Squirts, Salps, & Sea Pickles, Oh My!

There are some weird animals in the ocean. A few weeks ago, we talked about some of the strange worms of the deep. But there are some even stranger marine animals out there.

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A sea squirt, Ciona intestinalis. Image: NSF

Take the humble sea squirt. These sedentary, cylindrical blobs are a type of hermaphroditic animal called a tunicate. Ranging in size from 0.2 to 4 inches (0.5-10 cm), these animals are actually closely related to vertebrates – including humans.

Because of their similarities with humans, they are often used in medical research. And they have a very special skill – these tunicates are among the only animal that can reverse their heartbeat.

Yes, you read that correctly. They can change the direction of their blood flow. Check it out:

Another type of tunicate scientists are particularly concerned with is the salp.

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Salps are free-swimming tunicates that can be solitary or colonial. Image: NSF

Salps are free-swimming, tunicates. They move by contracting their gelatinous bodies to create a jet of water, propelling it forward. As the water is pumped through its body, phytoplankton is filtered out of the water for food.

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Krill forms the foundation of the Antarctic food web. As climate changes and salps have taken the place of krill in the food web. Image: British Antarctic Survey

Salps play an especially prominant role in the Antarctic. Increasingly, scientists are finding evidence that as climate is changing in the Antarctic, the environment is more suitable for salps than krill. And this is important because krill forms the foundation of the Antarctic food web. Should krill be replaced by salps, the entire Southern Ocean food web has the potential to collapse. While seabirds and seals have been known to consume salps, as they are composed of 95% water, they lack the nutritional content to sustain higher predators.

Another type of tunicate that has been making the news lately is the sea pickle. These planktonic tunicates, also called pyrosomes, are composed of hundreds (or sometimes thousands) of individual animals. Each one is only a few millimeters in length, but they share a common outer gelatinous tunic, making them appear to be a single animal. Even cooler, they’re bioluminescent – they glow when touched or when nearby pyrosomes glow.

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Sea pickles are colonial tunicates, where the individual animals share a common outer, gelatinous tunic. Image: NOAA

And some sea pickles are enormous. Check out the size of this one:

Lately, sea pickles have been making the news for another reason. In recent months, populations of sea pickles have exploded in the Pacific northwest. Last month, NOAA conducted a 5 minute trawl off the Columbia River and caught 60,000 pyrosomes.

And scientists aren’t really sure why that is. Ric Brodeur of the Northwest Fisheries Science Center has worked in the Pacific Northwest for 30 years, but had never seen a pyrosome before 2014.  And while the number of pyrosomes has increased in the region in 2015 and 2016, the number that have been observed this year is unprecedented.

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An unprecedented bloom of sea pickles in the Pacific Northwest has left scientists searching for explanations. Image: The Outer Shores

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