Ocean Fact – Halloween special

We reached the end of October and I (@pierrotheseapen) spent the past two weekends celebrating Halloween with my friends. It is about time I share the scariest facts sea critters. And what would be scarier than start with the sea devils!

Ocean Fact - Halloween Special - Angler fish illustration

The sea devils–also knows as angler fishes–are a family of deep-sea anglerfish. Fish in this family are characterized by the presence of a fishing-rode like lure on their forehead. Their lure is a good example of symbiosis between two organism: it contains bioluminescent bacterias. The bacterias inside the lure emits light that, in the darkness of the deep sea, attracts the prey ingested by the fish (Haddock et al. 2010). You probably have seen this fish in ‘Finding Nemo’. Anglerfish also use their lantern to signal their presence to mate. Life made easy in the deep-sea. However, partially glowing in the dark is not the only peculiarity that you will find in the sea devils. Be ready for the next anecdote because this has to be one of my favorite fact we ever shared on OceanFact! Until 1925, no scientists had ever recorded a male sea devils. Female sea devils can measure up to 2m and were often recorded with small parasitic fish attached to their body. Saemundsson (1922) first hypothesized that those fish would be juveniles, and that the female would provide some sort of care for the offsprings. The later work of Regan (1925) proved that those small parasitic fish were indeed dwarves male. Marine science had unravelled one of the weirdest sexual strategies in the animal kingdom. It appeared that when males would find females, they would bite the females, get a hold of them, and stay attached until the female would be sexually ready (Pietsch, 1976). If the hold gets too long, the male would fuse with the female to regress to its primary function: being a sack of balls for reproduction. One odd way Cupidon has found to make lovers meet in the darkness of the deep sea.

The second misfit on our list today is no less than the Goblin Shark. Weirdly looking slow predator, the goblin shark was given the tools to compensate for its poor swimming ability. First, the goblin shark is equipped with a long snout full of Lorenzini ampullae. Their function as in other shark species is to detect electromagnetic fields generated by muscles’ contractions of a prey. The goblin shark swims around in search for food and use its snout similarly as a metal detector, or the radar on an Hawkeye military airplane. However its elongated body with small soft fins prevents it from swimming at fast speed.

Instead, the goblin shark uses the slingshot technic. It is able to project its mouth forward at high speed and catch prey (e.g. fish, Nakaya et al. 2016). Nakaya et al. (2016) recorded that the shark projects and closes its jaws at a speed of 3.16m/s. That’s 1.3 times faster than the speed for the world record in freestyle swimming, and 4000 times faster than the top speed of a sloth! Ok, they are really slow, but still! You do find them ugly and scary? Wait to see what’s next! Another surprising thing about this shark is its color. The skin is pink when red pigments are possibly the most costly to display (Hill 1996, Prince et al. 2008). Looking that up, I found this really cool blog on pigments in nature.

A few other Halloween facts

The viperfish

The photic or euphotic zone (Greek for “well lit”) is the uppermost layer of water in an ocean or lake that is exposed to intense sunlight. In the open ocean, it typically extends to a depth of about 200m. Since the euphotic zone is where almost all of the photosynthesis occurs, the depth of the photic zone is generally proportional to the level of primary production that occurs in that area of the ocean. About 90% of all marine life lives in the photic zone!

The middle layer of the world’s oceans, referred to as Disphotic (Greek for ‘poorly lit’) or ‘Twilight zone’, extends from approximately 200 – 1,000 m and receives only faint, filtered sunlight during the daytime. In the disphotic zone, there is enough light to see during the day, but not enough light for photosynthesis to take place, so no plants live in this zone. Here, we begin to see the twinkling lights of bioluminescent creatures – great diversity of strange and bizarre fish can be found here, such as the viperfish!
By the way, did you know that the Twilight zone might have more fish biomass than in the rest of the ocean combined?

The aphotic (Greek for ‘without light’) or ‘Midnight zone’ is the portion of the ocean where there is little or no sunlight. It is formally defined as the depths beyond which less than 1% of sunlight penetrates and usually starts at depths from 1,000m onwards, however the depth of the aphotic zone can be greatly affected by such things as turbidity and the season of the year. In the aphotic zone, there is no light, so vegetal organism can’t grow and realize the photosynthesis, CO2 is accumulated and there is less Oxygen and a lower pH than in the photic zone. All the living organism develop adaptation to the lack of light like bigger eyes for the abyssal fish and cephalopods, light emission in some fish and shrimps to mate, defend, or attack and the tapetum lucidum, a structure in the eyes that reflect the incoming light.

The pearlfish

It is a bit hard to imagine but a weird relationship exists between sea cucumber and fish. The pearlfish uses the sea cucumber rectum to hide from predators. This fish is backing into a hole tail-first so its head can still be outside. Sometimes it is a commensal relationship because the cucumber is not harmed, but some pearlfish become parasitic because they are feasting on some of sea cucumber internal body parts… The sea cucumber provides a protection against predators and an unlimited food storage as many echinoderms (i.e. sea urchins, sea stars, sea cucumbers…) regenerates. The fish body is perfectly designed to slide in… When you think of it, on an evolutionary perspective, it means that somewhere in the evolution of fish, one fish of whatever species tried to hide in the rectum of a sea cucumber. Being succesful, it tried again and got a better protection from predators than for other fish species at the time. Along evolutionary process, this fish and this weird pearlfish-sea cucumber relationship were selected and preserved. I am as amazed as disgusted by the idea that natural selection favored such interaction. Who knows what might happen to us human-being to survive climate change? Someone might try hiding in the rectum of an elephant and succeed? The inside of the elephant would provide protection against the extreme heat outside, while climate change might not affect the elephant itself—our host—as it might already be adapted to future temperatures.

The take home message

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Haddock, S. H. D. et al. 2010. Bioluminescence in the Sea. – Annu. Rev. Mar. Sci. 2: 443–493.

Hill, G. E. 1996. Redness as a measure of the production cost of ornamental coloration. – Ethology Ecology & Evolution 8: 157–175.

Froese, R. and D. Pauly. Editors. 2019.FishBase.
World Wide Web electronic publication.
www.fishbase.org, ( 08/2019 )

Pietsch, T. W. 1976. Dimorphism, Parasitism and Sex: Reproductive Strategies among Deepsea Ceratioid Anglerfishes. – Copeia 1976: 781.

Price, A. C. et al. 2008. Pigments, Patterns, and Fish Behavior. – Zebrafish 5: 297–307.

Sæmundsson, B. (1922). Zoologiske meddelelser fra Island. XIV, 11, 159-201.

Nakaya, K. et al. 2016. Slingshot feeding of the goblin shark Mitsukurina owstoni (Pisces: Lamniformes: Mitsukurinidae). – Nature Publishing Group 6: 199.

Author of this blog post.

Pierre PhD student - CEO Ocean Fact
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