Cold temperatures as a source of stress: seasonality, sand burrowing and hemocyanin levels in Atlantic Canada sandy beach amphipods

Sandy beach species are adapted to a harsh physical habitat, but for those living at relatively high latitudes, the cold, often freezing winter conditions, entail a challenge that has not been thoroughly examined. We therefore examined the individual response of talitroid amphipods (Americorchestia longicornis; Say 1818) to the strong seasonality affecting sandy beaches in Prince Edward Island, Atlantic Canada (46°N). We then experimentally assessed the influence of low temperatures upon amphipod burrowing behavior and stress levels (hemocyanin concentrations), hypothesizing that cold and freezing temperatures prompt drastic behavioral and physiological responses in the amphipods. Biweekly amphipod samples collected over three years (2019–2021) made evident the narrowness of their activity season and its tight correlation with temperature (Spearman's r = 0.85). While amphipods were abundant above 10 °C, they were very few under 5 °C and none near 0 °C. In the laboratory, amphipods exposed to 10 °C remained at shallow depths in the sand (70% at 0–4 cm of depth). By comparison, amphipods exposed to 5 °C were found at several depths (0–40 cm), while those exposed to 0 °C concentrated (70%) at depths of 16–40 cm. The assessment of stress levels showed that in comparison to amphipods at ambient temperatures, those exposed to freezing conditions exhibited hemocyanin levels 55 and 82% higher after 1 and 2 weeks, respectively. Combined, these results suggest that cold and freezing temperatures shorten the season of the amphipods and prompt them to burrow deeper into the sand and increase their stress levels, possibly influencing other life history traits.