Hidden in plain sight: hyperspectral documentation of complex biofluorescence produced by the green sea urchin (Strongylocentrotus droebachiensis).

Biofluorescence in echinoderms is largely unexplored and even though the green sea urchin Strongylocentrotus droebachiensis is a well-studied species, the presence and/or function of fluorescence remains very poorly understood. Hyperspectral imaging was conducted on mature sea urchins (N=380) while fluorospectrometric analysis was conducted on sea urchin coelomic fluid (N=30). Fluorescence was documented in both the spines and coelomic fluid of S. droebachiensis. Intact spines exhibited a low intensity green emission (~550-600 nm), while broken spines averaged a high emission peak in the green spectrum (~580 nm). Sea urchins produce a red exudate with a pronounced emission peak (~680 nm) with a shoulder peak (~730 nm). The sampled coelomic fluid exhibited high variability, with a majority exhibiting a low-level green fluorescence while pronounced emission peaks (N=5) were found in the red spectrum (~680 nm). The complex fluorescence produced by S. droebachiensis warrants further investigation on its applicability for monitoring welfare of sea urchins in aquaculture facilities. &#xD.