Aiptasia

Aiptasia is a genus of a symbiotic cnidarian belonging to the class Anthozoa (sea anemones, corals). Other well known cnidarian groups include the jellyfish (Class Scyphozoa), the hydroids (fire coral, and the genus Hydra), and the box jellyfish (Class Cubozoa). Aiptasia is widely distributed tropical sea anemone of benthic lifestyle typically found living on mangrove roots and nearby hard substrates. This anemone, as well as many other cnidarian species, is found to contain symbiotic dinoflagellate unicellular algae of the genus Symbiodinium living inside nutritive cells. The symbionts provide food mainly in the form of lipids and sugars produced from photosynthesis to the host while the hosts provides inorganic nutrients and a constant and protective environment to the algae. Species of Aiptasia are relatively weedy anemones able to withstand a relatively wide range of salinities and other water quality conditions. In the case of A. pallida and A. pulchella, their hardiness coupled with their ability to reproduce very quickly and out-compete other species in culture gives these anemones the status of pest from the perspective of coral reef aquarium hobbyists. Ironically, these characteristics make it easy to grow in the laboratory and thus it is extensively used as model system for scientific study. In this respect, Aiptasia has contributed a significant amount of knowledge regarding cnidarian biology, especially our understanding of cnidarian-algal symbioses, a biological phenomenon crucial to the survival of corals and coral reef ecosystems. The dependence of coral reefs on the health of the symbiosis is dramatically illustrated by the devastating effects experienced by corals due to the loss of algal symbionts in response to environmental stress, a phenomenon known as coral bleaching.

Morphology

Cnidarian species are found in one of two body forms: the polyp and the medusae. Some alternate between these two forms during their life cycle. In the case of Aiptasia, and all anthozoans, the body form is the polyp. The body is composed of a pedal disc with which Aiptasia attaches to the substrate, a smooth and elongated body column and an oral disc which bears the mouth and long stinging tentacles.

Reproduction

In the case of the well-studied Aiptasia pallida and Aiptasia pulchella, individuals are dioecious, meaning that individuals are of separate sexes. During spawning, anemones release their gametes into the water where fertilization occurs. The resulting zygote becomes a free swimming planula larva which eventually settles onto a suitable substrate where it undergoes metamorphosis to become a small polyp. Newly produced larvae are aposymbiotic meaning they do not contain symbionts. The larvae or newly settled polyps can acquire symbiotic algae from the environment.

In the aquarium

Aiptasia sp. are considered pests in the marine aquarium hobby, because they are stressful to coral around them, and occasionally even sting fish and desirable invertebrates. They are often accidentally imported along with live rock. Once present in the aquarium, the polyps are notoriously difficult to remove as attempts to remove often inadvertently create more, due to new polyps regenerating from remnants. Hobbyists commonly put Peppermint shrimp inside the aquarium to control Aiptasia populations, as the arthropods regularly prey on small cnidarian polyps. The nudibranch Berghia verrucicornis is considered one of the best predators for Aiptasia sp.

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