Collaborative Research: Visual Adaptation in Hydrothermal Vent Shrimp the Therole in Feeding Modalities and Habitat Selection

Alvinocarid decapod shrimp are some of the most abundant mobile fauna at hydrothermal vents, occurring in massive swarms at Pacific, Indian and Atlantic vent sites. As in other crustaceans, the shrimp in this unique habitat must rely on perception of environmental cues to maintain interactions with the environment and other biota living there. Originally described as eyeless, vent shrimp are now known to undergo dramatic transformations in eye morphology with some species having massive fused eyes on their backs (dorsal eyes), which may be correlated to their feeding preferences. Gebruk et al. (2000) demonstrated that some vent shrimp species with dorsal eyes rely on carbon provided by epibiotic bacteria, while others with fused anterior eyes are predators/scavengers, and suggested that there may be a correlation between eye structure and feeding modality. Due to the different local habitats where these shrimp are found (in water column for post-larval, on black smoker sides for the species that graze on bacterial mats, out in the periphery for species that rely on predation), the eye morphology and visual pigments may also be adapted for finding the correct habitat. However, all the structural studies that have been undertaken on the benthic adults suggest that they are blind or the eyes are degenerating. As other studies demonstrated that the pelagic post-larvae/juveniles are visually competent, it is unlikely that the metamorphosis from normal stalked eyes (post-larvae) to the huge dorsal eyes (adults) results in a degenerated eye. All earlier studies utilized adult shrimp that had been collected under bright submersible lights, so it is likely that the “degeneration” resulted from significant photoreceptor destruction caused by too much light. An additional challenge of vent shrimp visual ecology is that the eyes were considered degenerate due to lack of enough ambient light to make the metabolic costs of vision worthwhile. However, there may be several sources of sufficient ambient light produced by both abiotic triboluminescence/chemiluminescence as well as biological bioluminescence. Although several studies suggest bioluminescence does not exist at these vent sites, incorrect methodology may have resulted in this conclusion. Using molecular, physiological, and structural methods the PIs have developed over decades to study vision and bioluminescence in deep-sea crustaceans, the visual capabilities of vent shrimp (postlarvae, juvenile and adults) will be tested against hypotheses related to both feeding modality and habitat selection. These measurements will be coupled with a systematic survey of pelagic and benthic luminescence at the vents to determine if these are viable visual stimuli