5 January 2013

Sea stars of Vancouver Island - part 3

In this post I present the remaining species of sea stars I found at Vancouver Island. The more 'common' forms with five arms (with one exception). Left: giant pink star. Right: rainbow star.

The blood star, Henricia leviuscula leviuscula. Henricia's are very difficult to identify. There are also a few subspecies, hence the double leviuscula leviuscula.

Philip Lambert notified me about the species in this post: 'You have homed in on three of the most difficult genera to distinguish from a photograph. I am far from certain for the Henricia without having them in front of me under a microscope. Even then, this genus is being studied by some others using DNA analysis, and they are finding more species. So it is an evolving study!' Just as Christopher Mah wrote (see bottom).

As I have written in an older post: in the future we just pick up our DNA-tricorder that tells us which species we have found. But then - after years - we long for yesterday when we had to study it ourselves. Then things were still a bit of a mystery. Those were the days!

Henricia leviuscula leviuscula (possibly). The blood star is not a very active hunter: it feeds on plankton, small organic matter, bryozoans and a few sponges. Species up to 32 cm across.

Although it seems I can do with a DNA-tricorder... I thought that this was the ridged blood star, Henricia aspera aspera, because its upper surface is more coarse in comparison to the blood star. But it is not. Philip Lambert informed me that it is just another subspecies of the blood star: Henricia leviuscula anectens. I am glad I was not totally off course, because in his book he says: 'is intermediate in appearance between H. aspera aspera and H. leviuscula leviuscula.' 

Again Henricia leviuscula anectens. The arm tips of blood stars are often slightly tilted upwards.

Evasterias troschelii, the mottled star embracing its prey. A typical posture for a lot of sea stars. Lambert (2000): 'To eat a bivalve, E. troschelii everts its stomach and inserts it between the shells while the tube feet pull from the outside. A specimen with an arm length of 22.5 cm can exert an average force of 4500 grams for six hours and a maximum force of 5500 grams.'

Up to 60 cm across.

Mottled stars in different colours.

Just as Henricia species: the species belonging to the genus Leptasterias, the six-rayed sea stars, are hard to identify. This six-rayed sea star with its short stubby arms is Leptasterias hexactis.

Up to 10 cm this is - at last - a smaller species. It is remarkable how many species of sea stars are to be found in these waters - Lambert (2000) describes at least 43 (sub)species - and how big they can get.

Another six-rayed species: Leptasterias aequalis. Philip Lambert: 'it has more slender arms than the one above, and even rows of plates.'

Orthasterias koehleri, the rainbow star. Up to 60 cm across.

Whereas a lot of sea stars have a very varied menu, the rainbow star prefers molluscs and sometimes sea squirts.

Gathering of three species, from left to right: giant pink star, rainbow star, again giant pink star and juvenile sunflower star.

Pisaster brevispinus, the giant pink star, is a monster. This specimen is about 65 cm across. It is - volume wise - one of the biggest sea stars in the world. Its arms can be as thick as a 1-liter soft drink bottle. Sometimes it looks a bit puffy.

The giant pink lives primarily on molluscs.

Pisaster ochraceus, the ochre or purple star. Not a very convenient common name: what is it ochre, purple, pink, greyish? It looks like the giant pink star, but it looks less puffy, more coarse and is smaller and more common.

A typical intertidal species: they are very sturdy and well adapted to heavy surf. For more information on the species, look here.

Four years ago I took two little specimens (6 and 10 cm) home. In my aquarium they appeared to be a bit obese and would not take one mussel, Mytilus edulis, as prey, but a cluster at once. After less than two years they were 46 cm across and weighing 1,7 kg! Not a problem in itself, but I grew tired of another problem. Every month I replenish water in my aquarium. A sign for these monsters to propagate: in 15 minutes their semen have changed the fresh clear water into low-fat yoghurt. Thanks fellows! Last year I rang Blijdorp, the Rotterdam Zoo, if they were interested in two big sea stars. They were; they already had a few Pisasters.

Pisasters with a lot more 'lebensraum'.

Many thanks to Christopher Mah (see echinoblog) and Philip Lambert (author of Sea Stars of British Columbia, Southeast Alaska and Puget Sound; see Literature) for helping me with the identification of quite a few sea stars and other information.

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