Corals have been observed and studied from depths of 40 to 2000 meters. There are extensive reefs found at 300 – 500 m on the continental margin. Found in the Gulf of Mexico, Norway, off Brazil and so many other places.
Phylum Cnidaria and the class Anthozoa. Anthozoa is broken down into two subclasses Octocorals (Alcyonaria) and Hexacorals (Zoantharia). Octocorals are soft corals such as sea fans. Octocorals contain eight body extensions. Hexacorals include sea anemones and hard bodied corals. Hexacorals have six body extensions. Most deep-water corals are hard corals, but like tropical coral systems, soft corals are also present.
Coral Polyps
Corals are made up of units called polyps. They are kinda an individual unit, but have a connection to other polyps. Hmmm…, forget what I stated about them being individual units, although sea anemones are individuals units. And some coral have single polyps. Okay, now I’m just confusing myself. Corals, most corals, are considered colonies of polyp unit. They are connected, by tissue called a coenosarc.
Coral use symbiotic algae, zooxanthellae, to get energy from Sun. The also use their tentacles to feed. Hard corals form the main structure of coral reefs systems, providing lots of habitat for other organisms.
is represented by the lowest line in this image.
These polyps are connected by tissue called a coenosarc.
a brain coral. Both photos are from shallow water Belizean reefs.
- Found in colder water
- No zooxanthella – little sunlight here
- Single polyps can be huge
- Very slow growing, even for corals. Maybe up to 25mm a year but usually slower.
Back to the Deep
The most widespread deep-water coral is Desmophyllum pertusum (once called Lophelia pertusa). This species has been known for some time, it was described by Linneaus in 1758. But knowing of the species and knowing about the species are two different things. Deep-water corals are hard to study, because, well, they are deep. But finally, mostly in the last 20 years, these hard to reach organisms are being studied more extensively. Desmophyllum pertusum reef systems, in Norway, are some of the most extensively studied.
Now, there is easier, but still expensive, access to the deep-sea. And the more exploration that is done the more reef systems we seem to discover, and many more species are described. But we are still lacking such basic knowledge as specifics foods consumed (there are suspension feeders so we have some idea), life cycles, and such like.
have caught up with and bypassed those of tropical corals.
There must be much more to find. (From Cairns 2007).
- About 3300 species have been discovered (worldwide).
- May live a long time, off Hawaii a colony of Golden Coral is thought to be 2742 years old.
- The reefs themselves, may be 40,000 years old.
- Some reefs are long, 40 km.
- The corals can be huge, tower to 10 m
- How deep; 40 m to 2000m
- Cold temps, down to 4C
- Found where current flow, bring food.
Some of the most common species:
Desmophyllum pertusum (Spider Hazards)
Most common/widespread deep-water coral.
Originally described by Linnaeus as Madrepora pertusa in 1758. Then swapped to the genus Lophelia in 1849, but that group of animals had already been described as the genus Desmophyllum in 1834 so the genus was swapped back to Desmophyllum (relatively recently so many paper still use Lophelia) were it currently sits. Isn’t taxonomy fun.
One of the most studied species, this organism can feed on very large, for a coral, animals, with observations of a large, 3 mm, copepod in its gullet.
From the paper of Strömberg and Östman 2016.
Widespread: Mediterranean sea, Arctic, Atlantic, Antarctic.
What else do we know about this species…not much.
Dominant species on Pacific Sea mounts.
The closeup of at the bottom is from NOAA.
Observed on some very large reefs in New Zealand, 40 m high, 700 m long. Apparently this species is found in the southern hemisphere only.
Like their tropical counterparts deep-water corals provide structure, including hiding places, for other organisms, and thus make up the base of reef systems. These reefs, again like their tropical counter parts, are diverse.
These systems contain soft corals. Leiopathes glaberrima is a deep-water black coral, which is widespread. The group of corals known as black corals are called this because their skeleton (chitin) is dark colored, almost black. Two others soft corals observed are Primnoa resedaeformis, found in the well-studied reefs off Norway, and Paragorgia arborea, known as Bubblegum coral.
The large sponge, Geodia barrette. Is common among these reefs. It can reach a diameter of over 1 meter.
