Visits to the coastline are often filled with feelings of enjoyment, relaxation and excitement through discovery and exploration. At Dalton Koss HQ we often see young children and teenagers having fun exploring the beach, especially when they find sea squirts exposed at low tide. The name giveaway here is the squirt of seawater that comes out of this animal when lightly squeezed.
Sea squirts live on the lower areas of intertidal zone (see this link), from rock platforms to human made structures such as groynes and seawalls.
Aside from the amusement they provide when squeezed, here are some interesting facts about sea squirts:
FACT 1: Sea squirts, in the adult form, are individual animals that permanently attach themselves to hard structures, such as rock platforms, groynes and sea walls.
FACT 2: Sea squirts are filter feeders meaning they filter their food and oxygen out of the water column. To do this sea squirts have two siphons, one for bringing in the water and one for getting rid of the water. The walls of the siphons are lined with cilia (think of cilia as microscopic arms that wave and move together) that grab plankton and absorb oxygen as the water passes through the intake siphons. Any unwanted matter and carbon dioxide is released from the outtake siphon
FACT 3: Sea squirts along Australia’s southern shoreline have a brown outer colour and a beautiful orange/red inner colour. This brown outer colour allows them to blend in with the seaweeds and hard structures they are attached to.
FACT 4: At low tide sea squirts close their siphons so water cannot escape while providing protection against predators and the elements (e.g. sun and air).
FACT 5: Sea squirts are also referred to as cunjevoi or ascidians (as they belong in the scientific class Ascidiacea).
FACT 6: Sea squirts are mostly hermaphrodites meaning they possess both male and female reproduction organs.
FACT 7: The larvae of sea squirts look like small tadpoles that can swim around in the water. They only stay in this form for a few hours before settling on a hard surface, which signals the start of its transformation into the adult form.
Perhaps one of the most interesting facts about sea squirts is their evolutionary link between animals without a backbone (think sea stars, sea jellies, sea snails) to animals with a backbone (such as fish, birds, humans). In the larval stage sea squirts have a notochord, which looks like a rod. The notochord eventually forms into the backbone. However, sea squirts do not form a backbone. When the sea squirt larvae settle onto hard structures, the notochord disappears. This is an interesting phenomenon for evolutionary scientists who study how animals and plants evolve over time.
Sea squirts have a few predators including humans who cut up the sea squirt and use the red part of its body as fish bait. Although we often see how much fun everyone has from squeezing and squirting each other with water from sea squirts, it does cause them a lot of stress while they are exposed to the sun and air at low tide. So while it is tempting to squeeze sea squirts, it is best to leave them in peace as they wait out the turn in tides.