The Losey Lab Research: Using UV

A good example of the value of the camera system is demonstrated by the Chromis viridis footage that we acquired while on the Quicksilver reef platform and at Lizard Island Research Station on the Great Barrier Reef. These fish appeared relatively well camoflauged against midwater in the visible range of the spectrum. However, when we switched to the UV filters, they appeared like a cloud of fireflies, flashing brilliantly in the UV. Chromis viridis has eyes that are extremely transparent to UV radiation, hence they can perceive UV (and it is likely that they have UV-sensitive visual pigments like other damselfish). Could it be that this "private" (most predators can't see UV) signal helps coordinate their nearly simultaneous retreat into their home coral head?

Chromis viridis, the blue-green damsel, in color

To see a short Quicktime video at any of the wavelengths below, just click on the photo! Or, if you've got a fast system, you can watch a longer clip with all the wavelengths in sequence (caution: file is 3.5 Mb)! Don't have a Quicktime player? Download one free here. Videos not launching for you? You may not have the proper plugins. Try this: go to www.apple.com/switch and click on any random advertisement at the top of the page. It will try to launch a Quicktime video and if it doesn't work, it should prompt you to download the correct plugin to fix the problem. If their video launches, then ours should too - come on back and try us again! Still having problems? Email us.

C viridis, at (L-R) 600, 480, and 400 nm

C viridis in the UV, at (L-R)380, 360 and 340 nm

Notice how much brighter the fish seem at 400, 380 and 360 nm, in the near UV!

When contrast of these fishes was calculated, here's what we found. The white points are parts of the fish that are brighter than the background, and the blue points are parts of the fish that are darker than the background. A score of zero means the fish part matches the background, and the higher the number, the greater the contrast between fish and background. The first graph is fish vs. coral background, and the second graph is fish vs. midwater background. As you can see, the light spots of the fish are much brighter than the coral in the UV, where predators cannot see them.. The dark spots are darker than the coral background in the high visible, but blend in against the midwater up until the deep UV, where predators cannot see them. Please note that the scales differ, so the fish are twice as bright against coral in the UV as they are against midwater.

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