Hopkins Marine Station Student Paper

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Title: Thermal tolerance limits of heart function in marine snail congeners (genus Tegula) from different tidal heights.
Student Author(s): Stenseng, Emily
Faculty Advisor(s): Somero, George
Pages: 26
Location: Final Papers Biology 175H
Date: June 2004
Abstract: Previous studies have demonstrated that a suite of physiological and biochemical factors contribute to the establishment of a species’ thermal tolerance limits and vertical distribution patterns in the marine intertidal. In this study, the thermal limits of heart function were determined for three congeneric marine snail species of the genus Tegula, all inhabiting discrete vertical zones in the intertidal. T. funebralis is found in the low- to mid-intertidal, T. brunnea in the subtidal to low-intertidal, and T. montereyi in the subtidal zone. Using impedance electrodes, changes in heart rate were monitored in field-acclimatized and lab-acclimated specimens of each species, in response to thermal stresses in water. Significant interspecific differences in Arrhenius break temperature values (ABT, the temperature at which heart rate began a sharp decline) were observed. Average ABTs for field-acclimatized T. funebralis, T. brunnea, and T. montereyi were 31ºC, 25ºC and 24ºC, respectively, establishing a positive correlation between cardiac upper thermal tolerance limits and maximum habitat temperatures. Flatline temperatures, defined as those at which hearts ceased to beat, followed the same trend-T. funebralis hearts stopped beating at significantly higher temperatures than the two subtidal species. In response to cold stress, T. funebralis maintained cardiac function at lower temperatures than its congeners, demonstrating that it is more eurythermal. In all three species, ABTs of specimens lab-acclimated to 22ºC were higher than those of 14ºC lab-acclimated snails. T. funebralis, however, showed the smallest ABT difference between acclimation temperatures, indicating that it may have a lower capacity for thermal acclimation. The results of this study suggest that the mid-intertidal species T. funebralis is living closer to its upper thermal tolerance limits. Thus T. funebralis populations, and perhaps warm-adapted intertidal species in general, may be at highest risk in the event of global climate change.
Notes: Published in Biological Bulletin, 2005 208:138-144