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Dive Dry with Dr. Bill

#598: The Little "Stinkers..." er, Stingers

Over the past two weeks I've had reports from divers and snorkelers all up and down Catalina's leeward side stating that they were getting stung while in the water. On one of my night dives I felt the nematocysts of some unseen critter penetrating the skin on my face. Since I'm covered from head to toe in neoprene, I rarely have that delightful experience while diving... but many snorkelers simply jump in the water with their "itsy bitsy teeny weenie yellow polka dot bikinis" on. Thank goodness for summer... but it does expose them to any of the cnidarians in our waters. I'm referring to the relatives of jellyfish and hydroids who carry those stinging cells for capturing food... or to prevent being captured for food. I was determined to solve the mystery of who these little stinkers... er, I mean stingers... were so I'll put on my detective badge and start looking.

Some boaters and snorkelers reported seeing tiny blue critters floating near the surface and stated they were the culprits. Their descriptions immediately had me thinking about the "by the wind sailor" or Velella velella if you are a marine biologist. These little blue "stingers" are occasionally seen in our waters, especially during periods of on-shore winds (on our shore, not the mainland). Why? Because they actually have a little "sail" on top. They have no other means of locomotion, so strong winds often drive large numbers of them into shallow water or onto beaches. Although they do possess stinging cells known as nematocysts, these generally do not bother Homo sapiens, only plankton and small critters. Another possible suspect would be Velella's close relative, the blue button or Porpita porpita. It has stingers that can irritate human skin especially if you are sensitive (unlike me).

Velella and its relatives have long puzzled taxonomists, those biologists who try to assign the critters and plants of the world to the different groups humans have created for them. They were initially believed to be hydroids. Others felt they were siphonophores and therefore related to the Portuguese man-of-war, or assigned to another group known as the Chondrophora. Back when I was teaching high school marine biology, scientists returned them to the hydroids which apparently welcomed them back.

So both of these species are colonies of hydroids that drift at the ocean surface. Critters that live at the interface of sea and atmosphere are referred to as pleuston. Both use their tentacles and stinging nematocysts to capture tiny plankton and munch them. Yes, they are vicious carnivores... if you are a small copepod or krill. You could also call them communists since each of the "tentacles" is a single polyp, but all have a common digestive canal. All share in the fruits of the polyps that actually capture food. The polyps of a single Velella colony are all male or all female. Kind of like the old boarding schools such as the Catalina Island School for Boys where I taught beginning in 1969. However, these cnidarians will not go coed like the school did!

About a week ago I went down to the dive park for another night dive. I've been terribly disappointed diving in the dark this summer as none of the subjects I usually try to film have been observed. All I've seen are large bunches of big kelp bass and several morays going after the poor blacksmith hiding in the rocks. I have yet to see a single southern kelp crab (much less two of them mating), black-clawed crab or the as-of-yet unidentified light sensitive sea cucumbers. I shouldn't complain too much as I did have solitary barracuda swim by me on two successive night dives, a bat ray "fly" directly over my head and a number of round stingrays swim alongside me. I was surprised to see several abalone out "attacking" live kelp plants. I assume that the strong surge and warm temperatures that decimated our local kelp beds recently have left little drift kelp to be captured by these snails while safe in their holes.

On that night dive I did make a thrilling discovery that offers us another potential suspect as to the identity of the little "stinkers..." er, stingers. Toward the end of my dive in fairly shallow water I began noticing strings of tentacles attached to a bluish "head" region. My first thought was that these were young members of a genus of stinging siphonophores known as Praya. Several years ago I encountered my first Praya at a depth of about 150 ft off Twin Rocks. I was certain it was a stinger but had no first hand experience with it. As I filmed up close and personal, the long string of tentacles wrapped around my face and gave me a good jolt! I certainly learned from that experience! When I researched my column on this species, I discovered that Praya dubia is one of the largest marine critters in the world, reaching lengths of up to 165 ft. This far surpasses the length of the blue whale... but that marine mammal still outweighs it by many tons!

When I finished my dive, I drove home and downloaded the video I took so I could look at this presumed siphonophore. I pulled out my copy of Wrobel and Mills Pacific Coast Pelagic Invertebrates and found that it was probably not a young Praya. Instead it most likely is a close relative of Praya with both classified as calycophoran siphonophores. Yes, I had to throw those big words in to impress you all. These siphonophores lack the large gas-filled swim floats found on the Portuguese man-of-war Instead they have a swimming bell at the front end known as a nectophore. Trailing behind is a tail-like structure composed of many individual structures. These structures may detach and become free swimming reproductive units. These small (3-6" for the ones I saw) siphonophores are able to move by causing the muscular swimming bell to pulse, sending out jets of water. Some have referred to them as "rocket ship" siphonophores. If necessary, they can become even more streamlined by pulling the trailing portion (called the stem) in close to the bell. The trailing segments and their stinging cells could easily create a line of dotted welts if one were stung by them.

So my detective work is done until further evidence comes in. If you are stung by either Velella or Porpita you have a name for the vicious beast... but if it was the calycophoran siphonophore, your attacker remains unidentified (kind of).. and no "names were changed to protect the innocent.".

© 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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By-the-wind sailor (Velella velella), the blue button (Porpita porpita); and the unnamed calycophoran siphonophore

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