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Every spring they appear in force, growing through the summer and then they seem to diminish in late fall. “They” are tunicates, affectionately known as sea squirts and sometimes sea pork.

Tunicates are invertebrates, meaning they lack a backbone. Invertebrates are a very large and diverse group of organisms that include crabs, sea urchins, jellyfish, sponges, worms, spiders and insects, just to name a few.

Tunicates come in many shapes, sizes and colors. They can be solitary, colonial or pelagic. And, they are all marine organisms. There are no freshwater tunicates, but some species can be found in fairly low salinity brackish waters. All tunicates are filter feeders. As such, they all have two siphons. The first takes in water, particles are extracted as a food source and then the water is expelled out the second siphon. Tunicates get their name from their “tunic” or outer covering that protects them from predators. The tunic is made of cellulose, a long chain of linked sugar molecules. Cellulose is more common in plants and is the substance that gives wood its strength.

As filter feeders, tunicates benefit water quality by removing particulates and excess nutrients from the water. Good water quality is important to all marine life and us humans too, but water quality may not be the only way tunicates benefit us. Researchers have been studying various properties of tunicates and have learned that they may possess important anti-cancer properties.

Specifically, a group of chemicals called “Palmerolides” found in the body tissues of an Antarctic tunicate species, is extremely active against melanoma, a potentially deadly skin cancer. But that’s not all: Scientists believe the cellulose found in tunicates could be used to help repair or even grow human muscle tissue. And just this year, researchers at the University of Bergen and Uni Research have found that a certain type of tunicate can be used as a renewable source of biofuel and fish food (for aquaculture).

Did you know? – (from the Smithsonian Institute):

¨ There are ~2500 named tunicates

¨ Tunicates are cultivated and eaten in many countries including: Japan, Korea, Chile and France

¨ Many tropical species have a single celled algae living as symbionts (meaning both the algae and tunicate benefits) inside their tissues (just like the algae associated with many corals)

¨ Tunicates are the only animals that reverse their blood circulation

¨ Tunicates are the animal group most closely related to vertebrates (fish, birds, reptiles, amphibians and mammals)

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