Thermal Tolerance Limits of Heart Function in Tegula Snail Congeners of the Marine Intertidal Marine Biology

1 The marine intertidal is one of the harshest environments on earth. Organisms inhabiting the transition from land to sea are subject to a host of environmental stresses, including temperature variation, dessication stress, wave force, and salinity [1, 2]. The daily tidal cycle is largely responsible for the drastic, rapid temperature fluctuations typical of the intertidal, exposing organisms to alternating terrestrial and aquatic conditions. Many species inhabit discrete vertical zones in the marine intertidal [3]. These zonation patterns are established by abiotic factors, such as temperature and aerial exposure, as well as biotic factors like competition and predation [3, 4, 5]. Studies have shown that species in the midto high-intertidal zones experience more extreme environmental stresses than subtidal species. For instance, some high-dwelling gastropods can undergo body temperature increases of 20-25oC during low tide emersions [6], whereas many subtidal animals never face temperatures above that of the ambient seawater. These drastic differences in thermal habitats exist only because intertidal organisms have differentially evolved adaptations for thermal tolerance. Numerous studies have shown that the upper vertical limits of species distributions are correlated with Thermal Tolerance Limits of Heart Function in Tegula Snail Congeners of the Marine Intertidal Marine Biology