Bleaching in Ningaloo?  I believe this is a first for high temperature-related coral bleaching. People have wondered why these reefs have not suffered from mass coral bleaching.  Unfortunately, that is no longer true. Here is a report by coral biologist, Dr Tyrone Ridgway (Australian Institute of Marine Science)

Coral bleaching has been reported on Ningaloo – a reef system that has not experienced widespread bleaching to date.  Coral bleaching likelihood is largely determined by sea temperatures, and during the 2010/2011 summer, sea surface temperatures across Ningaloo were anomalously warm.

Coral bleaching events are usually caused by long periods (usually 4 to 8 weeks) of warmer than average summer sea surface temperatures (SSTs), and SST estimates from the National Oceanographic and Atmospheric Administration (NOAA) Coral Reef Watch Program show that 2010/2011 summer SSTs around Ningaloo have been about 1°C to 3°C warmer than the long-term averages for the region.  As a result, Ningaloo was on Bleaching Watch for much of the summer and reached 4 Degree Heating Weeks (DHW)1 in mid-January 2011 (Figure 1A).  In situ temperature loggers (~ 6 m depth) at Bundegi in the Exmouth Gulf and 14-Mile Beach on Ningaloo (Figure 1B) confirmed that actual water temperatures had been above seasonal averages since mid October 2010.

Figure 1.  Temperature data for Ningaloo during 2010/2011 summer.  A. NOAA Coral Reef Watch forecasts for Ningaloo.  B. In situ temperature logger data for Bundegi and 14-Mile Beach.  The black dotted line is the NOAA seasonal averages from Fig. 1A overlaid on the temperature logger data.
Reef surveys by the Australian Institute of Marine Science (AIMS) and the Western Australia Department of Environment and Conservation (DEC) confirmed coral bleaching (Figure 2) at multiple sites during February 2011.  Initial shallow water surveys suggest low level bleaching (< 5 % of total coral cover) is wide spread, but areas such as Bundegi and Coral Bay have higher levels of bleaching of up to 80 % of total coral cover.

Figure 2.  Coral bleaching at Coral Bay (10 February 2011).  A. Acropora and Favia; B. Seriatopora;
C. Echinopora.  (Photo credits: Tyrone Ridgway, AIMS).
As of 24 February 2011, Ningaloo was at 6 DHW and the Predictive Ocean Atmosphere Model for Australia (POAMA) forecast anomalous SSTs to continue through March 2011.  The fact that the temperatures are forecast to remain above seasonal averages through till the end of the 2010/2011 summer is of concern because the risk of coral mortality is increased if the thermal stress persists once the corals have bleached (Figure 3).  As such, AIMS and DEC will continue to monitor the sea surface temperatures and reef health at Ningaloo over the coming months.  Depending on the magnitude of the 2010/2011 bleaching event, the need for follow up post-bleaching surveys to estimate mortality rates will be assessed.
Figure 3.  Bleaching does not necessarily lead to corals dying (mortality).  Bleached corals can recover and survive if water temperatures return to normal.  Mortality normally occurs if the temperatures remain warm for an extended time period after bleaching occurs.
The bleaching reports at Ningaloo follow on from multiple observations of mass bleaching from Southeast Asia, Sri Lanka and the Maldives in the central Indian Ocean between May and July 2010 – where sea temperatures were up to 4°C above summer seasonal averages.
1 Degree Heating Weeks (DHW) is an accumulation of any temperature HotSpots greater than 1°C over a 12-week window, which shows how stressful conditions have been for corals in the last three months. DHW is therefore a cumulative measurement of the intensity and duration of thermal stress, and is expressed in the unit °C-weeks. Based on previous bleaching observations worldwide, evidence suggest that 4°C-weeks (4 DHW) results in bleaching and that 8°C-weeks (8 DHW) and above result in widespread bleaching. For example, Scott Reef in West Australia and the Maldives in the central Indian Ocean suffered significant bleaching mortality in 1998, with 13 DHW and 10 DHW respectively.  For more detailed information see Coral Reef Watch.

Acknowledgements: Thanks to Frazer McGregor (Murdoch University), Kim Friedman, Heather Taylor, Tom Holmes, Shaun Wilson (DEC), and Martial Depczynski, Ben Radford, Tyrone Ridgway, Paul Tinkler (AIMS) for data and information.
 

20 Responses to First-time Bleaching in Ningaloo, Western Australia

  1. ChloeB says:

    Ningaloo’s first time warm water bleaching, 2006 was cold water bleaching ;)

  2. MarcH says:

    Lack of observational history along the WA coast prior to 1980/1990s is a major problem for any one claiming this event is unprecedented.

