delayed bleaching

[Paul Marshall]

Ray's recent message included a reference to delays in the onset of bleaching.
My colleague Andrew Baird and I also made some interesting observations on this
phenomenon.

We found that differences between species in the time to respond to stress were
a prominent feature of  the 1998 bleaching event on the Great Barrier Reef. On
the first trip to our study site at Orpheus Island, six weeks after the first
reports of bleaching, we recorded that all colonies of Acropora hyacinthus and
A. millepora had bleached and many had already died. In contrast, 40 % of
Platygyra daedalea and 80 % of Porites lobata appeared unaffected and none had
died. On the occasion of our 2nd census, 4 weeks later, all the P. daedalea
colonies were affected as were 80 % of P. lobata, forcing us to revise our
initial impression that these species had been largely unaffected.

By the time of our 3rd  census, 4 weeks later (i.e. 14 weeks after initial
reports of bleaching) most of the surviving acroporid colonies had recovered (or
died) while the condition of many of P. daedalea and P. lobata continued to
deteriorate. In general, the massive species took longer to respond, stayed
bleached for longer and took longer to die. However, the rates of whole colony
mortality were significantly lower.

Clearly the biology of a species plays an important role not only in determining
the susceptibility to bleaching, but also in the time to respond to stress. This
has implications for the way in which bleaching is assessed in the field. In
particular, the rankings of species susceptibility and estimates of the extent
of bleaching within assemblages will vary depending upon the time since the
stress occurred that a census is conducted. We would be interested in hearing
from others who might have documented this staged response in coral assemblages
affected by bleaching.

Regards
Paul Marshall
--
Research & Monitoring Co-ordination
Great Barrier Reef Marine Park Authority
Townsville QLD
Australia

email: p.marshall at gbrmpa.gov.au


Ray Berkelmans wrote:

> Hello Shaker! (and C-listers)
>
> They breed corals tough where you come from! But obviously still not tough
> enough...
> Your observations about increasing bleaching while temperatures cool are
> very interesting. These sound remarkably like the observations we made at
> Hardy Reef on the GBR (offshore) in early 1998. Temperatures peaked at
> 29.9°C (av. daily) on 23-24 Feb, but bleaching was not observed until 13
> March (18 days later), well after temperatures had cooled. Bleaching was
> only mild, suggesting that the bleaching threshold was only exceeded by a
> relatively small amount (& probably for a short duration). Observations
> about the state of the corals were made every day by a biologist (Jackie
> Shields) aboard a tourist vessel. To me these observations suggest that
> there may be a delay in the onset of bleaching (at least visible symptoms of
> bleaching) following stress. Observations of bleaching and temperatures at
> other sites indicate that this delay is considerably reduced (or absent)
> when stress temperatures are exceeded by a large amount. These field
> observations are consistent with the delayed bleaching response I reported
> in Coral Reefs (18:219-228) following experimentally induced temperature
> stress. Does any one else have similar observations?
>
> Ray Berkelmans
> AIMS
> PMB 3
> Townsville Q4810
> Ph 47534268
>
>  -----Original Message-----
> From:   owner-coral-list at coral.aoml.noaa.gov
> [mailto:owner-coral-list at coral.aoml.noaa.gov]  On Behalf Of Shaker Alhazeem
> Sent:   Wednesday, 20 September 2000 9:18 PM
> To:     Coral List
> Subject:        End of summer coral bleaching.
>
> Dear Coral-Listers,
>
> Kuwait is experiencing a major coral bleaching event now. Bleaching is
> occurring in excess of about 80% in some areas.  The phenomenon is
> recent having started within the last week. This is the end of the hot
> season so temperature had fluctuated last week, so temperature shock
> most likely was the effect on corals. The water temperature was around
> 32°C on the time of observing coral bleaching.
> About three weeks ago I have visited Kubbar island coral reef in Kuwait
> in August 12th 2000. I have found there was about 10% bleached coral
> colonies and water temperature was 35°C.  But this visit last weekend
> the coral was bleached about 80% and water temperature around 32°C in
> September 14th 2000. But Quro coral reef had showed about 40% coral
> bleaching only, that could be for the reason it is less stressed coral
> around in Quro, as it is farther away from the coast so less human
> impact. Last week we had sudden drop in the temperature and it came back
> up after that week, which could be the real cause of the coral bleaching
> is temperature shock.
>
> With Best Wishes,
>
> Shaker Alhazeem
>
> Research Associate
> Mariculture and Fisheries Dept.
> Kuwait Institute for Scientific Research
> P.O. Box : 1638
> 22017 Salmiya - Kuwait
> Fax : (965) 5711293
> Email: shazeem at safat.kisr.edu.kw