North-east parts of Indonesia going through a mild bleaching event

Unusual warm and wet weather got corals to mildly bleach in the coral triangle

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Most of the world-famous, and cherished reefs from North East Indonesia, from Raja-Ampat, the Banda-Sea, Moluccas, and Sulawesi, are going through a mild bleaching event.

A very wet ‘La Nina’ year!

This year ‘La Nina’ not only brought bad weather, with abnormal rains, and a very intense wet season, in all parts of Indonesia. Visibility has been dropping very low, on many of the popular Indonesian dive sites. It also brought high water temperature. Fortunately, the combination of high temperature with cloudy sky and reduced light intensity has a lower impact on corals. Nevertheless, still stress them.

A large colony of Acropora sp bleached among others not bleached, see the difference.

On the other hand, the very high amount of rain, and the consequent run-offs it generates, are a source of pollution and additional stress for the corals.

Unusual Sea Surface Temperatures:

The temperature has been unusually warm, with water temperature in the 30 C for a very long period of time. We don’t even remember when is the last time we had to use a wet suit. Normally in December – February, we should witness a drop in temperature. But the drop this year has been minimal. The temperature should drop in the mid-twenties, but it barely went lower than 30C. If the temperature were not crazy high. This unusually warm event lasted for a very long time, with higher water temperatures on a long period. And this long high temperature event had a toll on corals.

You can check Sea Surface Temperature (SST) in the coral triangle here: https://coralreefwatch.noaa.gov/product/5km/index_5km_sst.php

A mild bleaching event:

The bleaching event, is not major, with only in most parts 10-15% of colonies showing stress signs. Most colonies are also partially bleached, with only branch tips losing symbionts and color, or some other just getting slightly brighter. This is not very obvious to the untrained eye. That’s why we decided to write this post.

Even soft corals such as this Sclerophytum (Sinularia) flexibilis suffer from bleaching, note the pale branch tips.

It usually takes a while for the coral, to show signs of bleaching, but we expect corals in the southern part of Indonesia to start showing signs of bleaching around march. Right now they are still grinding it, and holding on to it.

Here a torch-hard coral, Euphyllia glabrescens partially de-colored and bleached

The good news?

The good news is that these mild events are actually good for coral adaptation, and scientists around the world, are witnessing more and more reefs, that actually changed symbionts. Using now zooxanthellae algae that adapted to higher temperatures. So these small events are actually a sign of stress but also a sign of adaptation. As we haven’t witnessed any mortality so far. We hope the corals will have the energy and time to get fully through this process.

The bleaching process is actually an adaptive process. Hoping that corals will have the time and energy to get that process fully through.

Monitoring these events and understanding the evolution mechanisms are very important. Being able to record such events, and their intensity is a part of our training. More information here: https://oceangardener.org/internship/

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