    • OveHG says:

      A fair point except that we have satellite measurements of SST going back to 1981. Given the close relationship between accumulated heat stress and coral bleaching and mortality, this gives us a fairly good metric of whether it happened before. It has been not been this hot for this long in the past (see the latest here – it is extraordinary), adding evidence to the suggestion that the lack of observations in the past is not due to observer bias. That said, many non-scientists (divers, film makers) have been diving the reefs of Western Australia and have not filmed or reported major bleaching events over the preceding 50 years (except for a small cold event). And major bleaching events are rather hard to miss even for a non-scientist!

      • MarcH says:

        Scientific interest in the Ningaloo reef only kicked off in the 1990s. Coupled with poor accessibility and the costs involved I doubt there were many to dive it prior to the 1980s.

        Some additional points that support observational bias:
        Reef diving only popularised in the 1950s so little access beyond the shore prior to this time.
        Glass bottom boats used only in the 1930s.
        Under water cameras only available in Australia from the 1960s.

        Of interest is the under reporting of a bleaching event in Puerto rico in 1969. Despite being well known this does not appear have been reported in the scientific literature until 1990 (Winter et al 1998 CR 17:377-382). This suggests to me that there was little interest in bleaching until the late 1980s, and earlier events (prior to 1980) may not have been noticed or reported.

        Any chance you could link me to a peer reviewed paper that suggests otherwise.

        • Thomas Moore says:

          >Any chance you could link me to a peer reviewed paper that suggests otherwise.

          Suggests what? That there was scientific interest in bleaching? That people dived in Ningaloo prior to the 1990′s? Your kidding, right?

          The literature is full of reports of bleaching events. You seem to be mistaking mass bleaching with localised bleaching.

          Also, go back to the literature on massive corals and growth bands and see what you can find relating to historical bleaching events.

          How’s this: Coral bleaching was not a widespread phenomenom in decades previous to 1990. Any chance you could link me to a peer reviewed paper that suggests otherwise?

          • MarcH says:

            Can something exist without being perceived? If a coral bleaches on a reef and no one is around to see it whiten, did it happen?

            Apparently not.

          • Thomas Moore says:

            >Can something exist without being perceived? If a coral bleaches on a reef and no one is around to see it whiten, did it happen?

            >Apparently not.

            Marc – According to google you are a geologist (unless i’m mistaken…) Go back to the geological literature instead of pointless pseudo-philosophical statements. I ask again:

            “Go back to the literature on massive corals and growth bands and see what you can find relating to historical bleaching events”

          • MarcH says:

            Peer reviewed paper indicating mass bleaching events prior to 1990s…

            Try this one:
            U-series dating of dead Porites corals in the South China sea: Evidence for episodic coral mortality over the past two centuries.
            Quaternary Geochronology
            Volume 1, Issue 2, May 2006, Pages 129-141

            Abstract:
            High-precision (up to ±1–2 years) U-series dating of dead in situ massive Porites corals on the reef flats of Yongshu and Meiji Reefs, Nansha area, southern South China Sea reveals that mortality of these massive corals occurred many times over the past two centuries, many of which appear to correlate in time with historic El Niño events. Despite different habitats of corals, at least six mortality events occurred simultaneously on both reefs (e.g. in 1869–1873, 1917–1920, 1957–1961, 1971, 1982–1983 and 1999–2000 AD), reflecting the occurrence of large-scale regional events. We speculate that many of such mortality events, especially those dated at 1998–2000, 1991, 1982–1983, 1971, and 1957–1958 AD with an overall uncertainty of ±1–2 years, are probably due to high temperature bleaching during El Niño years (e.g. 1997–1998, 1991–1992, 1982–1983, 1972–1973 and 1957–1959 AD). This study demonstrates that individual colonies of massive corals have died at different times over the past two centuries and mass spectrometric U-series dating of very young corals with a precision of up to ±1–2 years is likely to become a powerful tool for reconstruction of past coral mortality history and investigation of global warming and coral bleaching.

          • Thomas Moore says:

            Yep, South China Sea is a marginal environment for coral reefs. Where’s the evidence for this El Nino related episodic mortality on the GBR prior to 1990?

  3. MarcH says:

    See earlier comments regarding Observational bias.

    When is the coral research community in Australia going to conduct a similar study (to the one cited above Yu et al 2006) on the GBR? If it’s been done, please pass on the DOI.

    In the meantime the ENSO history of eastern Australia and close association with mass coral bleaching events (see for instance Figure 9 from Quaternary Science Reviews 19 (2000) 45-64 “New views of tropical paleoclimates from corals” M.K. Gagan et al. doi:10.1016/S0277-3791(99)00054-2) provides plenty of prospective years with an increased likelihood of mass bleaching events on the GBR, particularly years with strong ENSO events. Pity the aqualung wasn’t around so we could have got a report.

  4. Thomas Moore says:

    When is the coral research community in Australia going to conduct a similar study (to the one cited above Yu et al 2006) on the GBR? If it’s been done, please pass on the DOI.

    You mean coral cores from the GBR not showing any signs of historical mortality? Go look at one of about two dozen papers from AIMS – here’s one with 326 corals that spans most of the last century. There’s no observational bias.

