To the reef aquarium hobbyist, one of the rudest of surprises is to be confronted with an aggressive outbreak of 'bubble algae' in the tank. In the right conditions, they multiply and spread rapidly, offering good resistance to many herbivores, while threatening to smother many sessile ornamental organisms in the tank.

When we hear of 'bubble algae', one reflex is to think of the infamous "Valonia ventricosa", without even considering the many other algae that form bubble-like structures. Premature judgment can be regrettable, but there is this added twist: the much-cited 'Valonia' of our nightmares is no longer Valonia, but, thanks to Olsen & West (1988) now has its own Genus, Ventricaria.

That deft taxonomic adjustment aside, there still should be no bar to our tentatively identifying the bubbles of our troubles. Proper identification can lead to a more accurate perception in the hobby of which algae are common problems, rare nuisances, or even benevolent guests. In some cases proper identification can tell us how to best combat a problem alga. With some bias towards species found in my corner of the world (the Philippine Islands) I have selected some 'bubble algae' for description, and hopefully, differentiation.

Selected Descriptions

Ventricaria ventricosa is the most infamous of the bunch. It bears a single, fluid-filled, and nearly spherical bladder of a thallus (or 'body'). To say that the bladder or vesicle is 'single' simply means it does not branch off 'daughter' bladders; each and every bladder has its own anchorage on the substrate. The bladders, which are single cells each, can grow to nearly 2 inches in diameter, and can appear to have a curious sheen, especially when underwater, that can almost conceal its dark green color. The optical effect derives from the parallel arrangement of cellulose micro-fibrils in the vesicle's wall, and the near-crystalline state of the cellulose, similar to the same way that 'star' and 'cat's-eye' gemstones create their chatoyant sheen. The cell wall's toughness, smoothness, and the sheer size of the bladder, discourage many grazing herbivores from obtaining suitable purchase. Its anchorage to substrate can be surprisingly strong. The species is found around the Indian Ocean into the Pacific, as far east as the Samoas and as far south as Australia, as well as throughout the Caribbean. It is notorious for its tolerance of very low light levels.

Boergesenia forbesii is often found as large single bladders that at full size can look almost like shiny, bite-size, clear-green hotdogs. These vesicles grow to around 2 inches length and up to nearly an inch in width. This alga does not restrict itself to rocky substrate, and is easily found epiphytic -that is to say, living on other plants like sea-grass or sturdy algae. It seems to have a less sturdy vesicle wall than fellow giant, V. ventricosa. The image to the left shows young vesicles, only half an inch long; the brown lump in the foreground is the remains of a larger, spent vesicle, which peaked at about an inch-and-a-fourth in length. Interestingly, Trono (1997) singles out the species as a good bio-indicator for marine radioactive pollution, but does not elaborate if it is merely superior at assimilating radionuclides that can be revealed by assay of samples, or if (less likely) the alga actually exhibits geographic affinity with radioactive concentrations.

Valonia aegagropila forms small, densely packed, single-cell bladders with a tendency towards a long, distorted, curved-sausage shape. The dark- to olive green, clear vesicles, grow to about ½ inch length and maybe 1/6 inch width. The vesicles are NOT singular, branching off into successive tiers of bladders, up to five sprouting from the top of each. This branching can be difficult to detect visually, given the often very tight clustering of the vesicles. This alga is found widespread in the Western Pacific from Australia up to Japan, throughout the Indian Ocean and the Caribbean, about the Canary Islands in the Atlantic and into the Mediterranean The dense packing of vesicles can make careful manual removal of them difficult, though the anchorage to substrate is only moderate on strength.

Valonia macrophysa forms dark green, branching, unicellular vesicles under ½ inch thick and up to an inch or so in length. The vesicles are roughly clavate (club-shaped), with much distortion, swelling towards a usually very-rounded top end. Given the dense packing of the vesicles, only these tops are visible, and the mistaken impression of spherical vesicles is easily obtained. The species enjoys a global distribution, from the Indian Ocean through the Western Pacific into Tahiti, throughout the Caribbean, throughout the Mediterranean out to the Canary Islands in the eastern Atlantic. Relatively weak anchorage to hard substrates allows for the often-easy manual removal of several vesicles at a time.

