Polarization sensitivity as a contrast enhancer in pelagic predators: lessons from in situ polarization imaging of transparent zooplankton.

Journal Article

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 its potential 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 (approx. 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 when compared with the downwelling irradiance. In fact, the dominant radiance and polarization contrasts 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 increase visibility substantially.

Full Text

Duke Authors

Cited Authors

  • Johnsen, S; Marshall, NJ; Widder, EA

Published Date

  • March 12, 2011

Published In

Volume / Issue

  • 366 / 1565

Start / End Page

  • 655 - 670

PubMed ID

  • 21282169

Electronic International Standard Serial Number (EISSN)

  • 1471-2970

Digital Object Identifier (DOI)

  • 10.1098/rstb.2010.0193

Language

  • eng

Conference Location

  • England