Design and Characterization of a Portable Fluorescence Measuring System for the On-Site Monitoring of Marine Bioconstructors

Marine bioconstructors are put at risk by natural disturbances caused by climate change and anthropogenic stressors. Given their fundamental importance in marine ecosystems, it is essential to reverse this trend. In this regard, measurement techniques capable of early detecting alterations of marine colonies are essential. Traditional underwater surveys rely on in situ observations performed by divers, and in the last decade, such analysis has been increasingly supported by photogrammetry. Despite the significant benefits brought by photogrammetry and the notable progress of computer vision, to date, no measurement techniques have fully succeeded in the early detection of minor alterations in the state of health. In this regard, fluorescence imaging has the potential to support and improve both ecological and physiological assessments. Nevertheless, up to date, its use in the underwater environment is mainly exploited for qualitative nature photography and much less for quantitative analysis aimed at extracting biological information. One factor limiting the widespread use of quantitative fluorescence imaging to monitor marine bioconstructors is that studies in the literature generally do not allow for metrological traceability. Fluorescence intensity is usually reported in arbitrary units derived from the intensity of the acquired images. This study aims to support the transition from qualitative imagery to quantitative fluorescence imaging. To this end, we proposed introducing a simple and effective traceability obtained by relating the fluorescence intensity recorded by the instrument to the sodium fluorescein concentration that would generate the same intensity, namely, the equivalent fluorescein concentration. This makes measurement results independent of the specific measuring system, enabling research conducted by different groups to be synergised.