Making light of observing aquaria treatments: an application of optical coherence tomography to image subsurface tissue structure of Antartctic krill Euphausia superba

Nicola Bellini, Martin J.Cox, Danielle J. Harper, Sebastian R. Stott, Praveen C. Ashok, Kishan Dholakia, So Kawaguchi, Robert King, Tammy Horton and Christian T. A. Brown

PLoS ONE 9(10), e110367 (2014)

doi: 10.1371/journal.pone.0110367

Many small open ocean animals, such as Antarctic krill, are an important part of marine ecosystems. To discover what will happen to animals such as krill in a changing ocean, experiments are run in aquaria where conditions can be controlled to simulate water characteristics predicted to occur in the future. The response of individual animals to changing water conditions can be hard to observe, and with current observation techniques it is very difficult to follow the progress of an individual animal through its life. Optical coherence tomography (OCT) is an optical imaging technique that allows images at high resolution to be obtained from depths up to a few millimeters inside biological specimens. It is compatible within vivo imaging and can be used repeatedly on the same specimens. In this work, we show how OCT may be applied to post mortem krill samples and how important physiological data such as shell thickness and estimates of organ volume can be obtained. Using OCT we find an average value for the thickness of krill exoskeleton to be (30±4) µm along a 1 cm length of the animal body. We also show that the technique may be used to provide detailed imagery of the internal structure of a pleopod joint and provide an estimate for the heart volume of (0.73±0.03) mm3.