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Dive Dry with Dr. Bill

#588: Invasion of the Fire Salps

I've had a number of people ask me about a strange creature (or rather colony of creatures) that they have seen out in the waters off the island or even washed up on shore. Usually their descriptions are sufficient for me to come up with the answer as this critter is truly unique in appearance. I've occasionally referred to it as the French tickler, but there might be young children reading this column... you know, the twenty-somethings! Tee hee. At least I've never mentioned the Kardashians to boost readership of my column!

The descriptions I hear usually refer to a cylindrical or slightly cone-shaped object with "bumps" on its surface. Its tube is closed at one end and open at the other. The coloration may be pink to translucent. Although most of you will not see the family resemblance, it is a member of the most closely related group of invertebrates to humans. Yes, they have no backbone... but there are signs of a primitive central nerve chord in the larvae placing them in the Phylum Chordata along with Homo sapiens, fish and mammals... but in a sub-phylum (Tunicata) and a "class" of its own, the Thaliacea, which includes the other tunicates and salps.

The one many of you are seeing is commonly known as the "fire salp" and its scientific name is Pyrosoma atlanticum. The genus name means "fire body." It was described and named way back in 1804 by a French naturalist, François Péron. It is actually a colony of individuals known as zooids and it is reported they may be pink, white or bluish. The individual animals or zooids are about 1/3" long. Although most of the ones I've seen in our waters are about one foot long, they are said to grow to lengths of two feet and a diameter of more than two inches. New colonies are created through sexual reproduction and the growth of existing ones is through the budding of new individuals at the open end of the colony. The colony structure is gelatin like, causing some to think they are sea jellies. However, the fire salp does not sting.

The individual zooids have their own gills, and a structure that produces mucus nets. The gills' pulsing cilia draw water in through the mouths of the individual zooids alllowing plankton and other "munchables" to become trapped in the mucus and "devoured" by the zooids. They tend to capture larger particles and plankters which have greater nutritional value (although the FDA places no labels on them). The water movement due to the cilia then flows into the central cavity and out through the main opening allowing the entire colony to move forward in the water column. In turn, as part of The Mutual Eating Society, they are munched on by fish and marine mammals including dolphins and whales.

Fire salps are most common in temperate waters like ours, but many of their relatives are found in warmer, tropical waters. They are most plentiful at depths below about 800 ft. However, they undergo vertical migrations in the water column on a diurnal (daily) basis, undoubtedly following similar movements by their planktonic prey. They rise toward the ocean surface at night, then descend back to depth as day approaches. Vertical movements may be 300 to as much as 2,500 feet!

Although I've never spent much time observing them at night, they are bioluminescent and produce a blue-green light. It is this fact that gives them their common name of fire salp. Individual zooids produce the light, flashing on-and-off. There is no nerve connection between the individual zooids, but each one may be triggered by flashes of light from their neighbors. It is said their bioluminescence fascinated early sailors, but there really wasn't much to do on long voyages far from land! In my research I did find an image of a bioluminescing Pyrosoma on the Encyclopedia of Life web page if you care to click to it.

The last major influx of Pyrosoma in our waters that I observed was back in December of 2013. This was during the filming of our squid run with Jean-Michel Cousteau, Dick Murphy, Holy Lohuis and an IMAX film crew. Of course we were so focused on the copulating cephalopods that we didn't spend much time with the fire salps. A few years back Jason Mannix and I also observed a large influx of fire salps during another squid run at Moonstone. I believe the current appearance of these interesting critters may be due to the strong winds blowing from the open ocean towards our shores.

© 2014 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 29, 10:00 AM weekdays and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. You can also watch these episodes in iPod format on YouTube through my channel there (drbillbushing). Please help me climb out of self-imposed poverty... buy my DVD's (see this link). Yes, take Dr. Bill home with you... we'll both be glad you did!

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Pink colonies of Pyrosoma floating through the water column; upright one and open end of colony.

This document maintained by Dr. Bill Bushing.
Material and images © 2014 Star Thrower Educational Multimedia