Seastars and Urchins and Crabs, Oh My!

Today we went to service two of our sites in the morning, the one stationed by Roe Lake, our marshland site within Pender Island, and Roesland Coast, our grassy, forest and ocean rimmed site. Once we had collected and strained all of the insects from the different pans, pitfalls and intercepts, we then decided that today the weather and timing of the tides was perfect to do some marine aquatic collecting – a decision which I was enthralled with as a studying Marine Biologist. We headed down to the intertidal zone, where we had previously found some cool invertebrates, and began spreading out.

An Ochre starfish munching on a chiton.
An Ochre starfish munching on a chiton.

One of the first organisms we encountered was an Ochre Starfish (Pisaster ochraceus), a brilliantly purple starfish that is found all along the Pacific Coast of North America. These starfish are often keystone species within their ecosystems, keeping control of the numbers of mussels and other such invertebrates within the subtidal and intertidal zones. One of the Ochre starfish we found was even munching on a chiton (Class Polyplacophora) – an invertebrate with a hard segmented calcareous shell, and a single foot for locomotion. We found a variety of these healthy Ochre’s within the bay, which is a good sign of the health of the intertidal zone along Pender Island. Currently along the North American Pacific there is an unknown disease afflicting many different species of starfish, creating record mortality rates among these keystone predators (see CBC article here). The few starfish we saw within the intertidal zone at Pender Island appeared healthy and active and we can only hope it stays that way.

We also managed to find some Green Sea Urchins (Strongylocentrotus droebachiensis), which can be found in many places around the world, down to depths of over 1000 meters. They are eaten by a variety of predators, including the aforementioned Ochre Sea Stars. We were able to hold the urchins and see the individual movements of its hard walking spines, as well as its soft brown feelers (used to detect its environment).

Two green sea urchins we found in the intertidal zone.
Two green sea urchins we found in the intertidal zone.

Crabs (Order Decapoda) of multiple sizes were also common. There were hundreds of tiny crabs that may have been a combination of littler species as well as juveniles of larger species. We were able to find multiple fresh crab molts along the beach. Crabs grow by shedding their external skeleton, so ’empty’ crab casings, appearing fully intact, but hollow, were common. Crabs, when they shed their molts, can grow up to 20% larger than before due to a massive water intake.

As we were collecting and exploring this new environment, the Park Warden even dropped by to learn a little about our research, and make sure we had a permit to be removing these species from their habitat. We were extremely glad to see that the inhabitants of Pender were protective of their environment and its species, as well as interested in the scientific research being conducted there.

–          Danielle

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