MEPS 627:95-107 (2019)  -  DOI: https://doi.org/10.3354/meps13058

ABSTRACT: Temperate intertidal species frequently experience broad temperature fluctuations during emersion. However, the metabolic cost of exposure to a particular emersion temperature is not known for most species. We quantified oxygen (O₂) consumption by the intertidal barnacle Balanus glandula over a combined 5 h emersion and a 6 h immersion period. Barnacles were exposed to air temperatures of 10, 15, 20, 25, 30, 35, or 38°C followed by a 10°C immersion. Respiration was monitored using a fluorometric O₂ system. Total O₂ consumption over the 11 h period by B. glandula increased with increasing emersion temperatures, reaching a maximum between 20 and 30°C, where consumption was significantly greater than that at 10°C. Aerial and aquatic phases showed similar patterns with temperature, but significant differences among temperatures were only detected in the aerial phase. We also found that respiration rates peaked during the first hour at temperature during emersion and the second hour of immersion. A separate analysis of barnacle behavior over a longer immersion period suggested that stressful emersion temperatures require recovery periods longer than 6 h; thus, our results may underestimate the full cost of thermal stress. When compared to previously published measurements of barnacle body temperatures in the field, our results suggest a large vertical gradient in thermal exposure costs, nearly doubling with a 1 m increase in shore height. We highlight both the difficulty and importance of generating accurate estimates of emersion costs. Such costs are likely to be critical in determining organismal and population responses to changing climate.

KEY WORDS: Intertidal barnacle · Respiration · Temperature · Emersion stress · Energetic cost