No abstract

Annual growth segments of Ascophyllum nodosum (L.) Le Jolis (Fucales, Fucaceae) are denoted by air bladders that form each spring. By examining annual growth segments, it may be possible to infer information about the physical conditions during the growth period; however, it is uncertain whether the annual segments will expand in size after the initial growth. We examined A. nodosum segments from three populations in Nova Scotia, and statistically evaluated whether the annual growth (length, mass, and maximum diameter) of segments was independent of the age of the frond, whether the segments increased in size after the initial growth, and whether the segment lengths were correlated with mean water temperatures and mean air temperatures when the segments were formed. We found that the growth in length of A. nodosum is dependent on the age of the frond, but frond age explained less than 12 % of the overall variation in length. However, the mass and maximum diameter of segments were independent of the age of the frond. Differences occurred between the lengths of segments formed in different years, but there was no significant correlation with regional mean water or air temperatures. This study indicates that the length of A. nodosum segments may be an indicator of the annual physical characteristics of a site, but future studies are needed to identify which factors have the strongest influence on growth patterns.

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.