Sea Stars

Alex Re (00:00): Hello, welcome to On Wildlife. I'm your host Alex Re. On this podcast, we bring the wild to you. We take you on a journey into the life of a different animal every week. And I guarantee you you're going to come out of here knowing more about your favorite animal than you did before This week we'll be discussing an animal that you've probably seen in aquariums, in tide pools, or in your favorite cartoon. These animals are one of the coolest to look at and they have an amazing anatomy that's completely different from ours. So join me as we dive into the deep sea and shallow shores to talk about sea stars.

(00:58): The common name for a sea star is a starfish, but sea stars aren't fish at all. They're classified as echinoderms. Echinoderms are species of marine animals that have radial symmetry, which means that they're symmetrical around a center point. They also have no backbone, so they're invertebrates. A kind of germs usually have rocky, hard skin to protect themselves against predators. And the name even comes from the Greek word meaning hedgehog skin. And if you look closely at a sea star, you'll notice that they have spiny skin covering the outside of their body. The skeleton of the sea star is made up of plates that are connected through movable joints. Sea stars belong to their own class called Asteria, and you can kind of see where they got that scientific name because they look like stars. Some of their closest relatives are sea urchins and sea cucumbers.

(01:55): There are over 2000 different species of star and so much about them, like their diet, the environment that they live in and what they look like varies depending on the species. Sea stars can live in tidal ocean pools, shallow waters or the pitch black deep sea floor, and they're found in every ocean in the world. They only live in saltwater, though there are no freshwater sea stars. Most sea stars have five arms, but they aren't limited to that number. Some can have 10 to 40 arms and they had this really amazing ability to regrow a limb. If it's cut off and it doesn't stop there, some species would be able to grow back their entire body if there is still just one limb left. The sizes and weights of these animals can also range heavily. They're usually about five to nine inches long. But some species, like the Sunflower Sea star, which has 24 arms and is bright orange, can reach over three feet long.

(02:57): They can also be extremely small. The part of a vira is just over a centimeter long. The Sunflower sea star is also the heaviest sea star at up to 11 pounds. While some small species weigh less than a penny, sea stars can live up to 35 years old. And in captivity they usually only live for about five to 10 years. And speaking of captivity, when you're at an aquarium looking at a sea star, you might think that they're just stuck in the position that they're in, but they do move. Each arm of a sea star contains almost 15,000 tiny tube feet underneath their bodies that allow for movement. The tube feet really do act like feet. When a sea star runs water through them, they move to help it get from place to place, and they can move at one meter per minute. Their tube feet have multiple purposes though because they can also act like suction cups that help sea stars clinging onto rocks so that predators can't pick them up. They can also use them to catch prey, which we'll talk about right after the break. The science word that I want to talk to you about today is exoskeleton. Unlike humans and other vertebrates, invertebrates don't have an internal skeleton. They have an exoskeleton, which is like a layer of protection on the outside of their bodies. Some organisms that have exoskeleton are insects and crustaceans like crabs, and their exoskeletons aren't made of bone, but a substance called chitin.

(04:53): Okay, we're back. C stars have been around for an extremely long time and you can tell because they don't have the most complex structures, but they're really good at what they do. The fossil record for Asteria shows that C stars have been around for over 450 million years. They could have been around for even longer, but it's hard for sea stars to become fossilized because they decomposed quickly after they die. So when sea stars first appeared underwater plants had only been living on land for 50 million years. So sea stars are older than every terrestrial dinosaur species in the world. At the time, sea stars first evolved jawless fish and the first sharks started to appear. This also means that sea stars were able to survive four mass extinction events in history. That's pretty impressive for an animal that doesn't even have a brain. Sea stars are mostly carnivorous, but they're not going to be able to catch fast swimming fish.

(05:55): The animals that they love to eat are muscles, clams, and oysters, and they're easy to catch. But their main defense mechanism is their hard shell. Luckily for the sea star, their tube feet can act as suction cups that help pry the shell open. What makes sea stars incredibly unusual eaters is that they have a sack like stomach that comes out of their mouth and it encases the meat of their prey. It then digests the meat outside of their body, and when it's done digesting, it goes back into the sea star. It's the equivalent of a human stomach crawling out of our mouths and then eating a burger before moving itself back into our body. C stars can also resort to cannibalism, but it's been researched that this behavior has been used more to assert dominance than for nutrition. When C stars reproduce, females release eggs and males release sperm into the water where the eggs become fertilized and develop into free swimming larvae.

