Here’s a quick focus on sea anemones. You’ll probably be most familiar with the bubble-tip anemone, which is often associated with the anemonefish (clown fish) that live among its tentacles. Here on Norfolk Island we have a rare clownfish, called McCulloch’s anemonefish or McCulloch’s clownfish Amphiprion mccullochi, which is endemic to here and Lord Howe Island. Having said that, I’ve never seen this fish inside the lagoons. It prefers instead to live in around the island in more open water. I’ve also recorded six other species of anemone in Norfolk Island’s lagoons, and there could easily be more.
A close relative of corals and jellyfish, sea anemones are soft-bodied animals that ensnare and immobilise passing prey with their stinging tentacles and then digest them. Their digestive enzymes are so strong ‘they can digest the flesh of a small animal in 15 minutes’.[i]
When it comes to reproducing, they can do this sexually – by releasing gametes into the water column, which then form free-swimming planula larvae. These disperse, and eventually settle on to the substrate of the reef or in the sand after about ten days, although they can live in the water column for as long as 59 days.[ii] And asexually by a process of fission or fragmentation (depending on the species), thereby producing a clone of themselves – a genetically identical individual. By repeatedly producing clones, they can, in effect, be immortal!
Hemphrich's Anemone, Heterodactyla hemprichii, reproducing asexually by cloning itself. The process of tearing itself in two is almost complete.
The magic of telomeres
How long sea anemones live is not really known. Certainly, they are hard to keep in captivity and can die in just a few short months without proper care. A five-year-old aquarium-living sea anemone is considered quite old. In the wild, however, sea anemones are thought to live for more than one, or even two, hundred years. In fact, they don’t really die unless conditions change. If they lose a tentacle, they grow another, so unless ‘they’re … poisoned or eaten, they keep on keeping on.’[iii]
So how is this? It seems that their DNA is protected from damage by telomeres.[iv] Think of these as being like crash helmets for chromosomes. According to Michael Ellis:
One reason for an anemone’s longevity may lie in its telomeres. A telomere is a structure that caps each chromosome and protects it from damage during cell division … without telomeres, the DNA in those chromosomes eventually becomes so damaged that cells can no longer divide.[v]
Human telomeres grow shorter each time our cells divide. This speed of this shortening is thought to be associated with how quickly our bodies age. Maybe we could learn a thing or two from how anemones repair their telomeres to protect their chromosomes.
Another factor in the longevity of sea anemones is their genes appear to have low mutation rates, suggesting they can repair their DNA; moreover, they don’t develop tumours like other animals.[vi]
Audrey, the bubble-tip anemone, Norfolk Island
There are a few anemones in Norfolk Island’s lagoons that I like to keep track of. Two particularly noteworthy ones are the solitary Haddon’s anemone (see below), and a splendidly huge bubble-tip, which seems to have found her (?) perfect des res, just beneath the iconic Lone Pine in Emily Bay. Because of her long tresses that stream in the passing currents, I’ve nicknamed her Audrey after the character in Dr Seuss’s The Lorax (photo, right).
Sea anemones don’t have too many predators, thanks to batteries of stinging cells in their tentacles. Having said that, some fish, sea stars and turtles will feed on them. I’ve seen, for example, a green sea turtle happily munching on a sea anemone.
Below are a few examples of each of Norfolk Island’s seven identified species:
Bubble-tip anemone, Entacmaea quadricolor
Bubble-tips can grow as large as 30 cm in diameter. Juveniles will have around 20 tentacles, which increase in number as they age. Both male and females exist in the wild.
As you can see from the photos, below, the colour vary widely. And interestingly some exhibit the bubble tips, while others don’t. The ones without the bubble tips have longer tentacles, like Audrey (above).
Pale anemone, Exaiptasia diaphana
Pale anemones are relatively small, growing to no more than around 5 cm in height. These anemones can be either male and female (gonochoric) or hermaphrodite. Hard to find, they are usually tucked under rock and coral ledges, well out of sight.
Sand anemone, Heteranthus verruculatus
Often all you will see of the small anemones is the tentacles forming a small ring, while the central part is covered in sand. I’ve seen them as large as maybe 7 to 8 cm in diameter and some can be rather colourful, as you can see below.
Hemphrich's Anemone, Heterodactyla hemprichii
These anemones seem to grow a little larger than the sand anemones (to maybe 8 cm) and are noteable because of their branched tentacles, which gives them a furry appearance. These anemones (on Norfolk Island) are usually beige or brown in colour.
Frilly sea anemone, Genus Phymanthus
Like the sand anemone, these are often found partially covered in sand.
Haddon's anemone, Stichodactyla haddoni
This individual is probably somewhere over 30 cm in diameter, although they can grow as large as 80 cm, and has been sitting quietly in Emily Bay in this one spot for at least four years to my knowledge. If they don't like somewhere they’ll move. But this Haddon has stayed put, shrugging off drifting sand, fending off algae growth, and avoiding being nibbled by hungry wrasse. Like bubble-tips, these anemones will often host clownfish.
Mini carpet anemone, Stichodactyla tapetum
These are the smallest of the carpet anmones, growing to around 10 to 15 cm in size. Their real beauty is revealed when you magnify them on your computer screen and can say the pearly tentacles, which are seen in a variety of colours (see below for some examples).
[i] Green, G, ‘Introduction to sea anemones’, E-Fauna BC.
[ii] Scott, A & Harrison, PL 2009, ‘Gametogenic and reproductive cycles of the sea anemone, Entacmaea quadricolor’, Marine Biology, vol. 156, ed. 8, pp. 1659–1671.
[iii] Ellis, M 2020, ‘Do Sea Anemones Live Forever?’ Bay Nature Magazine, September.
[v] Ellis, M 2020, ‘Do Sea Anemones Live Forever?’ Bay Nature Magazine, September.
[vi] Ibid