Cetacean ultrastructural cochlear imaging through scanning electron microscopy

Abstract

The control of noise interaction between artificial and biological sources is essential to assess the development of sustainable marine technologies. Therefore, there is an emergent need to conduct morphological analysis of the acoustic pathways of marine organisms and detect possible structural alterations as a consequence of sound exposure. Cetaceans, because of their use of sounds in their daily activities, represent today the best bioindicators of the acoustic balance of the oceans. To access this information it is necessary to extract the ears of very fresh stranded individuals. One of the challenging steps after extraction and fixation of the samples is to decalcify the bone envelope to access the cochlea without damaging the soft tissues. A fast commercial decalcifier (RDO®) was used in 93 ears from 11 different odontocete species stranded in the Mediterranean Sea, the North Atlantic and the North Sea. Depending on the tympanic-periotic volume of the species, the decalcification time ranged from several hours to a few days, instead of taking few months with other decalcification agents, allowing a subsequently faster observation of the cochlear structures. Here we present images from cetacean cochlear ultrastructure through scanning electron microscopy. Following this protocol it is possible to obtain a fast diagnostic of possible acoustic trauma and relate the results to documented sound exposure. The output of this analysis will help calibrating theoretical results derived from deep-sea observatories.