Posted by: Anne Murray | September 29, 2015

Orange Sea Pens on Roberts Bank


Orange Sea Pens at Roberts Bank; photo courtesy Port Metro Vancouver

Heading out on the ferry from Tsawwassen, our family often scans the water for whales or porpoises, but seldom think about other underwater creatures, many of which live in the Salish Sea. Some are dramatic in shape and colour, such as the orange sea pen, a type of soft coral that grows up to 50 cm tall and looks like it belongs in a tropical ocean. Because it lives in the subtidal zone, deeper than is revealed at the lowest low tide, the sea pen’s presence generally goes unrecorded. I was surprised to learn we have colonies of these exotic-looking animals on Roberts Bank.

The orange sea pen is sometimes known as sea feather and it looks like an old-fashioned quill pen in an inkwell. It has a bulbous base that holds it in the sand, a rubbery central spine, and a “feather” of polyps that move in the currents. If disturbed it will pull back into its base and bury in the mud.  One remarkable feature is its bioluminescence: if disturbed by a predator, the orange sea pen will glow with a green light to scare the intruder.

These soft corals live in sheltered areas of the subtidal zone, with sandy substrate and a fair amount of current, but not too much turbulence. Paula Romagosa at The Shaw Ocean Discovery Centre told me that colonies are common off Sidney and Pender Islands. They also live off the deep end of the Roberts Bank port causeway and Tsawwassen ferry jetty. Many formerly occupied areas in Puget Sound have been abandoned, for unknown reasons. Sea pens eat drifting plankton, and are in turn eaten by sea stars and nudibranchs. With the current decline in sea stars, maybe sea pen populations will increase.

Port developments are unfortunately proposed within part of the orange sea pen habitat, so I asked John Parker-Jervis of Port Metro Vancouver what the future holds for this interesting species. He said that the port has been studying the feasibility of transplanting orange sea pens since April 2014. Three Roberts Bank locations have received 400 sea pens each, transplanted at densities of four to six sea pens per square metre, mimicking their natural distribution. The transplants are regularly monitored, with the next check-up due soon, and, according to Parker-Jervis, appear to be thriving in their new locations.

The richness of our local ecosystem means there is always something new to discover, though not always easy to see.


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