Burnaford, J. L.: The physiology of positive interactions: effects of shade and season on endogenous levels of hsp70 in field populations of the black chiton Katharina tunicata

Canopy-forming algae can be important to consumers by providing food and protection from predation or intense insolation. In the low rocky intertidal zone of the Pacific Northwest, the chiton Katharina tunicata is closely associated with the canopy-forming alga Hedophyllum sessile. In previous studies, Hedophyllum canopy removal resulted in a dramatic drop in Katharina abundances, but the cause of this decline was not determined. In a three-year field experiment, Katharina numbers were significantly higher in shaded plots (artificial shade or natural Hedophyllum) than in unshaded plots in the spring and summer, but abundances were not different in the fall and winter. During low tide on sunny summer days, Katharina body temperatures are 6 to 9^oC warmer in the open than in the shade. These data suggest that the shade provided by the algal canopy is important for reducing heat stress for Katharina. To examine the effect of shade on the physiological state of chitons in the field, I used fences to maintain Katharina under shaded and unshaded conditions from April to November of 1999 and April to August of 2000. From monthly tissue samples of these chitons, I quantified endogenous levels of heat shock proteins (hsp70 isoforms). To examine the effect of seasonal ambient temperature on hsp70 levels, I also collected monthly tissue samples from the unmanipulated Katharina field population from April 1999 to August 2000. These data on seasonal and shade-related variations in the heat-shock response of Katharina, combined with data from a long-term ecological study, give a unique picture of the interacting effects of physiology and ecology on community structure.