NoteLight comfort zones of mesopelagic acoustic scattering layers in two contrasting optical environments

•Depths of acoustic scattering layers (SL) are determined by water clarity.•SL organisms distribute vertically according to light comfort zones (LCZ).•Future SL studies require in situ light measurements at mesopelagic depths.

We make a comparison of the mesopelagic sound scattering layers (SLs) in two contrasting optical environments; the clear Red Sea and in murkier coastal waters of Norway (Masfjorden). The depth distributions of the SL in Masfjorden are shallower and narrower than those of the Red Sea. This difference in depth distribution is consistent with the hypothesis that the organisms of the SL distribute according to similar light comfort zones (LCZ) in the two environments. Our study suggest that surface and underwater light measurements ranging more than 10 orders of magnitude is required to assess the controlling effects of light on SL structure and dynamics.