I grew up on the west coast of Canada, so I spent my fair share of time on the ocean, on beaches, and rummaging through tidal pools for interesting sea life. One group of animals I remember most were starfish, which always impressed me for a number of different reasons. They were: a) very small and thus extremely cute, or b) very large and therefore impressive because of their sheer bulk or c) brightly coloured, which was very pretty. I also remember seeing a sunstar on a kayak trip. It was huge – I think about two feet in diameter, and had a ton of legs. I was fascinated, and today I’m going to honour my childhood interest in sunstars by blogging about them.
Common sunstars belong to the family Solasteridae, which is comprised of a number of different species of sea star. I’m pretty sure what saw was a common sunstar, because they’re found widely in the northern Atlantic and Pacific oceans. They prefer ocean floors that are rocky, or comprised of gravel or loose sand. Though I usually associate sea stars with tidal areas, sunstars can be found anywhere from the low tide line to over 300 meter deep waters.
Apparently my estimate about the size of the sunstar I saw as a child was probably blown out of proportion, as common sunstars only grow up to 30 centimetres in diameter. I was probably just impressed by its legs and inflated its size in my mind. Common sunstars are really quite beautiful, with red colouring on top, and bands of white, pink, yellow or dark red on its legs. They have a large middle disc with relatively stubby legs, of which there can be up to fourteen. Can you imagine having fourteen arms? Think of how many things you could do at once!
Have you ever wondered how starfish breed? I hadn’t, until today. They do it the same as us, with sexual reproduction. Except they fertilize their eggs externally, with the female laying eggs and the male depositing his sperm onto them. Juvenile sunstars spend their time in waters with soft sediment bottoms until they are five centimetres in diameter, at which point they move to shallow water with rocky bottoms. As they grow, they move deeper and deeper into the ocean.
Contrary to what you might think, sunstars are not sedentary animals that sit around waiting for food to come to them. They are hunters, and are often the dominant predator in their ecosystems. Common sunstars can cover over five meters in just 12 hours. When they find prey, they pull in their sensory feet, then push out tubular feet, which pushes the sunstars above their prey, allowing them to swallow the victim whole. If the animal is too big for the sunstar to swallow whole, the sunstar just covers the animal with its body, and then ejects its stomach to engulf the prey. They should make a movie about giant killer sunstars. I bet it would be really gross.
Sunstars also possess the ability to regrow limbs, as long as a part of the central disk remains intact. Which definitely makes a killer sunstar movie an interesting possibility. Perhaps I should write to Hollywood…
Cover image By Bengt Littorin – Crossaster_papposus_0792, CC BY 2.0