Small-scale thermal responses of hydrothermal vent polynoid polychaetes: Preliminary in situ experiments and methodological development

Hydrothermal vent systems represent a unique marine environment where high spatial variability allows the study of habitat selection with respect to small-scale temperature gradients. An autonomous time-lapse camera with a temperature logger array was deployed on four occasions to examine the thermal responses of two vent endemic polynoid polychaete taxa: Branchinotogluma sp. and Lepidonotopodium piscesae. Over a total deployment time of 52 h, we collected over 3,400 frames, in which 1,700 individuals were observed and monitored. Automated image processing and particle tracking routines were used to quickly process the imagery acquired in situ. Kriging interpolation was employed to create temperature maps (2.5–67 °C) of the field of view within which individual polynoids were tracked over time. Using the individual trajectories, we examined whether organisms selected for a narrower range of temperature than available in the environment and whether past information regarding the temperature encountered influenced subsequent movement decisions. A two state hidden Markov model was applied to predict behaviour based on movement patterns and examine whether areas characterized by different movement patterns differed in temperature. We found polynoids to be active over a wide range of temperatures and areas where different movement patterns were observed did not differ in temperature. Within their tolerated range of temperature, polynoids appear to thermoconform to the highly spatially variable thermal environment. Based on these preliminary deployments, we make suggestions for future studies over broader thermal regimes and longer time scales.