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Panamanian Caribbean coral reef temperatures have been very hot in 2017 and have hovered near the bleaching temperature threshold almost all year.
Bleaching began around March, unusually early, but by June waters had cooled down below the threshold, and corals went into a bleaching recovery phase at that time.
Water temperatures rose again above bleaching thresholds later in the year, leading to predictions of a second bleaching event in a single year.
Fortunately a second bleaching event did not happen despite high temperatures, for a very good reason! It has been a very wet rainy season, with heavy rains almost every day, and the sky is grey with dense clouds, or black with thunderheads, with little or no blue sky, so there has been much less sunshine and light stress late in the rainy season compared to in earlier in the season.
In the 1980s my bleaching experiments with Jamaican corals at combinations of different temperature and light levels showed clearly that:
1) Bleaching took place only above a temperature threshold, showing temperature to be the prime trigger for bleaching.
2) Above that temperature, the rate of bleaching was proportional to the light level, indicating that high light level was a secondary factor for bleaching.
Peter Glynn independently did similar experiments in Okinawa, and found the same.
These experiments explained the clear effects of shading of corals on bleaching responses that we studied in the field in the first Caribbean-wide high temperature bleaching event in 1987, why a second bleaching event did not happen in Panama this year, and why the wettest tropics will be a major refuge for corals against global climate change, but only in areas free of direct human impacts such as deforestation, sewage, and agricultural chemicals.
In Jamaica, where high temperature stress was much less than Panama this year, about half the corals were bleached two weeks ago, much more than in Panama. Jamaica has much higher light than Panama, where the skies are grey through most of the rainy season. Belize, which suffered temperature stress between that of Panama and Jamaica this year, but whose climate is more similar to Jamaica, is predicted to have had more severe bleaching in 2017 than either Jamaica or Panama, due to its combination of thermal and light stress. There have been no reports of bleaching from Belize yet. It will be interesting to see if there was mortality there.
The protective effect of high cloudiness in the warmest time of year is uniquely related to the extreme vertical circulation of the equatorial atmosphere right up to the tropopause. When one flies over Panama or Indonesia in the rainy season there is no blue sky to be seen, even at 10 Kilometers height (30,0000 feet). These refuges are limited to equatorial reefs, and Panama, Colombia, and Indonesia are likely to be the most important. As global warming continues, these corals may have a unique chance of survival due to protection by local weather patterns.
It must be emphasized that these are NOT refuges because the corals are more “resilient”, they are refuges because they are lucky to suffer much less stress from high light, on top of high temperature. Many Australian and American coral “scientists” claim any location where corals survive have “resilient” corals, but they have simply been lucky to escape additional stresses for purely local reasons!
In Panama we have recently found two reef refuges with exceptionally high live coral cover, diversity, and health.
1) We have surveyed a reef with 30-40% live coral cover in shallow water right in front of the eastern end of the Panama Canal breakwater. This reef is not only at the high end for coral cover in the Caribbean today, despite a century and a half of severe disturbance from dredging and pollution, it now has higher live coral cover than when it was last studied in the 1980s, an exceptional circumstance! However it is imminently threatened by dredging for a huge new port that will be constructed only a few hundred meters from the reef! GCRA and our Panamanian colleagues will soon issue a report with photos and video of this reef, and recommendations for protecting it.
2) We have found a truly exceptional reef of global significance in the Guna Yala Indigenous Territories with even higher live coral cover. This reef is remote from human habitation, is free of weedy algae caused by high nutrients (and has no Diadema). The shallow reef is covered with huge intact colonies of elkhorn and staghorn corals of sizes and abundance that I have not seen in the Caribbean since the 1970s. They are growing on top of a layer of even larger intact dead corals of the same species and are clearly regenerating because the reef is free of algae and sediment. Also astonishing is the size, age, and ecomorphotype (phenotype) diversity of coral species, including vast numbers of huge ancient coral heads from 1 to 6 meters tall, and up to 8 meters across. Nevertheless the reef is being affected by black band, yellow band, white band, dark spot, and white plague diseases. These diseases have been declining across the Caribbean over the last two decades, as the most susceptible corals die, or as the disease becomes less virulent. The virulence of diseases at this site suggests that the pathogens have only recently reached the area, since most of the corals are healthy intact with only relatively small areas affected so far.
In the 1950s, Thomas F. Goreau, in a paper on gigantism in reef corals, emphasized the importance of exceptional and rare reef habitats where all the corals were huge and healthy. Jamaica used to have about half a dozen such locations, only one now survives in degraded form. This newly discovered remote reef in the Guna Indigenous territories may be one of very few places left in the Caribbean like this, and urgently needs to be protected. GCRA is preparing a photographic report on this extraordinary reef, and will train Guna marine resource managers to monitor and assess such remarkable sites.
Although Guna Yala has long been regarded as having some of the finest coral reefs in the Caribbean, there has been essentially no work on the best reefs. Peter Glynn’s magnificent work has focused on the completely different Panamanian Pacific reefs. The Smithsonian Tropical Research Institution had a marine lab for many years in westernmost Guna Yala. This was located in the most densely populated area of the Indigenous Territory, where reefs have been in poor condition since the 1980s due to severe algae overgrowth of the corals caused by raw sewage. The Gunas threw the Smithsonian out because American coral researchers removed big corals without permission and then arrogantly treated the Gunas as ignorant natives who should mind their own business. As a result, the good reefs in Guna Yala have never been studied, and diving with tanks is strictly banned by the Gunas. There is therefore a crucial need to establish Guna coral reef monitoring, restoration, and protection efforts for these refuge reefs of global importance. There have also been Biorock coral reef restoration projects in Guna Yala for 21 years, which are doing well, and will soon be expanded.
As the current La Niña sets in, Indonesia and Australia are expected, from the well known El Niño Southern Oscillation teleconnections, to leave the “cold” phase they have been in during the long extended El Niño that is just over, and to enter the “warm” phase this southern summer. Already these areas are unusually warm, and there is therefore a strong likelihood of even more severe bleaching in 2018 than in the last three years. It will be very important to identify the major coral refuges in Indonesia that are protected, like Panama, by high clouds in the warm season.