UBC Undergraduate Research

Thermal Tolerance, Herbivory and Tide Pool Distributions of Littorina sitkana and Littorina scutulata : Implications for a Warming World Brownlee, Graham Robert Paul


As a consequence of climate change, both the magnitude and frequency of extreme temperature events are predicted to increase. Tide pools can experience dramatic fluctuations in their temperatures, and therefore may be strongly affected by future extremes. I looked to identify the effects of thermal variation among tide pools on the herbivorous intertidal snails Littorina sitkana and Littorina scutulata at April Point, Quadra Island, British Columbia. Through a thermal tolerance experiment, I found that L. scutulata is more tolerant to extreme temperatures than L. sitkana. I compared herbivory rates of the two species between a warmed (36 °C) and control (32 °C) temperature treatment, and found that each species has a unique mass-adjusted feeding rate, and that both had their rates inhibited by the hotter treatment. Through a tide pool heating experiment, I found that increased average and maximum temperatures did not contribute to changes in the abundances of adult L. sitkana, L. scutulata, the total abundance of both species, or the percentages of L. sitkana in the pools. Monitoring summer temperature and snail abundances in tide pools, the percentage of L. sitkana, the total abundances of snails, and the abundances of L. sitkana and L. scutulata changed through time, but were not influenced by average or maximum temperature, temperature variance, or temperature hours at or above thirty degrees Celcius. Thus, although the thermal tolerance patterns would suggest a shift towards L. scutulata in warmer (or warming) pools, I did not observe this pattern in the field. Nevertheless, the reduced herbivory rates for both L. scutulata and L. sitkana at high but realistic temperatures suggests that ongoing warming may lead to changes in littorine abundance and top-down control of macro-algae and epiphytes, but that other environmental, interactive, biological or behavioural factors may also contribute to how tide pool and the intertidal species respond to future change.

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