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Investigating adaptive camouflage at sea

The views expressed are those of the author and are not necessarily those of Scientific American.


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Guaymas harborEditor’s Note: Julie Huang is an undergraduate geophysics major at the University of Chicago. She is working as a summer intern with the Stramski lab at the Scripps Institution of Oceanography in La Jolla, Calif., and is currently on board the University-National Oceanographic Laboratory System research vessel New Horizon. This is her first experience at sea on a research vessel. She interviewed the scientists on board for this entry, which is a follow-on to the blog posts of marine biologist William Gilly, who wrote several entries about his recent expedition to study Humboldt squid on the New Horizon in the Gulf of California.

GUAYMAS, Mexico—Once again we are sailing out of this port city on the New Horizon, but the nature and participants of the new expedition have changed. The upcoming cruise is called Dynamic Camouflage 2010, funded by the Office of Naval Research for the Multi-disciplinary University Research Initiative. There are groups here collaborating from several different institutions: the University of California, Santa Barbara (U.C.S.B.), the Monterey Bay Aquarium Research Institute (MBARI), the University of Rhode Island (U.R.I.), the Scripps Institution of Oceanography and Duke University. This team includes biologists and oceanographers with a specialty in optics.

It is critical to understand not only how animals manage to camouflage themselves but also the properties of the light field and background that they are attempting to match. Several participants from the previous ASAT (All Squid All the Time) cruise will stay on for the next 10 days in the Gulf of California. They continue their experiments after consolidating their efforts as a whole new world of work unfolds around them.

UCSB

Squid hide from predators by matching the background radiance of light in the ocean with some sophisticated structures in their skin that manipulate the angle and color of light being reflected. Alison Sweeney, chief scientist of this cruise, and technician Anna Howell are both from the Morse lab and are interested in the different types of cells in the skin of squid that allow these animals to exhibit a kind of adaptive, or "dynamic," camouflage. Chromatophores (color-generating structures), which actually turn on and off like pixels in a computer monitor, are neuromuscular organs controlled by the brain—a unique feature of cephalopods. Individual chromatophores are easily seen in small juvenile squid, but they are much more numerous and densely packed in a large animal and give it a solid color. The UCSB group will be collecting samples of squid tissue, mainly of Humboldt squid, for microscopy work and molecular analysis upon their return to the lab.

Similarly, Danny DeMartini, also from the Morse lab, is gathering skin samples to specifically study iridophores. Iridophores reflect certain colors of light and generate a metallic appearance in the living animal. This effect results from proteins called reflectins. These specialized proteins are of interest to this team and have so far been found only in the skin of a few species of squid, such as Loligo.

Squid skinDo Humboldt squid also have a version of this protein, since their skin also contains abundant copper-colored iridophores? Can Humboldt squid change iridescence in a way that can be characterized as adaptive camouflage? These are the questions that are being addressed. By understanding the relevant cellular and biochemical structures, it may be possible to develop new and useful bio-materials.

Duke

In order to fully understand how squid employ their camouflage, it is important to consider how the squid’s visual system works and how their perception differs from ours. In light of this, the team from Duke, consisting of Sarah Zylinski and Nick Brandley, is collecting squid eyes and using microspectrophotometry (MSP) to elucidate how different species that live at different depths, and hence inhabit different light environments (for instance, deep-sea species versus vertically migrating ones), are "tuned" to absorb light of different colors. In addition, the Duke researchers are conducting behavioral experiments to investigate counter-illumination (a form of bioluminescent camouflage) and chromatophore use in cephalopods by placing them in tanks with walls of variable backgrounds and then photographing the body pattern responses.

Porcupine camScripps

A group from Scripps has scientists from two different labs, the Jaffe lab and the Stramski lab. The Stramski team (Mirek Darecki, Pierre Gernez, Eric Orenstein, and myself) is taking measurements of the underwater light field at various depths (from the surface to 50 meters deep) using radiometers oriented downward, upward and horizontally. This information is useful in determining the context in which the animals have evolved their camouflaging abilities. In particular, light measurements are performed at sunset because increased prey and predator interactions occur at twilight, when animals previously hidden in the deep, aphotic (without light) zone migrate vertically up to the surface. The team also hopes to deploy a "porcupine" light sensor designed to measure high-frequency underwater irradiance fluctuations. These "flashes" are generated by refraction and focusing of sunlight through the air-water interface.

CTD deploymentOther, more classical oceanographic measurements to be made include surface to 1,000-meter vertical profiles of conductivity, temperature, density, oxygen concentration, chlorophyll a fluorescence (a proxy for phytoplankton), and beam attenuation coefficient (a proxy for turbidity). Seawater is sampled just below the surface and at the subsurface fluorescence maximum, usually between 20 and 50 meters, and then filtered onboard. Subsequent analysis of the particle absorption, pigment composition, particle organic carbon concentration and particle mass will be performed back in the lab. These measurements are important because particles scatter and absorb light to produce the underwater optical environment surrounding the cephalopods.

The team from the Jaffe lab at Scripps (Ben Laxton, Justin Haag, and Fernando Simonet) is working with two systems of instruments. One system is the Omnicam, a spherical device that films simultaneously (and synchronously) in the six directions that define the faces of a cube.Omnicam

The second system is the Cooke cameras—one camera with polarizing filters and a second one with RGB (red-green-blue) and UV filters. With the former, the objective is to characterize the polarization of light in the underwater environment. Both cameras are also used to image the squid at night when they migrate to the surface to feed. These systems are currently in the testing phase, and this cruise is the first time they have been deployed in the field with the filters on. The Omnicam footage will be used back in the lab to construct an artificial three-dimensional underwater environment consisting of a tank with walls made of screens that will play back the images recorded in the field. A behavioral scientist from the Johnsen lab at Duke will place cephalopods in this tank to observe them for behavioral changes with the changing background.



heteropodURI

Brad Seibel’s team from URI is studying the physiology of marine animals related to environmental conditions such as low oxygen, high carbon dioxide and changing light conditions. Brad is continuing his biochemical work on squid blood, to determine how oxygen binding impacts survival in low-oxygen environments. On this new leg of the cruise, Stephanie Bush added an experiment involving a tank with different shades of blue light polarized in a particular plane to different degrees and, using an underwater camera, filming a cephalopod placed in this setup to see how it responds to the changes in the radiance of light. Trisha Towanda is also measuring the metabolic rate of transparent gelatinous animals, such as heteropods, and how much these strange organisms polarize the light that passes through them. Their work is funded by both the National Science Foundation and the Office of Naval Research.

MBARI

Steve Haddock and his colleagues from MBARI are studying bioluminescence, which is another method of cephalopod camouflage. Their funding comes from the National Institutes of Health and the Packard Foundation. The Haddock team’s basic research revolves around how light is produced by marine animals and how this ability evolved into its present form. More specifically, Steve and graduate student Meghan Powers are investigating the molecular biology of bioluminescence and what genes and proteins are responsible for this phenomenon in a variety of squid species.

Photo credits [top to bottom]: W. Gilly (in Guaymas Harbor); N. Burnett (adult and juvenile squid skin); W. Gilly (porcupine cam, CTD deployment, Omnicam); T. Towanda (heteropod)

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  1. 1. bucketofsquid 3:40 pm 07/6/2010

    I wonder if this research will lead to some kind of adaptive camo suit for military or police use. One suit that can change to fit any environment and even different backgrounds would be very useful.

    Link to this

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