Actinodiscus, The Indestructible Mushrooms (Dec 2006)

[zanzimog]

Actinodiscus: The Indestructible Mushrooms

This month’s invertebrate profile is a bit of a cheat. I did a hasty write-up on mushrooms a few months ago, and finally decided it was time to do a better job. The result is a little narrower, and hopefully more informative.


(Photo Credit: reiverix)

Pretty, Easy
Mushrooms in the genus Actinodiscus are often the very first corals a marine aquarist tries, and with good reason. They are extremely hardy, surviving and even thriving with high nutrient levels, low light and low circulation. On top of that, they come in a variety of colors, patterns, shapes and sizes. What’s not to like about a coral that’s pretty, reproduces readily, and is hard to kill?

Taxonomy and General Biology
Although often classed among “softies” because they do not have a skeleton, mushrooms are actually more closely related to the stony corals and anemones than they are to true soft corals (octocorals). Like all corals, they are in the phylum Cnidaria, class Anthozoa. The mushroom corals have their own order, the Corallimorpharia, which is supposedly more closely allied with the stony corals (Scleractinia) than the anemones (Actiniaria). The order has 5 families, and genera include the popular Ricordia, along with the predatory elephant ear mushroom, Amplexidiscus. Beyond that, the taxonomy of corallimorpharians is a bit of a mess. In fact, whether Actinodiscus is a true genus, or part of the genus Discosoma is currently unclear. Borneman refers to the genus as “Actinodiscus = Discosoma,” but I will use the less clumsy “Actinodiscus.”

Actinodiscus species all have the same basic body plan, consisting of an oral disk that comprises the “head” of the mushroom, with the mouth at the center, and a stalk, or column, connecting it to the pedal disk which attaches the animal to the substrate. The oral disk is often decorated with rows of vestigial tentacles that can appear as bumps or pimples, often in contrasting colors as in the green pimples on the red species below.


They all live as single polyps tightly stuck to the substrate. They are often found in dense aggregations because of their prodigious reproductive abilities. It did not take long for these guys to fill up a 10 gallon nano.


Care and Feeding
Actinodiscus mushrooms must be the easiest corals to maintain, aside from pest species such as Aiptasia. I have tried to find conditions under which they would fail to thrive, and have been beaten every time.

Lighting: They will grow, reproduce and spread under NO fluorescent, PC, VHO and metal halide lighting. There are very few species of photosynthetic corals that can make do with as little light as mushrooms can. A single NO striplight over a tank will probably not be enough, but a couple of NO tubes or a single PC lamp will probably be just fine. They will adapt to higher light levels, but often turn brown in response to intense light, so it is best to keep them low in the tank, or below overhangs in brightly lit aquaria.

Feeding and nutrition: Actinodiscus species do not need to be target fed, but the fact that they thrive with low-intensity light implies that they are getting nutrition from somewhere. Indeed, according to Borneman, they use mucus to collect suspended material from the water column and transport it to their mouths via cilia. This may help to explain the anecdotal observation that mushrooms do better in “dirty” tanks with higher nutrient loads.

Mushrooms do not like intense currents. Gentle water movement, that ruffles the polyps rather than blasts them, will keep them happy.

Reproduction
It is said that corallimorpharians can reproduce by splitting, but I have never seen an Actinodiscus actually split. All of the progeny in my tanks have arisen by "pedal laceration," which occurs when a polyp moves along the substrate and leaves little pieces in its wake. Amazingly, each of the little nondescript blobs of tissue can develop into a perfectly good mushroom, as can be seen in this photo of a proud parent and some of its offspring.


One of the more interesting, and potentially aggravating, behaviors consists of crawling off the rock and floating around the tank to find a new home, as shown in the photo below. This usually happens when a rock becomes filled to capacity and polyps leave to find space of their own. This is a great way to collect polyps for sale or trade, but it also can make it difficult to control the spread of these guys once they get established.


As with most corals at present, sexual reproduction in captivity is essentially unknown.

With such attractive colors, interesting shapes and incredible hardiness, Actinodiscus mushrooms have a lot to recommend them. As with anything, there can be too much of a good thing, and their hardiness, fecundity and propensity to migrate have earned them pest status in some reef aquaria.

References/more info:
Borneman, EH (2001) Aquarium Corals : Selection, Husbandry, and Natural History. TFH Publications
Sprung, J & Delbeek, JC (1997) The Reef Aquarium, Volume 2. Two Little Fishies
Tree of Life (for taxonomy)
Melev's Shroom Page

[FreddytheFish]

I like it! (Oh, BTW, I haven't forgot about the mantis, I've been pretty swamped with school and family recently and haven't had much time to look at it. Sorry!)

Also how big do most shrooms get?

[zanzimog]

I like it!

Also how big do most shrooms get?

Thanks! Mushrooms can get quite big. Polyps 3-4" are not unusual, and I have seen some up to 5".

BTW, I haven't forgot about the mantis, I've been pretty swamped with school and family recently and haven't had much time to look at it. Sorry!

Don't sweat it at all. Better to wait 'til you have time to relax and enjoy the process.

[FreddytheFish]

OK, I was looking at getting one, but don't really want a giant one.

[OrionGirl]

Another observational point--in lower light settings, they tend to 'swell', stretching up to catch any light that is available. In higher light settings, they are flat against the substrate or rock. I prefer the flat look, but many people get used to seeing them tall and lanky, then worry something is wrong with them if they add more light and the shrooms flatten out.

[forestal]

nice write up