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--> IYOR-Exhibition at RSEC in Dahab: Coral Reefs – a Paradise in Danger --> Reef Check Safari with Sinai Divers MAY 8-15 2008 - Places left - join now! --> Reef Check Receives Prestigious Award from German Diving Magazine --> New in Dahab: Fluorescence-Nightdiving -->Dahab Reef Monitoring 2007 - Short report from our Volunteers -->Extreme low tide caused coral death at South Sinai’s coast-->Banquet for corals: Nocturnal feeding with planktic wing snails on the menu |
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Coral Reefs – a Paradise in Danger Coral reefs belong to the most beautiful habitats nature has created. It is a paradise, which attracts numerous divers and snorkellers every year. It is a fascinating world with schools of colourful fish, enormous blocks of diverse corals, which provide shelter and food for countless species of coral reef inhabitants. Coral reefs belong to the most complex ecosystems of our world. They are not only of great importance for tourism, but also for fisheries, coastal protection and climate development. Nowadays, coral reef habitats are endangered due to anthropogenic factors and destruction and more than 20% of the coral reefs worldwide have been largely destroyed already. We are looking forward to meeting you! |
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Red Sea Reef Check Safari with Sinai Divers MAY 8-15 2008 - Places left - join now! http://sinaidivers.com/english.htm --> Live-Aboards --> Routes, prices & dates
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Reef Check Receives Prestigious Award from German Diving Magazine One of the leading German magazines for recreational divers, tauchen (=diving), celebrated its 10th year with an award ceremony on January 24 in Düsseldorf at the "boot 2008", the most important European watersports fair. Each year the magazine awards the best products, dive centers, and tour operators. Submitted by Georg Heiss |
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New in Dahab: Fluorescence night diving Get great night dive experiences with the reef gleaming in bright fluorescent colours! RSEC in Dahab offers now Fluorescence night diving with specific flashlight and filter glasses. See corals and other animals in an extraordinary way. This guarantees a thrilling night dive and is a must for every diver. Fluorescence night diving is also integrated in our reef biology course program. |
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Dahab Reef Monitoring 2007 - 17.8.- 8.9.2007 Scientist Christian Alter from the Red Sea Environmental Centre (RSEC) in Dahab has designed a reef-monitoring programme based on an extension of the standard Reef Check procedure. This extended Reef Check protocol, the ‘Dahab Reef Monitoring’, aims at a significantly higher resolution of both qualitative and quantitative information of selected reef areas. In short, the surveys on fishes and invertebrates, respectively, hold additional indicator species, and the substrate survey offers a diversification of over 30 categories. A forth survey, on coral damage, provides a comprehensive data set on coral injuries produced by natural causes (predation by coral-feeders) as well as human impact (breakage and abrasion). The survey uses volunteers for data recording. The volunteers are trained in identifying the indicator organisms and the different types of coral damage. The training for Dahab Reef Monitoring 2007 started on the 17th of August with presentation of the theory. The next day we practiced under water with training transects. On day three we had a test to see if everybody could identify the indicator organisms. Teams Authors: Julia Schnetzer / Nina Milton |
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1. Boot trip to Gabr-el-bint |
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2. Boot trip to Gabr-el-bint |
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| First transect | ||||
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| Volunteers at the final exam | ||||
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| Transect overview image | ||||
Extreme low tide caused coral death at South Sinai’s coast Tidal events belong to the most predictable natural fluctuations in coral reef habitats. They determine intertidal zonation patterns and limit the vertical growth of corals, but are rarely reported to cause mass mortality among corals. Corals are reported to tolerate a certain time of aerial exposure while enhancing mucus production to prevent desiccation. However, the combination of extreme low tides and high solar irradiances has the potential to cause widespread damage among corals. A report from the Great Barrier Reef reveals 40-75% of corals on reef flats were either bleached or suffered partial mortality from such an event. We observed a similar phenomenon on reef flats in Dahab at the end of March this year and assume an additional factor has contributed to the coral mortality during this event. Within four days (March 19-22), absolute calm conditions coincided with extreme low tides and high solar irradiances. Moderate to strong wind speed would produce waves, surf and spray which may prevent corals from drying out and decrease the effect of strong insolation. We observed the coral mortality on reef flats of various sites in Dahab. Most likely this natural disturbance affected the whole coastline of the Gulf of Aqaba. Many of the smaller coral colonies were killed completely whereas most of the larger ones only suffered partial mortality. It seems that coral tissues disintegrated and formed shreds hanging from the coral before getting washed away. First, the wall of coral skeleton became visible while tissue was still left inside. Understandably, the upper portions of colonies affected were more heavily damaged. Coral bleaching, in the sense of corals having ejected their symbiotic algae while retaining their elsewhere intact tissue, was not observed. Partly affected colonies certainly are able to recover to a certain extent but have to struggle against algae quickly taking possession of any part of stripped skeleton. After one week all the affected colonies were tinted in shining dirty yellowish-green hues covering the white witnesses of this event. We estimate the natural damage to coral colonies on the reef flat to be in the order of 25-75%. The first survey we did after the event revealed a mortality of 50 % at a known reef site south of Dahab. Author: Christian Alter |
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| Aerially exposed coral colony (Pocillopora verrucosa) on the first day | ||||
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Affected colony (Platygyra daedalea) on the second day. Bare skeletal parts are clearly visible on the upper part.
All photos by Christian Alter |
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| After one week, the bare skeleton of affected colonies is covered with green algae | After 2 weeks, a layer of algae covers the recently killed corals | Almost entirely killed colony (Pocillopora verrucosa) after three days | ||
Supplementary note: We wish to underline that the observed decimation of coral cover has been caused entirely by natural processes. The observed phenomenon may not be distributed equally among reef flat zones due to natural variations in geomorphology and, thus , various degrees of exposure. The observed event and its assessment described in this article is restricted to relatively shallow reef zones. However, the observed decimation may not be very obvious and only recognized by trained persons. Anthony, K. R. N. & A. P. Kerswell (2007) Coral mortality following extreme low tides and high solar radiation. Springer, Marine Biology, Vol. 151: 1623-1631. |
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Pocillopora verrucosa coral with revealed skeleton on upper parts at Masrsa Ghozlani, Ras Mohammed National Park, early april Photos by Georg Heiss |
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Banquet for corals: Nocturnal feeding with planktic wing snails on the menu Who has 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 photophobic/light-sensitive response of the polyps to disturbance from the divers torch. Quite commonly known is the mutualistic symbiosis between reef-building corals and single-cell algae (zooxanthellae) thriving in the tissues of the polyps. These algae are responsible for the coloration 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, though inconspicuously. This is the general appearance of stony corals divers and snorkelers are well familiar with. Some observant divers may yet 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 into danger to be pierced and narcotized or stuck at a touch with 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 (resorbed) 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. |
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| A smooth brain coral (Platygyra lamellina) covered with shells of wing snails | ||||
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| Shells stacking in the openings of a rough brain coral (Platygyra daedalea) | ||||
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| Honeycomb coral (Echinopora gemmacea) with “needles” | ||||
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