February 27, 2018 | David F. Coppedge

More Underwater Wonders Revealed

These news items will awaken the marine biologist in everyone.

In ancient times, people didn’t know much more about sea life than what they dragged up in fishing nets (or what they saw on the way down to Davy Jones’ locker, where dead men tell no tales). Pondering the bones and muscles of fish while eating seafood undoubtedly sparked some curiosity about their form and function. A few took more than a casual interest in studying fish. Wise King Solomon “spoke also of animals and birds and creeping things and fish” (I Kings 4:33). A psalmist included in his list of awesome creations “the sea, great and broad, in which are swarms without number, animals both small and great.” (Psalm 104:25). Sailors told tales about sea monsters. Those living by the sea undoubtedly saw ocean-going mammals like seals or sea lions, and some probably saw dolphins at play. Only a lucky few ever witnessed a whale.

Today, we have ships and boats of all kinds, scuba gear, submarines, robotic vehicles, scientific instruments, satellites and detailed maps of ocean currents and the ocean floor. If anyone should be awestruck by sea creatures, it’s us. And yet the sea is still at the frontier of scientific knowledge. Illustra’s film Living Waters featured just a few cases of amazing marine animals: dolphins, sea turtles, salmon and humpback whales. Here, now, are some of the latest findings from marine biologists about life under the water, where the vast majority of animals on the planet live out their complex lives.

Which Way Is Up?

Salmon eggs in stream, courtesy Illustra Media.

Some of the stars of Illustra’s film were Pacific salmon, which migrate from fresh water out to sea, travel thousands of miles, then return. A few scenes, very cute, showed the little hatchlings emerging from their gravel nests or “redds” dug out for them by their mothers. If you picture yourself as a hatchling just beginning independent life after using up your yolk sac, you have a problem: which way is up? It’s not as easy as it might seem. Knowing that hatchlings rise up unerringly day or night, scientists at Oregon State wanted to figure out how the hatchlings know to swim upward as they emerge from the nests for the first time. They know that adult salmon have exquisite magnetic sensing out at sea. Could the tiny hatchlings also be using the earth’s magnetic field?

They ran experiments in a lab with controlled lighting and magnetic field generators. Sure enough, the hatchlings could use magnetic information alone, even in pitch darkness, to figure out which way is up.

One group of salmon were exposed to the normal magnetic field in Oregon and another group of salmon to an inverted magnetic field. Fish in the normal magnetic field moved significantly further up the tubes than did those that experienced the inverted magnetic field. The team ruled out the possibility that fish were simply startled by the sudden change in electromagnetic conditions by running the same amount of electric current required to invert the magnetic field in the opposite direction.

“Given that only inverting the magnetic field influenced fish movement, it seems salmon use the direction of field lines to orient vertically during their emergence from gravel – our findings are difficult to interpret in any other way,” said Nathan Putman, senior scientist at LGL Ecological Research Associates in Bryan, Texas, and co-lead author on the study.

What’s required to sense the earth’s magnetic field? Humans can use a compass, but have very little sensation of its presence otherwise. Like the adult fish, these tiny hatchlings can not only sense the field, but determine its intensity and direction enough to figure out which way is up.

Invisibility Act

Cuttlefish can disguise themselves within seconds to look like coral, evading any predator that might come looking for them. How do they do it? Scientists from the Marine Biological Laboratory of the University of Ohio studied the phenomenon in cuttlefish (not fish, but cephalopods related to octopus and squid). They were amazed to watch the animals raise little spikes, called papillae, from their skin and hold them in that position for more than an hour. You can watch it happen in some embedded video clips. The scientists wondered how the cuttlefish were able to lock the papillae in place without spending excess energy, then unlock them later, to resume their smooth-skinned normal appearance. It reminded them of how clams can slam shut at the sight of a predator, and lock shut with a catch mechanism that works against the prying fingers of predators and children.

Amazing Facts“The catch mechanism allows a bivalve to snap its shell shut and keep it shut, should a predator come along and try to nudge it open,” says corresponding author Trevor Wardill, a research fellow at the University of Cambridge and a former staff scientist at the MBL. Rather than using energy (ATP) to keep the shell shut, the tension is maintained by smooth muscles that fit like a lock-and-key, until a chemical signal (neurotransmitter) releases them. A similar mechanism may be at work in cuttlefish papillae, the scientists found.

The story caught the attention of Veronique Greenwood of the New York Times, who calls the cuttlefish the “master of camouflage” and the “chameleons of the sea.” Side-by-side photos show the remarkable difference in appearance with papillae raised (see more photos on Phys.org). For the ultimate disappearing act, the creature can also change its color, and then bend its body to the reef to mimic the shape of coral as well as its texture. Octopuses have been known to do this, too, but “This is the first time anyone has seen anything like this in cuttlefish,” Greenwood says, “a reminder that even much-studied species still have some surprising secrets.

The Survivor

Did you know that some fish can reproduce asexually? The BBC News shows a photo of an Amazon molly, a freshwater fish that can save a lot of trouble by doing away with males and reproducing directly. While this costs less energy, it has the downside of accumulating mutations more rapidly. According to a principle known as Muller’s Ratchet, asexual species should go extinct faster because they lack the mutational sponge of sexual species. “The Amazon molly had been around for half a million generations – far in excess of what theory would suggest,” Jonathan Ball writes. This leads to a conundrum for Darwinism: “Evolutionary theory suggests that species favouring asexual reproduction will rapidly become extinct, as their genomes accumulate deadly mutations over time.” Scientists are not sure how this fish beat the odds.

Underwater Troubadours

Humpback whale with calf, courtesy Illustra Media / Dave Anderson

Illustra’s film showed a memorable segment about singing humpback whales, but those aren’t the only whale species with a song to sing. Blue whales—the largest animals in the ocean—are talented singers, too, but little has been known about the music of these secretive beasts. National Geographic reported on a 14-year effort by Scripps Institute in California to decode the vocalizations of 100 blue whales. Since the sound travels for miles, they could pick up the sounds remotely with underwater microphones, but they also synced the sounds with individual whales by outfitting them with suction-cup trackers. The results were surprising, changing assumptions about blue whale behavior:

The biggest animal to ever live is also the loudest, and it likes to sing at sunset, babble into the night, talk quietly with those nearby, and shout to colleagues 60 miles away.

The blue whale, which can grow to 100 feet long and weigh more than a house, is a veritable chatterbox, especially males, vocalizing several different low-frequency sounds. And for years scientists had only the vaguest notion of when and why these giants of the sea make all those sounds.

Both sexes vocalize, but only the males ‘sing’, the researchers found. They’re also the loudest. The reasons for all the noise are not well known, but the males seem to begin their “deep melodic songs” around sunset, serenading into the night probably to attract mates. “But no one has ever witnessed blue whale reproduction,” one researcher commented. For all the research effort, scientists are only beginning to decipher this underwater performance.

The more details you learn about living things, the less excuse you have to chalk it up to evolution.





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