Home Environment A coral banquet: Nocturnal feeding

A coral banquet: Nocturnal feeding

Who can say that they have ever observed stony corals getting in a sort of "hunting fever?" The role of corals as an important predator in the reef is mostly unknown. Food acquisition at night remains mostly obscured to divers, and the naked eye of the beholder, due to the microscopic size of the coral’s prey and the light-sensitive (or photophobic) response of the polyps to disturbance from the divers’ torch.

 
Quite commonly known is the mutual symbiosis between reef-building corals and single-cell algae (zooxanthellae) thriving in the tissues of the polyps. These algae are responsible for the colouration of the coral; and supply carbohydrates (organic carbon compounds) to the corals in exchange for nitrogen and phosphorus. Also, the zooxanthellae facilitate limestone precipitation of the coral by removing CO2 from the polyps’ tissues. Most corals are virtually inactive during daytime displaying retracted polyps. However they have an army of unicellular algae working for them all sunlit daytime long and performing photosynthesis, although it would seem inconspicuously.
 
This is the general appearance of stony corals that divers and snorkellers are well familiar with. Some observant divers may also have studied corals during their active feeding phase at night: A lawn of polyps moving their heavily armed tentacles with the water, each of them furnished with myriads of stinging cells. Thus, at night the corals have little in common with their appearance during daytime and pose a deadly threat for plankton organisms such as crustacean, mollusc or fish larvae. Indeed all these potential prey organisms run the danger of being pierced and narcotized, or stuck at a touch of the hostile tentacles.

The tentacles transfer the captured food directly into the “stomach” (gastric cavity), where it is decomposed except for the indigestible parts (skeletons, shells) and where nutrients are taken up (reabsorbed) by the “stomach wall”. After the meal, the polyps egest the indigestible remains through the mouth opening. In this fashion, innumerable populations of corals are filtering tons of plankton out of the water night by night, while we are basically unaware of it. On the next morning, usually nothing is left over to provide evidence of the precedent nocturnal feast.

In one instance, however, a different situation was encountered: In a particular morning in spring we saw a lot of coral colonies seemingly covered with “needles”, resembling a hedgehog. What had happened? An unusual nocturnal banquet of the coral community appeared to be responsible for the traces still visible on the
next day.
The event had obviously been triggered by a mass occurrence of tiny wing snails from the plankton; pteropods, in scientific terminology. This group of snails comprises species with various forms of shells, or without any shell, and with a foot reshaped to some sort of wing.

What we observed was that the majority of polyps still had the elongated shells stuck in their mouths with the thicker end of the shells inside. Perhaps the polyps had not completed their meals yet or they encountered some problems in finally ridding themselves of the bulky snail remainders over 1cm in length.

Most of the observed coral colonies riddled with “needles” were representatives of the honeycomb and brain corals (family Faviidae). These corals mostly exhibit larger polyps with larger mouth apertures. So just in case you happen to observe a coral during your dive that looks a bit like a hedgehog, you will know now what it is all about!

 

 


 

 

Read More in H2O


egypt%2011.jpg
Coming back from the southern dive sites of Dahab in the afternoon, driving with the car over the last hill, looking down to the lagoon with its
padi-0.jpg
September 17th is the 20th Anniversary of International Cleanup Day. Once again, SCUBA divers around the world will join in and contribute to make
foto1giftun.jpg
The Drums of Battle: It all started with a news item appearing on Egyptian TV in the first week of April. A major investment was being proposed to
Banner

Coming Issue

 

Next edition in English

    next English issue will be available in March  ...

Calendar of events

February 2019 March 2019
Su Mo Tu We Th Fr Sa
1 2
3 4 5 6 7 8 9
10 11 12 13 14 15 16
17 18 19 20 21 22 23
24 25 26 27 28
Post Your Event Post Your Event

More Articles

CORALS RESTORATION

There is no doubt that every skin diver enjoys the magnificent abundance of life on the coral reefs. The sad fact is that this extraordinary ecosystems are under the constant threat of destruction all...
Read More...

SS Maidan's secret revealed !

If you think there are no more secrets hiding in the deep waters of the Red Sea you are mistaken. Many rumours as to the whereabouts of the wreck of the British Steamship Maidan have circulated amo...
Read More...

Shearwater GF and VR3 - Technical dive computers

Technical diving is an extreme sport within the diving world, and like any other activity, the people who push their sport to the limit demand better and better equipment, which can deal with their ex...
Read More...

A LEGEND IS BACK IN TOWN "THE MISTRAL"

Older divers will remember the nostalgic days of the original twin house regulator and anybody who used to watch the Jacques Cousteau Saga’s on television will be familiar with it. The good...
Read More...

SOFT CORAL IN MEDIUM FORMAT

Every time I’m back from one of my trips in the hot and clear waters of the Red Sea, the colours of the alcionarian remain in my eyes and memory for days; they are certainly the most fascinating li...
Read More...

H2O Newsletter


Get diving news, trends, and business information delivered directly to your inbox!

Advertisement

Banner