Three types of green algae found in the Chlorophyta phylum that are commonly referred to as bubble algae are the smooth Valonia and Ventricaria, and the rough Dictyospheria genera.
These algae are single-celled plants that reproduce sexually and asexually (having no evident sex or sex organs), growing as bubbles in various shapes and sizes. Valonia macrophysa has large bubbles, Valonia aegagropila forms bubbles about three times as long as they are wide, and Valonia utricularis grows sausage-shaped bubbles.
Ventricaria ventricosa is the most common type found in aquariums and grows as individual rounded green bubbles of up to an inch or more in diameter. There is also a bubble stage of Derbesia (hair algae) that resembles Ventricaria ventricosa, but differs because it drifts when unattached, whereas Valonia sinks.
Dictyospheria form mats of small bubbles in a tight vicinity of each other in an irregular pattern and their growth follows the shape of the live rock or item they are growing on. Fast growing, these rough bubble species can cover rocks, prevent corals from attaching and may even overtake coral growths.
Colpomenia is another from of bubble algae, but found in the brown algae phylum Phaeophyta. Colpomenia grow rubbery, hollow, irregularly shaped masses that may float or drift when broken off. It grows especially well in nutrient rich environments, and if they were fast growing would be considered a nuisance algae.
Bubble algae are usually brought into an aquarium when introducing live rock. Living on very small amounts of nutrients and low lighting (even in dark areas of an aquarium), if they become a nuisance they usually require removal or thinning by hand. Reducing tank nutrients will not do the job with the Dictyospheria sp. Great care should be taken not to break open the bubbles. As the bubbles mature they contain spores, and if broken this can cause them to spread more rapidly.
We get asked questions all the time about using Emerald Green Crabs or Red Sea/Indian Sailfin Tangs for eating these algae. To help shed some light on this subject, here are some resources you will find helpful to answer those questions.
John Rice suggests the Emerald Green Crab (Mithrax sculptus) as a good natural herbivore choice to help keep bubble algae cropped in an aquarium. In Terry Siegel's Outer Reef Limits Algae Woes article (From the Aquarium Frontiers Archive), Terry discusses the use of Emerald Green Crabs with great success. This article is an excellent resource to learn more about Bubble algae, and includes mention of other common problem hair algae like the Bryopsis, Derbesia and Cladophora species.
John Rice also suggests the Red Sea/Indian Sailfin Tang (Zebrasoma desjardini). However, our Reef Fishes 500+ Essential-To-Know Aquarium Species book by Scott W. Michael states that it is, "One of the best choices for controlling undesirable filamentous algae in a reef aquarium; an occasional individual will even eat nuisance bubble algae". In other words, not ALL specimens may nibble on these algae. Our understanding is that if you get one of these fish, there is no absolute guarantee that it will eat your bubble algae. The other factor to keep in mind is that this fish grows quite large, to 15+ inches. A very big aquarium of a 135 gallon minimum is suggested for keeping this fish in captivity.
Tom Phillips (The Reef Guy) experienced these same situations. His Emerald Crabs did the trick, but the Red Sea Sailfin Tang didn't touch the stuff. To find out more, refer to the Bubble Algae - Valonia section on his Creative Reefs Algae Control page. Tom has other information about Valonia, including instructions for using his method for removing it by means of siphoning.
We have developed our own procedure for siphoning Bubble Algae from the frag tank in our pet store. The 4' by 3' by 6" high frag tank is about 3' off the ground and has a sump underneath it. We just put a fine mesh fish net on top of the sump and start a siphon using a length of 1/2" hose with the end of the hose in the net. It is quite easy to just siphon the Bubble Algae into the net without bursting the Algae or disturbing the coral frags. The tank water goes right back into the sump, so you don't have to top off or refill the tank.
In Part 5 of this series we discuss Cups and Brushes found in the green algae phylum Chlorophyta.