Deep Sea Reefs

9/2/2023

    

    Ever since humans were brought into existence, we didn't know a lot about the world. However, it never stopped our ancestors from exploring the nooks and crannies of every small place that interested us.

    

    But even with all of that time, we've barely scratched the surface as NOAA says that "more than 80% of our ocean [alone] is unmapped, unobserved, and unexplored." Said in Layman's terms, we know next to nothing about our oceans, even though they fuel the fundamentals of life on Earth and cover up to 71% of the Earth's surface, let alone the rest of the world. 

Storytime:

Around a March ago, I heard a lot about the possibilities of harvesting polymetallic nodules at the seabed (they're potato-sized nuggets of elements necessary for electronics). 

    At the time, I was both surprised and skeptical of the implications of mining the seafloor. Surprised, in the sense that they said we could finally extract critical elements from the seafloor without any environmental repercussions, and skeptical because it was too good to be true that there wasn't anything down there to harm. 

    Sure enough, after prospectors chose a spot in the Pacific deep-sea called the Clarion-Clipperton Zone, scientists conducted environmental surveys and found about 4900 - 5100 NEW SPECIES (88% - 92% of 5578 total species are new).

So yeah, it's safe to say that old explorers were bums compared to us and all of this new technology we have. Sorry, Magellan!

    However, the deep sea is not just scattered animals dotting the seafloor. Hundreds of meters down below the surface, in 39 - 54℉ (4 - 12℃) water and mostly without sunlight are bustling cities of fish, crabs, shrimp, sponges, and ... coral reefs?

These are deep-sea reefs!

Deep-Sea Reef Gallery:

Deep sea reef from Komodo, Indonesia

(Taken by Raimundo Fernandez Diaz)

Deepwater coral reef in Tahiti that was discovered in December 2021 

(Taken by Alex Rosenfield)

 

"Deep sea bamboo coral taken south of Florida Coast" 

Røst Reef, the deepest known reef known to man

    As you can see in the pictures, deep-sea reefs have great variety due to their varying depths; the corals with vibrance are closer to the surface while the colorless corals are at deeper depths. 

This is mostly because deep-sea reefs are separated from shallow-water reefs past the 150 ft (45.72 m) depth all the way down to 10,000 ft (3048 m). The range is crazy large compared to what we currently know as the deepest reef we've discovered so far is the Røst (Røstrevet) Reef at 984 - 1,312 ft (300 - 400 m) down, a picture of the reef being the last one in the gallery.

    The range NOAA scientists set is reasonable, because who knows what's down there? The Clarion-Clipperton Zone which I described at the beginning is about 12,000 - 18,000 ft (~4,000 - 5,500 m) down and includes stupid weird organisms like the gummy squirrel I can't get enough of:

The upside of a Gummy Squirrel, found in the CCZ at a depth of 5,100 m. 

(Picture taken by the DeepCCZ expedition)

The underside of the gummy squirrel has a suction cup-like palp near the front.

(Picture taken by a UH/NHM/UG/DeepCCZ expedition)

    With organism oddities out of the way, how do corals even survive in such crushing and extreme conditions? The coral reefs we see up near the surface at the epipelagic (sunlight) zone have beautiful colors, which they get from their symbiotic connection to zooxanthellae: a single-celled, dinoflagellate algae that fuel a majority of their life systems.

 

    They live in the coral's translucent "skin", giving its beautiful color which dazzles the reef.

    I say translucent because if you've ever seen coral bleach (I assume you have because we've seen a lot of it nowadays), it turns ghostly white and you can visibly see the membrane separate from the calcium carbonate skeleton.

Here's a good diagram of how the tissue covers the skeleton

    So if zooxanthellae powers a good majority of a coral's life processes, then why aren't all deepwater corals dead in an area where there's virtually zero sunlight?

