When I arrived at the Port Townsend Marine Science Center (PTMSC) from Texas, I was prepared to show off my knowledge of marine mammals while learning more about other organisms such as birds and invertebrates. Little did I know that I frequently made a common slip – “starfish? Don’t you mean sea star?” After decades of confusion, scientists have pushed for a change from starfish to sea star, and nobody told me! If you’re lucky, you can catch me for an easy opportunity to poke fun at this simple transition.
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| A blood star (Henricia leviuscula) with abnormal arm growth. Photo: PTMSC |
I knew these invertebrate animals were named for their trademark five-armed, radial symmetry, and are not fish. More than 2,000 species of colorful sea stars sport five arms, even though some species can have 10, 20, or up to 50 arms. It is also not unusual for a five-armed sea star to have six arms due to abnormal growth.
Sea stars are echinoderms, which translates to “spiny skin.” Their living relatives include sea cucumbers, sea urchins, and sand dollars. The PTMSC Marine Exhibit hosts all of these, with short to long spines, and colors ranging from purple, pink, and orange!
I had never felt a sea star’s leathery skin before I began working at the Marine Science Center, nor was I aware of how varied the colors can be. They use colors as camouflage in a number of environments, ranging from tide pools to more than 6,000 m below sea level. The sea stars in the Marine Exhibit (ME) are a deep purple, peach, or neon orange, and are within your reach. Sea stars move and flex using a water vascular system. They pump seawater through their body, filling and emptying tiny, suction-cupped tube feet to extend, retract, or even create suction to scale any surface. One leather star (Dermasterias imbricata) even used its tube feet in an effort to help clean their tide pool tank! The tube the star is grasping a gravel tube, which staff and volunteers use to clean the gravel of the tanks, while in the meantime picking out any discarded clam shells from a sea star’s previous feast.
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| Giant Pink Star helping to clean. Photo: Mattie Stephens |
Most sea stars also have the amazing ability to consume prey outside their bodies. Using their tube feet, they pry open clams or oysters. Then, the upper portion of their stomach (known as the cardiac stomach) emerges from their mouth and oozes inside the shell. The clam’s muscles tire against the strong, hydraulically operated tube feet, and eventually open. The stomach then envelops the prey to digest it, eventually withdrawing back into the body. At this point, the lower, or pyloric, stomach digests whatever is remaining.
Sea stars are famous for their ability to regrow limbs and entire bodies. This feat is possible by housing most or all of their vital organs in their arms. Rarely, the “central body disc must be intact to regenerate, but a few species can grow an entirely new sea star just from a portion of a severed limb” (National Geographic, 2016). Sea stars can willingly detach an arm to distract a predator to get away, or in a method of reproduction. There is a spreading epidemic of arms shedding and sea stars dying due to disease (National Geographic, 2016).
What factors cause these arms to shed unwillingly? Sea stars have been known to suffer from desiccation, or drying out, resulting in lost limbs. However, even healthy sea stars can suffer from sea star wasting disease. This disease causes rapid tissue degradation in sea stars, resulting in lesions on the arms and the body deflating (referred to as a loss in turgor pressure), giving the sea star a melted appearance. The process happens quickly, fully enveloping a sea star within three days, usually ending in death. The disease can spread between individuals, and has resulted in devastating losses, not only in natural habitats, but in aquariums as well. A few weeks ago, I watched as PTMSC lost its last mottled star to sea star wasting. Over the past few years, over 50% of the sea stars in the Marine Exhibit have succumbed to wasting.
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 losing water pressure. Photo: PTMSC Bottom: A mottled star succumbing to sea star wasting disease |
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| Sun Star discovered in this year’s monitoring program. Photo: Betsy Carlton |
The ecosystem recovery process will take a long time. Activists and citizen scientists are working hard on improving the overall health of the ocean, as even the slightest increase in temperature can wreak havoc on an ecosystem. The Marine Exhibit and Natural History Exhibit have taught me several ways that I can individually reduce my impact and waste output. Living in Port Townsend has illuminated healthier living practices for me, and I have been embraced by an environmentally conscious town. The more I learn about sea star wasting, the more pressing environmental stewardship becomes.
Please consider donating today. https://ptmsc.org/get-
- Mattie Stephens is the Marine Mammal Stranding Network Coordinator/Educator and AmeriCorps member serving at the Port Townsend Marine Science Center
Please consider donating today. https://ptmsc.org/get-
- Mattie Stephens is the Marine Mammal Stranding Network Coordinator/Educator and AmeriCorps member serving at the Port Townsend Marine Science Center
Thank you, Mattie, for educating us about the incredible number of sea stars in the world-- 2,000 with five arms!-- and reminding us that we can make a difference with our own choices in how we live. Great post!
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