Both like it hot? Influence of temperature on two co-occurring intertidal barnacles in central Chile

Jehlius cirratus and Notochthamalus scabrosus, two chthamalid barnacles common to the upper rocky intertidal coast of Chile, often overlap extensively in their vertical distribution, with Jehlius extending slightly higher on the shore. Previous studies examining competition between Jehlius and Notochthamalus have come to differing conclusions regarding the nature and direction of their relationship within a hierarchy for space, but together suggest that temperature may play an important part in meditating their competitive interactions. Here, we address the role of temperature during emersion on Jehlius and Notochthamalus via species-specific responses in abundance, growth and reproduction to varying thermal conditions during tidal emersion. Results from a shading experiment conducted at two high intertidal elevations indicated that both species responded similarly to reduced temperatures in terms of abundance and space occupation. Growth rates differed between species, however, suggesting that Notochthamalus may be more limited by higher temperature than Jehlius, but growth rates of both species were similar under the warmest (high zone, unshaded) and coolest (mid zone, shaded) treatments. Although we found a greater proportion of Notochthamalus individuals brooding eggs in unshaded control areas (where sample size allowed analysis) and greater numbers of Jehlius individuals brooding under shades, no differences in reproductive output (egg mass) were found among brooding individuals between shading treatments and tidal elevation for either species. Overall, we found no evidence of temperature mediated tradeoffs in performance between adult Jehlius and Notochthamalus. Instead, our results indicate a lack of a strong competitive hierarchy between Jehlius and Notochthamalus and suggest that temperatures experienced during emersion may reinforce vertical patterns of adult abundance established during settlement.