The alias, or common name for this sponge is the polychaete sponge. You may know that a polychaete is type of marine worm. These worms differ from their more familiar earthworm and leech cousins in bearing many leg-like appendages which are covered with bristles. So a polychaete, is a many (poly) bristled worm. Therefore, the polychaete sponge is a sponge that looks like a polychaete worm. Very logical- eh Watson? Look at my image of Isodictya erinacea and I think you will agree that it looks very spiny and bristly.
So now you are wondering - why Bill has placed such a high bounty on this spiny yellow sponge? In my previous “Sponge Pod” entry I described that one aspect of our project is investigating chemical interactions between sponges and other animals, particularly amphipods that live in and on these sponges.
From previous years’ work here at Palmer Station, Bill (our chemistry wizard) has determined that the polychaete sponge produces some very interesting chemicals (secondary metabolites). One chemical in particular, erebusinone has a makeup that is very similar to a naturally occurring crustacean hormone that inhibits molting (shedding of the exoskeleton) in crustaceans. Hmm, you ponder, why then would crustaceans like our ‘ruling’ amphipods be associated with this sponge? Our thoughts too so, this is in part why we pursue the polychaete sponge.
We know of two dive spots around Palmer where we can be assured of finding Isodictya erinacea. Both are deep, steep walls on the south side of islands. These are great hideouts for our elusive sponge as often the wind and/or ocean swell make diving these sites impossible. Earlier this week Bill and I tried to dive the wall at Hermit Island but the swell was too much so we opted to try a new site that Bill and Chuck had identified previously by echosounding.
Upon reaching the new site off Bonapart Point, Bill and Chuck repeated the echosounding with our onboard depth finder. That day Chuck served as Captain, Tender and Diver which is why he is wearing his drysuit as he and Bill stare into the wooden box encasing the depth finder. (Bill and I would later flip a coin to see who would make a short second dive with Chuck to retrieve amphipod traps.) This particular wall yielded some goodies but not the polychaete sponge. (Bill then lost the coin toss.)
Today Bill and I tried to dive Janus Island, the other spot where we can be pretty much guaranteed of collecting Isodictya. It is often a guaranteed site for an unwelcome outlaw. Sure enough, just as Bill and I began to descend in the sapphire blue clear water, a leopard seal swims up right behind Bill. Up we go.
Away we go to try another new, nearby site. We zodiac-ed far into glacier lined Arthur Harbor alongside Palmer Station. Though a scenic place above water, even on this cloudy day, the visibility underwater was not so pretty. Our glacier, as you have read in several of our entries, drops huge chunks of ice into the water on a daily basis. This constant glacier calving keeps the water pretty churned up and also introduces a lot of sediment. Most sponges, especially the polychaete sponge, prefer cleaner water. No surprise that we were skunked here in our hunt for Isodictya.
Tomorrow we will continue our search for the elusive Isodictya erinacea. Maybe conditions, both meterological and biological (seal that is) will allow us to dive at either Hermit or Janus. We do have a few more potential sites yet to investigate. Somewhere, sometime we will capture the desired polychaete sponge. A bountiful find would be like a pot of gold neath a rainbow to Bill!