If you are like me, you often get excited when opening a present. Intrigued, you are left to wonder what could be inside. Just like the element of surprise that comes with opening wrapped gifts, the same reaction is seen when a skipper retracts his dredge full of marine invertebrates onto the boat. Unveiling a dredge is a thrilling experience as the first sight of what the apparatus has towed along the surface of the ocean for collection purposes is unparalleled.
At our class trip to Bamfield, our purpose of dredging was to collect and observe marine invertebrates from Trevor Channel. As the skipper released the bundle of surprise onto the boat, we became even more eager to see what came with it. What first looked like a pile of sediment became a table full of many species of invertebrates. Some were smooth, others were rough and spiky, and some were even slimy! This made me wonder… Does their texture play an important role in their daily life?
For example, sea cucumbers are slimy and have a leathery texture. Their fleshy bodies help them to undergo contractions to allow for movement – but watch out! Although these creatures seem harmless, they have a secret weapon. Sea cucumbers can entangle their prey with their sticky intestines. Even stranger is that they can shoot them out of their anus. Indeed, they are not as gentle as they look!
Tube feet on underside of a sea cucumber found at Trevor Channel. (Photo credit: Prabh Sahota)
Self-defense mechanism of a sea cucumber. (Video from https://www.youtube.com/watch?v=aCxKFc3XtJs)
On the other hand, sea urchins do not look as innocent. In fact, they are the complete opposite to sea cucumbers as they are not as soft and squishy. They use their sharp spines as their main source of self-defense to penetrate their predator’s flesh. The most fascinating fact about sea urchins is that they can move their spines at any angle using muscle located at the base of each spine.
Different colour morphs of a sea urchin. (Photo credit: Prabh Sahota)
Sea stars are slow moving and cannot always swim away from predators. Like sea urchins, they use their spines for protection, though they are less sharp – a fact their predators must appreciate!
Spiky spines for protection! (Photo credit: Prabh Sahota)
After rummaging through the dredge collection and observing the diversity of marine invertebrates, it was time to send these creatures back to the ocean. We sent them over the edge of the boat, one by one, back into Trevor Channel.
Whether you are an expert in the field or you are being exposed to marine invertebrates for the first time, you are bound to find something interesting from a dredge collection. Try it and you will be amazed to see what lies deep within our oceans!
To learn more about the morphology and defense mechanisms of echinoderms, check out http://www.mesa.edu.au/echinoderms/echino03.asp.