(06:56): These larvae are actually considered temporary plankton because plankton refers to many different species. Female sea stars can release up to 2.5 million eggs into the water at a time, and most of these won't reach adulthood, but the plan is to release as many as possible in the hopes that a few will survive. After about three weeks, the larva begin to mature and morph into adults without any parental supervision. Before they begin to undergo their transformation from larva to adult, they'll settle on a rock or another hard underwater object to develop. But C stores can also reproduce asexually. They can literally just break themselves into two halves. Each half will then just grow another half. So now you have two separate organisms with this process. They're basically just cloning themselves because both individuals will be genetically identical. Sea stars aren't necessarily social creatures, but they are able to communicate through touch.

(07:59): Sometimes they'll slowly wrestle each other for territory or dominance on the sea floor, and they do congregate together during certain times of the year, usually when there's a lot of food around and when the temperature of the water is optimal. C-store don't have a vascular system. The way we do theirs is called the water vascular system. They rely on water to move through the body as a way to move around. And because of this, they're not able to move outside of the water. They take in water through a structure on their body called the maite, and that water flows through their vascular system. This pumping of water through their body also allows the seastar to gain nutrients and get oxygen to breathe. While some people think that removing a star from the water is okay, they're actually quite susceptible to suffocation out of the water after a matter of minutes.

(08:52): They're also susceptible to chemicals that run from land into the water, such as pesticides. And while they don't have noses, they can detect chemical changes in the water. And this is how they figure out if there's a predator. Nearby C-store also have light sensors on each of their arms, which are called eye spots. So their primitive eyes, they don't technically see surroundings, but they detect which direction light is coming from. So this gives them somewhat of a perspective of their environment. Sudden light blockages indicate predators or a competing sea star that might be nearby, and the sea star will react to that. And something that's really interesting is that some species of sea stars have been observed having a mutualistic relationship with a small species of shrimp. The shrimp eat bacteria and parasites on the sea star and they get a free meal out of it. Alright, we're going to take our last break, and when we get back we'll talk about a sea star's importance to its ecosystem Time. For our trivia question, which animal is known as the king of the ocean? A great white shark, B, a killer whale, C, a blue whale, or D, a manta ray.

(10:29): The answer is B. Killer whales really are the apex predators of the ocean.

(10:41): Alright, welcome back. Sea stars are considered keystone species, which means that they have a disproportionately large effect on their ecosystem. Compared to other species, they prey on organisms that have no other natural predators. So if they were to be removed from their environment, their prey would overpopulate and drive other species away. Some sea stars prey on sea urchins, which reproduce rapidly. If the sea urchin population were to boom, they would eat all of the kelp in the area. And kelps are primary producers that help create sustainable habitats for all different types of aquatic organisms. While sea stars are great predators, they're also prey for a high number of species ranging from fish to crabs to birds, because they're able to reproduce so quickly and produce a high number of offspring, they provide lots of nutrition in their respective ecosystems. Even though they have sharp scaly backs, many predators are able to flip them over and eat their soft underside.

(11:47): They also eat a bunch of different things on the sea floor, so they kind of act like the cleanup crew. Sea stars are facing some issues though due to chemical runoff and interference with the sea stars' natural habitat. There's been an emerging disease called seastar wasting syndrome, which causes abnormally twisted and deflated arms, limb, dismemberment, and discoloration. The US Fish and Wildlife Service is trying to reduce the amount of human interference in the sea stars environment, but it's really getting out of control. Another issue that they're facing is that people like to take them out of the water. And if you go to shops by the beach, you'll probably find hundreds of dead dried up sea stars for sale. Right now. One species called the Sunflower Sea Star is critically endangered, and we just talked about how if they're removed from the ocean ecosystems, a lot of other organisms won't be too far behind.

(12:45): So if you want to help sea stars and the ecosystems that they live in, check out the Sea Star Foundation, stars for the Sea and the N O A A. Thank you so much for coming on this adventure with me as we explored the world of sea stars. You can find the sources that we use for this podcast and links to organizations that we reference at onwildlife.org. You can also email us with any questions at On Wildlife dot podcast@gmail.com, and you can follow us on Instagram at On Wildlife or on TikTok at wildlife. And don't forget to tune in next Wednesday for another awesome episode, and that's On Wildlife.

Jess Avellino (13:33): You've Been listening to On Wildlife. With Alex Re. On Wildlife provides general educational information on various topics as a public service, which should not be construed as professional financial, real estate, tax, or legal advice. These are our personal opinions only. Please refer to our full disclaimer policy on our website for full details.