Journal of the Marine Biological Association of the United Kingdom

Research Article

Adaptations of tapeta in the eyes of mesopelagic decapod shrimps to match the oceanic irradiance distribution

P. M. J. Sheltona1, E. Gatena1 and P. J. Herringa2

a1 Department of Zoology, University of Leicester, University Road, Leicester, LEI 7RH

a2 Institute of Oceanographic Sciences Deacon Laboratory, Wormley, Godalming, Surrey, GU8 5UB

Eyeshine brightness was measured in a number of species of oplophorid shrimps and one sergestid. Eyeshine varies in a systematic way across the eye. Forward and downward looking parts of the eye often have the brightest eyeshine. In many cases eyeshine is graded in the horizontal and vertical axes. Eyeshine brightness can be explained in terms of underlying tapetal morphology. These features of the decapod eye can be rationalised in terms of the normal irradiance distribution in the sea and the need for certain parts of the eye to have enhanced sensitivity. Contrary to the expected results, when six species of oplophorid were compared there was a clear trend of decreasing brightness with depth at whichthey occurred. In a number of species the tapetum is incomplete with distinct holes. Such holes occur in the dorsal region of two species of oplophorid. In one deep-water species the central tapetum is lacking. This feature, and the observed decrease in eyeshine with depth, may be adaptations to reduce the signal that eyeshine provides to potential predators.