Helical swimming as an exploratory behavior in competent larvae of the eastern oyster (Crassostrea virginica)

© 2018 Elsevier B.V. Helical swimming is a common behavior in larvae of many marine invertebrate species that may facilitate either exploration or feeding. Swimming in helices may increase exposure of larvae to settlement cues localized to the seafloor by enhancing their horizontal scanning motion near potential settlement sites. Alternatively, helical swimming may increase feeding efficiency by allowing an organism to maximize time spent in vertically-constrained food patches. In this study, we investigated whether the prevalence and geometry of helical swimming in competent larvae of the eastern oyster (Crassostrea virginica) vary in response to a settlement cue or to food. We performed two experiments, one examining helical swimming behavior in larvae exposed to different concentrations of a chemical settlement cue (“Cue Experiment”) and the other examining helical swimming of fed and starved larvae in conditions with and without algal food (“Feeding Experiment”). In the Cue Experiment, the proportion of larvae swimming in helices increased with decreasing cue concentration, and helices became wider, which suggests that helices may be an exploratory behavior that is curtailed when preferred habitat is detected. In the Feeding Experiment, neither the proportion of larvae performing helices nor helix geometry varied with food availability or satiation. Our results indicate that variations in helical swimming likely enhance the ability of C. virginica larvae to detect lateral variation in waterborne cues and locate suitable habitat prior to settlement

Discovery of active off-axis hydrothermal vents at 9° 54'N East Pacific Rise

International audienceWe describe the discovery of a large, active, high-temperature off-axis hydrothermal vent field on the East Pacific Rise. Hydrothermal vents are more prevalent across the crestal region of midocean ridges than previously thought. Our finding has important implications for understanding the fundamental controls on vent location and hydrology of hydrothermal systems along the crest of fast-spreading midocean ridges. The site provides a validation point for observations and models that call for significant hydrothermal heat loss beyond the immediate spreading axis. Finding an active off-axis vent field implies that temporally stable off-axis vent-endemic populations may provide a source of colonizing fauna to on-axis hydrothermal ecosystems after seafloor volcanic eruptions