58 — Olive anemone, Isactinia olivacea

Some green Isactinia olivacea, Lion Rock, Piha,
22/12/15.

The olive anemone (Isactinia olivacea (Hutton, 1878) is a common sight on rocky beaches around New Zealand and southern Australia. They're a smallish green–brown-coloured anemone, which can also be greener or browner depending on the population.

Olive anemones are interesting, because they (like tropical corals) contain symbiotic photosynthetic algae (zooxanthellae). Healthy zooxanthellae produce starches, which the corals can't consume, so corals keep their zooxanthellae in a slightly starved state. Then the algae's metabolism produces sugars, which the coral can use as food. This is the basis for the symbiosis between the two organisms: the zooxanthellae get a place to live, but not quite all the food they can eat, while the coral gets a food source in return for some house guests.

Some brown Isactinia olivacea, South Piha,
15/04/16.

Having the zooxanthellae extends the range of viable habitats for the anemone. It may enable to anemone to live higher on the shore out of the reach of crawling predators.

Olive anemones also contain carotenoid pigments and it has been speculated that these act as a kind of sunscreen, protecting the anemone from sunburn; they are often seen in direct sunlight, with their tentacles fully extended.

Isactinia olivacea, Pilot Bay,
Mt. Maunganui, 27/7/18.

Like corals, anemones can bleach when placed under stress and may eventually die without their zooxanthellae. However, it's not an area with a great deal of research.











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