SEA SQUIRTS

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.

Sea squirts attached to a pylon and sea wall on Hampton Beach, Victoria, Australia. Notice that each individual sea squirt has two siphons for intake and outtake of water and gases.
Sea squirts attached to a pylon and sea wall on Hampton Beach, Victoria, Australia. Notice that each individual sea squirt has two siphons for intake and outtake of water and gases.

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.

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The Intertidal Zone

Over the past few weeks, quite a number of the Dalton Koss HQ Marine Facts have referred to the intertidal zone. Many DKHQ readers have curiously responded with the questions:

  1. Where is the intertidal zone located?
  2. Exactly what is the intertidal zone?

At Dalton Koss HQ we are more than happy to answer these two questions.

The intertidal zone is located along our coastlines, specifically where the sea meets the land. This zone varies all across the globe. It can be made up of rocky shores with many fun rockpools, mudflats or sandflats, mangroves, salt marsh and seagrass beds, sandy beaches and coral reefs. The intertidal zone can be exposed to the rough and tumble of open oceans or located in sheltered places such as bays and inlets. Some scientists refer to the intertidal zone as the littoral zone.

An exposed intertidal rocky shore at low tide along Victoria's Great Ocean Road. Notice the prolific range of seaweeds adorning the rocks.
An exposed intertidal rocky shore at low tide along Victoria’s Great Ocean Road. Notice the prolific range of seaweeds and mussels adorning the rocks.

At Dalton Koss HQ we often refer to the intertidal zone being in a liminal state. This is because the intertidal zone is either covered with ocean waters or exposed to the sun and air due to the constant movement of tides. It is never in one state of being within a 24 hour period; rather it is in continuous flux.

Being exposed to two completely different types of conditions means that as an animal or plant living in this zone, one needs to have some incredibly amazing adaptations to survive. Intertidal plants and animals need to be resilient to wave wash, tides and currents, sun exposure, predators and drying out all while trying to photosynthesise/eat and reproduce.

An exposed intertidal sandy flat located along Cape Conran Coastal Park in eastern Victoria, Australia.
An exposed intertidal sandy flat located along Cape Conran Coastal Park in eastern Victoria, Australia.

This makes the intertidal zone a fascinating area to explore and discover the spectacular range of marine animals and plants. To conserve this amazing zone while you explore, please be careful where you tread/snorkel, place rocks back to their original positions when you examine what is beneath and keep all rockpool animals and plants fully immersed in water to reduce their stress.

An intertidal coral reef exposed at low tide located in Fiji's Coral Coast.
An intertidal coral reef exposed at low tide located in Fiji’s Coral Coast.

Chitons

Visitors to coastal shores often come across unusual looking animals hidden in rock crevices. Here at Dalton Koss HQ we strive to help make sense of these unusual sea creatures by sharing our marine knowledge.

Chitons are one of these more unusual finds that many coastal visitors find on the rocky shoreline. With the Ch pronounced as a k sound, chitons have a fossilised appearance due to their numerous armoured plates. In fact, some people call Chitons the armadillos of the ocean as they are able to curl up into a ball using their armoured plates as protection.

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The armoured plates grow from the head to the foot of their body providing protection and camouflage from predators, hence why this animal is also commonly known as the coat-of-mail. The actual animal grows and lives under these armoured plates and its body is not segmented like its armour.

Here are a few interesting facts about chitons:

1. Chitons can only be found in the intertidal and upper subtidal zone of rocky shores.

2. The majority of chitons are vegetarian, grazing and eating seaweeds using their radula (see earlier What creates those circular holes on seashells? DKHQ Marine Fact to find out more about radulas).

3. Chitons can live from 1-20 years or more.

4. All chitons have a girdle around their body and plates.

5. Chitons prefer to move around during dusk and at night to reduce their chances of being prey to birds and other larger animals.

6. Sexual reproduction is often associated with a particular phase of the moon or with a tide, in some instances both.

The most fascinating and favourite Dalton Koss HQ Chiton fact is their homing ability. Chitons are able to have a night out crawling around rocks and feeding, but they are able to return to exactly the same spot before the sun comes up. Just amazing for a creature that has no eyes!