World’s largest chiton (Cryptochiton stelleri) is an inefficient thermoregulator

Abstract

Rocky intertidal zones are some of the most thermally stressful environments on earth, where ectotherms deal with tidally driven fluctuations in air and water temperatures that can exceed their maximum thermal tolerance. However, not all intertidal ectotherms face the same exposure risk. In northern regions of the eastern Pacific, summertime low tides occur during midday, exposing ectotherms to potentially stressful temperatures, whereas cooler pre-dawn low tides in southern regions buffer ectotherms from thermal stress. Gumboot chitons Cryptochiton stelleri are thermally sensitive intertidal grazers that range from southern California to Alaska, exposing them to a mosaic of thermal stresses. We quantified chiton thermal performance limits in the laboratory by testing the effects of elevated air and water temperatures on grazing. We also compared the thermoregulation efficiency of chitons from thermally benign northern California sites with those from thermally stressful San Juan Island, Washington sites, using 3 components: (1) biomimetic thermal models deployed intertidally, (2) chiton body temperatures in the field, and (3) chiton thermal preference in a laboratory-based thermal gradient. We found that chiton grazing performance was greatly reduced at 18°C in water, and they reached their grazing performance limit after exposure to 20°C in air, confirming previous work documenting thermal limits on chiton respiration. Chitons preferred body temperatures within 3°C of their thermal performance limits, but they rarely achieved body temperatures that would maximize grazing in the field. This suggests that chitons are not thermoregulating efficiently with respect to maximizing grazing performance, but instead are minimizing exposure to temperatures that would be detrimental to their performance.

Variable Environments in an Upwelling System Trigger Differential Thermal Sensitivity in a Low Intertidal Chiton

“…In general, this thermal refugia are positively correlated with air temperature and solar radiation on marine invertebrates and where selection of these cool microhabitats produces a low respiratory performance (see Monaco et al, 2015). For example, a recent study in the chiton Cryptochiton stelleri indicates that its large size and reduced mobility force it to select lower temperatures to avoid overheating in those favorable thermal habitats (McIntire and Bourdeau, 2020). The previous may be the case of Acantopleura echinata due to their larger size (see Ibáñez et al, 2021), which can also be a poor thermoregulator, since therefore, future scenarios of increased temperature will expose chitons to more stressful temperature and can have a detrimental effect on organismal performance (see Miller, 2013) especially in highly variable thermal environments as Talcaruca location.…”

Mosaics of climatic stress across species' ranges: tradeoffs cause adaptive evolution to limits of climatic tolerance

“…With few exceptions [ 42 – 44 ], almost all subsequent references to climate stress mosaics concern intertidal systems in which stress mosaics are driven very directly by mosaics of temperature and moisture from which sessile organisms cannot escape (e.g. [ 45 – 47 ]).…”