Lindsay, S. M.. University of Maine, firstname.lastname@example.org
Latz, M. M.. Scripps Institution of Oceanography, email@example.com
EXPERIMENTAL EVIDENCE FOR LUMINESCENT COUNTERSHADING BY SOME EUPHAUSIID CRUSTACEANS
Nearly all euphausiid crustaceans are bioluminescent, with ventrally located light organs on eyes, thorax and abdomen. Even though euphausiid bioluminescence has appropriate spectral and angular properties to serve as camouflage against downwelling light, most studies have not used ecologically relevant stimuli to elicit bioluminescence. Furthermore, the bioluminescence stimulated by either photoflash or chemicals is too bright for camouflage. Using techniques designed to study luminescent camouflage behavior in mesopelagic shrimp, bioluminescence produced in response to dim downward directed light (490-500 nm) was measured for four species of euphausiids: Thysanopoda orientalis (mesopelagic), Nematoscelis difficilis, Euphausia gibboides, and Euphausia eximia (all epipelagic). All specimens were collected and maintained in dark conditions prior to testing. In all species, the magnitude of bioluminescence depended on stimulus light intensity. The level of illumination eliciting a threshold response was approximately one order of magnitude higher in the epipelagic species. At the depths inhabited by these species, daytime irradiance is equal to or greater than these behavioral thresholds, suggesting that the ambient illumination would be sufficient to elicit bioluminescence. These results provide direct behavioral evidence that euphausiid bioluminescence serves as camouflage against downwelling light.
Day: Thursday, Feb. 4
Location: Sweeney Center