Olive anemone — Isactinia olivacea

Where
The olive anemone Isactinia olivacea (Hutton, 1879) is another common anemone from mid-tidal rock pools throughout New Zealand and southern Australia. They tend to like moderate to open coasts and clean water.

Identifying features
A small to medium-sized anemone (~30 mm across) and about as wide as high. Olive green tentacles, which are uniform in colour. The oral disc is brownish.

Similar to 
Mudflat anemone is smaller and lives in less wave-exposed areas. Also the mudflat anemone can have speckled tentacles. The brooding anemone is of s similar size and colour, but is found on seaweed. The red warratah anemone is of a similar size, but is red and lives in shade higher on the shore.

Ecology
The olive/brown colour comes from photosynthetic pigments and it is likely that these pigments are contained within algal cells (zooxanthellae). These zooxanthellae enable the anemone to supplement its energy, much in the same way as the mudflat anemone. 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.

Not much appears to be known regarding what feeds on this anemone. However, the damage shown by one of the anemones in the fourth picture suggests that some form of predation may occur (perhaps the cropping of tentacles by fishes or sea-slugs). There’s a small project there for someone 🙂

Olive anemones in sand amongst green-lipped mussels in a mid-tidal rock pool at north Piha. This picture was taken in bright sunlight during February 2015.

A close-up of an olive anemone in a mid-tidal rock pool at north Piha.

A slightly wider view of the same Olive anemone in a mid-tidal rock pool at north Piha.

More olive anemones in a mid-tidal rock pool on Lion Rock, Piha. Note the damage to the anemone in the upper-centre-left of the picture.

Two olive anemones in a crevice between two rocks in a mid-tidal rock pool at north Piha.