Sun Anemone, Stichodactyla helianthus
Sun Anemone, Stichodactyla helianthus. Underwater photographs taken in coastal waters off Akumal, Quintana Roo, March 2021. Photographs and identification courtesy of Marina Sutormina, Stockholm, Sweden.
Phylogeny: The Sun Anemone, Stichodactyla helianthus (Ellis, 1786) is a member of the Stichodactylidae Family of Carpet Sea Anemones. The Genus Stichodacyla is one of ten genera in this family, and there are five species in this genus. This species is also known as the Atlantic Carpet Anemone, the Caribbean Carpet Anemone and the Caribbean Sea Anemone and in Mexico as anémona sol.
Morphology: The Sun Anemone is carpet-like. It has a soft body, with a flattened disc that is covered with numerous short, thick tentacles. The tentacles have rounded tips and have nematocysts (stinging cells) on their tips, which they utilize for predation and for defense. The nematocysts contain a variety of polypeptide neurotoxins, one of which is Sticholysin II, a 48-amino acid neurotoxin. They are a uniform golden-brown, green, or yellow color. They are large in stature, ranging from 10 cm (3.9 inches) to 20 cm (7.9 inches) in diameter.
Habitat and Distribution: Sun Anemones are found either as single individuals or in dense aggregations. They attach to hard surfaces, in shallow water reef environments with mild to strong currents. They live at depths up to 10 m (30 feet). The Sun Anemone is a resident of all Mexican waters of the Atlantic Ocean including the Gulf of Mexico and the east coast of the Yucatán Peninsula in the Caribbean.
Diet: Sun Anemones are zooxanthellate, meaning that they have a symbiotic relationship with single-cell dinoflagellates, known as zooxanthellae. Zooxanthellae live within certain Coral Polyps, Sea Anemones, Jellyfish, and Nudibranchs. The zooxanthellae produce energy, during daylight, by means of photosynthesis. This energy is passed along to their hosts, sometimes providing up to 90% of the host’s total energy needs. In return, the host provides nutrients, carbon dioxide, and a secure, sunlit, platform for the zooxanthellae. Sun Anemones are also carnivores, using their tentacles to capture prey such as fish, small shrimp, and zooplankton.
Predators: Predation of Sun Anemones specifically has not been documented. Other members of this family are eaten by fish, sea stars, gastropods, and nudibranchs.
Reproduction: Sun Anemones are gonochoric (male or female for life). They rarely reproduce asexually, through fission. They more frequently reproduce sexually, through broadcast spawning. The eggs are fertilized externally, and hatch into planular larva. This species lacks a medusa stage, exhibiting the polyp stage exclusively.
Ecosystem Interactions: Sun Anemones live in commensal relationship with other organisms such as crabs, hermit crabs, and shrimp.
Human Interactions: The neurotoxins of Sun Anemones are of interest to the scientific community for their potential use in the treatment of various human diseases including diabetes, lupus and multiple sclerosis. There sting is considered to be highly venomous and may cause anaphylactic shock and acute liver failure. The Sun Anemone has not been formally evaluated from a conservation perspective; however they are common, with widely-distributed populations, and should be considered of Least Concern.
Synonyms: Actinia helianthus, Discosoma anemone, Discosoma helianthus, Hydra helianthus, Stichodactylae helianthus, Stoichactus anemone, and Stoichactus helianthus.