Meeting Abstract

52.4  Thursday, Jan. 6  Using sunglasses to find the best burger in town: Polarization vision as a camouflage breaker in pelagic predators JOHNSEN, S*; MARSHALL, N.J.; Duke Univ.; Univ. of Queensland sjohnsen@duke.edu

Because light in the pelagic environment is partially polarized, it has been suggested that the polarization sensitivity found in certain pelagic species may serve to enhance the contrast of their transparent zooplankton prey. We examined the potential for this during cruises in the Gulf of Mexico and Atlantic Ocean and at a field station on the Great Barrier Reef. First, we collected various species of transparent zooplankton and micronekton and photographed them between crossed polarizers. Many groups, particularly the cephalopods, pelagic snails, salps and ctenophores, were found to have ciliary, muscular or connective tissues with striking birefringence. In situ polarization imagery of the same species showed that, while the degree of underwater polarization was fairly high (~30% in horizontal lines of sight), tissue birefringence played little to no role in increasing visibility. This is most likely due to the low radiance of the horizontal background light compared to the downwelling irradiance. In fact, the dominant radiance and polarization contrasts of the object are due to unpolarized downwelling light that has been scattered from the animal viewed against the darker and polarized horizontal background light. We show that relatively simple algorithms can use this negative polarization contrast to substantially increase visibility.