The Moon and Marine Critters

Everyone has heard of lunatics (luna-moon), and menstrual cycles (menses-month). Both suggest that there is an effect of the moon on critters living on the earth. And indeed there should be an effect if, as many scientists believe, life arose in an ocean affected by tides that occur on a monthly basis (about 28 days). The ebb and flow had to have an effect on critters that lived in the shallower seas, in particular. Let's look at two of these critters and the way the moon affects them. They are the grunion, a small fish of West Coast waters, and the fireworm, a worm found in tropical and subtropical waters, particularly in the Caribbean/West Indian areas and Bermuda.

The Grunion

The grunion is a small sardine like fish that lays its eggs high up on the beach where they can rest, undisturbed by the waves at the crest of each tide, for two weeks while the eggs develop. They come in on the last 30 or 40 waves of a spring high tide. That is the exceptionally high tide that occurs every 14 days, year round. However they select certain high tides, perhaps one of the two or three highest spring tides of the year. That way their eggs, laid only at the crest of the tide and at the upper edge of the wave swash, buried a few inches below the surface, are not washed out by any other wave for two weeks. During this time they hatch and when the next spring high comes and fresh salt-water percolates down around the eggs, they come alive, wiggle to the surface through the very loose wet sand, and down the beach into the sea. A new generation of grunion is ready to repeat the cycle.

To accomplish this feat they are very carefully adjusted to the lunar cycle and the degree of adjustment quickly sorts the survivors from the unsuccessful breeders.

I first learned of the grunion while studying at Scripps Institution of Oceanography in LaJolla, California. One day a another student asked me if I’d like to go on a grunion hunt. I said, “Sure, but what are grunion?” He replied that they were a small cigar shaped fish that came ashore at high tide and could be picked up by the hundreds for eating later. He then suggested that I be ready about 9:15 that night and we would go to a nearby beach for the hunt. I was to wear old clothes, dive booties or old shoes and carry a bucket to put them in. Well, again, I’d been on a snipe hunt as a Boy Scout and figured this was a marine version. But I was there when he came by and all prepared.

We went to a long beach right below US Highway 101 and found, to my amazement that there were already 50 people on the beach with lanterns. We joined them and there I learned that in about 15 minutes the grunion would begin to come ashore and would do so for perhaps 20 minutes before the run was over. And sure enough, right on schedule small 6 or 8 inch silver fish began to ride the waves to the upper beach and wiggle their hind end into the wet sand. I was told they were laying eggs. A male would curl around the female and deposit milt (sperm) next to her body where it would presumably settle into the sand and fertilize her eggs. The male then wiggled back into the sea while the female had to extricate her lower half from the sand and get back herself, or die. Some few did get stranded above the tide and waves but most made it back-well perhaps not most, but all that were not taken by the whooping madmen and women on the beach. We grabbed all we could see and put them in our buckets that were soon full.

Meanwhile traffic had slowed on 101 and a chauffeur driven car stopped and a lady in a fur stole and brocade dress got out to watch. It was too much for her and she soon came down the very rickety stairs to the beach where she joined in the hunt. She destroyed a pair of fancy slippers and worse yet, as she got into the real swing of things she picked up the hem of her gown and started putting grunion into the brocade. After about ten minutes of wild enthusiasm, during which many of us normal mortals stopped to watch her, she suddenly stiffened, looked around, dropped the hem and the fish into the water and sheepishly headed back to the stairs, with a ruined pair of shoes and probably fancy dress. But I’ll bet she had more fun in that ten minutes than with anything she had done for a week!

There is a very good educational film put out by one of the Christian ministries, which plays the grunion story straight until the very end when their message is only “Don’t you think there is a higher hand at work here?” The film is called “Fish out of water” and if you ever find it, show it to the kids.

The grunion are reported to be as edible as smelt and other similar fish and some of our graduate students ate grunion for two weeks after the run. And some of our group jumped in their cars and followed the high tides up the coast to catch more on the next beach north. Tides come in at different times in different places.

Both the grunion and the fireworms life cycles are absolutely bound up with the tidal cycle; so tightly that those that forget the time or do not get the genes for the "time to spawn" probably die out. These are some of the best examples of natural selection. Any mistake in timing takes that fish out of the breeding pool.

There are a lot of other lunar cycle controlled critters including fiddler crabs but these two are descriptive enough of this effect.

And incidentally, menses are also pretty well controlled by a 28 day lunar cycle although as we get more and more biologically complex, the cycle strays from high tide or the dark of the moon to a more random, but still 28 day cycle. When you talk to your neighborhood policeman, ask the cop if the full moon means anything around the station house? That is another and not particularly marine tale for another day.

The Fieworm

While in Bermuda I got a call from some friends at the Bermuda Biological Station for Research on Ferry Reach. They asked me if I was interested in helping them catch fireworms for one of their researchers. “Hell, yes!” I answered.“

Then come to Ferry Reach, to the Causeway at 10:27 tomorrow night”, they said. “Can we do it another night?” I asked. “No way!” was the reply. “Then how about a little earlier?” I asked? “It’s got to be at 10:27, cause that’s when the fireworms come out!” I thought it was a snipe hunt all over again, having almost forgotten the grunion. So I humored them and was there at 10:20. They had a driftwood fire going, a cluster of small boats and buckets and some funny looking nets, with fine screen and almost flat in the middle. And the lady we were collecting for told us about fireworms.

She said they live in the mud and sand all year long except for this one night, when they come to the surface for about a half-hour while the sky is darkest. This is very tightly attuned to the dark of the moon and only a few minutes during the magic night. The female rises to the surface and lays green luminescent eggs as she swims in a tight circle about 5 inches across. The male, also celibate for all but this one magic night comes to the surface driven by the same lunar biological clock, looks for a circle of fire and fertilizes the eggs. Then both retreat to the bottom sediments for another year, having done their duty and propagated the species. Not very romantic but quite effective.

And about then someone shouted, “There’s one!” and another and ten more and 100 and 1000. The whole stretch of water was filled with circles of fire about a meter apart. We jumped in the boats and dipped up the females and put them in our buckets and in a short time, the lights winked out and we were left with an almost dark channel. The few that missed the exact time were often left without mates and their line died out. A perfect case of survival of the fittest.

Out of curiosity I went to Ferry Reach the next two nights. The next night there were about a dozen who had missed the boat. Many were probably too far away from a mate to be seen and fertilized. The second night after the magic night, there were two circles of fire.

I was led to believe that Bermuda was the only place this happened. 600 miles from any other land, it seemed reasonable. But while I was teaching oceanography at FAU, a lad in one of my classes asked me what would make circles of fire on the water in the Leeward Islands. His description was exactly of fireworm spawning. Since then I have heard of two other examples of circles of green fire on the water in the Caribbean and saw what was probably fireworm spawning in the Keys last week. The circles were poor but the green fire was pronounced and when I ran my hand through one cluster it broke up into hundreds of tiny green spots, the eggs I’d guess

[Home] [Cirriculum Vitae] [FAU Page] [Ray's Corner]