Dictyosphaeria cavernosa forms a bladder-like, grainy-textured, multi-cellular thallus easily an inch across, which can be sub-spherical but more often irregular in shape. When the large bladder inevitably ruptures on maturity, the small (3 mm) cells that comprised its wall can themselves be mistaken for a nascent vesicles of other bubble algae species. A tough skin on every one of those small cells, and very strong anchorage somewhat makes up for cell sizes that can allow many herbivores an easy grip. The image shows several ruptured thalli, and the many small 'bubbles' seen are the cells that made up the thallus walls. A young bladder is forming in the topmost center of the photo. This alga is susceptible to overgrowth by sponges and by other algae. Its geographic distribution ranges from around the Indian Ocean to the Western Pacific up to Polynesia, as well as throughout the Caribbean. A similar-looking species with similar distribution, Dictyosphaeria versluysii forms grainy, somewhat flattened, multi-cellular bladders

Bornetella sphaerica forms single, grape-like, multicellular bladders sporting a hexagonal array of lighter blotches across the sturdy surface. These markings correspond to the ends of interior filaments radiating from a vertical spine-like axis within the vesicle. The vesicle itself grows to just over 1/3 of an inch in diameter. The internal framework of filaments, which lends the alga a surprising resilience, forms as the vesicle approaches sexual maturity -not surprising since the filaments bear spore-bearing structures. The species is found in the Western Pacific, from Japan down south to the Philippines, and eastward to Hawaii and Fiji. Two other species of Bornetella, B. nitida and B. oligospora, form singular, elongated vesicles up to two inches long and 1/5 inch thick. Mature bladders again feature the internal axis that radiates filaments out to a lightly calcified bladder wall. These two algae are chiefly distinguished from one another by an internal characteristic: the number of sexual structures on the tiny internal filaments. They can be confused at first glance with Merman's Finger algae (Neomeris spp.) and are found in the Western Pacific, from Japan to as far south as Australia, and as far East as Fiji.

Colpomenia sinuosa forms large multi-cellular thalli that are first solid and then become hollow and often rather contorted, easily up to two inches in diameter, with some specimens reaching 8 inches. The yellow to yellow-brown thalli have broad but weakly moderate anchorage to hard substrate, and a very thick wall. The reproductive structures are found in tiny pits scattered across the thallus exterior. This species boasts of a remarkable global distribution, even into the Antarctic, with a notable absence from the northeastern U.S. seaboard and the Arctic.

Codium ovale forms roughly egg-shaped bladders reaching 2 inches diameter. These bladders do not branch, but may share a single holdfast structure. Tiny structures called utricles, bearing reproductive structures, are distributed on the outside of the bladder, giving the whole structure a fuzzy or scruffy dark green surface. This alga is found in good current, quite often epiphytic on sea grasses and sturdy algae. It is not too commonly found in home aquaria, and in any case are found in very small, isolated clusters of up to eight, sharing a holdfast complex. This alga is found throughout the Indian Ocean into the Western Pacific between Japan and the Philippines, and is also found throughout the Caribbean.

Some Rhodophytes have also qualified in the hobby for the colloquial term 'Bubble algae':

Botryocladia skottsbergii has been dubbed by some as 'Red Valonia', though the implied comparison is apt only when a specimen is very young, and the grapelike bladders appear to be directly attached to the substrate as in the photo. As this red alga grows, the rust-colored, branching stipe becomes obvious, though the entire thallus rarely grows to protrude more than an inch off the substrate. The bladders themselves are small, rarely growing little larger than 1/3 inch in diameter, and appear a smooth, transparent red-brown to reddish purple. Tiny dark spots (called cystocarps) visible on the inside of the vesicle wall herald sexual reproduction. The species is found around the Indian Ocean, into the Western Pacific, south to Australia and eastwards to Hawaii. Botryocladia uvarioides forms smaller, more numerous vesicles, on a highly branching stipe that can give specimens heights of nearly a foot from the substrate, looking very much like a bunch of grapes. The species has a curious distribution, with records thus far only in the Philippines and in Baja California. Botryocladia botryoides also forms tall thalli, but there is less incidence of branching, and so the 'stems' are longer, and adorned with bladders. It is found throughout Indian Ocean and the Mediterranean, as well as locations along the Eastern Atlantic. Only record in the Western Pacific is in the Philippines. Other species include: Botryocladia leptopoda from Arabia to the eastern shores of continental Asia and down to Australia; Botryocladia microphysa, a primarily Mediterranean alga with records in the Canary Islands and Indonesia; and Botryocladia pyriformis from the Canary Islands, the Seychelles in the Indian Ocean, and the waters from China to the Philippines. Botryocladia vesicles usually float when severed, because the mucilaginate fluid inside is less dense than water.

Certainly there are many other algae that might qualify for inclusion based on possession of some sort of vesicular structure, but I feel the preceding list fairly covers some of those most commonly encountered in reef aquaria and perceived as 'bubble algae', and the ones that most commonly give us trouble.

