Meeting Abstract
Several species of sea urchin that inhabit spatially complex environments like kelp forests and coral reefs are known to have spatial vision, with acuities ranging from 10° to 33°. Researchers have proposed that these urchins use this relatively poor vision to find shelter from diurnal predators in dark crevices. However, whether sea urchin species that inhabit flat, sandy areas also have spatial vision is unknown. Such habitats are much less spatially complex and rarely offer dark places in which to shelter. Testing urchin species from these habitats can help us understand whether vision is widespread among the urchins or is only present in species that inhabit environments that offer spatial complexity. Three sandy flat-dwelling species, Lytechinus pictus, L. variegatus, and Arbacia punctulata (all n=30) were tested for spatial vision with an orientation experiment. Animals were placed in the center of a round, featureless tank illuminated from above, with a black target of angular size 9°, 25°, or 35° on the wall. Each urchin’s movement relative to the target was observed. None of the species of urchin responded to the targets, but some did respond to the visual cue of a researcher. When urchins were moved from their dark adaption chamber to the experimental tank in the light, the animals moved away from the researcher. When urchins were moved to the experimental tank in darkness, however, the animals moved randomly. This suggests that shelter-seeking cues are not important to urchin species in flat, sandy environments, but that visual stimuli may elicit other behavioral responses.
