Category: General Article
When you think of animal migrations, what images pop into your head? Is it flocks of squawking Canada geese flying south for the winter? Or massive gray whales cruising along the West Coast en route to their breeding grounds in the Gulf of California? Maybe it would surprise you to learn that every day tens of millions of animals move from the lightless depths of the deep sea upwards to the surface waters — then approximately ten hours later move back down again. This phenomenon, known as vertical migration is the largest mass movement of animals on Earth… but very few people know about it.
Dr. Tamara Frank of Nova Southeastern University in Fort Lauderdale, Florida, has been studying deep-sea ecosystems and vertical migration for years and has made some amazing discoveries about this mass movement of life.
In a phone interview with the Oceanscape Network, Tammy elaborated on the importance of this phenomenon:
“A lot of the deep-sea animals are vertical migrators, meaning they come up to surface waters to feed. The fish are sitting there waiting for them, so they’re a major source of food for a lot of the fish we all like to eat. [These migrations] are also really important in ocean biogeochemistry, and by that I mean that the ocean’s absorb carbon dioxide which takes it out of the air, which means there are fewer greenhouse gases so things don’t heat up as quickly… One of the ways that the carbon gets transported down to the depths is by the vertical migrators. They come up at night to eat stuff in the surface waters and as they digest they release some of the organic carbon into the deep-sea which takes it out of the surface waters. Now there’s more room in the surface waters to absorb carbon dioxide so less of it goes into the atmosphere.”
One of Tammy’s interests is the “light cues” used by animals to trigger vertical migrations, the most obvious of which may be nightfall. The diminishing light from above may actually “jump start” the migration, with hundreds of species taking advantage of the darkness when they’re not as visible to predators to move higher into the water column to feed.
To better understand the vision of deep-sea organisms and how this affects vertical migration, Tammy must observe living animals under controlled circumstances. And this is where things can get difficult.
“A lot of these animals are really, really sensitive to light,” Tammy said. “If you drag them up through surface waters and expose them to surface light levels, that would be like you staring at the Florida sun for five minutes without blinking.”
To protect the animals from both light and temperature changes, Tammy adapted a colleague’s invention to create what’s known as a closing cod-end. This simple device is essentially a long tube with ball valves at either end. Attached to a Tucker trawl net, deep sea animals are funneled into the tube and the valves are closed remotely to lock them in. Because the tube is light-proof and heavily insulated, the animals can be brought to the surface without causing them any physical harm.
“When the Tucker trawl comes to the surface, we can remove the canister from the trawl net and carry it closed into a cold, light-tight room,” she said. “Then we can sort the animals out under a dim red light because they’re really not sensitive to red light at all. This allows me to study intact visual systems on live deep-sea animals.”
The closing cod-end has proven to be an efficient way for Tammy to gather the specimens she needs. Not only has it increased her understanding of deep-sea life and vertical migrations, but has also raised her awareness of the perils currently facing these vital ecosystems.