Positive phototaxis of the brine shrimp Artemia salina to monochromatic light

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Abstract
The brine shrimp Artemia salina was photopositive in response to monochromatic light of approximately equal quantum intensity of two absolute levels. At the higher level (about 3 × 1014 quanta s−1 cm−2), the spectral response was bimodal with peaks near 560 and 700 THz frequency (about 535 and 430 nm wavelength, respectively), with an antimode at about 640 THz (465 nm). Response at the lower level (about 2 × 1014) was slightly lower and the midspectrum peak was shifted to higher frequencies (shorter wavelengths) and depressed relative to the high-frequency peak near 700 THz. The results suggest that positive phototaxis is mediated by two visual pigments, the high-frequency (short-wavelength) pigment being activated at lower illuminations than the midspectrum pigment. A similar bimodal response is known from a crab larva, but this appears to be the first anostracan crustacean to have been tested.

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