The influence of multiple environmental stressors on the limpet Cellana toreuma during the summer monsoon season in Hong Kong

Although environmental stressors affect natural systems in a multitude of ways, the interactive effect of multiple stressors on ecological assemblages remains largely misunderstudied. On tropical shores which experience seasonal monsoons, rocky intertidal habitats are physiologically stressful environments, being strongly affected by high temperatures and monsoon rains during emersion. In Hong Kong the limpet, Cellana toreuma, often takes refuge in mid-shore tidepools. In summer, these populations experience high mortality, probably as a result of stressful environmental conditions during low-spring tide days with high temperatures and/or intense rainfall periods can occur. Laboratory experiments were designed to mimic the effects of temperature stress (and increasing pool salinity) and reduced salinity as a result of monsoon rains on C. toreuma in tidepools. In general, haemolymph osmolality increased with salinity and limpet mortality increased with temperature. As salinity decreased after simulated rainfall, haemolymph osmolality (after 60 min) and survival (after 180 min) were significantly lower than in control treatments. Salinity fluctuations, coupled with high temperatures during emersion had both sub-lethal physiological effects and lethal effects on limpets in tidepools. Conducting experiments of multiple stressors simultaneously, however, revealed no interaction between hot temperatures and salinity variation, both of which operated independently for different response variables. Individually, therefore, hot temperatures and large salinity changes associated with the wet monsoon season are likely to play an important role in the population dynamics of intertidal species such as C. toreuma, and as a result will influence the structure and functioning of tropical rocky shores.