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Bird's Head Seascape > Biodiversity > Warming Waters Trigger Coral Bleaching in areas of Raja Ampat
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Warming Waters Trigger Coral Bleaching in areas of Raja Ampat

30 Dec 2024
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Warming water temperatures in West Papua’s Bird’s Head Seascape, especially in the Raja Ampat region, have initiated a significant coral bleaching event in certain areas.

“Hope and Despair”: Bleached and unbleached coral in Raja Ampat

What is Coral Bleaching?

Coral heads or coral bommies, are comprised of individual coral polyps, 1000’s of them, all living together and forming a colony.  Coral polyps prefer stable conditions. When corals are stressed by changes in conditions such as temperature, light, or nutrients, they expel the symbiotic algae, called zooxanthellae (a single-celled dinoflagellate), living in their tissues, causing them to turn completely white.  Hence the term “bleaching”. If conditions return to normal within a certain (variable) period of time, the zooxanthellae re-colonize the coral polyps and all is well.  Without the zoonanthellae, which supplies most of the coral’s nutrient intake, the coral polyps will eventually die.

The present problem facing Raja Ampat’s corals is warming ocean temperatures and corals are fussy about the temperature of the water in which they live. Some cool water corals are happy with water temperatures of around 18°C/64°F, while lots of tropical corals, like Raja Ampat’s, live in waters with temperatures between 23 and 29°C/73 and 84°F. Some, like those in the Arabian Gulf, can experience temperatures up to 34°C/93°F or more.

Although most corals can cope with higher temperatures for short periods of time, they don’t like it if temperatures stay high for long periods—a coral that lives in 27°C/81°F  water may cope with the water being 29°C/73°F for a day or two, but wouldn’t like to be in 31°C/88°F for a week.

During past warming events in 2016/17, 2021, Raja was mostly spared from bleaching due to the numerous currents that converge and intermingle in the region. Some of these currents cause upwellings of cooler water, which keeps the coral polyps healthy.  This present warming event, however, appears to be more serious and has the potential of lasting longer than previous ones.

What does this mean for Raja and its magnificent coral reefs? Honestly we won’t know for a while; potentially a few months.  But if current predictions continue (see NOAA Heat Stress map), this event could cause significant damage in some areas.

NOAA’s Coral Reef Watch Regional Heat Stress Map for West Papua.  These maps track and predict water temperatures over time and any region of the world can be monitored via NOAA’s maps.  To give you an idea this is a screen shot of the NOAA’s map for West Papua as of today (note that if you do your own search the map will look different virtually every day).  This screenshot is from December 8th.

My intention with the remainder of this post will be to provide all concerned with an overview of the current conditions and how you can potentially help.

We have received reports from numerous areas of Raja Ampat.  While some areas, especially in northern Raja Ampat, show significant bleaching, others thankfully remain virtually untouched.

*A December 13th report from Misool Resort (Misool is in southern Raja Ampat):

“We have also heard about the bleaching event taking place in North Raja Ampat at the moment, it’s really unfortunate. One liveaboard sent us a WA message on the 5th of December, informing us that a huge percentage of corals were bleached across numerous dive sites in the Dampier area, also stating that the water temperature was ranging around 31°C/88°F.

We, of course, are never in that area to see for ourselves, however, we immediately experienced the rippling effect of 28 liveaboards all coming to the Misool Marine Reserve to find their guests alternative options. This began on the 9th of December.

We haven’t see any bleached corals, though there is a leather coral in the shallows under our bridge that is showing signs of being stressed. We have also received one photo of a soft coral in Gorgonian Passage that appears to be quite a faded pink. Besides this singular report, we are waiting and hoping that we will have a better outcome here than in the north.

The water is very warm, running around 29°C/84°F at least. With the full moon, we are also receiving big tides that are keeping the corals in shallow waters exposed for a few hours in the morning the past couple of days.”

Reports from northern Raja Ampat:

*On December 14 and it was reported that areas around Gam Island, specifically at the site known as Gam Hole, show no visible bleaching, despite temperatures ranging from 30°-31°C/86°-88°F.  Interestingly this area is shallow and the water is always warmer than the outside reefs.  This likely indicates that the corals there are more resistant and more tolerant of temperature variations

*A marine biologist just back from Wayag Island (Dec. 10), states there was no evidence of bleaching in that area.

*The Yenbuba area, in the Dampier Strait between Kri and Mansuar Islands, is showing significant bleaching.

The following report is from the Dampier Strait area of Raja.  This report is provide by Arno Brival of The Sea People. Their Yaf Keru Reef Restoration Program is “one of”, if not THE largest, coral restoration programs in the world. And it works!  Arno is based on north Mansuar Island near Yenbekwan village.