    Corals themselves are actually colonial animals, made up of individual polyps. As they are animals, they rely on prey for sustenance so they catch phytoplankton and sometimes zooplankton. Of it, their deepwater brethren do the same as they heavily rely on passing phytoplankton and a really cool phenomenon called marine snow.

    Marine snow is the particulate matter, like dead bits of fish, animals, plants, minerals, and whatnot that falls down from the epipelagic zone and feeds the deep sea. The snow is formed via coagulation (a bunch of stuff getting stuck together) by small organic and inorganic particles, which are rich in carbon, nitrogen, and traces of phosphorous and iron.

    Catching and feeding itself, however, is not a constant stream of energy for the corals like zooxanthellae provides. Because of this, these deep-sea corals grow extremely slowly. Most of them grow at a couple of millimeters per year due to this, compared to shallow water's growth rate of ~10 centimeters per year! A lot of the corals in the dark are hundreds, if not thousands of years old. The oldest one we know of is black coral, at 4,270 years old! 

Type of deepwater black coral image taken by NOAA Hawaiian Undersea Research Lab (by the way, it's called black coral because of its skeleton)

    WAIT A MINUTE why does this coral have color on it?! A majority of deep-sea corals don't carry zooxanthellae?!

    According to this mission log by Dr. Scott France, the carotenoids (pigments) in photosynthetic organisms (such as the phytoplankton mentioned earlier or bacteria) that travel via marine snow or the water column are absorbed by the corals during digestion. These carotenoids are mostly orange, yellow, and deep red, but can also change color due to where it's being bound. Additionally, if you are knowledgeable about healthy eating, you've probably heard that carotenoids are antioxidants for animals. For corals, it's "suggested [that] carotenoids may function as antioxidants ... by strengthening the immune system ... [and acts] as antibacterial compounds."

    And if this post wasn't long enough, I saved the best for last. Not only can shallow-water corals do this, but deep-water corals can glow in the dark!

This is called bioluminescence, and it is just one of the prettiest things in the world to me:

Glowing coral deep in the Red Sea

Another thing is some soft-bodied corals also respond to disturbance by producing light, similar to how the bioluminescent waves we see on the shores are caused by plankton.

So not only for looking just like eye candy but even in deep water, corals use their bioluminescence as a way to lure prey similar to how other animals like an angler fish would. They need to lure as corals are, obviously, stationary. Because of this, they utilized a spring-lock mechanism of stinging cells called cnidocytes/nematocysts:

    An organism would rub itself against the trigger "hair", and the barb would shoot out into the organism. Through the tube, it would pump venom to incapacitate it, which helps the coral to drag it into the "mouth" which I will not show because, my god, this post has become way too long.

Angry Magellan

    Anyway, thank you for reading!

(Numbers are ordered top-down for links)

[Update: Links are broken I spent all of that time numbering for nothing]

References

DeepCCZ Expedition. (2018, june 18). [Gummy Squirrel at 5,100 meters depth on abyssal sediments in the western CCZ]. NOAA Ocean Exploration. https://oceanexplorer.noaa.gov/explorations/18ccz/logs/june12/june12.html

#12, #13

Deep sea corals may be the oldest living marine organism. (2009, March 23). Lawrence Livermore National Laboratory. Retrieved September 2, 2023, from https://www.llnl.gov/news/deep-sea-corals-may-be-oldest-living-marine-organism

#18

[A diagram of a cnidocyte, the stinging cells presents in most Cnidarian species]. (2020, November 22). Biology Dictionary. https://biologydictionary.net/sea-anemone/

#26

Encyclopedia Britannica. (n.d.). Coral Polyp [Photograph]. Encyclopedia Britannica. https://www.britannica.com/animal/coral

#15

[Ferdinand Magellan]. (n.d.). Encyclopedia Britannica. https://www.britannica.com/biography/Ferdinand-Magellan

#27

 

Haha he's angry

Fernandez Diez, R. (n.d.). [Soft Corals]. Livekindly. https://www.livekindly.com/scientists-discover-hundreds-deep-ocean-coral-reefs/

