419 Dive Log Australasia AUGUST 2026

STAYIN ALIVE THE DEFENCES OF SEA SLUGS - Part 9 Reactive Defences continued

Illumination Response Bioluminescence has been discussed before here, several years ago, but a revision is included here to make the series on Defences comprehensive. BIOLUMINESCENCE Bioluminescence is defined as: The emission of visible light, produced through chemical reaction, by animals or (rarely) their symbionts. Not to get too technical, bioluminescence is typically created due to the oxidation (reaction with oxygen) of luciferin molecules made possible by an enzyme catalyst called luciferase. Luciferin and luciferase are generic names used to encompass a range of related molecules able to perform this same function. Bioluminescence is believed to have evolved independently many times (estimated at more

than 40 times) across many animal phyla. In the case of nudibranchs, it is intrinsic, being produced via chemical reactions by the nudibranch itself rather than through the hosting of symbiont bioluminescent bacteria. BIOLUMINESCENCE or FLUORESCENCE Bioluminescence and Fluorescence should not be confused - they are two separate phenomena. Bioluminescence can be produced by the animal in complete darkness. Fluorescence, on the other hand, requires excitation by a light source, so is not visible in total darkness. With fluorescence, an external light source energises the electrons of certain molecules temporarily. That energy is then released as a longer wavelength lower energy i.e. a different warmer colour. Blue or violet light usually excites to release green, yellow or red fluorescent emission. Bioluminescence is

This reef-dwelling specimen of Plocamopherus ceylonicus has lost its left anterior bioluminescent globe. Perhaps it has done its job of being sacrificed to save the gill. Note the bright pink colour of the three remaining

A pair of Mexichromis trilineata foraging through the substrate. The specimen on the left in the image has rhinophores and gill extended while the specimen on the right has completely retracted everything.

globes of a clean water specimen. DIVE LOG Australasia #419 August ‘26

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