[Coral-List] BIOT coral bleaching event
douglasfennertassi at gmail.com
Fri May 1 19:56:49 EDT 2015
Thanks very much, Andy!!
Just to be clear in case anybody doesn't know, BIOT (British Indian Ocean
Territory) consists of the Chagos Archipelago, including Diego Garcia.
On Fri, May 1, 2015 at 5:35 AM, Andrew Bruckner <
Bruckner at livingoceansfoundation.org> wrote:
> Hi All,
> The following is a brief report of a recent bleaching event we've been
> following in the British Indian Ocean Territory.
> During recent coral reef surveys in the British Indian Ocean Territory
> (BIOT) conducted by the Khaled bin Sultan Living Oceans Foundation, we
> noticed a dramatic increase in bleaching and bleaching-associated
> mortality. On our first research mission (March 10-31, 2015) bleaching was
> rare; only a few isolated pale colonies were noted. Beginning on April 15
> we started to see a high number of table acroporids that were pale to
> yellow in color, and partial bleaching (mottled and pale colonies) on other
> corals. Over the next week bleaching increased substantially on table
> acroporids, with over half showing signs of bleaching. Completely bleached
> colonies of Pocillopora, small digitate acroporids, Seriatopora and other
> smaller corals were also common in shallow water, and several genera, such
> as Stylophora, displayed bleached branch tips. By April 25, most of the
> table acroporids (especially A. cytherea) above 15 m were white, light
> yellow or light blue, while fewer (20%) deeper colonies were bleached.
> Numerous other corals, especially Lobophyllia, all of the fungiids, most
> acroporids, Stylophora, Symphyllia and Goniopora were various fluorescent
> shades of blue, yellow or green; many massive corals, such as Galaxea and
> Pocillopora, numerous genera of faviids, hydrozoan corals (Millepora) and
> certain anemones were stark white. Bleaching has continued to increase in
> severity on reefs off Salomon Atoll, with most corals in shallow (<10 m)
> fore reef locations fully bleached (e.g. Isopora, Stylophora, Pocillopora,
> digitate and branching acroporids, faviids, Astreopora, Hydnophora, Pavona,
> and Physogyra) as of April 26. Shallow lagoonal reefs (2-10 m depth) are
> also showing severe signs of bleaching, and more than half the corals in
> deeper areas being pale, mottled or fully bleached, including many of the
> large Porites lutea colonies, plates of Porites rus, foliaceous Echinopora
> colonies, and plating Leptoseris, Pachyseris, Merulina and Mycedium, with
> bleaching seen to 35 m depth. On the fore reef, bleached table acroporids
> (mostly A. cytherea), Acropora tenuis, digitate acroporids, Isopora and
> some smaller colonies of Porites are beginning to show signs of tissue loss
> and algal colonization. Other species are currently showing less mortality.
> There appears to be considerable spatial variability in the extent of
> bleaching. Some atolls and reef systems, especially lagoonal and fore reef
> systems off Salomon and Peros Banhos show the highest prevalence of
> bleaching, while others (Speakers, Blenheim, Great Chagos Bank) had many
> fewer bleached corals. Within a reef system, passes between islands and
> deep reefs (below 30 m) show less bleaching, as do murky lagoonal
> environments below 15 m depth, while bleaching is often concentrated on
> either side of a sand channel with affected corals extending down the reef
> slope. We've seen a high variability within species, with bleached
> colonies occurring adjacent to a normal unbleached colony of the same
> species. In several instances, the white bleached colony is exposed to
> full light, while normal, fully pigmented colony usually are shaded.
> Weather conditions have been ideal for diving (but not for the corals)
> with weeks of doldrum-like conditions, gin-clear water, and warm
> temperatures. Surface water is 31-32° C at the surface, on both fore reef
> and lagoonal reefs; reef temperatures are approximately 30° C to 35 m
> depth. In March, sea water temperatures on the reef were closer to 29° C,
> while temperatures in April have only been as low as 29.2° C in a few deep
> The duration and ultimately the impact of this event is unknown. It
> appears that we may be near the end though, as the seasonal trade winds
> appear to be increasing and we've noticed some upwelling of cooler water.
> Even if some corals die, it appears that these reefs are likely to bounce
> back quite rapidly. There is evidence that BIOT sustained high mortality
> (up to 100%) following the 1998 El Niño, but the reefs quickly rebounded.
> A study carried out in 2006 suggested that shallow reefs were similar in
> structure and cover to that of 25 years earlier. Based on the sizes of the
> large table acroporids we have documented, these likely recruited after the
> 1998 event and now cover 60-80% of the reef in many locations, to depths of
> 20 m or more. We see unusually high levels of recruitment on most reefs..
> On sites that were damaged in the recent past by crown of thorns starfish,
> bleaching (2010?), and white syndrome there are high numbers of coral
> skeletons in growth position, but these sites also have high numbers of
> recruits and populations of healthy, juvenile corals (possibly 3-5 years
> old, based on their sizes). Most reefs also have high cover of red
> crustose coralline algae, near absences of cyanobacteria and macroalgae,
> and a high biomass of herbivores. Furthermore, previous studies have also
> reported very high levels of herbivory, low nutrient levels, and a near
> absence of pollutants, all of which suggest these systems can rebound
> quickly from a bleaching event.
> For photographs and more information on this event please see:
> Andrew Bruckner, Ph.D.
> Chief Scientist, Khaled bin Sultan Living Oceans Foundation, 8181
> Professional Place, Suite 215, Landover, MD 20785, 301 577 1288 ext. 203
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