#7

France, S. C. (2017, May 16). Color in Deep-sea Octocorals. NOAA Ocean Exploration. Retrieved September 2, 2023, from https://oceanexplorer.noaa.gov/okeanos/explorations/ex1705/logs/may16/welcome.html

#20

[GIF of section in David Attenborough's Life That Glows]. (n.d.). GIFER. https://gifer.com/en/7PQg

#24

LaJeunesse, T. C. (2018, July). Zooxantheallae [Photograph]. Wikimedia Commons. https://commons.wikimedia.org/wiki/File:Zooxanthellae.jpg

#14

[Lophelia pertusa colony at the Røst Reef, Norway]. (n.d.). ResearchGate. https://www.researchgate.net/figure/Lophelia-pertusa-colony-at-the-Rost-Reef-Norway-a-typical-cauliflower-growth-form_fig1_256378893

#10

Malmquist, D. (2005, February 4). Marine Snow. https://www.vims.edu/blogs/archives/ivars_blogs/marine_snow.php#:~:text=Marine%20snow%20is%20ultimately%20a,inorganic%20materials%20into%20their%20tissues.

#16

MBARI. (2020). [Bamboo coral bioluminescence]. Monterey Bay Aquarium Research Institute. https://www.mbari.org/news/glow-in-the-dark-corals-light-up-the-deep-sea/

#25

National Geographic Society. (n.d.). Ocean. National Geographic Education. Retrieved September 2, 2023, from https://education.nationalgeographic.org/resource/ocean/

#3

NOAA. (n.d.). Deep-Sea Coral Habitat. NOAA Fisheries. Retrieved September 2, 2023, from https://www.fisheries.noaa.gov/national/habitat-conservation/deep-sea-coral-habitat

#5, 11, 17 and used throughout the post

NOAA. (n.d.). How much of the ocean has been explored? NOAA Ocean Exploration. Retrieved September 2, 2023, from https://oceanexplorer.noaa.gov/facts/explored.html

#1

NOAA. (n.d.). Why should we care about the ocean? National Ocean Service. Retrieved September 2, 2023, from https://oceanservice.noaa.gov/facts/why-care-about-ocean.html

#2

NOAA Hawaiian Undersea Research Lab. (n.d.). [Leiopathes (deep water black) coral]. Lawrence Livermore National Laboratory. https://www.llnl.gov/news/deep-sea-corals-may-be-oldest-living-marine-organism

#19

NOAA-OER 2005. (n.d.). [Deep-sea bamboo coral]. NOAA Ocean Exploration. https://oceanexplorer.noaa.gov/explorations/17sedci/background/coral-ecosystems/coral-ecosystems.html

#9

Rabone, M., Wiethase, J. H., Simon-Lledó, E., Emery, A. M., Jones, D. O., Dahlgren, T. G., Bribiesca-Contreras, G., Wiklund, H., Horton, T., & Glover, A. G. (2023). How many metazoan species live in the world's largest mineral exploration region? Current Biology, 33(12), 2383-2396.e5. https://doi.org/10.1016/j.cub.2023.04.052

#4

Rosenfeld, A. (2021, December). [Bed of Roses]. AP News. https://apnews.com/article/pristine-coral-reef-found-tahiti-9b392d63cc2033924b3b51a7e26dda07

#8

Tel Aviv University. (n.d.). [Glowing corals]. The Times of Israel. https://www.timesofisrael.com/deep-sea-corals-glow-in-the-dark-to-lure-prey-israeli-researchers-find/

#22

Wiedenmann, J. (n.d.). [The deep-sea glow of coral]. Australian Geographic. https://www.australiangeographic.com.au/news/2017/07/why-do-deep-sea-corals-glow/

#21

Wiedenmann, J. (n.d.). [Glowing corals in the Red Sea]. Smithsonian Magazine. https://www.smithsonianmag.com/smart-news/deep-water-corals-glow-their-lives-180963967/

#23