Bubble algae, smart raiders

You should not ignore

They show up as bright and small isolated spheres, usually clinging to the rock, lack of movement and very decorative. It can take weeks and even months without this situation varies, but suddenly, one day we discover that the aquarium rock are upholstered by these small green pearls (and the less common brown and red). In cracks, under ledges, or directly exposed to the light, not even a square centimeter is free of threat; even on the tissue of many corals (usual case sarcophyton and other leather corals).

And it's too late. With an amazing reproductive capacity, and with few natural predators, it is very difficult to stop their expansion. Bubble algae should be removed when they are detected in the aquarium since if they spread, they can become a real problem.

The designation bubble algae is very broad and includes varied species that share several common characteristics such as a spherical shape, absence of stem and reproduction by spores.

Let's have a look at the most common in the aquarium.

Ventricaria ventricosa

It is probably the most infamous and common in aquariums. Hobbyists usually know them as Valonia ventricosa, but the truth is that long ago it was renamed as the only member of their own gender: ventricaria. (Olsen & West, 1988)

It tends to grow isolated, bladder shaped, up to five centimeters in diameter and is easily recognizable by a single tiny root with which it is held firmly to any surface. Each bladder is an individual and a single cell with a hard, shiny membrane that makes this species a tough and unappetizing bite for most herbivores (especially when it reaches a big size).

Valonia utricularis

It is an elongated, curved shaped bladder that grows in compact clusters which are firmly bonded together. Each bladder or cell may have a length up to four centimeters, although typically in each cluster, most are much smaller.

They grow haphazardly and are relatively delicate, so be careful when removing to avoid pop and release of spores. Fortunately the root of these bubble algae is usually quite weak and simply slide a flat object under the cluster to remove a piece.

Valonia macrophysa

Similar to the previous one, although somewhat smaller and rounded, these bubble algae tend to swell at its upper end which makes the cluster look neater. It is a common weed in all the seas and oceans (Indian, Pacific, Atlantic, Caribbean, Mediterranean…)

Valonia fastigiata

Easily recognizable by its branched structure, each cell divides to create a small lateral stem forming its characteristic silhouette which is easily confused with some other species of the genus salicornia. The bladders are usually small, no more than one centimeter in length and slightly curved.

On the left of the picture we can see a cluster of these bubble algae, very similar to a salicornia shown on the right. They are rare bubble algae in aquariums, original from the Indian and western Pacific Ocean.

Valonia aegagropila

Finding these bubble algae in the aquarium is not good news and I advise against introducing any coral or rock in the tank containing any of them on its surface. In my opinion this is one of the most difficult species to get rid of.

It is a unicellular algae made of tiny bladders (a few millimeters), with an elongated and branched shape, which is not always obvious at first sight because of the compact way the clusters are arranged. Their cell wall is quite delicate compared to other bubble algae, while its root allows it to adhere strongly to any surface, which makes it almost impossible to remove them cleanly and without releasing spores in the water. Another species that is widespread all over the seas and oceans, including non-tropical waters.

Dictyosphaeria cavernosa

Is one of the few bubble algae that do not pose a threat. It grows very irregularly shaped and with deflated bladders. Its walls, grainy textured, are actually a group of small unicellular bubble algae. It grows slowly and is usually easy food for most herbivore animals, especially sea urchins, and therefore it does not usually last long in the aquarium.

This kind of bubble algae is spread across the Indian Ocean to Polynesia and the Caribbean. In the aquarium it is rare and because of their shape and color, is easily confused with a sponge.

Colpomenia sinuosa

It is a yellow algae that grows as large deflated vesicles (some up to ten centimeters in diameter). They have a thick and leathery wall which makes it uninteresting for many herbivores. Their roots are moderately strong, so it is easy to remove them in one piece without breaking.

The distribution of these bubble algae is one of the most extensive, even to be present in the cold waters of the Antarctic (although not in Canadian waters or in the Arctic).

Botryocladia sp

It is a genus of bubble algae easily recognizable by their red colour, reason why they do not go unnoticed in the aquarium. They use to form clusters composed of cells of no more than one centimeter or two depending on the species and most are translucent allowing to observe the small cystocarps black coloured (reproductive organs).

Much appreciated by all herbivores and with a not very tough membrane, usually be quickly swallowed up in the aquarium and rarely becomes a threat. Depending on the species, you can find these beautiful bubble algae in almost all the world's oceans, including subtropical waters, but are more frequent in the Indian Ocean and the Pacific Islands.

Bornetella spherica

A very different from the others bubble algae species. They are grouped into hundreds of small cells that are compacted into a cluster with spherical shape of one to two centimeters in diameter. Each small vesicle is attached to a central trunk with a filament carrying the reproductive spores.

