A new NOAA outlook released to the media in June of 2016 indicates coral reefs around the earth will likely be exposed to higher thermal stress due to increasing sea temperatures for an unprecedented third year in a row. This will lead to increased bleaching worldwide, with no signs of the process stopping.
Coral reefs are very fragile and highly complex communities. They are currently at risk because of a phenomenon called coral bleaching. In a nutshell, coral bleaching is the loss of color in the relationship between algae and the coral. This happens when the algae is expelled from the body of the coral or from the loss of algal pigmentation.
Ocean service (NOAA) describes the relationship between the two:
Most reef-building corals contain photosynthetic algae, called zooxanthellae, that live in their tissues. The corals and algae have a mutualistic relationship. The coral provides the algae with a protected environment and compounds they need for photosynthesis. In return, the algae produce oxygen and help the coral to remove wastes. Most importantly, zooxanthellae supply the coral with glucose, glycerol, and amino acids, which are the products of photosynthesis. The coral uses these products to make proteins, fats, and carbohydrates, and produce calcium carbonate.
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In addition to providing corals with essential nutrients, zooxanthellae are responsible for the unique and beautiful colors of many stony corals. Sometimes when corals become physically stressed, the polyps expel their algal cells and the colony takes on a stark white appearance. This is commonly described as “coral bleaching” (Barnes, R.S.K. and Hughes, 1999; Lalli and Parsons, 1995). If the polyps go for too long without zooxanthellae, coral bleaching can result in the coral's death.
Because of their intimate relationship with zooxanthellae, reef-building corals respond to the environment like plants. Because their algal cells need light for photosynthesis, reef corals require clear water. For this reason they are generally found only in waters with small amounts of suspended material, i.e., in water of low turbidity and low productivity. This leads to an interesting paradox—coral reefs require clear, nutrient-poor water, but they are among the most productive and diverse marine environments (Barnes, 1987).
Queensland University of Technology coral researchers for the first time have captured the exact behavior of a coral as it’s bleaching. They have been able to show for the first time how coral removes the algae as a result of stress from heated water.
Science Bulletin reports:
“What’s really interesting is just how quickly and violently the coral forcefully evicted its resident symbionts,” said Mr Lewis, from QUT’s Science and Engineering Faculty.
“The H. actiniformis began ejecting the symbionts within the first two hours of us raising the water temperature of the system.”
Mr Lewis said previous studied had shown H. actiniformis was one of the very few corals on the Great Barrier Reef considered to be relatively resilient to bleaching, even as neighbouring species suffered the full effects.
“Our observations suggest this resilience could be due to the rapid expulsion of the coral’s algal symbionts during thermal stress, and could very well increase H. actiniformis’s chance of survival during abnormally high sea temperatures.”
From the study that was published in Coral Reefs (see page 20) titled Expulsion of Symbiodinium by pulsed inflation under hyperthermal stress in Heliofungia actiniformis:
Heliofungia actiniformis specimens were exposed to elevated water temperatures in a 10-L aquarium system for up to 8 d to encourage bleaching. An image was collected every 3 s. Temperatures were raised from 26 to 32 °C in the first 12 h and maintained at 32 °C (±0.5 °C) for the duration of the experiment. Within the first 2 h of exposure, H. actiniformis began expelling Symbiodinium from the tissue. A green plume of symbiont cells was expelled via the mouth during tissue inflation and contraction (Electronic Supplementary Material, ESM, Video S1). The intensity and magnitude of the pulses increased over a 55-h period, with coral tissue expanding up to 340% of its original state (Fig. 1b). Corals survived between 2 and 8 d under elevated temperature conditions. There was some degradation of the epidermal tissue during the later stages of the experiments.
Temporal sequence of pulsed inflation by Heliofungia actiniformis to remove Symbiodinium. a Acclimated coral at 26 °C. b Inflation maximum before contraction. c Contraction and expulsion of zooxanthellae. d Even after expulsion the corals often maintain a level of inflation. Scale bar 5 cm
This is alarming news for the health of our oceans, but the worst is still to come.
We are in the danger zone at this very moment. Every single fossil fuel molecule that we pump into the atmosphere is pushing us closer and closer to total biosphere collapse.
“Our H. actiniformis used a pulsed inflation to expel Symbiodinium over time (seen as greenish plumes in the video) – inflating their bodies to as much as 340 per cent of their normal size before suddenly and violently contracting and ejecting Symbiodinium through their oral openings over the four to to eight day duration of the experiments,” Dr Nothdurft said.
From the June 26, 2016 NOAA media release titled — U.S. coral reefs facing warming waters, increased bleaching:
While the bleaching event is global, it will hit the U.S. hard, especially in Hawaii, Guam, the Commonwealth of the Northern Mariana Islands, Florida Keys, U.S. Virgin Islands and Puerto Rico. The deeper reefs in the Flower Garden Banks National Marine Sanctuary, 100 miles off the coast of Texas in the Gulf of Mexico, are also in the crosshairs.
NOAA Coral Reef Watch finds there is a 90 percent chance of widespread coral bleaching in the Pacific island nations of Palau and the Federated States of Micronesia during the probable La Nina. La Nina conditions can cause high ocean temperatures in the western Pacific. NOAA is currently predicting a 75 percent chance of La Nina development this year.
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This third global coral bleaching event began in mid-2014 is ongoing. Global warming, coupled with an intense El Nino, continues to make this the longest and most widespread coral bleaching event on record. Since its onset, all U.S. coral reefs have seen above normal temperatures and more than 70 percent of them have been exposed to the prolonged high temperatures that can cause bleaching. Studies have shown that about 93 percent of Australia’s Great Barrier Reef was bleached as of this April.
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A bleaching event is not always a death sentence for corals. In fact, corals are remarkably resilient creatures. Just as a healthy person is more able to fend off a cold, healthy corals are more likely to resist large-scale stress like a bleaching event. Resilient corals that do bleach have a better chance of recovering if ocean temperatures return to normal relatively quickly and other human impacts are kept at a minimum.
