Imagine yourself enjoying a stroll down one of Sanibel’s beautiful beaches, taking in the fresh air and soaking up the sun, when all of a sudden you feel something squishy between your toes. When you look down and realize that a lumpy, brown blob is squeezing through your toes, your first reaction may be utter disgust. After taking a closer look at the wrack line, you realize that there is not just one of these strange blobs – the whole beach is littered with them!
The wrack line inundated in sea squirts - a common sight on Sanibel lately.
The brown, wrinkly blobs in question are actually sea squirts, referred to as tunicates in the marine biology world. Tunicates are animals that house their tiny body in a thick covering that resembles a tunic – that’s how they get their name. Individuals have the ability to form dense colonies, which often end up looking like the irregular blobs we are now familiar with. These animals attach to docks, mangrove roots, and live shells, and spend their days filter-feeding plankton. The species you may have encountered recently (if you're on Sanibel) is the sandy-skinned tunicate (Molgula occidentalis), which is often covered in sand and bits of shell.
Up close and personal with Molgula occidentalis - the sandy-skinned tunicate.
It’s hard to believe that tunicates are animals, but they are fully equipped with siphons for feeding, a stomach, and even a small brain. What is really interesting to us is that tunicates are closely related to vertebrates because they begin their life with a notochord, a row of specialized cells found in all animals with a backbone. But unlike vertebrates, the tunicate’s notochord disintegrates as it matures into an adult.
When the tunicates wash ashore, they often die off shortly after being stranded on the beach.
Last month, Sanibel Island was getting high winds from the North and West, which resulted in the tunicates becoming dislodged from the substrate and pushed up on our beaches en masse. Even though these creatures are quite unsightly, they aren’t harmful – they might just squirt out a little water if you handle them, which we encourage!
More windy weather this week deposited a fresh batch of tunicates near the lighthouse.