Seeing in the dark
July 18, 2012
Today was the last day of our expedition and we needed to be back in the harbor by 6:00 p.m., meaning that the remotely operated vehicle (ROV) must be on deck by 4:00 p.m. We didn’t have a minute to lose! As we do everyday, today’s dive started at 6:30 a.m. This would be our last chance to search for target species for our researchers. We got the chance to observe the fish Aristostomias scintillans that has bioluminescent organs producing red light under each eye. While most midwater species do not see red light, this fish can see this range of wavelength. Researchers believe that Aristostomias scintillans uses its red bioluminescent organs as night vision goggles for finding prey, and as a way for individuals of this species to see each other.
During this expedition we have collected amphipods for Karen Osborn, curator at the Smithsonian National Museum of Natural History. She tells us more about her research on amphipods:
Hyperiid amphipods are small—up to approximately five centimeters (two inches) long—crustacean invertebrates that are abundant from the surface of the ocean down to the deepest depths, with particular abundance in the twilight zone or mesopelagic—200 to 1,000 meters (650 to 3,280 feet). At twilight-zone depths, available light is limited to increasingly dim and blue down-welling light and bioluminescence. In this zone, the competition to see and not be seen is a matter of life or death. As a result, hyperiids have huge variation in the shapes and function of their eyes, likely an evolutionary response to the complexities of the midwater optical environment.
Hyperiids generally have one or two pairs of compound (multiple part) eyes. In some hyperiids the dorsal eyes are greatly enlarged and cover the entire head. In others, optic fibers connect the lenses to the retinas, or they have cone-shaped retinas that allow a 360-degree field of view. Still others have retinas with mirrors that boost light collection. My postdoctoral fellow, Jamie Baldwin, who recently graduated from Duke University, and I will study the visual adaptations of hyperiids to life in the twilight zone by examining the morphology, physiology, and behavior of various species spanning the depth distribution and eye morphology of the group. Hyperiids live in close association with many gelatinous midwater animals, feeding on them, living on them, and brooding their young on them.
The ROV was back on deck by 1:20 p.m. and as usual, the scientists took care of the sampled animals while the pilots hurried up to get everything ready for the second and very last dive of this expedition. During this dive the ROV recovered the MRS we left at the mooring 24 hours ago. We were back on deck at 4:00 p.m. Everyone was very busy tidying up the labs and getting everything ready to disembark.
As we are heading back to Moss Landing, I want to thank every single person on board (scientists, crew, pilots, and steward) for welcoming me so warmly on the Western Flyer and introducing me to the exciting world of midwater ecology. This cruise was a mind-blowing and unforgettable experience for me. I really hope to have the opportunity to join other marine research expeditions in the future!