Crustaceans and Echinoderms

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ON THIS PAGE:

Arthropods:

  • Dungeness crab
  • Helmet crab

Echinoderms:

  • Sunflower star
  • Red Sea Urchin
  • Ochre Star

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Dungeness crab (Metacarcinus magister)

Its name usually conjures up the image of melted butter, the smell of garlic, the sound of cracking carapaces. Because of its delicious taste and relatively fragile exoskeleton, the Dungeness crab is a popular catch for commercial fishermen and weekend pier dwellers alike. Octopus, spiny sand sharks and sea birds also love to eat these crabs, which explains why they spend much of their time in hiding, buried under the sand. They also travel very quickly, using their four pairs of walking legs to move. Their claws distinguish them from other species, with their slender shape and white tips making them hard to mistake for the black-tip claws of red rock crabs.  Dungeness crab claws are also serrated, so watch out for your fingers! This large species, which can weigh up to 2kg, is protected by regulations on size and sex to maintain populations. All harvested species must be male and have a carapace at least 16.5cm across.

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Helmet crab (Telmessus chiragonus)

Sometimes known as the hairy helmet crab, it is smaller than dungeness and red rock crabs and much, much fuzzier. The helmet crab is covered in setae, coarse little hairs, from its claws to its carapace. Unlike kelp crabs, which have a long protrusion between its eyes, this species has a few notches like those on the back of the carapace. Because of the length of its legs, the helmet crab can pinch an unsuspecting investigator even when being held from the back. The helmet crab spends time in eelgrass, one of its food sources, but will also move into the rocky intertidal for mating during the summer.  We found it on both the rocky Sidney beaches and at Pat Bay. Certain sculpins  and gulls are their main predators, making their camouflaging green-brown  or red-brown colouring an important defence. Helmet crabs were officially classified in 1812, and since then have remained an interesting but mostly overlooked species.

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Sunflower star (Picnopodia helianthoides)

These beautiful and terrifying seastars can grow to one metre across, have as many as twenty-four arms and with its thousands of tube feet, can move very very quickly.  They come in a variety of colours and have a soft, almost mossy body or spongy body. They are extremely predatory, feeding on bivalves, snails, sea urchins, sea cucumbers, sea urchins and dying vertebrates. So practically everything. Sunflower stars prefer habitats with algae or seagrasses, shallow to intertidal but never high up since they need water for support. They have few predators, but large crabs will sometimes eat them. This species was one of the hardest hit by seastar wasting disease, although after seeing several juveniles on our trips to Pat Bay, things are looking up for this pretty and voracious seastar.

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Red sea urchin (Mesocentrotus franciscanus)

With colour being one of the most unreliable methods of identification, it shouldn’t come as a surprise that Red sea urchins can also be a burgundy almost purple colour (some of these are actually hybrids). Unlike their tropical cousins, they have dull, harmless spines that they use mainly to move around and to intimidate. These urchins, who are the favourite food of sea otters and wolf eels, feed on kelp and seaweed, usually in rocky areas where there isn’t much wave action. They are often found in large groups, as juvenile sea urchins will purposely live underneath the spines of adults, protecting them from possible threats. With the loss of sea otter population to hunters in the 1800s, urchins have become a nuisance, eating away at large swathes of kelp forests. Fortunately these urchins can be sold commercially as food, giving us a strategy for controlling populations.

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Ochre star (Pisaster Ochraceus)

When people on the west coast think of seastars, the species they’ll usually come up with are ochre stars. This species is found from California to Alaska, often clinging to rocks or pilings, easy to spot because of their bright orange or purple colour and rough white ridges. They are well adapted to rocky, wavy areas and use their powerful tube feet to hold on and move around.  Ochre stars are found mostly in the intertidal, where they can play an important ecological role  by keeping bivalve populations in check. In the Salish Sea they more often feed on barnacles and snails.  Very few things in turn, mainly sea gulls and sea otters, actually eat sea stars. Until the last few years, their populations were mostly affected by humans and the dangers of the intertidal. Unfortunately seastar wasting disease infected ochre stars, and many, including some at the Centre, were lost. Although they can survive out of water for long periods of time, ochre stars are very sensitive to heat, explaining why they often live under rocks or in shadowed cracks and crevices, overlapping limbs with other individuals.

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