Dive Dry with Dr. Bill

#398: The Worms Swim Up... The Worms Swim Down

I LOVE summer. No, not because of all the bikinis on the beach. I love it because the nasty Japanese Sargassum is gone until fall and I can resume my favorite night time activity. No, I'm not referring to dancing up at the Chi Chi Club. Nor am I thinking of the barbecues out at Descanso Beach... or even sipping a buffalo milk there during the day. And it certainly isn't the crowds... much as I welcome our visitors. It's the only time of the year I do lots of night diving! And the critters that come out for the "night shift" can be very interesting. They are often cryptic and hidden during the day. So once again, my diving focuses on what goes on under the full moon... under the sea... in an octopus' garden.

I think back to a dive I made during daylight at Hen Rock a few years ago. I emerged from a 50 minute dive screaming with joy because I had just had a long encounter with a male mantis shrimp in mating coloration. They are only occasionally seen outside their burrows... usually for either "munching" or "mating." Tony Heeter, the captain of SCUBA Luv's King Neptune, yelled down that "Only Dr. Bill could get that excited over a worm." Well, Tony is a great boat captain, but he's not much of a marine biologist since worms and mantis shrimp are classified in two completely different phyla! However, one of the things I do get turned on by is seeing worms on my night dives... as long as they aren't the type of worms that "crawl in... and crawl out." Not ready for that yet. During the day most worms without hard shells are well hidden and difficult to see... and even more difficult to film.

Last summer I had great luck filming at least two different species of worms involved in what appeared to be mating behavior. They were swimming upwards from the reef to the ocean surface... towards the light of the full moon. Now being a certified vampire (just check out my fangs, the guys in the "Twilight" series have nothing on me), full moons make me think of something other than mating... nice type O positive red blood to "munch" on! My dive recently was around the time of a full moon... and the worms did not disappoint. I only saw one or two of the species from last summer. However the "new" species I filmed was even more spectacular. This rather long worm appeared to be one known as the mussel or sand worm, Nereis vexillosa. I only see it occasionally during the day.

Most marine worms are in the phylum Annelida or segmented worms along with the earthworms. Many are categorized in the class known as the Polychaeta, and nearly all in this group are marine. Their bodies are composed of segments known as somites which are separated by grooves (I'm a child of the 60s... how groovy!). Many live within tubes and feed using tentacles or specially adapted gill structures that capture food from the water column. You can see these often colorful structures as you swim along our rocky reefs. They have tiny brains, blood vessels that form a primitive circulatory system, occasionally eyes, and fleshy extensions known as parapodia on each segment. Most of the segments also have bristles known as setae or chaetae made of chitin that give these worms their name, polychaetes ("many bristles").

Non-divers often assume that Jaws is going to pop out of the darkness and munch you a bunch if you dive at night. Well, the only shark I encountered was a harmless horn shark. As I was filming this fish (yes, sharks ARE fish) one of the new polychaetes swam into my viewfinder. Another did the same as I was filming a nearby moray in its crevice. I backed off so I could film the worms, and was surprised to find they big, about 12 inches in length. Most polychaetes are less than four inches, but some species approach 10 feet! Now that might give even the intrepid Dr. Bill a fright. I could see the numerous parapodia flailing around to push the worm up towards the surface. But it wasn't the full moon they sought... most of them went straight towards my video light and got entangled on it.

Although I haven't asked Leslie Harris, the L. A. County Museum's expert on polychaetes, after editing the video I feel reasonably certain that the species I saw that night was indeed Nereis vexillosa. I have seen it before on drifting kelp holdfasts and our rocky reefs. They normally live in burrows on sandy bottoms or hidden in the reef, often associated with mussels or barnacles. They are predators having a proboscis (think elephant but much smaller) with "teeth" that can be extended out to capture prey. Their color is often a beautiful iridescent green although I couldn't capture that in the dark water due to the high contrast. I was surprised to learn that in one source its distribution was reported as from Siberia down along the North American continent as far as Santa Barbara. I guess they didn't check our island!

So why swim up into the water column towards the full moon... or my video light? Why do young men and women head to the bars and dance halls in town. I certainly hope I don't have to explain that to my readers... do I? When these polychaetes are sexually mature, their bodies are transformed into what is known as an epitoke. Without going into all the gory details, the body is full of gametes and its sole purpose at this stage in life is to procreate. Nereis worms are either males or females. At least in that respect they are similar to humans (with the exception of certain residents of West Hollywood). At the right time of the month, these worms come out of their burrows and swarm up through the water column to caste off their sperm and eggs. I think I may have captured some of that on videotape as a few of the worms seemed to "explode" when they hit my video lights. Fortunately for us humans, any similarity ends at this stage. Mating essentially completes the life cycle of these annelids, so I guess you could say they are "loved to death."

© 2010 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM 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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Nereis vexillosa still image and individuals swimming through the night sky...
er, water column... in the Casino Point dive park.

Nereis vexillosa swimming towards video light and releasing gametes upon "explosion"

This document maintained by Dr. Bill Bushing.
Material and images © 2010 Star Thrower Educational Multimedia