22 — Giant shore anemone, Oulactis magna

Giant shore anemones, south Piha, 13/9/16.

The side of a giant shore anemone with a parasitic
snail (Epitonium (Hyaloscala) jukesianum),
(lower centre left). The Gap, south Piha, 2015.

Juvenile, south Piha, 2016

Juveniles, south Piha, 2016.

South Piha, 2016.

Adult giant shore anemones, south Piha, 2016.

Rock pool assemblage of giant shore anemones,
south Piha, 2016.

Juvenile, south Piha, 2016.

Juveniles, south Piha, 2016.

Juvenile, south Piha, 2016.

Juvenile, south Piha, 2016.
Unusual colour pattern.

Juveniles, south Piha, 2016.

Lion Rock, Piha, 2016.

A juvenile among little
black mussels, south Piha, 2016.

Juvenile, south Piha, 2016.
Unusual colour pattern.

Stoney Point, Mt. Maunganui, 4/11/17,
showing the anemone's stalk.

Stoney Point, Mt. Maunganui, 4/11/17,
showing the anemone's stalk and spent
acrorhagi (white pustules with holes in them).

The giant shore anemone (Oulactis magna Stuckey, 1909) is a large (up to 12 cm across the disc) and spectacular sea anemone, endemic to, and found throughout New Zealand. It is found in areas of high wave exposure and clean water, from mid to low tide. You tend to see them on exposed coasts were rocks meet sand.

Giant shore anemones are particularly common on the west coast of Auckland, where dozens of large colourful anemones can be found in almost every deep rock pool. They are at their most colourful when they are small, often with an amazing array of colour schemes. Once they grow larger they tend to assume a single colour combination.

Often at Piha sand is scoured away from the rocks, exposing new potential living areas for these anemones and other marine life. Then there seems to be a rapid influx of beautiful juvenile anemones which quickly colonise this new living space. However, this can all be be in vain, for the sand can just as quickly return, burying and killing off these opportunistic invaders.

Not much seems to eat these anemones, although occasionally you do see them with what appear to be bites taken out of them. However, a small snail called a wentletrap (Epitonium (Hyaloscala) jukesianum Powell, 1924), is known to parasitise them. It uses a modified radula (mouth parts) to pierce the anemone and feed on its bodily fluids.

You often see this species of anemone at the bottom of rock pools, which is a great place to be if other animals get detached and fall off. You sometimes see the empty shells of little black mussels in the centre of the anemones, which could be seen as evidence for this.



































































































More info:
Anemone guide: https://shapeandtheidea.wordpress.com/2015/10/13/giant-shore-anemone-oulactis-magna/

Morton, J. E., & Miller, M. M. 1968. The New Zealand Sea Shore. Collins.