When I was a young fellow, I had crushes on girls all the time. I was continuously infatuated. I believe on the old Andy Griffith show the word was fickle.
What a way of life. No consistency, no roots to put down, no stability. But what the heck, I was in my twenties at the time. I was opportunistic.
When I see a sharksucker zipping around a host fish, it reminds me of the fickle life of my wayward youth. It seems as though their attitude is, If this parrotfish doesnt work out, theres a goliath grouper around the corner under the ledge I can grab. There will always be another opportunity.
I see sharksuckers on Goliath groupers, nurse sharks and turtles more than any other species. I see them bothering a lot of other fish, too, like parrotfish, snappers and several grouper species. And of course, the occasional attack of a divers fin is comical. They attach for three basic reasons transportation, protection and feeding.
My first question is how did they get that giant velcro patch on their head? According to Dave Johnson, zoologist at the Smithsonians National Museum of Natural History, the sucking disc is actually a greatly modified dorsal fin. He traced the development of remoras from larvae to adult, and describes the modification of the dorsal into the sucking disc.
They start out with the same characteristics as dorsals in many other species, then expand and shift forward towards the head. This sucking disc if fully formed when the animal is about 30 millimeters long.
Before the disc is formed, however, they have very sharp hooked teeth on the bottom jaw. Larval stage remoras are not commonly found in plankton mixes sampled by scientists. Dr. Johnson has a theory that remora larvae are not free swimmers, but use the sharp hooked teeth to attach to the interior gill cavities of other fish until the disc forms. See http://phys.org/news/2013-01-sharksucker-fish-strange-disc.html for some interesting images of this development.
In a study by Fulcher and Motta, the suction action of the disc could support the weight of 9.5 to 11 kilograms (about 21 to 24 pounds). So that old TV commercial with the vacuum cleaner holding up the bowling ball is weak compared to your average sharksucker.
The disc is comprised of some bony plates (lamellae), with tooth-like structures (spinules) and two muscle groups which raise and lower the disc. This is surrounded by a fleshy lip that creates the seal, providing an ambient pressure difference. The lemallae and spinules initially latch onto the host, but the suction action of the reduced pressure under the disc is just as important in keeping the sharksucker attached.
Different host skin and scale surfaces require differing efforts on the part of the remora to stay attached. For example, fish with rougher skin or scales, like sharks, require less effort to stay attached since the spinules and plates have more texture to grab. And, as the host picks up forward speed, the suction action adjusts by creating a slightly larger suction cavity, further reducing the pressure inside the sealed disc, increasing the holding power. You can see this paper here:http://timgimages.com/PDF/FulcherMotta2006.pdf
Sharksuckers are one of eight species of remoras worldwide. Their closest relatives are cobia and mahi mahi. The name, in Latin, means delay, and the scientific name in Greek means hold the boat. Remora have a place in ancient lore as playing a significant role in slowing ships down. The most cited story is from Roman times, when remoras attached to Mark Anthonys flagship and left him vulnerable in the battle of Actium, leading to his defeat.
Remoras are so efficient in securing hosts that in some cultures even to this day they are used to fish. In one of the earliest observations I could find, Columbus son Ferdinand wrote about Indian fishermen using remoras to catch turtles in 1494, off Cuba.
This is an entertaining read, and can be found on page 447 in a 1919 work from E.W. Gudger in American Naturalist, here: http://www.jstor.org/stable/2456185?seq=2. Their manner of fishing was so strange and new to our men... they had tyd some small fishes they call Reverso by the tail, which run themselves against other fish, and with a certain roughness they have from the head to the middle of the back they stick fast to the next fish they meet; and when the Indians perceive it, drawing their line they hand them both in together. And it was a tortoise our men saw so taken by those fishermen, that fish (the Reverso) clinging about the neck of it, where they generally fasten, being by that means safe from the other fish biting them; and we have seen them fasten upon vast sharks.
In the most modern application of the power of sharksuckers, scientists at Georgia Tech are examining ways to use remora disc characteristics to fashion better adhesives. Some of the applications include pain and residue-free bandages, attachment systems in aquatic or military uses, robotic climbing and surgical clamp replacement mechanisms.
Their goal is not to replicate the entire disc system, but to use elements of the remora to construct a new class of attachment systems. See http://www.gtri.gatech.edu/casestudy/GTRI-remora-adhesion-study-bio-inspired-adhesive.
Most of the information I read says remoras and their hosts have a relationship called commensalism, where the remora gains but the host is not affected. I have to wonder about that. I often see a conflict, with a host trying to shake or scrape a remora off itself. I have also seen what I think is damage to the host around the area the remora is buzzing.
Tim Grollimund is a freelance photographer and PADI divemaster based in Key Largo. He can be reached at firstname.lastname@example.org or through his web site at www.timgimages.com.