Sunburst Anemone, Anthopleura sola

Sunburst Anemone, Anthopleura sola. Underwater photographs taken in coastal waters off San Diego, California, March 2016. Photographs and identification courtesy of Bob Hillis, Ivins, Utah.

Phylogeny:  The Sunburst Anemone, Anthopleura sola (Pearse and Francis, 2000) is a member of the Actiniidae Family of True Sea Anemones. The genus Anthopleura is one of fifty-six genera in this family, and there are forty-eight species in this genus. This species is also known as the Starburst Anemone and in Mexico as anémona estallido estelar.

Morphology: Sunburst Anemones derive their common name from the radiating reddish lines on the oral disc. The disc, stalk, and tentacles are green. The tentacles are marked with white banding. They have radial symmetry, a hollow digestive cavity, and specialized stinging structures in tentacles surrounding the mouth. Their polyps have a flower-like appearance, with the tentacles located on the margin of the disk and they lack a calcareous skeleton. Sunburst Anemones are fairly large in stature having a maximum of 25 cm (9.8 inches) in diameter. The Sunburst Anemone is similar in appearance to the Aggregating Anemone, Anthopleura elegantisima, which  has a more southerly range.

Habitat and Distribution:  Sunburst Anemones are found attached to rocks and other hard surfaces from the intertidal zone to depths up to 18 m (60 feet). They are solitary individuals that are often attached in a hole or crevasse, with only their disc visible. In Mexican Waters the Sunburst Anemone is a resident of the Pacific but has a very limited range being found from Punta Banda, Baja California, northward along the extreme northwest coast of Baja.

Diet:  Sunburst Anemones use their stinging tentacles to paralyze prey which include crabs, fish, mollusks, sea cucumbers, and other invertebrates. Sunburst Anemones are also  zoochlorellate, meaning that they have a symbiotic relationship with single-cell algae, known as zoochlorellae. Zoochlorellae give these anemones their green color.  The zoochlorellae produce energy, during daylight, by means of photosynthesis. This energy is passed along to their hosts. In return, the host provides nutrients, carbon dioxide, and a secure, sunlit, platform for the zoochlorellae.

Predators: Sunburst Anemones are preyed upon by fish, gastropods, nudibranchs, Loggerhead Sea Turtles and starfish. To avoid predation, their defense mechanisms include: stinging tentacles, an ability to roll its tentacles and disc inward forming a stumpy blob that is difficult to attack, and detaching themselves from the substrate to drift or roll to safer environments.

Reproduction: Sunburst Anemones are gonochoric ( male or female for life). They have the ability to reproduce sexually, or asexually by longitudinal fission. Sexual reproduction is accomplished through broadcast spawning, with the gametes released through the mouth. Fertilization is external. The eggs hatch into planular larva.

Ecosystem Interaction: Other than the symbiotic relationship with the green algae discussed above, the available literature does not discuss the relationship of Sunburst Anemones with commensal or parasitic species.

Human Interaction: Sunburst Anemones have no direct impact on human activities. From a conservation perspective they have not been formally evaluated however they are fairly common with a relatively wide distribution and should be consider to be of Least Concern.