A Light Show at Sea

12 Jan 2014

Unlike most groups on A16S, the trace metal team are not working shifts. This means that every now and then it is not possible to avoid a cast in the middle of the night. Last night (or rather early this morning) was one such occasion. We had a cast that was due to go in at 01:45, which means that we have to prepare the CTD rosette before the scheduled cast time so that we don't fall behind schedule. At about 01:00 Mariko and I walked into the main lab and were greeted by an excited Dr. Landing, who told us that we should go and take a look at the sea off the stern of the ship. We went outside and were treated to a fantastical display of bioluminescence, of the like that none of us had seen before.

We were able to see the track of the ship lit up by bioluminescence as the deck lights were off as we were still underway. The water was getting churned up by the passage of the ship and causing the squid, which had migrated to shallow waters to feed under cover of darkness, to flash and glow frantically. Unfortunately, they did not produce enough light to photograph them, but that didn't make the experience any less magical.

Of the squid (the cephalopods), there are at least 70 luminous genera, which can produce an impressive variety of luminescent displays. Bioluminescence by squid is thought to serve both defensive and offensive roles - even within a single organism. For example, counter-illumination is a defense mechanism employed by some squid. As predators view their prey from below, bioluminescence emitted from ventral photophores (light emitting cells) camouflages the squid's silhouette so that they become effectively invisible when viewed from below. As an offensive strategy, bioluminescence may be used by squid to confuse their prey. In the case of the squid we saw, the churning of the water in the ship's wake caused sufficient mechanical disturbance to cause the squid to flash, and remain illuminated for up to about 10 seconds.

An interesting myth-busting fact:

Light is typically generated by the organism itself and only rarely due to symbiotic bacteria that live in/on the host organism (Haddock et al. Annu. Rev. Mar. Sci 2010. 2:443-93).

With all this talk of amazing, exciting wildlife, here is a picture to show that the science stops for no man (or woman)! This is a picture of Dr. Landing and me sampling seawater in the clean van. Water is filtered through 0.45  µm filters for dissolved trace metal determinations. The filters are retained for trace metal determination of particulate trace metals.

Dr. Bill Landing and Dr. Rachel Shelley sampling seawater in the clean van