Dive Dry with Dr. Bill

#456: A Terrible Tingle, not a Tickle

Non-divers frequently ask me what the most "dangerous" creature I encounter under the sea is. I should probably answer Homo sapiens sapiens, but since I'm a solo diver I rarely have a problem with them in King Neptune's realm. Topside is a different story. Of course most expect me to say sharks, given the fears instilled in them by "Jaws" and such stupidity as "Shark Week" on the Discovery Channel. I've had a 14 ft. great white swim past me here off the island. Back in the very early 70s I had an encounter with a 22 ft man-eating tiger shark in the Sea of Cortez. Fortunately I was kayaking and the shark didn't like the feel of the rubberized canvas hull or I might not be here today. I filmed dozens of soupfin (tope) sharks checking me out in Lover's Cove a decade ago. In Tahiti I had at least 50 sharks swirling around me with several dozen more off in the distance. I even landed on top of a zebra shark doing a giant stride on a night dive at Australia's Great Barrier Reef.

However, the only time a shark has actually tried to "attack" me was right in the Casino Point dive park. I was atop Little Casino Reef trying to film an "monstrous" 18" horn shark. I wasn't satisfied with the composition of my shot so I gently moved the shark into a better position. My model apparently did not agree with my choice, rose up from the bottom and started biting me on the chest. Of course its tiny, dull teeth and the thickness of the wetsuit gave it no chance of penetrating to my skin. I laughed so hard, the regulator fell out of my mouth. So sharks have not really posed any danger. Besides, most of them are long gone from our waters due to long liners, gill netters and commercial fishers working both here in California and elsewhere around the Pacific.

What is the most "dangerous" critter then? I've chosen one that is hardly capable of consuming me intact (or otherwise), but one which has undoubtedly caused me more pain while diving in the dive park than any other single species. I'm speaking of the "lowly" white feather or plume hydroid. I have been told that the scientific name is Plumularia setacea, but I am not entirely positive about that ID. Members of the genus Plumularia are difficult to tell apart unless you use a microscope and I just don't carry one of mine when I dive, nor have I ever taken a specimen home to observe under one.

How can these tiny (generally one to two inches) colonies pose any threat to a diver like myself? Well, they are members of the phylum Cnidaria (formerly Coelenterata) whose members have in common the fact that they possess stinging cells known as nematocysts. Even non-divers are generally well aware of their stinging relatives, the jellyfish and siphonophores like the Portuguese man-of-war. Having been stung once by a siphonophore known as Praya, I can attest to the power of their sting. I first discovered the stinging power of the white feather hydroid back in the days when I dove with just a 3mm shorty wetsuit during summer. I would gently rest on the rocky reef to film, and end up getting very irritating stings that often left small red welts. Once I discovered the cause, I started diving with a full suit for protection.

These hydroid colonies have a degree of specialization in their jobs. Some of the tiny polyps function as "feeders," grabbing goodies from the water column using their tiny tentacles. The colony has a common gut or digestive tract, so the food harvested by the feeding polyps is shared with the non-feeding ones. I guess those on the Right politically would abhor these invertebrates since they definitely practice a form of socialism. Those that do not feed may function as soldiers, defending the colony by stinging the heck out of anything that touches it... like yours truly!

Hydroids have interesting sex lives for something so tiny. No, it wouldn't render a documentary about them X- or even R-rated. Actually they have a sex llife, and an asexual life, reproducing both ways. The colonies have structures known as corbulae which contain the sexually reproducing stage of the hydroid with the genders separated. This stage, known as the medusa, looks very similar to a TINY jellyfish. However, they are not free-swimming, but held captive in their respective corbulae. The males release sperm which then fertilizes the eggs of the females in their respective corbulae. The fertilized egg grows into a tiny larva that looks something like a worm. The larva crawls away and starts another hydroid colony. Since these diminutive stages are not long-distance runners, the new colony is usually located fairly close to the old one. Therefore these hydroids are often found in clusters on the rocks.

For those of you who dive or snorkel in our waters, the lesson is simply this. These white feathers will sting like a bee rather than just tickle your fancy. If you see them on the rocks, please don't touch... for your own sake. Of course that really goes for just about every form of marine life. One should not touch them unless you are a trained biologist with knowledge of their sensitivity and the damage you could cause. Real harm could result from simply touching some species. I recently watched an instructor and two other divers playing "catch" with a sea cucumber in the dive park. Now that sea cucumber probably wasn't overly disturbed by this activity, but it really did not convey respect for other life to the new divers. And in the case of the white feather hydroid, they may EARN your respect by stinging you!

© 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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White feather or plume hydroid colonies on submerged rocks in the Casino Point dive park.

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