May. 07, 2012

The Surprising Sea Cucumber

by Coastal Studies for Girls

Click to enlarge images
by Cynthia, Coastal Studies for Girls
As part of our Marine Science class, Coastal Studies for Girls students went on a field trip to the Bowdoin College Marine Lab. I was amazed to see all the marine biological diversity there. There were many animals which I would otherwise never be able to see up close or to have contact with. I saw sea urchins, brittle stars, red sea anemones, and hermit crabs.
One species that surprised me was the sea cucumber (Cucumeria frondosa) because they are a species that I would rarely see up close as I did in the lab that day.  I could pick them from the aquarium and feel their long, slimy body slip through my hands; it was an amazing moment. What I found astonishing was the way they squirted out water from their anus as though it were excreting urine, but instead it was the water they had absorbed.
Sea cucumbers are invertebrates, echinoderms similar to starfish and sea urchins. They are part of the class Holothuroidea. There are about 1,250 known species of sea cucumbers in the world, and they are unlike other echinoderms. Sea cucumbers are omnivores and can live for 5 to 10 years. They come in a wide range of sizes, from only ¾ of an inch to 6.5 feet in length.
All sea cucumbers are ocean dwellers but some live in shallow water and others in deep water. Sea cucumbers are common in warm waters of the Indian ocean and the Southwest Pacific Ocean. They live on or near the ocean floor and some might be partially buried under the floor, camouflaging themselves by hiding under sediments. This camouflage protects them from any predator that may be looking for a meal.
They have many tube feet running down their bodies, and around their mouths are tentacles. They feed on algae, minute aquatic animals, or waste materials. They are deposit feeders: sand and mud are passed into their mouths by their tentacles and the small amount of organic material is digested.
When sea cucumbers are threatened they release a sticky thread that distracts their enemy. In some species these threads can be poisonous, containing a toxin called holothurin. As a defense mechanism some sea cucumbers can self-eviscerate parts of their own body. They do this by violently contracting their muscles together and secreting some of their organs out of their anus. Sea cucumbers tend to do this so their predators think that they are dead. The organs left behind distract the predator, while the sea cucumber leaves. The lost organs are later regenerated.
Sea cucumbers can reproduce either asexually or sexually. In sexual reproduction, the more common way to reproduce, animals release their sperm and eggs into the water and fertilization occurs. In order for this to be successful there needs to be many individuals near each other.  Sea cucumber eggs and young larvae are eaten by fish and are also eaten by humans, especially in Asia. Sea cucumbers also can reproduce asexually by dividing into two halves, with each half regenerating the missing organs in a few months.
In the ocean there are many different species of sea cucumber. Going to the Bowdoin College Marine lab made me realize that the most common organisms like sea cucumbers are both simple and unique. Sea cucumbers amazed me because they have a way to protect themselves by obliterating their body, but they can also regenerate. Their body structure is simple, but very beautiful in the way it functions. I believe the sea cucumber has now become my favorite marine animal.


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