Emergency Response to Mass Coral Bleaching

I visited Christmas Island, Kiribati from 8- 15 June 2016 at the request of Mr. Taratau Kirata, head of the Government Fisheries Department for the Line Islands, Kiribati. The purpose of the trip was to assess the condition of the reefs after the major warm-water coral bleaching that had hit the reefs in 2015-2016 during the severe El Nino weather event and to investigate the need for restoration of the coral populations.

Christmas Island (spelled Kiritimati and pronounced Ki-ri-si-mas), is the largest of the Line Islands, which is composed of nine islands or Atolls, three of which are US dependencies (Jarvis, Kingman and Palmyra), the rest belong to the island nation of Kiribati (pronounced Ki-ri-bas). The islands run Northwest-Southeast, with Christmas Island being the Southern most of the group.  Christmas Island, with a population of some 7,000 people, has the largest land area of any atoll on the planet (>400km²), about half the total land area for the nation of Kiribati.  The island is out of the cyclone belt, being very close to the equator, but is in a vulnerable area for repeating El Nino events.  Formerly Christmas Island had the highest coral cover and highest coral diversity of the Central Pacific, but the present disaster has severely impacted the island and has changed that status.

Christmas Island was in the center of the 2015-2016 global mass bleaching crisis, impacted by the strongest and most prolonged El Nino weather condition ever recorded. By June 2016 the bleaching had passed, and the bleached corals had mostly died, with very few recovering. An estimated 80-90% of massive and lobate corals have died on outer reefs, an estimated 98% of all corals are dead in the lagoon areas, and virtually all (~99.99%) branching corals are now gone overall.  This loss will undoubtedly have major ecological consequences over time, as the branching Acropora and Pocillopora corals are vital as habitat for small planktonivorous and post-larval reef fish. 

We searched extensively for three days in both inner lagoon and outer lagoon areas, reef front, and passes, over shallow dead former Acropora dominated zones of the shallow fore reef zone and the formerly staghorn coral dominated mid and inner lagoon, and we could find absolutely none of these corals alive. 

The corals of the inner lagoon certainly must have formerly been adapted to very hot water, but this event must have gone way over that threshold. In hindsight, if some of these thermally adapted corals had been moved from the hottest inner lagoon to the cooler outer lagoon, they might have survived this bleaching event unscathed. This is a possible lesson learned for other reefs preparing for unprecedented heat stress levels; to move the thermally adapted corals into less heat stressed waters, so that the bleaching resistant corals have a chance of surviving and passing on their superior qualities to help reefs adapt into the future, rather than allowing them to cook to death within enclosed lagoons, where under normal conditions only the strongest of the strong can survive.  

With the thought that the former populations of thermally tolerant corals of the inner lagoon might have already produced larvae that carried the traits for tolerance, and that these heat tolerant larvae might have settled in areas of less thermal stress, I began searching the cooler shallow reefs between the lagoon and the ocean, in the hope that some progeny of the exceptionally tolerant corals had settled and grown in that area of somewhat less stress and had therefore survived the mass bleaching. With this strategy, we did finally find a few surviving corals near the pass at Cook Islet. 

Pocillopora formerly dominated the outer lagoon reefs, with some colonies as big as a minivan, but we could find none of the species alive in the main outer lagoon area.  We finally found four Pocillopora colonies alive in shallow areas in the South pass; three very healthy colonies, and one half dead and still partially bleached colony, all of these corals were surrounded by dead corals of the same and other species.  This helps verify my hypothesis that the pass area remained cool enough for the few super tolerant corals which carry the resistance of their parents, while the same heat levels killed off all corals that were adapted to the cooler waters normally found there.  

In a 1M deep enclosed lagoon pool adjacent to shore at the Cook Islet Conservation Area, we found two small living branches of Acropora, part of a much larger dead colony.  We also found a 10cm, bright blue, juvenile Acropora coral in the adjacent enclosed bay, again near shore in an area that would be heat stressed during normal years. This coral must have recruited during or right before the mass bleaching.    

We were greatly relieved that the notorious coral-killing crown of thorns starfish were not seen, neither were the coralivorous Drupela snails.  However coral predation is a continuing concern.  After the 2000 mass bleaching in southern Fiji, coral predators succeeded in killing off virtually all of the surviving bleaching resistant corals within months.  The danger is that the major coral predators much prefer the branching Acropora and Pocillopora corals, but they can survive on the less favorable massive coral species when their preferred coral prey species are gone.

