Temperature, desiccation, and species performance trends along an intertidal elevation gradient

Abstract

This study investigated the effects of intertidal elevation on ecologically relevant temperature traits and the intensity of organism desiccation during low tides on a subpolar NW Atlantic shore. The goal was to relate those descriptors of environmental stress to elevational changes in the growth of dominant sessile species (algae and mussels) that influence overall community structure. In-situ measurements taken at the low, middle, and high intertidal zones revealed that daily temperature maxima, daily temperature range, and desiccation rate increased significantly from low to high elevations. Conditions were especially stressful at the high zone, as the highest temperature (47 °C, recorded during aerial exposure at low tide) more than doubled seawater temperature and desiccation rate surpassed 90 %. Transplant experiments showed that seaweed (Ascophyllum nodosum) and mussel (Mytilus edulis) growth rate decreased dramatically from low to high elevations. Therefore, although subpolar shores are mostly known for their harsh winter conditions, the pronounced vertical stress gradient that characterizes the intertidal zone during ice-free months also plays a major role in determining spatial changes in benthic species performance. Our study also suggests that inferring stress differences between habitats based on growth data from transplanted specimens may be a useful field method to further develop stress ecological theory.

The Subhabitat Dependence of Biogeographic Pattern

“…As a result, physiological stresses related to desiccation, thermal extremes, and osmotic potential also increase considerably with elevation. Although such changes occur gradually across elevations, average differences between coarse elevation zones (e.g., different thirds of the full vertical intertidal range) are pronounced (Eckersley and Scrosati, 2012;Watt and Scrosati, 2013;Umanzor et al, 2019). Therefore, such elevation zones represent different subhabitats especially for sessile species, because such organisms are permanently attached to the substrate and, thus, must cope with very different conditions depending on elevation zone.…”

Changes in barnacle recruitment and recruit body size with intertidal elevation on wave-exposed rocky shores in Nova Scotia

“…These findings agree with 7 the study's hypotheses, which stemmed from knowledge on basic environmental differences between high and middle elevations. Because of tide dynamics, high elevations often experience more extreme levels of temperature and biological desiccation during low tides than middle elevations (Eckersley andScrosati 2012, Watt and. During low tides, such extremes could have killed a number of recently settled cyprid larvae before they had the opportunity to metamorphose to recruits, in that way limiting recruit density (Shanks 2009).…”

Barnacle recruit density and size increase from high to middle intertidal elevations in wave-exposed habitats on the Atlantic coast of Nova Scotia

“…These findings agree with the study's hypotheses, which stemmed from knowledge on basic environmental differences between high and middle elevations. Because of tide dynamics, high elevations often experience more extreme levels of temperature and biological desiccation during low tides than middle elevations (Eckersley andScrosati 2012, Watt and. During low tides, such extremes could have killed a number of recently settled cyprid larvae before they had the opportunity to metamorphose to recruits, in that way limiting recruit density (Shanks 2009).…”