The number and diversity of glowing animals in the deep sea is undoubtedly large, but until recently little work has been done documenting the numbers of light-producing animals at different depths. You would think that these glowing, or bioluminescent, animals would be easy to spot in an area of otherwise total darkness, however many animals can glow faintly and very few cameras are sensitive enough to capture this glow. An additional issue lies in that many marine animals glow for only small periods of time since producing this light is energetically costly and may draw the attention of predators.
In a new study, the Monterey Bay Aquarium Research Institute (MBARI) showed that three-quarters of the animals in Monterey Bay waters from the surface down to 4000 meters deep are bioluminescent. This was the first study that quantitatively analyzed the number and types of bioluminescing animals at different depths. Prior to this study, estimates of glowing animals were based on scientists’ observations through submersible windows.
The leaders of the study, MBARI researchers Séverine Martini and Steve Haddock, analyzed more than 350,000 individual animals that appeared in videos from over 240 dives by remotely operated vehicles (ROVs). They compared this list with published descriptions of species and groups of animals that were known to be bioluminescent.
Conclusions from the study:
The proportion of glowing to non-glowing animals was similar at all depths.
Different groups of animals were responsible for the light produced at different depths.
From 0-1500 meters deep most of the glowing animals were true jellyfish or comb jellies
From 1500-2250 meters deep most of the glowing animals were worms
From 2250-4000 meters deep about half of the glowing animals were larvaceans (small tadpole-like animals)
At least 97% of the jellyfish and siphonophores (long and thin marine animals related to corals and jellies) were bioluminescent.
Only about half of the fishes, squid and octopuses were bioluminescent.
To read more about this recent study, check out MBARI’s press release or read the research article in full at the link below.
Martini, S. and S.H.D. Haddock. 2017. Quantification of bioluminescence from the surface to the deep sea demonstrates its predominance as an ecological trait. Scientific Reports 7, 45750. DOI:10.1038/srep45720.