Bioacoustics is the study of how animals communicates with any acoustic waves. Strickly speaking, it involves any substrates where the acoustic waves propagate: liquids (water), gas (air) and solids (e.g. plant stem, soil).
However, differences in methodologies can be found to record in each medium. For instance, people studying surface-borne acoustic-wave communication usually refers themselves as biometrologists and not as bioacousticians (see here and here), which probably highlights some differences.
I would like to focus my question on the recording techniques to pick up the diversity of acoustic waves in the different media. In particular, what are the main differences to be taken into account when recording solid-borne, water-borne and air-borne sounds?
EDIT: initially, there were multiple questions in the body text which was confusing for people answering, so I've tried to make it more focused on the main question (the one which is and was in the title) and I've created another question focused on difference between biotremology and bioacoustics