A review of the thermal biology and ecology of molluscs, and of the use of infrared thermography in molluscan research

In an era of global change, thermal biology and ecology are becoming increasingly popular topics in invertebrate research, including molluscs. However, this area of research is still very limited, essentially due to the intrinsic spatial limitations of traditional single-point temperature measurements (e.g. thermocouples, iButtons and infrared thermometers). This is not the case, however, with infrared thermography, which has the desirable attribute of producing images that allow for simultaneous measurements of multiple molluscan individuals, species and communities. Infrared thermography allows for spatial and temporal monitoring of microclimates at scales relevant to individual organisms and hence may represent a first step to bridge the gap between field-based approaches (typically spanning from centimetres to tens of metres) to climatic scenarios (typically coarse-grained, i.e. 10 x 10 km). This review first provides a brief history of infrared thermography, followed by a description of the fundamental physical properties and quantities that bridge the gap between the physics of heat transfer and the physics of infrared thermography. We then thoroughly review the thermal biology and ecology of molluscs, and the previous biological and ecological applications of infrared thermography-including the very few in molluscan research. We provide detailed recommendations related to the proper use of infrared thermography. Finally, we discuss the potential applications of infrared thermography in molluscan research, based on case studies involving both terrestrial and intertidal molluscs, with emphasis on its use as a tool for monitoring impacts of climate change.