The direct and indirect effects of acute thermal stress on Haustrum scobina: A thermal tolerance assessment of three intertidal invertebrates

Abstract

Episodic exposure to extreme temperatures is believed to be one of the main drivers in climate change related local extinction. For intertidal species, exposure to increasingly intense extreme temperatures can push organisms past their physiological thresholds. Predicting the responses of species and communities to climate change remains a challenge. Unanticipated outcomes of warming are generally a result of indirect effects, i.e. those resulting from changes in interaction strength among co-existing species within an environment. Predator-prey interactions provide an ideal relationship to investigate and can lead to a broader understanding of community wide responses. The major purpose of this study was to examine the relationship between Haustrum scobina, across multiple life stages and their corresponding prey species Chamaesipho spp. and Saccostrea glomerata. Accordingly, the thermotolerance and current in situ thermal conditions were assessed for the three focal species, acclimatized to summer and winter conditions. The influence of nutritional stress and exposure time were further analysed for H. scobina. The temperature that resulted in 50% mortality (LT50) of H. scobina populations did not differ with season, nutritional stress or ontogenetic stage, averaging 38.2 °C. The critical tolerance, (Tcrit) the temperature that resulted on 90% mortality, however, fluctuated with both season and age, with a range between 38.4 - 44.4 °C, where winter acclimated specimens and juveniles performed worse at critical temperatures. This research indicates that exposure to future extreme temperatures will negatively impact H. scobina populations residing in north-eastern Auckland. During these extreme temperature events microhabitat occupation will be inadequate to alleviate thermal stress in this species. In contrast, both Chamaesipho spp. and S. glomerata rarely experience physiologically stressful conditions in situ, and are considerably less vulnerable to future extremes. Increased exposure to acute thermal stress may reduce the influence H. scobina has on their dominant sessile prey species, with likely flow on effects on intertidal community dynamics within north-eastern Auckland.