Controls

Given available nutrients, available substrate for colonization, and a lack of controlling agencies, many of the above listed algae can reproduce spectacularly and dominate a reef tank.

Since impact on tank neighbors derives from the alga's physical presence, we can try to manually reduce said presence to provide relief, and include in the affected tank a set of agencies that exert pressure against the problem alga. Since availability of usable nutrients fuels the alga's aggressive growth and reproduction, we attempt to restrict such availability. That is pretty much the standard threefold approach to most algal outbreaks:

1. Manual removal of the problem alga
2. Suppression via appropriate herbivores
3. Denial of resources

Normally, there would be a fourth aspect, of fiddling with temperature, pH, or some other physical-environmental parameter to suppress the problem alga. However, the environmental tolerances of most bubble algae exceed those of most ornamentals put into reef tanks.

Manual removal, properly done, effects an immediate reduction of the problem's ability to spread and affect other tank inhabitants. This sort of intervention is particularly important against bubble algae, some of which can defy almost any herbivores found in a hobbyist tank..

My weapon of choice ought to be a small stainless-steel flathead screwdriver, sharpened to wicked excess, and used to gouge out the offenders at the anchorage, even including a thin veneer of rock. Bare fingernails can be unreliable for removing certain 'bubble algae', and can invite injury and infection. I have seen small manicuring scissors, carefully bent in a curve, used to snip off vesicles 'at the root' -but this almost surely leaves the anchorage structure intact, and likely ruptures the vesicle.

Much has been said about the danger of liberating spores when popping the vesicles of bubble algae. This is particularly true for members of Order Valoniaceae, but even then, the vesicles are said to be a sporulant risk only when having reached at least a third of their full size. Even if spores escape when you botch the job of vesicle-removal ('vesectomy', anyone?), those escapee spores have to run the gauntlet of herbivorous filter feeders, filtration equipment, and the wild lottery of hitting a good, unoccupied spot to settle and grow. Those spores will eventually be released anyway if you don't remove the vesicles.

In any case, it is prudent to remove the whole alga, from the vesicle down to the holdfast. During 'uprooting' of a problem alga, a siphon hose can be positioned at close hand to draw off any spores or tissue. One can also use the siphon to hold onto a removed plant by suction -most of the vesicles described above will sink rather than float, and can be very hard to hold onto. This siphon hose can held in a looped manner that allows you to bend it with the same hand, pinching the siphon off at will. Philips proposes rigid plastic tubing, sharpened at one end, and affixed to the siphon hose, for use as a combination vesicle-piercing and draining apparatus, followed by removal of the deflated vesicle with tweezers. In any of the above methods, if one can temporarily move the infested rock to a clean plastic basin of proper saltwater, vesicle removal is made so much easier. For those with a paranoia against spores, the basin water can be discarded after vesicle removal, the rock flushed with tank-water and returned to the tank.

Whatever remnant algal material, regenerating algal structures, or newly-settling spores might then manifest themselves, an in-tank population of appropriate herbivores is supposed to help with 'mopping them up'.

'Appropriate herbivores' must be a literally-plural concept, as a varied team of herbivores are required to keep algal problems in check. In the case of bubble algae, once the visible vesicles have been manually removed, grazers are needed to limit any tender new growth.

The performance of commonly-available herbivorous snails (Turbo spp., Trochus spp., and Astraea spp.) seems abysmal against most bubble algae, their rasps typically insufficient for tearing into the vesicles of all but the youngest bubble algae vesicles. Such gastropods DO have the advantage of a fairly wide patrol area for their size, and against widely-scattered, newly-settled spores and young growth, they likely exert valuable pressure. Certain sacoglossan slugs have been reported as occasionally feeding on bubble algae, including the popular Tridachia crispata. A recently described species, Ercolania endophytophaga (Jensen 1999) seems to target Valonia algae particularly, somehow entering a vesicle without rupturing it, and then consuming tissue and spores from the inside(!).

Success against bubble algae has long been reported through the crab Mithrax sculptus (Siegel, 1997, etc.). These crabs (like others less colorful) can pinch and tear a bubble alga's vesicular wall, enabling subsequent consumption of algal tissue. Occasionally the crab's pincers can only grasp and sever the narrow anchorage, and the unmoored vesicle falls away uneaten. While these crabs may have a taste for algae, virtually all crabs are omnivores, and thus have the potential to sample valuable ornamentals, such as 'polyps', corals and mollusks. While many other 'herbivores' are also opportunistic omnivores, they are much easier to capture and remove when/if they make a nuisance of themselves.