The bivalve Mollusks, Acesta excavatea and Delectopecten vitreus reside among these deep systems. The second is a widespread scallop species, with that name, it’d better be delicious. The first is shown below.
Live on the substrate, and attache to it. Thus it would be referred to as a mussel in the common tongue.
Aside:
In the common vernacular:
Clam: Live within substrate (mud usually). Shell are nearly mirror images of each other
Mussel: Live on top of substrate, and attach to it. Shells nearly mirror images.
Scallop: Live on top of substrate, do not attach to substrate. Shells are not distinctly different.
The Big Question
How will these species and associated reefs, deal with changing currents, warming waters, pH, and salinity drops, brought on by climate change?
Some work has been done to start answering these questions. Our most widespread friend, Desmophyllum pertusum, was found to tolerate temperature changes pretty well. However, in another study, the species Solenosmilia variabilis, did not do so well when pH was altered (see the Dorey et al 2020 article on the temperature study and the Gammon et al 2018 article for the details on pH).
These studies are just a beginning to exploring these problems so let’s wait until we reach our final conclusion on their susceptibility, or not, to temperature and pH changes.
Last note:
I hope you caught the image with snails on it. What is that species crawling over the top of that deep-water coral?
Citations
Addamo AM, Reimer JD, Taviani M, Freiwald A, Machordom A (2012) Desmophyllum dianthus (Esper, 1794) in the Scleractinian Phylogeny and Its Intraspecific Diversity. PLOS ONE 7(11): e50215. https://doi.org/10.1371/journal.pone.0050215.
Alcock AW. (1902). Report on the deep-sea Madreporaria of the Siboga-Expedition. Siboga Expeditie. 16a: 1-52, pls. 1-5., available online at https://doi.org/10.5962/bhl.title.11383.
Allard, Karel & Carricart-Ganivet, Juan P. & Moore, Michael & Barr, Brad & Lawson, Jack & Deyoung, Brad & Rothfels, Mary & Kenchington, Ellen & Mageau, Camille & Hart, Dvora & Loder, John & Alvarez Torres, Porfirio & Scanlon, Kathryn & Fogarty, Mike & Zavala-Hidalgo, Jorge & Joyce, Terry & Vanderlaan, Angelia & Kulka, Dave & Deegan, Linda & Hernandez, Alvaro. 2010. Report of the Study Group on Designing Marine Protected Area Networks in a Changing Climate (SGMPAN).
Cairns, SD. 2007. Deep-water corals: an overview with special reference to diversity and distribution of deep-water scleractinian corals. bulletin of marine science, 81(3): 311–322.
Cairns, S.D. (2009-2017). On line appendix: Phylogenetic list of the 711 valid Recent azooxanthellate scleractinian species with their junior synonyms and depth ranges, 28 pp. In: Cold-Water Corals: The Biology and Geology of Deep-Sea Coral Habitats. Cambridge University Press, Cambridge.
Dorey N, Gjelsvik Ø, Kutti T and Büscher JV (2020) Broad Thermal Tolerance in the Cold-Water Coral Lophelia pertusa From Arctic and Boreal Reefs. Front. Physiol. 10:1636. doi: 10.3389/fphys.2019.01636
Duncan PM. 1873. A description of the Madreporaria dredged up during the Expeditions of H.M.S. 'Porcupine' in 1869 and 1870. Transactions of the Zoological Society of London. 8: 303-344, pls. 39-49.
Gammon MJ, Tracey DM, Marriott PM, Cummings VJ, Davy SK. 2018. The physiological response of the deep-sea coral Solenosmilia variabilis to ocean acidification. PeerJ 6:e5236 https://doi.org/10.7717/peerj.5236
López Correa ML, Freiwald A, Hall-Spencer J, and Taviani M. 2005. Distribution and habitats of Acesta excavata (Bivalvia: Limidae) with new data on its shell ultrastructure. 10.1007/3-540-27673-4_9.
Rogers A. 2018. The Biology of Seamounts: 25 Years on. Advances in Marine Biology 79: 137 – 224.
Strömberg, S and Östman, C. (2016). The cnidome and internal morphology of Lophelia pertusa (Linnaeus, 1758) (Cnidaria, Anthozoa). Acta Zoologica. 98. 1 – 23.