24 November 2012

Sea stars of Vancouver Island - part 1

started this blog with some posts about the marine biology of Vancouver Island. I was impressed by the rich underwater life of this part of Canada. That was before I could dive. So last summer we revisited the island. I made 10 dives, 3 snorkeling trips and did some beachcombing.

I hoped for a lot of new species and to do something I dreamed about since 1976: diving in an underwater forest of kelps. To be honest: I already had been diving in kelp forests last year in Ireland and in May in France. But this was different because of the size of the kelp forest. I dived at three spots in the vicinity of Nainamo: Cottam Point, Tyee Beach and Neck Point. The fourth divespot was Rock Bay (40 km north of Campbell River).

My first dive was special. I expected clear water, as I could remember of my trip in 2008. It was not.  A bit of a disappointment, but the number of species of sea stars made my day: 12 species in total! That's why I start with a post about sea stars.

The 16 species of sea star - I found in total - in this and the next post are presented in taxonomical order.

This is the vermilion star, Mediaster aequalis. Up to 20 cm across. It is an omnivore: it feeds on sponges, bryozoans, loose algae, detritus and dead animals.

This specimen has lost one of its arms, which is regenerating. A little spider crab is hitchhiking.

The beautiful upside (called aboral) with table-like tops (called tabulate plates). Like little flowers.

The leather star, Dermasterias imbricata. A common species in British Columbia.

Lambert (2000; see further ahead) about the diet: 'On exposed coasts it eats primarily sea anemones and compound sea squirts. In sheltered waters mostly sea cucumbers, encrusting sponges and sea pens. ... All those observed in Gabriola Passage were feeding on bottom detritus.' He does not mention bryozoans like the kelp-encrusting bryozoan, Membranipora serrilamella, on which I have seen a lot of them feeding. In this case growing on five-ribbed kelp, Costaria costata. The leather star seems to be a rather opportunistic feeder: it likes whatever is around.

Membranipora serrilamella in detail, showing the honeycomb like structure and individual polyps. 

It is a thick and leathery sea star, up to 30 cm across.

The stomach inside out. At lectures and nature trips I often tell about the feeding habits of sea stars in relation to human table manners. What if you were in a restaurant and you pulled your stomach out of your mouth and put it on the artistically arranged food on your plate? 'Sir, would you like to leave this restaurant at once!'
I took this leather star of five-ribbed kelp, where it was feeding on the before mentioned bryozoan.

This is the common sun star (English/European name) or rose star (North American name), Crossaster papposus (NL: zonnester).

The colour is variable, usually with a concentric pattern, as is not the case with this specimen. Up to 34 cm across. It eats sea slugs, bivalves, bryozoans, sea squirts and other sea stars.

This is the same species but from Ireland. It is one of the few species of sea stars you can find in the Pacific and the Atlantic ocean. This colour pattern is rather typical for European specimens.

The typical polyp-like structures are called pseudopaxillae. These are skeletal plates consisting of a broad base and an erect column bearing small spinelets.

Solaster dawsoni, the morning sun star. It can grow up to 40 cm in radius. This is a juvenile.

It is a 'top predator': it feeds on a lot of sea star species, including other morning sun stars. A cannibal, but that is not so unusual in marine species. Lambert (2000) on attacking its own species: 'but its success rate is low because of a well developed escape response. S. dawsoni bends its arm back and pushes the attacker off while rapidly moving away (10 cm/min.).'

He does not mention the morning sun star preying on the California sea cucumber, Parastichopus californicus (left on the photo above), but mentions that it swims away when contacted. Sea cucumbers are related to sea stars, the primal food of this sea star. And as other sea stars are preying on sea cucumbers, I am in no doubt he is also preying on them.

Solaster endeca, the northern sun star. Looks like a bloated version of Solaster dawsoni. Another species you can find in the Atlantic and Pacific Ocean. Although their diets are very different. Lambert (2000): 'In the Atlantic it is reported to be a voracious feeder on sea stars and molluscs. On the Pacific coast it neither attacks nor evokes escape responses in other sea stars.' There it feeds on sea cucumbers, bryozoans and sea squirts. Up to 40 cm across.

Solaster paxillatus, the orange sunstar. It is said to be rare in British Columbia.

Lambert (2000): 'is probably carnivorous, like other species of Solaster. Stomach contents recorded are a sea cucumber and the blood star, Henricia leviuscula leviuscula.' Up to 37 cm across.

Another beautiful sea star of BC-waters: Solaster stimpsoni, the striped sun star. I saw a lot of these sea stars: they are easily observed and identified with their striking colour pattern. Up to 50 cm across.

This is the excellent identification guide by Philip Lambert I am referring to. With a description, photo's, drawings and information about biology, diet, distribution, propagation etc., including an explanation of the scientific name.
A whole lot of information in this post comes from this book, as well as their identification. For sale at a very reasonable price of $26. Highly recommended.