Photo Synthesis

Scleractinian corals in many forms

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Scleractinian corals, also known as stony corals — or just hard corals — are the primary reef builders in the oceans. Their polyps secrete calcium carbonate to form a skeleton. A minority of species live as single polyps, but most stony coral species are colonial, and the structures they build ‘grow’ over time. They form a myriad of shapes: mounds, branches, fingers, plates, and encrustations.

In several previous posts I discussed and displayed photos of a number of so-called soft corals, all of which are octocorals, i.e., their polyps have eight tentacles. Stony corals are hexacorals: their polyps have tentacles in multiple of six. Most seem to feed at night, so you are not likely to see the tentacles extended during daylight hours.

The coral in the first photo (top right) forms a rounded hemispherical head that is grooved in a meandering, maze-like pattern. Corals that form these kinds of colonies often are referred to as ‘brain corals’ because the patterns of the ridges and grooves are reminiscent of the sulci of a brain. The one pictured is Diploria labyrinthiformis, a species common throughout the Caribbean Sea.

Below is another example of a ‘brain coral’ — this one from the Red Sea. This species (Platygyra daedalea) forms massive colonies, sometimes more than a meter in diameter. Most brain corals belong to the family Faviidae.

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I mentioned above that some hard corals live as single corallites. Members of the family Fungiidae fit that description. Known by the common name Mushroom Corals, these are free-living, i.e., they are not attached to the substrate. The photo below is a macro image of Fungia scutaria, an Indo-Pacific species. This is the most common mushroom coral found in Hawaii, where this one was photographed. The overall shape of the corallite usually is oval, with septae radiating from a central mouth, as shown in the photo. The corallite can attain a width of 15 cm to 18 cm (6 in to 7 in).

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While hard corals all have calcareous skeletons by definition, the rest of their anatomy consists mostly of soft parts. Some of those can obscure the skeleton to the point that it is hard to tell, just by looking, that some species are indeed hard corals. A good example is Bubble Coral (Plerogyra sp.), shown in the next photo, below. The stalked corallites of this genus form rounded colonies. The skeleton of the colony is obscured during daylight hours by bubble-shaped vesicles. When this coral feeds, the vesicles deflate, and the tentacles emerge.

By the way, in this macro image you can see clearly that this coral is infested with little pancake-shaped critters. They are Waminoa flatworms. The photo was taken at Bunaken Island, Indonesia where much of the bubble coral seemed to be sporting Waminoa.

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Corals of the genus Goniopora seem to feed mostly during daylight hours. The polyps have 24 tentacles arranged in a way that makes them look like flowers. The macro photo below shows the clustered polyps of a Goniopora species from the Red Sea.

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A favorite subject with underwater photographers are the colorful members of the family Dendrophylliidae. They grow tubular skeletons topped by a cup-shaped calyx, so they are known by the common names Tube Corals or Cup Corals. Another common name is Cave Coral, a name that refers to this family’s habit of growing on the walls and roofs of underwater caves, and underneath ledges. Some members of the family are colonial, while others are solitary. All of them have gloriously colored tentacles, usually in shades of red, orange, or bright yellow.

I will close with two photos of a colonial Dendrophyllid species from Hawaii, Tubastrea coccinea. Both photos are of the same colony, located inside a small underwater cavelet, but taken at two different times. The first image was captured during daylight hours and the tentacles are retracted into the calyces.

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The final photo is a macro image of a polyp from the same colony as above, but this one was taken during a night dive. When their beautifully colored tentacles are extended for feeding, these corals are a sight to behold.

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I hope the readers of Photo Synthesis have enjoyed my underwater photos as much as I have enjoyed presenting them during the past month.

Comments

  1. #1 Lowell
    August 31, 2009

    Fantastic pictures. I have enjoyed every one of your posts this month. Thanks for sharing your photos.

    As a diver, I have observed much of what you shared, but I certainly learned a great deal from each set of pictures.

  2. #2 trailrider
    August 31, 2009

    Your pictures are wonderful as are your descriptions. Thank you.

  3. #3 Prem
    August 31, 2009

    This has been my first month following the blog and I quite enjoy it.

  4. #4 B. N. Sullivan
    August 31, 2009

    Thank you all. I’m glad to know you have enjoyed the photos (and the information).

    @ Lowell – Observant divers are continually learning new things about what they see underwater. We (divers) never seem to run short of new revelations.

  5. #5 Alex
    September 1, 2009

    You’re leaving already? That’s a shame- I’ve really enjoyed the photos as well as the commentary.

  6. #6 B. N. Sullivan
    September 1, 2009

    Hi Alex – Thanks, I’m very glad to know you enjoyed the photos and the info. It’s time to give someone else a turn here, but you can always see more of my photos and marine critter info at my blog, The Right Blue. ;-}

  7. #7 Size
    September 3, 2009

    I have very much enjoyed your photos. Thanks for sharing them!

  8. #8 Ken Kryszak
    September 4, 2009

    Great pics!
    Questions; The pics of the brain corals are in the retracted state? What do they look like in the active extended state?
    What is the purpose of the bubble coral’s bubbles?

    Thanks,
    Ken

  9. #9 B. N. Sullivan
    September 4, 2009

    @ Size Thank you. I’m glad to know you enjoyed my photos.

    @ Ken Kryszak – The tentacles of the ‘brain corals’ pictured in this post are indeed retracted. They reside in — and at night they protrude from — the ‘valleys’ between the raised ridges. When the tentacles are extended, the whole coral head has a sort of furry appearance.

    Regarding the bubbles, as I understand it, they are believed to serve a light-gathering role. The surfaces of the vesicles are populated by zooxanthellae, which produce nutrients through photosynthesis (some of which benefit the coral). By definition, then, they need exposure to light. Inflation of the vesicles during daylight hours provides more surface area for available light to reach the zooxanthellae.

    The bubbles are a curious adaptation, but they do make for interesting photos.

  10. #10 Adrian Thysse, FCD
    September 6, 2009

    Thanks for a great month of interesting facts and photography. The closest I get to underwater photography is through the glass of an aquarium.

  11. #11 B. N. Sullivan
    September 9, 2009

    Thank you, Adrian. BTW, I wouldn’t apologize about taking pictures through the glass of an aquarium. That’s not as easy as some might imagine!

  12. #12 metin2 hileleri
    May 8, 2010

    Great pics!
    Questions; The pics of the brain corals are in the retracted state? What do they look like in the active extended state?
    What is the purpose of the bubble coral’s bubbles?

    Thanks,
    Ken

    very icei

  13. #13 metin2 hile
    July 27, 2010

    Regarding the bubbles, as I understand it, they are believed to serve a light-gathering role. The surfaces of the vesicles are populated by zooxanthellae, which produce nutrients through photosynthesis (some of which benefit the coral). By definition, then, they need exposure to light. Inflation of the vesicles during daylight hours provides more surface area for available light to reach the zooxanthellae.

    The bubbles are a curious adaptation, but they do make for interesting photos. thanks…very nice post admin

  14. #14 video
    January 5, 2011

    Thanks for the constructive feedback :) regarding the Overworld limitations and linearity, I only felt it limited in the sense that you aren’t truely able to ‘explore’ fully in the way that could in other Zelda games – remember the underground caverns you could once find? – and quite frankly I miss that and it is basically linear in the sense that your destination is already chosen, yes you are still exploring and in a wonderful new way but this Overworld ‘Transport’ also highlights the limitations of what Nintendo can do with a 3D Zelda game on the DS but what they ‘have’ achieved is still impressive and I do acknowledge that fully.