This post is part of a series associated with a recent trip by The Osborn lab and several colleagues to the Smithsonian Marine Station (SMS) in Florida, where they used the R/V Sunburst to investigate midwater animals from the Gulf Stream.
At first glance, the fine mesh net that we pulled up from approximately 150 meters depth may have looked as if it didn’t hold much, but the bucket was teeming with transparent life. I yelled with delight when I looked into our catch bucket and saw four tiny black dots (eye retinas) that belong to an almost entirely transparent animal – Phronima spp. – an alien looking, pelagic crustacean that is a member of a group known as the hyperiid amphipods.
As you might imagine, finding a mostly transparent, tiny (less than an inch long) amphipod that lives in the open ocean is not an easy task. I had been on the hunt for these clear creatures for over a year. However, pulling a 4 mm mesh net through Gulf Stream waters off Fort Pierce aboard the Smithsonian Marine Station's 39' R/V Sunburst was like hitting the planktonic jackpot. I was able to collect more than 50 specimens of the elusive Phronima from just a couple tows. When I viewed a dish of these animals under the microscope, their glass-like appearance made it seem like I was looking through a crustacean kaleidoscope!
The ocean is filled with amazingly clear animals, but we still don’t have a good understanding of how oceanic animals structure all the tissues that make their bodies transparent. I am particularly fascinated by transparent crustaceans that have sturdy bodies and powerful muscles. Phronima's transparency is an excellent form of camouflage, but transparent surfaces can become apparent due to reflections from downwelling sunlight or from the bioluminescent searchlights of predators. My current research explores how these animals may be adapted to minimize such reflections. I will take these specimens back to Duke University, where I am currently a 4th year PhD student in Sönke Johnsen’s lab, to examine these hyperiids, hoping they provide me with enough specimens to complete my study of transparency in Phronima.
I’d like to thank everyone who has helped me to have a successful and fun trip. It was a pleasure to work with Woody and Hugh, who took us out on the Sunburst and made sure we had everything we needed for successful trawling operations. Also, I’ve had a great time meeting other scientists here at the Smithsonian Marine Station, working with my dissertation committee member (Karen Osborn), and I hope to return in the future to continue looking for the invisible inhabitants of the open ocean!
by Laura Bagge, graduate student, Duke University