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What’s Worse or Corals Heat or Cold?


For the extinction of coral reefs, climate changes are the reason we all know. Measures are being taken o preserve them as far possible. But a recent study by in the coast of Western Australia by Justin Billis took the efforts to find out whether extreme heat or extreme cold was more injurious to corals. In both the cases corals suffer, either from freezing or burning off. Both the climate conditions need to be in equilibrium for corals to thrive and survive. Extreme rise in temperature during summer months have led to destruction of coral reefs and so has lowering of temperature beyond normal contributed towards vanquish of many coral reefs.

In this study, Melissa Roth, a marine biologist at the University of California, Berkeley, and some more researchers set out to investigate how corals’ reactions differ depending on whether they are subjected to hot or cold temperatures. Dr. Roth says that in order to study the different reaction corals show when subjected to the different conditions, it was necessary to try both the changes on them.

For the study, they separated individual branching corals into three factions. One of them was kept at normal, ideal temperatures, and the other two were subjected to extreme temperatures that of 9 degrees above or below the average for 20 days. As expected, both the corals with extreme temperatures showed negative effects. But the interesting fact was that they both showed different changes and at different intervals of time. In the first five days of the study, cold had caused more damage to the corals whereas damage to corals in extreme heat was noticed only after five days had passed.

This difference was credited to the responses of minute algal organisms called dinoflagellates, which supply corals with energy through photochemistry. Without them, branching coral cannot survive. The corals in return provide refuge to the dinoflagellates. When dinoflagellates are subjected to exceedingly severe temperatures or too much sunlight irradiance, this symbiotic system subsides, and the corals then turn down or die. The incident is what we generally call as coral bleaching.

In both the corals in extreme temperatures, dinoflagellate populations were reduced. But the heat-stressed coral dinoflagellates declined to less than 1 percent of their usual numbers, while the cold-stressed ones leveled off at around 40 percent of the normal population.

The heat-exposed corals, however, were found to be deeply stressed and the change was irreversible whereas the cold-exposed corals showed stabilization during the final stage of the experiment. This proves that corals subjected to extremes of cold can acclimate with somewhat slower growth rate and ill health that will take time to get normal but those in extremes of heat might not.

Dr. Roth elaborates that branching corals used in the experiment depend on dinoflagellate-driven photosynthesis for continued existence so corals that assemble their nutrition by catching plankton might possibly have a superior possibility for surviving extreme temperatures but only to a certain point. Too much heat will cause harm to any coral species.

The researchers were of the view that while a momentary decrease in temperature is unfavorable to coral health, extended increases in temperature would eventually be more detrimental. Around 86 degrees Fahrenheit they say is to be the grave verge for collapse between symbiotic coral and dinoflagellates. Scientists have found that certain waters, particularly those around the tropics, have the prospective to reach or surpass that verge.

Corals are getting affected by climate changes everywhere even if they are highly managed under proper conditions. In 2010, corals off the Florida coast experienced one of the coldest winters on record, while those off Indonesia suffered through one of the hottest summers. In both the places corals reefs saw damages and bleaching to a large extent.

Ocean acidifications and rise in sea level are other natural causes that are destroying many coral species. Coral diseases and pollution are no less in causing adverse effects. The scientists on this research conclude their experiment with the final words that said, “The best way to prevent all of this would be to reduce the potential for climate change.”