Anthopleura sola

Anthopleura sola is found in the Pacific Ocean, along the west coast of North America from Alaska to Baja California. (Harbo, 1999)

Anthopleura sola commonly lives on exposed rocky surfaces and in tidepools and crevices. It is found in the middle intertidal zone of semiprotected rocky coastlines of both the outer coast and bays. It is a hardy species that survives well in areas where there is industrial pollution or sewage. (Francis, 1979; McFadden, et al., 1997; Ricketts, et al., 1985; Salinas, 2000)

Anthopleura sola is found in clonal groups of aggregating individuals. Individuals range from 2-5 cm across the oral disc, but are usually less then 3.5 cm across. The disc can be twice that size when extended. Solitary animals are larger, averaging 6.5 cm across the oral disc; once considered a solitary form of the same species, these larger, non-cloning individulas have recently been described as a sibling species, Anthopleura sola (Pearse and Francis, 2000). Anthopleura sola has short tentacles with pink or lavender tips. There are radiating lines and other patterns on the oral disc. The column is green to white with large rounded tubercles, called verrucae, arranged in vertical rows. Anthopleura sola is often covered with sand, shells, and rocks which adhere to its tubercles and serve as protection from desiccation and solar radiation and provide camouflage against predators. Males and females of A. sola appear similar.

Some of the color variation in Anthopleura sola is due to golden-brown photosynthetic dinoflagellates (zooxanthellae) and/or green unicellular algae (zoochlorellae) that live in the tissue that lines the digestive tract of A. sola. These photosynthetic symbionts provide the green coloring and nutrients to *A. elegantissima*. Anthopleura sola that are white in color lack these symbionts and are usually found in areas of deep shade. Individuals that contain symbionts respond to light conditions, either moving toward or away from light until the right intensity is found. Anthopleura sola are unusual because they play the role of both producer and consumer in intertidal communities, and it is believed that they contribute at the same rate to primary productivity as do some intertidal algae. (Ricketts et al. 1985; Francis 1979; Salinas 2000; Pearse and Francis, 2000).

Anthopleura sola can reproduce both sexually and asexually, although most individuals reproduce asexually. Anthopleura sola are either male or female. The gonads are in the gastrovascular cavity, and eggs and sperm are released through the mouth.

In sexually reproducing A. sola, gametes are released during the summer and fall into the surrounding water. A planula larva forms after fertilization. The free-swimming larva undergoes further development and then settles down to form a new sessile anemone. Large numbers of gametes are produced, although very few larvae will survive to adulthood due to predation and the inability to find suitable habitat. Sexual reproduction results in new genetic combinations and a chance for the larvae to disperse away from their parents and populate new territories.

Asexual reproduction is a form of growth and seems to occur when an individual has found a suitable habitat. Anthopleura sola reproduces asexually by longitudinal fission. During longitudinal fission, the anemone divides into half forming two smaller anemones. Asexually reproduction takes place mainly from September to March and may be triggered by a reduction in food supply. Asexual reproduction results in genetically identical clones that have the same color patterns and sex. These clones rapidly spread out and form large aggregations of individuals, hence the common name of aggregating anemone (Johnson et al. 1977; Ricketts et al. 1985; Salinas 2000).

Anthopleura sola found in aggregations exhibit polymorphism. All of these individuals are cloned from one original asexually reproducing individual. Individuals in the center of the aggregation are larger, have developed gonads, and reproduce sexually. Individuals at the edge of the colony are smaller, have larger fighting tentacles (acrorhagi), and reproduce asexually more frequently. This division of labor allows individuals in the center to expend more energy on sexual reproduction, as it is unlikely that they will encounter individuals that are genetically different. Individuals on the edges of aggregations expend their energy on developing large acrorhagi to fight the individuals of adjacent clones.

When the individuals on the edge of an aggregation come into contact with individuals from adjacent clones, a battle ensues. They use their acrorhagi, which are large projections loaded with nematocysts located at the base of the tentacles, to sting, injure, and even kill members of the other clone. This inter-clonal fighting results in clear boundaries between adjacent agregations. This aggressive behavior is focused on non-clonemates, as members of each clone can distinguish their own clonematess and do not attack them. Intraspecific competition of the inference sort has also been observed in experiments where two adjacent clones competed over the resource of space.

Nudibranchs, especially Aeolidia papillosa, prefer to prey upon Anthopleura sola. Other predators include snails and sea stars. Sea stars can engulf an entire small anemone. Most predators avoid contacting the nematocysts of A. sola, but nudibranchs readily eat anemones and store the nematocysts in internal sacs at the tips of their cerata to use for defense purposes against other predators. Anthopleura sola release a chemical signal when under attack that warns other nearby anemones that danger is near. These anemones use their nematocysts, coloration, and camouflaging abilities to avoid predation (Ricketts et al.1985; Francis 1979; Pitkin 1995; Ayre and Grosberg 1996; Salinas 2000).

Anthopleura sola are carnivorous and feed on almost anything offered when hungry including copepods, isopods, amphipods, and other small animals that come into contact with their tentacles. The anemones grasp prey with their tentacles, which harbor stinging structures called nematocysts that they paralyze the prey. Once paralyzed, the prey is ingested and later expelled as pieces of shell and other debris through a central mouth (Ricketts et al. 1985; Pitkin 1995; Salinas 2000).

Studies are being conducted on the medicinal properties of Anthopleura sola tissue. A crude extract of Anthopleura sola has demonstrated antitumor activity against two experimental mouse tumors, P-388 lymphocytic leukemia and Ehrlich ascites tumor. The extract also showed cardiac stimulatory activity on isolated rat atria. Separate constituents of A. sola are responsible for these three biological activities (Quinn et al. 1974).

Anthopleura sola is not listed as an endangered or threatened species. A. sola appears to be doing well throughout its geographical range.

The life span of Anthopleura sola is not known, although evidence suggests that they may live for a century or more. In one case, specimens of A. sola lived in captivity for eighty years and only perished due to human error (Ricketts et al. 1985).