Intertidally cultured oysters encounter high aerial body temperatures that pose physiological challenges, including reduced growth, disease-resistance and survival. Husbandry practices, such as a farm’s chosen stocking density, may impact these body temperatures, potentially leading to differences in growth and survival. Accurate monitoring of body temperature, with which most temperature loggers struggle, could allow growers to assess their stock’s thermal risk. Synthetic mimics of organisms with embedded temperature loggers, or “robo” loggers, have accurately mimicked body temperature and could effectively measure thermal risk in intertidal oyster culture.
We conducted wind tunnel experiments to evaluate the effect of stocking density on oyster body temperature. Adult Pacific oysters (Magallana gigas) fitted with thermocouples were placed in bags at the top and bottom of an oyster group at ten densities from 50 to 500 and then heated for 3 hours at “calm” and “windy” wind speeds (0.3 and 1.4 m/s). We hypothesized that higher stocking densities would reduce oyster body temperature. Oysters in densely stocked bags (> 250/bag) were ~5°C cooler than those in sparse ones, but temperatures of oysters positioned on top were not density-dependent and 5-15 °C warmer (to 26-37 °C).
Concurrently, we evaluated “robo-oyster” loggers’ ability to mimic oyster body temperature by collocating them with live oysters, hypothesizing that the loggers would accurately approximate oyster body temperature. Robo-oysters respond like real oysters to changes in density, wind speed, and bag position, but generally overestimate body temperature.
Our findings suggest stocking densities > 250/bag may protect some stock from acute heat stress, but may increase thermal heterogeneity, which may lead to differences in growth and survival. We find biomimetic “robo-oysters” to be a useful tool for monitoring oyster body temperature because they can approximate real oysters while being more robust and user friendly for long term field deployment. These results emphasize the importance of studying thermal risk on a micro-scale in intertidal culture environments, particularly as the climate warms.