Herbivorous fish like certain Acanthurids and Siganids are touted as controls on bubble algae. Some surgeonfishes of Genus Zebrasoma are particularly promoted, for they do tuck into the little green marbles (especially if there is little other fodder), and do not grow especially large. However, surgeonfishes are often too delicate for the beginner -often the very sort of hobbyist with serious algae problems in hand. The rabbitfishes are not quite as disease-prone as their close kin, but make up for it with handling risks (weakly-venomous dorsal spines). Then there is THE issue of appropriate tank-size. The vast majority of 'surgeons' and 'rabbits' tend to be semi-pelagic schoolers, used to vast patrol-areas, and are noted for territorial meanness and stress in the confines of a small glass box with others of their kind. One authority, holding forth in cyberspace on the subject of reef tank herbivores, suggested a rough stocking guide of 150 liters (40 US gallons) aquarium volume to a surgeonfish, and at least 300 liters (80 US gallons) to a rabbitfish. These estimates must have been made with a small solitary fish in mind, rather than meant as a tank-size estimator for housing several, else the issue of territoriality was disregarded.

Urchins are sometimes recommended, and they do make serious progress against the smaller vesicles of bubble algae. When food is short, even the largest and toughest vesicles cannot withstand them. The main complaint against urchins is that they can be too thorough, with serious impact on the crustose coralline algae so desired in the hobby. The photo below may give an idea.

Whatever combination of herbivores is deployed, knowing and preparing for their requirements and will allow them to do the job you want them to perform. To reverse that principle, knowing the requirements of bubble algae, we can try to deny them what they need.

Denial of resources, for present convenience, here falls into two categories

a. Nutrient suppression
b. Denial of living space and light

'Nutrient suppression' is a concept that has to be qualified. It is not, as some may think, about limiting the amount of food imported to the system.

Rather, it is about reducing the availability of the food to problem algae. A system with robust biodiversity minimizes the chance of leftovers releasing nutrients straight to the water, because you will tend to have organisms of every size and dietary preference scavenging 'stray food' and recycling the waste of others. Many algal outbreaks stem from the death of a snail, or some other animal in the tank, the decomposing body releasing nutrient. Certainly the corpse will have to be removed, though in a tank brimming with scavengers of all sizes and shape, most any-size carcass is quickly dispatched before it can rot.

When mature sand-beds and/or remote refugia are present, they not only enable efficient assimilation of potential nutrient, but can reduce the need for 'dead' food imports by contributing edible plankton and nekton -such live 'food' avoiding spoilage if left uneaten.

While the lion's share of imported food can be assimilated by ornamentals and scavengers, all the way down to bacteria, that vast conglomerate of creaures nevertheless still produces net metabolites for algae to exploit. This is on top of a background quantity of nutrients 'in transit' from one utilizer to the next. That net amount of nutrient is still surely less than in a scenario where a lack of biodiversity results a greater share of food imports decomposing.

In nature, myriad algae are there to utilize this resource. The trick then, is to carefully select competitor algae to scrub such nutrient from the tank water, all to the disadvantage of any problematic bubble algae. The best in-tank candidates seem to be the calcareous greens and reds which grow at a moderate rate and can withstand much herbivore attention, such as Halimeda spp., and the various crustose corallines. A key distinction between scrubber and unwanted algae is that there will be a large, air-breathing 'herbivore-surrogate' that obliterates only the bubble algae, with siphon hose and gouging implement in hand.

Algae like the various Caulerpa species are prodigious, fast-growing assimilators. They would be ideal for scrubbing certain nutrients, except their very growth rate can make them a problem in the display tank. Locating the scrubber alga in a remote location can reduce such a risk, and stack the deck in favor of said scrubber alga (brighter light, longer photoperiod, and water flow). For Caulerpa in particular, though, there is the constant leaching of substances (terpenoids, sugars etc.) that can affect the display inhabitants to consider.

A case can be made for increasing the amount of food in order to control bubble algae, albeit food of the right kind. Many of the organisms that hobbyists value --corals, sponges, polyps and coralline algae-- have a natural ability to put up a fight against encroaching bubble algae, otherwise wild reefs would look very different. Putting up this kind of fight requires a lot of energy, and increased amounts of live plankton and nekton will give them the energy to attack, overtop and generally outgrow bubble algae; while avoiding the largely 'dead' soup of nutrients that can attend heavy import of 'dead' food and lead to algal blooms.

