Two weekends ago I was standing at the dive park talking to my friends Yin You and Brian after their dive. I asked if they had seen squid eggs, and when I described the "candles," they said they had. They then asked about another unidentified critter they had seen... a gelatinous cylinder with "warts" on it. My mind searched its ancient memory banks and formed a thought (rare event, I know). Just then Jon Council came up with such an object in his hand and asked about it. I looked at it for a few seconds and said it looked like a species of Pyrosoma, but in 40+ years here I'd only seen three that I remembered, and they were all orange in color. This one was transparent, or at least translucent.
After saying goodbye to my friends, I hopped in the Dr. Bill Mobile and raced (at 8 mph) up to my house to look at my Pelagic Invertebrates field guide. By gum (Wrigleys of course), there was the pyrosome Pyrosoma atlanticum, and it was clear in color. Searching further on the Internet, I discovered that although my previous three sightings were all of orange specimens, they did come in a clear phase as well. What surprised me was that divers in the dive park were reporting dozens of them, and when I posted the picture I took on Facebook and described what it was, several mainland divers chimed in that they had seen them too.
Although Pyrosoma could be mistaken for a sea jelly, or possibly even a sea cucumber or "worm," they actually belong to the phylum Chordata. What other species is found there? Why Homo sapiens... human beings... you and me (well, I'm sure about me...). Now I don't see the "family resemblance," but perhaps some of you do! Why are these jelly-like blobs placed alongside such advanced amphibious creatures like myself? Because several of them have primitive nerve chords in their larval stage... and that takes a lot of nerve! The scientific name means fire ("pyro") body ('soma"). These pelagic (open ocean) chordates, more commonly referred to as fire salps are categorized in the Class Thaliacea. Don't worry, that won't be on next Thursday's test. They are related to the other salps and tunicates one finds drifting in the water or attached to the bottom.
These cylindrical critters may measure anywhere from less than half an inch to nearly a yard, with other species reaching several yards (meters for my metric friends) in length. Pyrosoma is actually a colony of tiny individuals that form a hollow tube with an opening at one end and the other end closed. There may be thousands of the small zoids, which face out from the colony and are joined together by the gelatinous "tunic" that gives them the appearance of a sea jelly. Don't worry, these do not sting.
Each individual zoid has an oral siphon with cilia that beat and force water into it. This creates a current which the individual uses to filter out yummy plankton using a net of mucus. The current from each individual zoid is then exhausted through the hollow colony and out the large opening in the posterior. Thus they take water in from the outer surface of the colony, and expel it through the inside of the cylinder. This gives Pyrosoma a degree of mobility even though they are considered planktonic, or free-floating. I have speculated that the color of the colony may depend on what planktonic critters are dominant in the surrounding waters for food.
The colonies are also bioluminescent, giving off a fairly bright blue green light. Sailors at sea have marveled at the glow they give off after dark when present in large numbers. Each individual zoid has bioluminescent structures, possibly containing tiny bacteria that actually create the light. The light pulse may travel in waves along the colony, with each zoid triggered to luminesce not by nerve impulses but in response to the light from adjacent individuals.
Pyrosomes are usually found in the upper layers of warm seas, but this species is one of the few that actually visits us here on the West Coast with any frequency. Other species may be found at great depths, and may undertake daily (diel) migrations traveling down as deep as 2,500 feet and then returning to the surface. These vertical movements in the water column may be important mechanisms for the transfer of carbon from the upper layers where photosynthetic plankton are present, and fix carbon from carbon dioxide in the atmosphere into carbohydrates, to the deeper waters where their excretions and death may release this carbon for organisms down there including anemones, sea urchins and crustaceans.
Pyrosoma may be present in very large numbers. I dove Moonstone Cove recently with Jason Manix to film them and the dying squid. Jason found hundreds of the salps lying dead on the bottom. I found two... but plenty of dead squid, eggs and one live squid swimming about all by his lonesome after the orgy. Following the BP oil spill last year there were mass die-offs in the Gulf of Mexico. When they die, they may drop to the ocean floor in large quantities. These are referred to as "deposition events." Some scientists are predicting that sea jellies and pelagic salps will increase in density as a result of global climate change. If so, their mass die-offs in even greater numbers may alter some deep water food webs important to humans as well. The Japanese already eat jellyfish sushi, but I'm not sure I want to try salp sashimi! Give me beef, or give me... vegetables?
© 2011 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. 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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Pyrosoma in Jon Council's hand, picture of one from Moonstone Cove dive; cluster of dead ones (Jason Manix photo)
and one with diver Rick Guerin in the dive park (courtesy of Dr. Jim Haw, USC Environmental Studies Dept.).
This document maintained by
Dr. Bill Bushing.
Material and images © 2011 Star Thrower Educational Multimedia