non-branching specimen of any size in the worst cases." On a branching colony, "if a brown-jelly infection strikes individual branches on a branching colony, those branches are doomed", "but the others may be just fine". Manta Systems says it can destroy corals "within a few days if not treated promptly" and that it spreads to neighbouring corals with the water flow; that second claim comes from a retailer and we found no study testing it.

The only measurement we found is from the 2013 study: tissue loss of 15–20 mm² a day on its three brown-jelly Acropora, figures the authors caution "may not be accurate." The practical point is to check corals daily after any fragging, shipping or injury, and to act the day you see jelly.

What to do, step by step

1. Siphon the jelly off first. BRS: "If you can, siphon off dead tissue before disturbing the coral." Use a turkey baster or a siphon hose and draw the jelly away gently rather than blasting it around the tank. Manta Systems warns that "Scraping often worsens the situation by spreading the infection." Wear gloves.
2. Take the coral out, or isolate it. Move it to a bucket or quarantine tank of display water. Goemans moves treated hammer corals to a hospital tank and changes water every other day until the jelly has stopped.
3. Dip it in an iodine dip at the label dose. For Seachem Reef Dip: 5–10 mL in a US gallon (4 L) of water taken from the tank, for 15–30 minutes depending on severity, with a double dose only "In very severe cases". Seachem also says that "With clear and accessible lesions, dip concentrate may be painted on lesions directly before placing in dip." Remove crabs and shrimp from the coral first, and watch for "adverse reactions such as excessive sliming". Never add the dip to the display. Goemans uses Lugol's iodine in tank water, brushing the jelly off with a soft brush and basting the area over an empty pail, and writes that "I've found the sanitizing effect of the Lugol's to often quickly end the invasion of brown jelly"; that is one experienced keeper's experience, not a trial. Lugol's products vary in strength, and Brightwell's retail listing gives no dip dilution, so use a product with printed dip directions unless yours has them.
4. Cut away what's lost. On branching corals, BRS: "Cut the coral at least ½ inch ahead of the creeping necrosis or jelly." Fatherree: "You can cut/break away any dead branches and typically spare the rest of them." Discard the affected pieces. Cutting makes fresh wounds, and wounds are where brown jelly starts, so dip the healthy pieces after cutting; BRS calls fragging and dipping the approach that seems most successful against tissue necrosis.
5. Rinse, watch, repeat if needed. Rinse the coral in clean tank water after the dip, keep it isolated, and check it at least daily. If jelly comes back, siphon and dip again; Goemans repeats his cleaning when needed.
6. Fix the cause. BRS's advice for tissue necrosis: "Do all you can to eliminate stressors like high water temperature and poor water quality." Check temperature, salinity and alkalinity, and correct them slowly: no more than 1.4 dKH of alkalinity or 1 ppt of salinity a day, so the fix doesn't become the next stress. The water change calculator keeps a salinity correction inside that limit. Look for hermit crabs or other animals climbing on the coral.

Other dips and products

• Fauna Marin Cili Dip is sold as a coral bath that "gently removes unwanted parasites such as ciliates bacteria, as well as algae." Its sheet doesn't mention brown jelly. The dose depends on the coral group in its table, the bath is "max. 3 minutes" (90 seconds for SPS), and it warns: "Never use a higher dosage than recommended as this may harm the corals." We found no independent test of it.
• Reef Primer did well in one hobbyist's microscope test reported by Reef Builders in 2021: it was the only product tested that had any effect on the ciliates from brown-jelly Euphyllia tissue. The article itself says it remains to be seen whether the result is repeatable, and we found no follow-up.
• General pest dips such as CoralRx are sold against "parasites and bacterial infections", and BRS lists brown jelly among the problems coral dips address, but none of the labels we read names brown jelly or reports a test against it. The coral dip guide has each one's label dose and time.

Antibiotics and medications

We found no peer-reviewed study testing any antibiotic against brown jelly in aquarium corals, so this guide gives no antibiotic or dose. Some retailer guides list antibiotics for brown jelly, including at least one that is generally prescription-only, and the one we read carries its own warnings: "Most antibiotics are not reef-safe and can harm beneficial bacteria, corals, and other invertebrates", and some medications are restricted or prescription-only, so check local rules. Part of the gap is that researchers rarely test treatments at all: Sweet, Jones and Bythell note that treatments "are not commonly sought by scientists working in the natural environment", because of their cost and potential environmental impact. If you consider a medication, talk to an aquatic vet, use it only in a separate container, and never put it in the display.

Prevention

• Avoid injuries. Handle hammers and other Euphyllia by the skeleton (Maidenhead Aquatics also warns that the hammer's sting "can be particularly painful"), and check freshly cut or shipped corals daily.
• Watch who climbs on it. If hermit crabs keep walking over a hammer or frogspawn, move one of them.
• Dip and quarantine new corals. Seachem says Reef Dip can be used "prophylactically (without evidence of disease)". The coral dip guide covers the routine, and the starting a reef tank checklist covers the quarantine tub.
• Keep water stable. The same stresses that bleach corals (heat, swings in alkalinity and salinity) weaken tissue. The ideal reef parameters guide has the targets.

What the evidence does and doesn't support

• Supported: a ciliate found in brown jelly lesions burrows under the tissue and eats it, and is genetically very close to a ciliate from wild white syndrome and brown band disease (Sweet et al. 2013); a related ciliate eats coral tissue in wild brown band disease (Lobban et al. 2011). Injury is the trigger every hobby source we read names.
• Not settled: whether the ciliates cause brown jelly or follow tissue that is already dying. The 2013 study had only three brown jelly samples, all Acropora.
• Standard practice, not tested: siphoning, isolating, iodine dips and cutting ahead of the jelly. Seachem says its iodine dip works against "bacteria, fungus, and protozoans", and we found no published controlled test of it, or any other dip, against brown jelly.
• No evidence we could find: for antibiotics against brown jelly, or for spread between corals through the water.