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VIVO Corals 17 W hen I was diving and snorkeling in the Arabian Sea off the Oman coast a couple of years ago, I noticed the extremely high water temperature in late autumn. It was still around 32°C (90°F) in November. Such “bathtub temperatures” are usually fatal for stony corals, but in contradiction of what I learned the stony corals surrounding me were perfectly healthy. The water current also was ex- tremely weak, and the temperature was constantly high until more than 10 m (33 ft.) water depth. I was informed on location that the water temperature in midsummer was even higher for weeks and is supposed to reach more than 35°C (95°F) at times. Furthermore, temperatures regularly caused unbelievable densities of single-celled green algae that concentrate at the surface of coastal water so strongly that it be- comes impossible to see your own hand in front of your diving mask when snorkeling. It is said that there is a “red tide” besides this “green tide” during other seasons, plus very low tides that directly expose cor- als close to the coast to the desert sun for hours while they are sepa- rated from the water. Stony corals with the highest stress tolerance in the entire world probably live in this region of the Arabian Sea. Unfor- tunately, most corals in our aquariums do not have such capacities. We therefore must keep temperatures within narrower limits. There are often actually the same coral species as in Asia or the Arabian Sea, but their zooxanthellae possibly belong to different species. The idea behind the symbiosis is: The animal partner supplies the light requiring herbal partner within its tissues with nutrients and compounds that arise from its heterotrophic metabolism (ammonium, CO2 ). In return, the zooxanthellae within the animal tis- sues supply their host with oxygen and carbohydrates. However, the function of the zooxanthellae is not re- stricted to this: Their CO2 consumption (due to photo- synthetic activity) influences the calcium equilibrium in a way that calcium hydrogen carbonate, which is easily soluble in tissue water, precipitates as poorly soluble calcium carbonate. This is regulated by the animal component of the symbiosis, and precipitations of the calcium carbonate construction material only take place where the animal requires it for skeleton growth. The zooxanthellae must therefore permanently be moved. The even skeleton growth reveals how well this functions. There is an ideal temperature for every physio- logical process. Depending on the coral species and their environment, this ideal value is between 24 and 28°C (75 to 82°F). The cooperation gets under pressure especially when temperatures rise above approxi- mately 28°C (82°F). Under adverse conditions, the physiologically powerful zooxanthellae do not produce any oxygen anymore (other plants behave in the same way and stop their photosynthetic performance), but only process their carbohydrate supplies into CO2 (light-independent reaction, a breathing process that does not depend on light). This CO2 adds to the CO2 of the animal component of the symbiosis and presum- ably leads to hyperacidity within the tissues of the polyp. The polyp now in return puts the brakes on and expels most of its partner who now only generates CO2 and consumes oxygen. Coral bleaching is the result: the polyps appear pale, transparent and without color. Most of its herbal partner is now missing. However, a new population can be grown from the remaining zoo- xanthellae within the polyps in case the conditions im- prove. If the high temperature phase lasts too long, however, the coral cannot recover anymore and dies. Some corals already expel their zooxanthellae at 29°C (84°F) water temperature, others only at even higher temperatures or simply longer exposition. Such high temperatures in coral seas have occurred in suc- cession of El Niño. They have repeatedly led to massive damage and large-scale dying of coral reefs in the In- dian Ocean during the past 10 years. But it of course almost never happens that all specimens of a species die within a region, and so the survivors can spread via sexual and non-sexual multiplication. The survivors ap- parently have specific abilities or higher tolerance. Green tide Daymaniat Islands, Oman When applied together, sera marin COMPONENT 1 and 2 provide calcium hydrogen carbonate for stony corals in an aquarium. They are particularly easy to use.

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