Boergesenia forbesii

These elongated bubble algae of about five centimeters in length usually grow in small unbranched clusters where all individuals are linked to the same root. They have a marked epiphytic character, namely, they like growing on other organisms's tissue, mainly algae but may also do so on corals.

Their cell wall is more delicate than you would expect in these big bubble algae, so you must be especially careful if you try to detach them. They have a wide geographical distribution so it is quite common to find some of these bubble algae on newly imported live rock.

Control of bubble algae in the aquarium

It much depends on the species, and although it is true that most are a major threat and must be eliminated as soon as they show up, there are others that are quickly consumed by any herbivore so they are not a concern.

There is no foolproof method of control, and sometimes it is difficult to remove certain species of bubble algae from our aquarium; and as with most pests, the best way is prevention and observation: acquire rock and substrate from reliable suppliers, quarantine and observe carefully its surface.

The most effective way against the most problematic bubble algae as ventricosa ventricaria and some species of valonia is to apply a combination of three actions:

Reduce nutrients
Remove algae manually
Introducing animals that consume the algae

Reduce nutrients

The first step to combat bubble algae is weakening and to do so, nothing better than limiting their energy sources: dissolved nutrients in the water and light. Because they are algae with low light requirements, able to thrive even under ledges with almost no light, it is very difficult to weaken them up by reducing their exposure to light (unless we have an aquarium without any corals and not to mind to cover it for a couple of weeks).

Perhaps the best way to reduce nutrients is growing other vegetal organisms that compete for certain trace elements and even space, such is the case of calcareous algae like halimeda, or just coraline. Many hobbyists install scrubber filters or refugiums chaetomorpha or certain species of caulerpa.

Remove algae manually

It can be complex and laborious but generally essential if we want to eliminate the problem. Bubble algae share a common feature: inside their cells threre are a small reproductive organs (called cystocarps), when the bladder reaches maturity (about one third of its final size), it is capable of producing spores, which will be released into the water if the membrane is torn. The truth is that if the aquarium is mature and has a good filtration system, the chances of a spore becoming an algae are low and most of them die, but an immature system it can be like a freshly plowed field waiting for the first rains to upholster with weeds.

Each species is to be removed in a different way: ventricaria ventricosa and some valonias such as macrophysa or boergesenia forbesii can be easily removed with the fingers the same way you'd pick grapes from a vine. In contrast, other bubble algae require careful removal and you should use a flathead screwdriver to break its roots beforehand. If we find any cluster of valonia aegagropila, it would be more sensible to take the rock out of the tank and remove the algae outside, being careful not to break the bladders.

Introducing animals that consume the algae

This could be the great solution: we spend some money on getting new fish or invertebrate and…no way, I'm sorry but no way.

There are few, if any, animals that have proven to be truly effective against algae bubble, we will discuss potential candidates:

Mithrax sculptus

This cute crab is omnivorous and won't really eat bubble algae unless it is very hungry, which rarely happens in an aquarium with fish. There is a false belief that they eat bubble algae, but what they actually do is pop the smallest and immature (which fortunately do not have reproductive spores)

This makes it easy to be consumed by other animals such as sea urchins and some fish. Mithrax crabs have become very popular and are already a quite common animal in specialized stores.

Ercolania endophytophaga

It is a specialized nudibranch on algae of the genus valonia. This small mollusk is able to penetrate inside a bladder without tearing it and eat from inside. But the most surprising fact is that they lay their eggs in the inside of the bubble algae, something that provide two great benefits: security against any possible predator and food availability for their offspring after the eggs hatch.

On the right picture you can see a nudibranch ercolania next to an egg cluster inside what it looks like a valonia utricularis.

However, it is far from an ultimate solution because this is an animal that poses a number of problems:

It's very delicate and easy prey for any fish of “usual ones” (hexataenia, synchiropus and any wrasse to give some examples).
It is a highly specialized animal, which means that when the bubble algae are eaten, they will not find food and die hopelessly.
It is very hard to find in shops and when available they are usually at a very high price.

Siganus magnificus

Some hobbyists say it is a fish that likes to eat bubble algae. Actually it is quite a “whimsical animal”, I've seen specimens clean the aquarium in a few days from valonia, but I have seen others which devoured caulastreas and other types of corals.

Other invertebrates

If it is to remove small bubble algae, whose cell wall is not yet fully formed, we can use some snails although bear in mind that they usually will consume them if they are very hungry. Possibly the most effective is the tectus, a snail that reaches large a large size and has a powerful and sharp radula able to chew these algae.

Another option is some species of sea urchin, such as tripneustes family and the diadema (forget about mespilia and echinometra), which will eat some of these little bubbles, but only as a last resort if no other algae is available.