They are out there, thousands of them, lurking on the seafloor, unseen and unheard. It is only by chance that we are made aware of their presence at all. A storm or wading out into the water. They come close to shore looking for food, either prey or the rich micro buffet that lives in our sandy shores. This pursuit comes with risks, getting stranded during a low tide event or caught in the wild surf of a storm. They are the nine-armed sea star, Luidia Senegalensis.
Some recent storms have resulted with the beach littered with thousands of these beautiful and delicate creatures. Behind those delicate arms and translucent orange-tubed feet lies a fearsome predator. Well, maybe it doesn’t invoke a panic attack in us, but it might if you were a mollusk, small crustacean or polychaete worm that populate the near shore of San Carlos Bay. Nine-armed Sea Stars are opportunistic feeders, but it is as a predator that they shape our near shore environment.
The Sea Stars can be delicate compared to the Coquina Clams and tiny Mole Crabs that make up some of their prey. Their prey try to hide in the wash, an environment that is too violent for the Nine-Armed Sea Stars. This process is called Zonation, where creatures tend to stay where they can thrive and are reasonably safe from predation. Moving this prey to the shallow waters also help out the shore birds who prey on the same small creatures. The Sea Stars chase them in to the wash, and the shorebirds chase them back. No one ever said it was easy being a Mole Crab.
Some studies suggest that sea stars can be a Keystone Predator, a predator that is disproportionately important in maintaining the health of an ecosystem like our bay. A major culling event, like a storm, can cause thousands of Nine-armed Sea Stars to die and wash up on our beach. With fewer predators to control populations of some of their prey, their populations will increase until the sea star populations recover. But, their populations will recover from these types of natural events and they will continue their role in keeping our bay’s ecosystem healthy.
Sea Stars are some of the most interesting and beautiful of our near shore creatures. Some Sea Stars have suction cups on their tube feet that are powerful enough to pry open clams. Pretty impressive to someone who has come close to injuring himself with the added benefit of opposable thumbs and clam knife. The Nine-armed Sea Star, like the rest of its genus, doesn’t have the suckers. It positions itself over its prey and engulfs it by inverting its stomach and consuming it whole. It can also take in a belly full of sand and filter out what it wants. The simple digestive system just releases the remains after digestion, out the same way it came in.
Stars are romantic, and Sea Stars are no exception. When the mood and season move them they liberate their gametes into the sea. Once fertilized, the eggs hatch into bipinnara larva, a microscopic zooplankton that bears little resemblance to a Sea Star. These bipinnara swim around for about a month, trying to avoid other filter feeders while feeding on even smaller particles. They settle onto the sea floor and metamorphose into juvenile sea stars. This process is somewhat similar to other invertebrates. The relative shelter of San Carlos Bay is crowded with microscopic creatures that are busy feeding, trying to avoid being food while developing into their next stage. Terrestrial food chains seem simple by comparison: the sun makes the grass grow, deer eat the grass, panthers eat the deer. Marine food chains seem considerably longer and more complicated. Nature’s drama is played out on scales from microscopic, all the way to Bottle Nose Dolphins chasing Snook into the shallows of the beach. This plankton is a rich food source, how else could the largest sharks and whales live on these microorganisms – a considerable short cut in the food chain.
The Nine-armed Sea Star can be found as deep as 130 feet, but prefers the sandy, muddy or shelly seabeds that are shallow and sheltered. They have the ability to regrow lost limbs, but even that didn’t help the thousands that were washed ashore during a couple of big storms over the last six months or so. It is almost like the stars fell from the heavens and landed on our beach. They were probably dead or critically stressed by the time they washed ashore. It was a gruesome sight, but is part of the cruelty and cycles of nature. Lots of invertebrates get beat up in storms and wash up on the beach a day or so after a big storm.
Many of these creatures are here because it is usually sheltered and rich in edible critters. Often, these violent events give us a glimpse into a world that we cannot otherwise see. It is a world where sea stars prowl the shallows, daring themselves into shallow waters and putting their lives at risk in pursuit of food.
Maybe risking our island traffic to get to the restaurant isn’t such a big deal.
Photos by Bill Veach