BY ALPER ÖZKAN (MSN/PhD)
d_ozkan@ug.bilkent.edu.tr
I’ve been aware for a while that Bilkent has a swimming pool, but only recently did I decide to see what it was all about. This rapidly proved to be a poor decision.
Now, I hail from Antalya, and I certainly drank my share of brine during my childhood, but I had somehow forgotten my youthful drowning adventures and deluded myself into believing that I was, in fact, a capable swimmer. These preconceptions were swiftly and decisively eliminated when I took my first step into the pool and sank like an awkwardly dog-paddling rock, and the following days were a humbling experience in discovering just how out of shape I was—and so, to restore some shred of my honor, I’ll be talking about animals that aren’t me and actually swim quite well.
The young, or nymphs, of dragonflies possess some of the strangest modifications of any insect, their mouthparts having been transformed into a claw-like “mask” that can stretch out to capture distant prey. That alone makes them terrifyingly effective ambush predators, and many rely on their drab color to avoid notice, but if they need to get out of trouble in short order, they may also resort to their jet-propelled anus. Dragonfly nymphs breathe through internal gills on their abdomen, pumping water in and out through their rectum—and if necessary, they can force water through it with great force, producing a sudden burst of speed. Indeed, even their mask is water-powered, as its extension is only possible through the reverse of this process: the larva blocks the escape of water from its anus and suddenly constricts its abdomen, using the trapped water to force its mouthparts forward like a water-piston. Dragonflies are not the only animal capable of jet propulsion, however—cephalopods may also block the entry of water into their mantle cavity and constrict their mantle wall to force water out of their siphon, and their water jet is used both to ambush prey and to evade predators. Unlike those of dragonfly nymphs, cephalopod jets can also be used out of the water, and an octopus at a German zoo even made a name for itself because of its tendency to destroy bothersome lamps by shooting water at them until they short-circuited (the offensive use of a water jet is also seen in archerfish and scorpionfish, which “spit” water to either shoot down overhead insects or confuse smaller fish).
Breathing underwater is a major issue for many animals, and even worms, which can normally survive just fine in water, may falter in oxygen-poor swamps—but almid earthworms, such as Alma and Drilocrius, have conquered even these environments by evolving a tail that transforms into a bona fide oxygen tank. Before foraying into the anoxic unknown, the worm Alma emini will force its tail to the surface and find a packet of air or clean water, and the body wall of the animal will then invert and zip itself (literally—the tail groove even comes with fastener-like teeth) into an airtight bag, which the animal will use to respire while remaining hidden in the mud. The larvae of certain mosquitoes and leaf beetles have developed an equally ingenious solution to the air problem: aquatic plants tend to accumulate oxygen in sections below the water surface, and specialized breathing spiracles on these insects are able to pierce such regions and allow the insect to steal air. Oxygen problems also plague aquatic mammals, but in a different way—these animals need to sleep but must do so without drowning by accident, and so generally alternate their idle brain hemispheres to maintain a level of awareness while in the water. Dolphins in particular can’t even be administered anesthetics, as their breathing is actively regulated by the animal—a dolphin will suffocate if it ever truly loses consciousness.
Animals that normally prefer the bottom of the sea can also swim quite well in a pinch. Scallops, for example, can escape starfish by “clapping” their shells, while basket stars beat their many arms alternately to stay afloat, and some sea cucumbers may even flap their pompadour-like head extensions to float their way to new feeding places (one, the aptly named Pelagothuria, is known to be entirely pelagic, possessing a set of webbed tentacles that allow it to continue swimming indefinitely while collecting floating particles into its waiting mouth). In contrast, certain sea anemones and one group of siphonophores subscribe to a borderline form of “swimming,” where the animal detaches from the bottom and floats along it, feeding like a living trawling net on corals (for the anemone) or any small organisms that it may come across (for rhodaliids, which are also unique among siphonophores in their benthic habits: while other siphonophores either swim with the help of specialized polyps or are free-floating, these oddballs tether themselves by their tentacles like grounded air balloons).
My own way of swimming, though, most closely resembles that of the spidery isopod Munnopsis, which beats its limbs with such frequency that it can effectively climb its way through the water column. I am considerably less efficient (and more frenetic, since I am in any case not very keen on sinking) at this, but I’m getting there.