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Dive Time with Tim Grollimund
Look for the fish in a box
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Posted - Thursday, June 07, 2012 07:12 PM EDT
Tim Grollimund
The triangular body shape of the smooth trunkfish has many advantages for swimming and maneuvering on the reef. (Photo by Tim Grollimund)
When I’m on the reef and I want a chuckle, I look for a fish in a box. Not a cardboard box of fish like you find in the bait shop, but a body box that fits perfectly and is color matched to its occupant. I bet I have seen some sort of fish in a box on every dive. On some occasions we find juveniles, too. They are about the size of a quarter and look like floating marbles.
I’m referring, of course, to a group of animals called boxfish. They’re fun to watch. Sometimes, I think they look like little robots scooting around the reef in search of a new power source. The Energizer bunny with fins and armor — and in some cases, horns. Some versions are friendly, some are quite shy. But they are always entertaining.
What do they do to earn their living on the reef?
They eat small bottom dwelling mollusks, crustaceans, starfish, tunicates, sea grass, algae and brittle stars. One of the most enjoyable sites is watching a smooth trunkfish puffing up a storm of sand while a juvenile bluehead wrasse picks through the debris.
In the Keys we have two varieties of cowfish (scrawled and honeycomb) and three types of trunkfish. Cowfish are more colorful, featuring bright blues and mottled greens. They have sharp spines above each eye, which distinguishes them from the three trunkfish species. Cowfish change color quickly and blend into the background easily.
They are normally shy, but I have found that if you anticipate where they are headed and get in front of them, you can get quite close before they turn away. Even though the Reef Fish Identification book lists honeycomb cowfish as “occasional” in Florida, we see them on the majority of dives. Smooth trunkfish are quite easy to approach and are the most prolific on the reef. We see very few spotted trunkfish, but the largest of the three (Lactophrys trigonus) is the most elusive of all.
The fish identification book lists the large trunkfish species as “occasional to uncommon”, which means they have not been to the deeper part of the reef lately. We see them in the 50 to 60 foot range on almost every dive. They are quite a bit larger than the smooth and spotted varieties, growing to almost twice the size of their smaller cousins.
I think there is some mating going on this last month or so. We have seen the large trunkfish in groups of up to six at a time, hovering over barrel sponges. I have not been able to get close enough to this behavior yet to get a good shot.
There are also references to trunkfish excreting a toxin that is lethal to other fishes in the immediate vicinity. The toxin is a surfactant type of mucous called ostracitoxin. Some scientists have studied this toxin and attempted to make shark repellant out of it, but were not successful in creating an effective marketable product.
The main difficulty was maintaining a high enough concentration for a time long enough to be effective. Google “Icthyocrinotoxins and Their Potential Use as Shark Repellents” if you want the details.
Trunkfish have some unique movement characteristics that have also been the topic if intense scrutiny. Since they are encased in a triangle of bony plates, their core body does not flex like other fishes. The only moving parts are the fins, eyes and mouth, which protrude through the bony plates.
Robotic studies have looked at the movement of fins for propulsion and the turning radius of the animal. Maneuvering in tight spaces with a near zero turning radius is important for underwater vehicles, and nature’s boxfish design is a key element in vehicle development.
The body design has also been found to have self-correcting vortex properties that make boxfish stable in moving water. It’s like having a gyroscope built into your skeleton, and always being upright no matter what the water conditions. Current or surge do not seem to make much of a difference to a boxfish.
The lift effects demonstrated by the boxfish body design are similar to a delta wing aircraft. Or is it the other way around? I’ll never look a stealth aircraft profile again without thinking of my diminutive friends on the reef. For a great explanation of this, see the article by Sarah Tilley entitled “Smoothly Does It” at http://jeb.biologists.org/content/206/4/637.1.full
Carmakers are also riding the boxfish body craze. A few years ago Mercedes used the boxfish for a concept car design. You will get a kick out of this video: http://www.youtube.com/watch?v=xEz3AC40MLk&feature=related
That slow little energizer bunny fish is really a superlative swimmer, with built in stabilizers, a zero turning radius and low energy consumption. My new goal is to dive like a boxfish!
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 at www.timgimages.com. Keep tabs on his activity for the Coral Restoration Foundation at www.timgimages.com/crlogbook.