It always appears more frequently in the sales tanks of the aquarium trade after the summer vacations: Actinia equina, the sea anemone with the beautiful German names “Erdbeerrose”, “Purpurrose” or “Pferdeaktinie”.
This article is part of a series of articles on “Experiences with saltwater aquariums”. In this loose collection, our author Andreas Berns — an aquarium consultant with many years of experience with aquariums of all types and sizes — reports anecdotally and entertainingly on special aquarium inhabitants, interesting integration projects and curious experiences. He also gives valuable tips on keeping the species described.
The following stories have been published so far:
Beware of poison: Lionfish in the reef aquarium
Pretty clever: a pallet doctor moves house & gets socialized
Tridacnidae: A myth in the sea
Tough little gemstone in the marine aquarium: the horse actinia Actinia equina
The appearance of these flowering animals at the same time of year is not due to a special reproduction cycle or other biological factors, but is simply due to the fact that many aquarists — unfortunately! — go “actinia picking”. Actinians can be found almost everywhere in the Mediterranean in the intertidal zone, but also at depths of up to 8 meters. Often the number of individuals is so high that within a short time not only the personal requirement of perhaps 5 or 8 animals is found, but in an often terrible “passion for collecting” the “sea lover” takes far more animals from the sea than he himself could maintain in his aquaria. As a result of this criminal act, which damages the natural habitat, the animals taken from nature then fill the dealers’ tanks after the vacations.
Hint
Please remember: The sea is not a self-service store for us aquarists! Behavior such as the “actinia picking” described above damages nature — and marine biotopes in particular are already suffering massively even without such interventions! Moreover, it is not even necessary to tear the animals out of the wild: 2-3 of the beautiful and robust actinia are enough to get them to reproduce quickly with good water values and sufficient, varied feeding. You should therefore always use captive-bred specimens and never wild-caught specimens (neither your own nor those from other sources)!
Care and feeding
If you want to keep Actinia equina in an aquarium, you only need to pay attention to a few things. However, these few rules are crucial for successful keeping and especially breeding.
The strawberry rose – as the appearance of Actinia equina is perhaps most accurately described – occurs in the Mediterranean mainly in the red coloration in the strongly moving intertidal zone. This fact must be taken into account in aquarium keeping, as the animals have a very high mucus production to protect them from drying out. This mucus means that they can easily survive a “dry period” at low tide and the animals are not harmed in any way.
However, the mucus produced must be regularly expelled; in the sea, this is done by the natural current and wave action. In the aquarium, we need to enable this with a medium to strong artificial current to keep the actinia healthy.
Once it has chosen a location in the sea, the strawberry rose generally does not leave it. It is only forced to change its location in the event of extreme changes in the water current or other major disturbances. Depending on the conditions in its natural habitat, the horse arctic rose adopts a vertical or horizontal and often “upside down” position. Once accustomed to this position, it tries to reproduce it throughout its life.
It can happen that animals placed in an aquarium are apparently dissatisfied with the seemingly ideal location and wander restlessly through the aquarium until they hopefully find a place that suits them, which doesn’t seem so ideal to us aquarists. But the sea anemone alone decides according to the criteria of current, light, body axis placement — and not least according to the food supply!
Rich food necessary
The latter is a crucial point in the successful care and breeding of the horse actinia: Actinia equina needs regular, rich food to avoid slowly starving to death. At least once a week, the animals need a large chunk of food, such as a sand shrimp, halved smelts or mussel meat.
In between these feedings, they will help themselves to any animal food they can somehow reach. This includes krill, artemia and even Cyclops as well as the occasional unwary small fish, shrimp or even a larger sickly fish!
If actinia are not fed sufficiently, they use up their own body substance and shrink so that they become smaller and smaller. Once this process is well advanced, it can often no longer be halted, even with heavy feeding. The reason for this is that the tentacles shrink disproportionately faster and more strongly in relation to the body mass. As a result, neither catching food nor transporting food into the mouth is possible and the animal starves to death.
When lighting becomes a danger
Another important factor is the light: When introducing actinia for the first time, make sure that the lighting is compatible! Experience has shown that too strong, direct light is dangerous for the animals. HQI light in particular can cause considerable damage.
Although the animals usually live just below the surface of the water in nature, they avoid direct sunlight by positioning their habitats under ledges and the like.
In an aquarium with HQI light, a correspondingly high level of UV protection must therefore first form before the animals can be safely exposed to this light. As this adaptation can take up to 3 months, it is essential that you offer the actinia shaded areas for this period.
Society and compatibility
The ca. 200 tentacles of the horse actinidae have an extraordinarily high cnidation and adhesion capacity. Once caught, a fish has little chance of escaping certain death. As a rule, however, the danger is low, as it only happens very rarely, usually only sick and weakened fish fall victim to Actinia equina.
In contrast, anemonefish often enter into a substitute partnership with actinians in the absence of a host anemone. Although the size ratios usually do not match at all, the actinians tolerate this and leave these fish undisturbed.
Actinia are quite insensitive even to nettling by other sessile invertebrates. Conversely, they do not bother other invertebrates – despite their great nettling power – unless there is too much competition for space. In this case, however, care must be taken.
In a reef aquarium, an actinid of approx. 5 cm diameter and regular 4 cm body height tolerated a fast-growing Xenia colony up to 2 cm close to its body. Then, however, it changed its body shape within a few minutes to around 8-9 cm in length with a shrunken body diameter, and it entangled all the Xenia within the entire reachable radius, which died within a very short time. As you can see, it is advisable to be a little vigilant and, if necessary, to “help” steer the competitors into other directions.
Propagation
The reproduction of actinia can be stimulated by a good, plentiful and vitamin-enriched animal diet. The actinia form polyps in their bodies, which they then usually expel at night. Some of the polyps regularly survive and settle in places in the aquarium that are protected from the current. The polyps are best reared in the original aquarium itself, as moving them to another tank is critical due to their initial sensitivity to changes in the water parameters.
The small actinia initially require plankton for rearing; feeding with freshly hatched artemia is possible after approx. 1 week.
Header image: “5350755” via Pixabay
