Growth in the margins: Field measured protein metabolism rates in the common limpet, Patella vulgata

Intertidal shores are characterised by a high variability in abiotic conditions, resulting in marked daily, tidal, seasonal and vertical differences in stress conditions, yet our ability to understand the consequences for key physiological processes at corresponding scales are limited. In particular, no previous studies have directly measured protein metabolism, the key process underpinning animal growth, in the field, in any organism. We measured whole-animal (SGR) and tissue (TSGR) mass growth, protein metabolism (synthesis (k_s), degradation (k_d) and growth (k_g)), RNA to protein ratios and oxidative stress in Patella vulgata in the field every season during a year, at three different shore heights. There were significant seasonal variations in TSGR, protein metabolism, RNA to protein ratios, and oxidative stress. k_s was highest in spring, whereas k_g peaked in summer and was lower in spring due to increased k_d. TSGR were higher in spring/summer compared to winter/autumn, whereas no seasonal differences were found in SGR. Oxidative stress peaked in spring and was at its lowest in winter, in line with other metabolic processes. Gamete production in P. vulgata has been associated with shell growth rate decreases. Current differences observed between juveniles and adults suggest that reproductive cycle could also drive seasonal variations in protein metabolism and TSGR in P. vulgata. Shore height had a significant effect on oxidative stress, with higher lipid peroxidation levels in high shore animals. This study demonstrates how spatial and temporal variations in different aspects of protein metabolism underpin organismal growth in the field.