The influence of intertidal location and temperature on the metabolic cost of emersion in Pisaster ochraceus

In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: a b s t r a c t a r t i c l e i n f o Vertical zonation within the intertidal results from an interaction between the physical environment and an organism's physiological limits. Bioenergetic costs of emersion are likely to vary based on an organism's vertical location in the intertidal. The present study quantified the metabolic costs of microhabitat choice in the important intertidal predator Pisaster ochraceus. Rates of oxygen consumption (VO 2) were measured at a range of ecologically relevant temperatures in both water and air. In both media, rates increased with increasing temperature but, at any given temperature, aerial VO 2 was approximately 50% that of aquatic VO 2. These rates, along with biomimetic body temperature data from two field sites in Bodega Bay, California, were used to estimate the metabolism of sea stars at different vertical locations over a 10-day period in the summers of 2006, 2007, and 2010. Results suggest that vertical location would have a much smaller effect on sea star VO 2 than would inter-annual temperature differences. The influence of higher body temperatures experienced by sea stars at low tide in the mid-high intertidal, as compared to the low intertidal, was almost negligible because aerial VO 2 was lower than aquatic VO 2. By contrast, the higher average water temperature experienced by sea stars in 2006 yielded a 50% higher metabolic cost relative to sea stars in 2007 and 2010. These results suggest that energetic demands of intertidal organisms can vary markedly according to global environmental fluctuations such as El Niño and Pacific Decadal Oscillations. The intertidal habitat is physiologically challenging because of the dramatic temporal and spatial variations in temperature. The extent to which an organism is subjected to large temperature changes depends largely on its vertical location in the intertidal. At high tide organisms experience a relatively stable thermal environment because of the high thermal inertia of the large body of seawater (Helmuth, 1998); by contrast, the low tide thermal environment shows comparatively large fluctuations Fluctuating air temperatures, along with wind and solar radiation, during a summertime low tide can affect the heat flux within an organism, causing …