Dive Dry with Dr. Bill

030: Sex in the Underwater World

We all know that Hollywood, television stations and the print media often resort to racy sexual content to improve ratings or sell products. I don't want any of you to think this column is experiencing a sagging readership, and needs to do likewise! However, as John Steinbeck wrote in The Log from the Sea of Cortez "Marine biologists are the tenors of the scientific world: temperamental, moody, lecherous, loud-laughing and healthy... The best man fitted to observe animals, to understand them emotionally as well as intellectually, would be a hungry and libidinous man, for he and the animals would have the same preoccupations." Eating and sex, or perhaps I should say reproduction, are the two foremost activities of all species.

On Christmas Day of 2002 while SCUBA diving tiny Isla San Francisco in the Gulf of California, I witnessed an orgy unlike any I have seen since the "love-ins" of the 60's (during which, of course, I was merely a scientific observer). As I swam along in the shallows with my video camera, I noted one of the common brown urchins with what appeared to be streams of white smoke pouring out of its body. In an untypically irrational moment, my first thought was that it was on fire and I looked for a fire extinguisher! Fortunately my cerebral matter functioned more clearly after a few seconds, and I realized I was observing the brown urchin releasing its sperm into the open water.

Knowing that when one urchin begins to release its gametes others follow, I looked around and saw an incredible sight. Many of the brown urchins, sitting in the open on the rocks, were also releasing their gametes. In fact as the event proceeded, wispy clouds of sperm and egg literally obscured my vision in several directions. Not knowing the habits of this particular species, I do not know what triggered the first urchin to spawn. Perhaps it was some chermical in the water or other cue. Once one begins release, others of the same species will follow as they sense the presence of the sperm or eggs in the water.

Simultaneous release of sperm and eggs is critical for success. If they were released at slightly different times, the probability of fertilization occuring before the gametes dispersed with the currents would be even lower than that of my winning the California state lottery (assuming I bought a ticket!). Given the distance between many individual urchins, each must release incredible numbers of sperm or eggs to ensure enough reach other urchins for possible fertilization. Of course this external fertilization method requires great expenditure of energy by each individual (although probably less than I expend visiting Internet dating sites).

The larvae that develop from eggs fertilized in this fashion often spend their initial weeks drifting in the plankton. I was able to take several plankton tows in the Gulf of California from the ship to show our guests the tiny larval sea urchins found in the samples. Of course it is these temporary planktonic larvae (known as meroplankton) that allow many marine organisms to colonize the offshore islands of the Gulf of California... or the Channel Islands region in southern California.

Many other marine invertebrates use this broadcast spawning approach. It is very similar to the release of pollen by land plants, although in this case both eggs and sperm are cast into the water. I have observed other species like the giant keyhole limpet reproducing this way underwater, but nothing was as spectacular as this Christmas Day event. It made me think about the consequences of such a method. Obviously those successful in this effort did not choose which other urchin(s) to reproduce with. They did not select mates based on the size of their spines, or the shape of their test. The process, and the resulting exchange of genetic material, was quite random compared to our own more complex (and often irrational) method!

Not all marine animals are broadcast spawners. A number of species reproduce in ways more reminiscent of our own (although I doubt they have read the Kama Sutra or Joy of Sex). Some, like the shell-less snails known as nudibranchs, exhibit an interesting twist. These animals are hermaphroditic, each having both male and female sex organs. When they mate, the male part of one fertilizes the female part of the other and vice versa. I don't think this is what the Wm. Wrigley Jr. Co. meant by "double your pleasure, double your fun." However it does make reproduction far easier. Any time a nudibranch meets a fellow member of its species, it immediately "knows" it can reproduce with it. Back in the 1970's while doing some kelp research off Catalina's East End, my students and I encountered a group of thousands of lion nudibranchs all in the process of mating. Sure beat anything I saw in the 60's.

As you may have gathered from this and other columns, I am convinced that Steinbeck's description applies to good marine biologists. Without reproduction there would be no more life on Earth. I think a healthy attitude towards sex is important and personally I place a high value on being healthy in mind and body! However given the serious ecological impacts of our own species (thanks to its highly "advanced" technology), we should consider the concerns of groups like Zero Population Growth. Now I'm really getting controversial!

© 2003 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.

Image caption: Brown sea urchins in the Gulf of California, Mexico releasing gametes in the water

This document maintained by Dr. Bill Bushing.
Material © 2003 Star Thrower Educational Multimedia