The Berghia genre
With this article we would like to direct the attention on a nudibranch of the genre Berghia, a very interesting species, useful for marine reef aquariology. Of course in the matter of specialized literature there has been an availability of information for quite some time regarding the reproduction of nudibranchs Berghia stephanieae (Berghia verrucicornis), but after around ten years since their entrance in this hobby it is surprisingly almost never available on the market, playing therefore only a minor role in the fight against glass anemones. On the contrary of nudibranchs of the Aeolidaceca suborder, extremely hard to not say impossible to maintain, Berghias are not only attractive, but they are also easy to nurture reproduce. And not only that, because their alimentation has specialized itself in an animal species which can turn out to be a real plague in our aquariums: sea anemones of the Aiptasia genre. The Berghia genre is vastly spread in tropical and warm seas. Snails, usually employed in aquariology for the control of glass anemones, are normally called Berghia verrucicornis (Costa, 1864). In all case, discussions are still underway regarding the number of species that this genre is made up of and their specific name. The images of countless specimens of Berghia stephanieae (Berghia verrucicornis) of the Atlantic, Caribbean and Mediterranean seas do not only evidence different color schemes, but also morphologic diversities, for example in the shape of the rinoholes or the Cerata or in the presence or not of tubercoles or furrows; even the shape of their eggs is variable. It cannot be excluded that we are effectively dealing with more than one species. In the Pacific there is one further species of Berghia, also feeding itself with glass anemones: Berghia major. Most of the Berghia specimens offered in the aquariologic market in the USA have been harvested in the Florida Keys (east coast).
Berghia stephanieae (Berghia verrucicornis)
All snails illustrated in this article belong to that group the representatives of which are normally defined as Berghia stephanieae (Berghia verrucicornis). Over the course of this article, for simplicity, I will keep on using said definition. Adult Berghia verrucicornis reach a length of around 25 mm, occasionally they can grow even bigger. Their back (dorsal side) is covered with attractive appendices defined Cerata and needed for gas exchange, metabolism and defense. These snails, by devouring glass anemones, also ingest lively symbiont algae gaining an advantage from them, because they get stored in their dorsal appendices. Anyhow, they are not able to keep these unicellular vegetables alive for long so that they can permanently take advantage of their photosynthesis. For this reason they have to get multiple times per week, even better daily, some sea anemones to feast on. If they get enough anemones, a Berghia population is able to self-sustain itself continuously generating young animals. Because of their reproductive vivacity and for the high price (here in the USA a specimen costs between 10 and 30 US Dollars), they are good candidates for the aquariologic market.
Two of the biggest problems in the maintenance of these nudibranchs are their small size and their predisposition to fall prey to over filled pumps, filters, and to other aquariologic techniques. Besides, young snails, after coming out of the egg, are not visible to the naked eye for around eight weeks. Most animals available on the market do not measure more than 12 mm in length and are still very delicate. To favor their acclimatization they should be left in the transport bag for 20 minutes in the tanks to make a protective temperature adaptation possible. Following that the bag can be opened letting the animals come out spontaneously. All this should take place considering their nocturnal lifestyle. Of course the water in the aquarium has to be mature, and the appetite should not be underestimated. Hundreds of sea anemones are in fact necessary to nurture an adult couple of Berghias for the first few months. Those who would really establish these nudibranchs in their aquarium shall proceed systematically.We would recommend to initially isolate the new specimens. To this purpose a refugium is initially adapted or a deposition tank for fresh water fishes fluctuating in the aquarium. Those who are intentioned in reproducing these animals, are in fact obligated to raise them in a purposefully prepared tank. Even those who would like to introduce them in their reef aquarium only to decimate sea anemones, should initially keep the isolated to favor a good acclimatization. During the first two weeks several single rocks covered in Aiptasia are to be placed in the isolation tank until the nudibranchs have adapted to the new water conditions. As remembered above, it is strictly unadvisable to release new specimens of Berghia directly in the reef tank. Many coral fishes would bother the newcomers with weak bites out of simple curiosity. Besides, the strong current could easily drag them into the filter, in the skimmer or in an outflow tube, before they are able to acclimate and generate some discendants. Besides, if their high purchase price is to be considered, it makes sense to nurture them separately for a few weeks, until they are able to produce the eggs. With a little patience, from only one couple it is possible to obtain 20, 50 or 100 specimens, that can be employed to devour glass anemones in the aquarium. A high number is, in fact, necessary, because despite their conspicuous appetite for Aiptasia, it is very likely that the most recent adult specimens of Berghia may fall victim to some inhabitant of the aquarium, before eliminating the very last glass anemone.
The prey-predator dependence
On this point of view several other question marks are generated, already evidenced by Eric Borneman and others (1998): are some Berghia specimens really able to eradicate a plague of glass anemones in a reef aquarium? And if yes, what happens than to the nudibranchs? In this case, we simply have to deal with some kind of prey-predator dependence: the population of nudibranchs develops while the preys (glass anemones) decreases. Ultimately the big Berghia population is no longer able to sustain itself, collapsing, while the anemone will get better. It is indeed a reciprocal dependence, one that in nature will be found in countless cases, and this particular case determines the fact that the population of Berghia specimens will not be able to thrive in a reef aquarium without the intervention of the aquariophile. Initially a big number of preys (Aiptasia) will be available, followed by a lot of predators (Berghia). Following that a recession in preys will be evidenced, followed by a reduction in the population of predators. On the contrary of what happens in nature, we cannot be certain that, in a closed system like an aquarium, many specimens of Berghia could survive or that others may come from the outside, to exploit the reinforced glass anemone population. Therefore, I cannot stress enough times the importance of keeping in a separate site a “couple of reproductive specimens” of these nudibranchs, even if the intention was to occasionally control the increment in anemone population and not nurturing the snails beforehand in a targeted way. Otherwise, in every case of necessity, it will be necessary to find the animals in commerce, a rather expensive eventuality.