Dive Time by Tim Grollimund
The great Hamlet debate
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Posted - Friday, October 14, 2011 11:01 AM EDT
A pair of hamlets on Deep Molasses, at about 80 feet. (Photo by Tim Grollimund)
I used to fish a lot when I was a kid growing up in the mountains of Virginia. My favorite fish to catch was largemouth bass. As far as I can tell, the saltwater equivalent is grouper.
In both venues they are aggressive predators, popular to catch, and even more popular to eat. Freshwater bass come in significantly less color schemes and species. In the marine environment the grouper family has a large number of species and is prolific in many places, with tremendous variation in color, size and diver-friendliness. One of the most wide-spread groupers in the Caribbean is also the smallest.
Hamlets are tiny groupers, but in the same family. It's like finding out Goliath and Tom Thumb are cousins. I guess that's what intrigues me about all the different types of groupers on the reef. There are many game-fish-sized grouper species, but I never paused to consider the tiny hamlet as a tremendous predator. Hamlets feed mostly on small benthic crustaceans like crabs, shrimps — including mantis shrimp — and bristle worms. Hamlets get my immediate respect for munching on bristle worms.
Talk about nibbling on something with a kick! And I think I might just follow a butter hamlet around sometime to see if he will find a mantis shrimp for me. As always, the proverbial exception to the rule has also found its way to hamlets. There is one species that feeds almost exclusively on small fish, blue chromis, to be exact. Somebody always has to be different.
I looked all over the internet and have yet to figure out why a hamlet is called a hamlet. Maybe mini-grouper (not to be confused with a small BMW) is the right term. In my research on why a hamlet is a hamlet, moniker difficulties notwithstanding, I found a few interesting items.
There has been a debate for decades on how many species of hamlets exist. The original classification was for one species (Hypoplectrus unicolor), and color variations didn't matter enough to differentiate a new species. As this debate has raged, scientific research is shedding light on the differences - or not - for the many color variations of the hamlet group.
The crux of the debate runs like this: All of the hamlet color variations are strikingly similar in physical characteristics and behavior - body shape, fins, size and diet. The indigo hamlet is the only color variation that is different, in two important ways. Indigos are the largest of the hamlets, and they feed primarily on blue chromis rather than crabs, shrimp and worms.
Looking a bit deeper into the debate, we find good arguments for color patterns as definitive criteria for defining species. And now scientists are finding some differences in the molecular structures of the color variations.
Another interesting study shows areas of concentration by color pattern. These areas are called population centers, defined by the predominantly abundant species of all hamlets in the area. And according to that map blue hamlets are the kings of the reef in the Keys. While I have seen a fair number of these, I see far more butter hamlets here than anything else. It was originally thought that blue hamlets were only present in the Keys. The only other place they have been seen is in Belize, and that was a long time ago. Even though we have more butters than blues, we have more blues than anywhere else.
There is another study I found postulating food sources as a contributing factor to the color-scheme thing. After all, you are what you eat. Is that true for hamlets? Are pigmentation genes, as delineated in the studies, food-dependent? I don't even know if it's the right question to ask. But others are asking similar questions now.
All these approaches to the separation of different color schemes as distinct species have been examined through some lab work, too. Since hamlets exhibit simultaneous hermaphroditism — each one is a he and a she — and are capable of self-fertilization, the experiments were quite revealing. In instances where two species were crossed, a hybrid resulted. And for the same species breeding, or in the case of self-fertilization, the species offspring held intact with the parents. This supports the color-as-species argument. In the field only two to three percent of observed cases where cross-breeders. Hybrids are quite rare.
My hamlet image collection has a lot of butter and blue hamlets, one shy, a fair number of barred, some black and a few indigo hamlets. There is one hamlet my dive buddy Phil Darche found I think is a hybrid. I think it's a cross between a barred and an indigo, which would be very rare. It has the bar pattern markings of an indigo. But it also has a distinctive stripe under the eye and some of the color of the barred. So if you see a weird-colored hamlet on your travels around the reef, you're not alone, and your observation is valid, not a rapture-of-the-deep-induced vision.
One of the best parts about doing research for these columns is the opportunity to learn more about reef critters and pass what I learn on to others. I had no idea there was such a great debate, or the depth and breadth to which hamlets have been studied. But I still don't know why they're called hamlets. Is a species to be, or not to be? That is the question.
Tim Grollimund is a freelance photographer and PADI divemaster based in Key Largo. He can be reached at tim@timgimages.com or through his web site atwww.timgimages.com. Keep tabs on his activity for the Coral Restoration Foundation at www.timgimages.com/crlogbook.
