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Dive Dry with Dr. Bill

#481: Invasion of the Salps

I've had a number of people, both divers and "top siders," come up to me recently to ask about the strange chains of "jellies" they've seen while diving or out on boats fishing. Some thought they were weird jellyfish (the PC crowd calls them "sea jellies" now... but I don't) or possibly related to some other dangerous critter capable of stinging you from 50 feet away. Well, frankly, I'm surprised you haven't seen the family resemblance, and some of you certainly should after looking in a mirror. What y'all have been seeing is one of our closest relatives in the invertebrate world, the salp.

These critters are invertebrates because they lack a backbone (I know a few people who lack a spine as well). However, they are members of the same major taxonomic group that humans are in, the phylum Chordata. What we all have in common is a spinal cord or central bundle of nerves. Of course the resemblance pretty much ends there for most humans and salps. The salps have two openings, one at each end of the body. They use bands of muscles to pump water through the hollow interior both to propel themselves and to feed. Although they look like the soft sea jellies, their outer body or tunic is actually pretty firm and they feel almost like soft plastic.

Salps are tunicates, a group commonly seen in the dive park attached to rocks on the reef and other hard surfaces. However, the salps have abandoned the stationary or sessile lifestyle for a life of adventure out in the open ocean. Salps are a common sight in the blue water a few miles offshore. I used to film them while waiting for that occasional blue or mako on our shark dives out in the Channel over a thousand feet or more. I'd hang on the line or just remain neutrally buoyant as these beautiful creatures zoomed past me in the current. Sometimes the currents and/or wind bring them in close to shore where they are encountered by more people.

A specialist in salp taxonomy (classification) should have an easy time of it. There are apparently only 24 different species. Most are found in tropical and subtropical waters, but we seem to get our share here as well. They are able to drift through the water column because they are essentially neutrally buoyant... a skill many new divers (and some old ones) lack. Inside their body cavity is a cone-shaped mucous net used to trap plant plankton (phytoplankton) and other small particles to munch on. Nothing like a little microscopic salad to fill your belly I always say! Salps grow and reproduce at incredible rates... 10 to 100 times that of other planktonic drifters. Their poop (known technically as fecal pellets) is also prodigious and is a major pathway by which potential food sinks to mid-water and deep water critters. Oh, yummy... not!

Salps have a higher percent of solid matter in their bodies than do sea jellies and other jelly-like critters, making them better quality food for predators. These may include sea jellies and siphonophores, turtles, marine birds and a number of species of fish. On my dives at Casino Point, I observed large numbers of fish including blacksmith, garibaldi, sheephead, rock wrasses and others swarming around the chains of salps near the bottom in the vicinity of the wreck of the Suejac. Salps have no stinging cells or other effective defense against them. One of the ways salps deal with predators is by simply out reproducing them!

Salps have a very interesting sex life (at least if you're a marine biologist like me). They alternate between an aggregating form that often join together to create large chains and these reproduce sexually; and a solitary form that reproduces asexually. The solitary form keeps duplicating itself to create the long chains. Of course individual members of the long chains may break off and exist independently too. The sexually reproducing individuals generally begin as females and their eggs are fertilized by the older individuals which have turned into males. When a critter begins life as one gegnder and changes into the other, like our friend the salps and sheephead, it is known as a sequential hermaphrodite.

The individuals I've seen recently appear to be of the species Thetys vagina. Sorry, no common name, and as far as I know they do not perform monologues. They bear a pair of pigmented projections at the rear end. This species is reported to be the largest salp on the West Coast, reaching up to about 12" in length. They are found in the Atlantic, Pacific and Indian Oceans.

I've previously written about another species, Cyclosalpa affinis, which I often see out in much deeper water out in the Channel, say 1,500 to 2,000 feet. Whatever you do, don't drop your weight belt or your camera housing when you're out there! The aggregate form of this species forms a series of linked whorls. They are known from tropical and temperate waters, reaching as far north on our coast as the Gulf of Alaska. That's temperate? Brrrr.

© 2012 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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Aggregate chain of Thetys vagina and individual broken off from the chain; fish congregating
around a chain in the dive park, and Cyclosalpa affinis out in deeper water.

This document maintained by Dr. Bill Bushing.
Material and images © 2011 Star Thrower Educational Multimedia