The Alarming:

– This is the largest event we have seen to date. Bigger in scale than the ones of 2021 and 2016/17.  So this is scary!!!
– Several reefs, including monospecific deep water ones, are fully or near fully bleached.
 – There is a strong fear or Evidence appears to indicate that the most frequented sites will suffer more severely from bleaching events, mostly due to the accumulation of     localized pressures (sunscreen usage, fin breakage, nutrification from inadequate waste disposal, disease spreading, overly stressed reefs, etc.) while at the same time dealing with global warming.
– Still quite unclear of how long it will last.

This mono-specific deep water reef is more bleached than in past events

The Hope:
– Water has cooled a bit around the Dampier strait over the past few days with current hopes that we may have past the peak and that water will eventually cool down in January.
– Some corals are showing no signs of stress and remarkable resilience after several months of overheating – signs of natural adaptation.  Raja Ampat still has a fantastic array
   of  positive feedback loops and ecological functions supporting both resistance, resilience and recovery:
  • Large and diverse populations of grazers to control competing algae.
  • Large amount of planktonic food and strong currents providing a substantial alternative food source to corals whilst they don’t photosynthesis.
  • Corals are heterotrophs (an organism that doesn’t produce its own food) and it’s crazy to see all the predation strategies, the amount of available prey and how much they eat around here, especially at night.
  • Many regions of Raja Ampat are swept by strong currents and a complex hydrology with deep water upwellings, alternating  tidal currents, etc., which provides regular water renewal and cold water refuges.
  • Alternatively, many creeks and shallow inlets can heat up remarkably.  Over geological time, they play the role of selecting and training grounds in the same way a scientist would test and select for the heat resistant species in a lab, but in this case it’s nature’s lab on a much larger scale and at no cost!
The Opportunity:
– Now is the opportunity to learn and distinguish heat resilient species and colonies from others in order to improve and adapt conservation and restoration initiatives.
– Provided that some/many coral survive this event, and provided that they are given enough favorable recovery time, which has been the case for the past three years since 2021, such events will train corals to become more and more heat resilient. The principle is that systems exposed to intermediate levels of disturbance tend to become the most diverse and most resilient systems.
– To inform and warn stakeholders (tourism, fishermen, and land owners) of the importance to maintain and sustain all ecological functions contributing to the resilience of the region, which include good water quality, fish stocks, abundance and diversity of seeding reefs, mitigation of over exploitation of popular sites, good diving skills and no sunscreen. This can be achieved by keeping land and islands forested, by improving wastewater systems, by advocating for good tourism practices, and by ensuring effective management of fish stocks and keystone species (grazers).
The Take Home Message:
– It is normal to feel powerless when confronted with such a global and generalized event. Yet, it is essential to understand that while none of us will be able to “turn down” the heat, there are still multiple levels where we, individuals, operators, regional custodians, and yes politicians, can act to minimize additional and cumulative local pressures which will further diminish the natural capacity of the reef to adapt to a changing climate.
– In other words, pressures are cumulative!  A reef may recover much faster if the grazers keeping the reef and substrate clean from algae while the corals can’t compete (because they are busy trying to survive and adapt to the heat). Without the grazers, reefs are more likely to shift to an alternative, less beneficial (to us) ecological state, such as a monotypic algal or sponge reef. (Same concept applies to eutrophication, the excessive introduction of nutrients, i.e. land fertilizers, waste water, etc.)
– Raja Ampat’s abundant reefs, its large and diverse genetic pool, along with its massive production of alternate coral prey species (eggs, worms, larvae, and all the zooplankton buffet), which provide nutrient sources during bleached phases, are a big source of its resilience.
– Other important factors include the strong currents, the complex topography, creating plenty of refuges, as well as training grounds for coral to survive or adapt to bleaching events.
– Nature is often underestimated, but often tends to surprise us when left undisturbed.  How strong and adaptive could it even become if we started supporting it?

Stylophora colonies are among the first to bleach but can withstand bleaching for the longest period of time. They were never this white during previous bleaching events. Mortality is expected if waters don’t cool down!

What Arno and The Sea People are Doing Today:
At the moment, The Sea People are NOT transplanting corals, as they strong advocates of not “planting trees in a forest on fire”.  Rather they are focusing on monitoring, capacity building and are also trying to come up with lists of resilient versus non-resilient corals.  These lists will be invaluable to scientists, future researchers and those involved in restoration projects as we are faced with more frequent events.
It’s not as simple as a resilient species versus sensitive species list.  We are making fascinating observations seeing at times, the same colonies (or at the very least very closely related phenotypes) react completely differently to bleaching (part resisting, part under stress). Also, some species are currently looking like they are having a very challenging time now, and it is possible they are opting for a Phoenix strategy (die and quickly revive) over a resist and survive strategy.
How YOU, Your Liveaboard, Resort or Homestay Can Get Involved:
Arno has set up a short survey in GIS that is quick to fill in, and results will provide a geo-spatial map of bleaching when data compiled.
NOTE: The success of this survey depends on YOU and your liveaboard, resort or home stay, submitting the data! Get involved!!
GIS survey link here.

The way it should be! Multiple species of healthy corals provide the substrate for a swirling mass of fusiliers.

 

 

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