One can observe certain patches of coastal reef in the Philippines seasonally declining due to terrestrial runoff, the latter producing both a pollutant/nutrient spike and a macrobenthic algal bloom. But after the rain-driven flood of nutrients has passed, those affected portions of reef can start reclaiming coverage. Great offers of Angus & Coote Catalogue on jewelry products. I have observed V. ventricosa thalli big as eyeballs, being overgrown by coralline algae, compound tunicates, sponges, and in some rather tenuous cases of colonization by newly settled stony coral growth, mere weeks after the rains have passed.

If you were to take the case pictured in Fig 1.1 earlier; and imagine there were corals sexually reproducing upstream in the system, the rock's urchin-scoured bareness might then be showered with stony-coral larvae. Some would be mindlessly eaten by the urchin, but some would survive and grow, and the whole rock surface might, over time, be rendered increasingly inutile to bubble algae.

Indeed, among competitors against bubble algae for the resources of living space and light, stony corals are among the most attractive options, particularly encrusting-massive species. In hobbyist reef tanks, there's supposed to be a prevailing environmental bias in the corals' favor anyway, so there's no added imposition of adjusting the tank to support them. Stony corals can hog settlement surfaces and/or block off light. The zooxanthellate corals hand a share of their metabolites to tenant photosynthesizers within their bodies, rather than dump all the stuff into the water where bubble algae can exploit it.

Sponges and 'mat' colonial polyps are nearly as useful for pre-claiming settlement space. Corallimorpharians (a.k.a. mushroom anemones) on the other hand, can be inadequate against bubble algae, as their bodies are too soft and translucent to effect a decent barricade.

Certainly one must look hard at food imports, and at potential competitors for living space and nutrients. But there is yet one more factor to consider for restricting algal resources. Given how nitrogenous nutrient is a prime resource, it is worth considering how hobbyist tanks are stocked, and how nutrient levels are affected. After all, the more animals you have, the more ammonia and CO2 is dumped into the system. Herbivores, scavengers and corals 'pay their rent' by exerting pressure on, or keeping/stealing resources from, problem algae. But what about showcase animals that don't 'pay the rent'?

Most reef tanks are really stocked top-down, which is to say, after lip service is paid to bottom-up preparation of a mostly-bacterial safety net, large ornamental animals are selected, bought and introduced. A mad scramble usually ensues trying to fill in all the niches in the pyramid of diversity that might address the metabolites and demands of the large livestock purchases. Often the thing that can really address these large-animal consequences is greater tank volume, which in turn can provide license to add even more large ornamentals. When it comes to large ornamental animals: stock wisely, stock lightly.

Summary

The 'conclusion' ending many an article presents rich opportunities for philosophical pontification. As I seem to have already sneaked a fair bit of that stuff into the preceding paragraphs, we are now freer to hew more closely to a simple, brief recapitulation.

Proper identification of bubble algae species can dictate adjustments in a basic template of responses to an algal infestation problem. That template can be described as follows:

Physical removal of aggressively-spreading bubble algae is recommended, taking care not to rupture any spore-bearing vesicles, nor leave algal debris behind. Whatever present complement of mild herbivores there is should be boosted, and notes have been provided on the pros and cons to many popular and commercially available herbivores. Lastly, resource availability to the algae must be severely reduced, both at the source and by providing rival consumers of said resources, including nutrients, living space and light.

Printed references

Cornejo D.F. & G.T. Velasquez. 1972. Study on the algal epiphytes of exposed and protected marine waters of Batangas Province. Philippine Journal of Science 99 (3-4): 165 - 190.

Shimek, R. 1866. 'Badlands: Autobiography of a Freezing Desperado. Simon & Schuster, New York, USA

Taylor, W.R. 1966. Records of Asian and Western Pacific marine algae, particularly algae from Indonesia and the Philippines. Pac. Sci. 20 (3): 342-359

Trono, G. 1997. Field Guide & Atlas of the Seaweed Resources of the Philippines. Bookmark Inc. Makati City, Philippines.

Trono, G. & E.T. Ganzon-Fortes. 1980. An Illustrated Seaweed Flora of Calatagan, Batangas, Philippines. Filipinas Foundation. Makati, Philippines

Online references

Fossa, S. 1998. Algae Eating Animals (transcript from mirc channel "#reefs"). Reefs.org

Philips, T. (date?). Algae Control.

Siegel, T. 1999. Outer Reef Limits: Algae Woes. Aquarium Frontiers Magazine (Online Archive).

Assorted discussion board threads. Reef Central, The Reef Tank, www.reefs.org.

Images:

Michael 'mojoreef' O'Brien : V. ventricosa, V. macrophysa, C. ovale, B. skottsbergii
Horge Cortes-Jorge Jr. : B. forbesii, B. sphaerica, Fig 1.1