We set up a coral nursery in the area of the South pass, in a shallow (2 meters deep) area adjacent Cook Islet and within the no-take conservation zone, near where we had found the few surviving branchingcorals. We trimmed and planted branches from the wild corals and we were also able to pick up the rock that the juvenile Acropora had settled onto and bring that into the nursery.  We established four genotypes of Pocillopora, and one genotype each of two species of Acropora in the nursery.  The coral nursery is in an ideal area for observation and monitoring over time, has good water circulation so that it is ideal for coral growth, is well protected from storm surge, is predator resistant by design, and the area has a large population of grazing fish to keep it cleaned of algae.

Unless more Acropora and Pocillopora individuals can be found, there is very little hope of recovery of the branching corals on Christmas Island, as survivors will be too far from others of their species for successful spawning, and as no coral reefs exist up-current of Christmas Island.  Local extinction of several species of branching corals has most likely already occurred, but much more work is needed before drawing that conclusion.  Certainly if nothing is done to intervene, the possibility of recovery of the branching species appears to be quite bleak, in particular for the Acropora species.  Fanning Atoll is the nearest reef to Kiritimati, and although a few hundred kilometers up-current, is near enough to be considered the same ecoregion for restoration purposes.  No assessment has yet been done for Fanning Atoll.

What is needed now is a systematic project to search more systematically on Kiritimati and Fanning Atolls, with the goal of finding more surviving colonies of branching corals. These colonies should be marked with GPS for monitoring over time, and branches should be trimmed for inclusion in nurseries, which in time would become gene banks for recovery.  The goal would then be to propagate these corals into large “mother” colonies of each of the surviving species, to re-trim these corals twice annually in order to propagate many colonies of each coral genotype of each species and then to replant them back to restoration patches located on the reef.  The challenge would be to find at least two genotypes of each species, so that sexual reproduction, through successful spawning, can eventually be re-established. The end goal of the coral nursery work would be to establish genetically diverse patches of each coral species at key positions on the reef, so that coral larvae are once more produced in large numbers, restoring the natural process by which coral reefs recover.  It is impractical to replant large areas of reef, and really no need, once sexual reproduction is restored.

The proposed coral gardening strategy is a strategy that has potential to bring the branching coral species that have survived back from the brink of local extinction. We should go forward with a sense of urgency, realizing that all corals that have survived are in fact genetic treasures- they are “super corals”, proven by this crisis to be bleaching tolerant in hot water. These corals offer a thin ray of hope in the face of climate change, and they must be nurtured and protected, otherwise the coral reef is unlikely to recover to its pre-bleached condition- ever.  Urgent action is therefore needed for the conservation, propagation, and restoration of the bleaching resistant corals. 

If there is a positive side to this crisis, we now have a heightened level of community awareness that something is very wrong in the environment, especially among commercial and subsistence fishers in Kiribati, with the entire nation experiencing mass die off of corals, and so we have an excellent opportunity to educate communities to the impacts of climate change and sea level rise.

Communities should become involved at this stage, as the best way to urgently find the surviving corals would be to involve the wider community in searching for the branching corals during their fishing activities; to mark them with a small plastic bottle buoy, so that samples can be later taken and incorporated into the coral nursery by trained Fisheries staff. Additional involvement of community volunteers should also take place during the outplanting phase which would begin about two years later.

Funding for a major project is needed, and for at least five years if possible. Reports indicate that the main islands of Kiribati have also been badly affected by severe bleaching and coral death, so the project should become a national level one if at all possible.  Other affected island nations, such as Samoa, the Marianas, FSM, and Palau, where severe bleaching is presently occurring, might also want to be included in a regional project. 

This proposed strategy of bringing branching corals back from the brink of local extinction has already been effectively carried out in Belize, where bleaching and disease wiped out virtually all of the Acropora corals on the southern sector some ten years ago.  We successfully located the few surviving super corals, grew them within nurseries, and replanted them within the national park, restoring many acres, with over 60 thousand second and third generation corals replanted, restoring natural reproduction and recruitment processes in the wider reef system.  I have included a brief description of that work in an appendix at the end of the report.

A short report on our findings on Christmas Island has already been published in MPA News and has also been reported to the NOAA coral bleaching reporting network.

Acknowledgements:

Accommodation was kindly provided by Ereti Tekabwaia through the Tekabwaia lodge. Boat, fuel, nursery materials, and staff were provided by the Kiribati Fisheries Department.

• MPA News report on the Kiribati Project (DOC)