T. Aran Mooney monitors the squid as it is sedated by Magnesium Chloride before beginning the brainwave experiment. Credit: Joseph Caputo/MBL
The 2nd installment of “At MBL,” Joseph Caputo’s experience as a science writing intern at the Marine Biological Laboratory in Woods Hole, Massachusetts.
The ocean is a noisy place. Although we don’t hear much when we stick our heads underwater, the right instruments can reveal a symphony of sound. The noisemakers range from the low frequency bass tones of a fish mating ritual to the roar of a motorboat. The study of how underwater animals hear is a growing topic in marine science, especially with regards to naval sonar and whales. This summer at the MBL, zoologist T. Aran Mooney will be the first scientist to look at cephalopod hearing, using the squid, Loligo pealeii, as a model. To learn how sensitive the translucent animals are to noise, he is monitoring squid brainwaves as they respond to various sounds, specifically the echolocation clicks of its main predators, the sperm whale, beaked whale and dolphin.
“Sound is one of the most important cues for marine animals. Light doesn’t travel well through the ocean. Sound does much better,” says Mooney, who is a Grass Fellow at the MBL and beginning postdoctoral research at the Woods Hole Oceanographic Institution this fall. He predicts that squid probably hear very low frequency sounds, which means they pick up on fish tones and boat traffic. A better understanding of what these animals hear could reveal how human-induced noise affect cephalopods and how their auditory system evolved separately from that of fish.
Reading a squid’s brainwaves will take days of preparation. Mooney has been testing his experimental protocol for the past few weeks. He begins his experiments with a trip to the Marine Resources Center, where dozens of squid swirl around in a tank the size of a small above-ground pool. They travel as a school, so catching one doesn’t look like much trouble. But squid with their big yellow eyes are visual animals, and can see a net coming as soon as it hits the water. He catches one that suits his experiment, transports it to a bounce-proof wagon and covers it with a black plastic bag so not to stress the squid out during its trip to the lab.
In the corner of of one of the wet labs in the MBL’s Loeb Laboratory is a sound proof booth designed with a squid in mind. Mooney places his catch, now sedated, on a netted hammock within a plastic basin filled with water. As carefully as a doctor tends to his patient, he hooks the squid up to an IV with the sedative, Magnesium Chloride, so it remains calm during the experiment. As soon as the squid stops jetting, pushing its body forward with a splash of water, he inserts two pin-sized electrodes near the squid’s brain.
The squid is submersed in a soundproof booth while Mooney measures its brainwaves. Credit: Joseph Caputo/MBL
With the squid in place, Mooney turns to his computer and watches the brainwaves. Another scientist, MIT/WHOI fellow Wu-Jung, keeps an eye on the squid. “Give it a squeeze,” Mooney says to her, “make sure it’s ok.”
“Yeah, he’s breathing,” Wu-Jung replies, referring to the squid.
While the squid is relaxed, Mooney transmits a sound chosen from a computer program he helped design while a Ph.D. student at the University of Hawai’i. The sound is just a tone, nothing the squid would recognized in nature. By playing a number of these tones across a frequency, Mooney can tell which the squid recognizes according to its brainwave activity, measured by the electrodes.
Mooney has many more weeks to go before he knows what squids can hear. If they happen to respond to one of the predator echolocation clicks, it would mean the two species might have an evolutionary relationship. His experiment teaches us that science doesn’t yet have all the answers, and finding them requires getting a little wet.