    In the meantime the ENSO history of eastern Australia and close association with mass coral bleaching events (see for instance Figure 9 from Quaternary Science Reviews 19 (2000) 45-64 “New views of tropical paleoclimates from corals” M.K. Gagan et al. doi:10.1016/S0277-3791(99)00054-2) provides plenty of prospective years with an increased likelihood of mass bleaching events on the GBR, particularly years with strong ENSO events.

    Pity the aqualung wasn’t around so we could have got a report.

    No need for the aqualung. Coral bleaching causes declines in growth and coral mortality. If there was evidence of bleaching, it’d be there in the geological record. There is no record of historical bleaching on the Great Barrier Reef – plenty of people have gone looking for it, and plenty of cores show no evidence of declines in growth rates or evidence of mortality. Sure there’s (some) evidence of partial mortality related to historical stress on the GBR (DOI: 10.1007/s00338-003-0304-7), but that’s not direct evidence of ‘bleaching’, and only two events exist: 1782–85 and 1817. It’s not observational bias, either.

    • OveHG says:

      Thank you Thomas for the rational and evidence-based response. Personally, I am surprised that people with limited expertise and understanding are so loud about these issues (e.g. Bolt and his mates). I really wonder what motivates them?

  5. MarcH says:

    Thomas,
    Your comment above just broke your argument. We were looking for signs of mass bleaching prior to 1990 (recall” Where’s the evidence for this El Nino related episodic mortality on the GBR prior to 1990?”) and you found it well done!

    “Sure there’s (some) evidence of partial mortality related to historical stress on the GBR (DOI: 10.1007/s00338-003-0304-7), but that’s not direct evidence of ‘bleaching’, and only two events exist: 1782–85 and 1817.”

    So two more event to add to the list. Amazing what you can find if you bother to look.
    Talk about being stuck in a paradigm trap.

    • Thomas Moore says:

      I think you are misled – there is no paradigm here. I cited the paper to show a point: two cores from one location show signs of mortality (one attributed to temperature, one attributed to a low salinity flood event) against 326 cores from the GBR. Both mortality events were over 200 years ago. Again, where is the evidence for El Nino related episodic mortality on the GBR prior to 1990? There is no lack of observational history, there is no observational bias. If this is the only trace of it in the geological record, you’d be hard pushed not to argue that coral bleaching was not a widespread phenomenon in decades previous to 1990.

  6. MarcH says:

    By the way Thomas, Lough et al (see link below)show the current decline in calcification is not unprecedented even in the last 100 years. With several other periods with low Cal rates going back to the 1400s. Indeed they speculate (page 61):
    “The majority of the 35 very large colonies of Porites analysed here show a decline in calcification in recent decades. However, a decline in calcification equivalent to the recent decline occurred earlier this century and much greater declines occurred in the 18th and 19th centuries (Fig. 8~). Analyses of annual density banding provided here indicate that the 20th century has witnessed the second highest period of above average calcification in the past 237 years. The observed decline in coral growth
    in recent decades may be, simply, a return to more “normal” conditions.”

    Several centuries of variation in skeletal extension, density and calcification in massive Porites colonies from the GreatBarrier Reef: A proxy for seawater terature empand a background of variability against which to identify unnatural change doi:10.1016/S0022-0981(96)02710-4

    • OveHG says:

      The reason for the high calcification and growth rates of Porites during this period? Exceptional increases in sea temperature. The only problem is that the relationship between calcification and growth is optimal around 1°C below today’s sea temperatures, leading to speculation that the 15% decrease in calcification since 1990 is properly a combination of decreasing carbonate ion concentrations and increasing sea temperature (beyond this optimal temperature).

      Here is a more up-to-date reference which discusses the previous assessment by Lough and Barnes (1997).

      Note the rather well-published group of authors!

      Kleypas, J.A., Buddemeier, R.W., Eakin, C.M., Gattuso, J.P., Guinotte, J., Hoegh-Guldberg, O., Iglesias-Prieto, R., Jokiel, P.L., Langdon, C., and Skirving, W., 2005, Comment on” Coral reef calcification and climate change: the effect of ocean warming”: Geophysical Research Letters, v. 32, p. L08601.

      I hope that this helps you understand the subtleties of this issue, Mark H.

  7. Thomas Moore says:

    Lough et al (see link below)show the current decline in calcification is not unprecedented even in the last 100 years

    Actually, it doesn’t. The coral data from Lough’s paper was collected in the early 1980′s and ends between 1982-1991. The figure and relevant text you cite on page 61 ends in 1982, prior to the onset of mass bleaching events. There’s a more recent paper by De’ath covering the entire record and recent decades (up until 2005). Compare Figure 8 in Lough’s paper (published in 1997 with 35 corals up until 1982) with Figure 2a in De’aths paper (published in 2009 with 326 corals up until 2005). To quote De’ath: “The data suggest that such a severe and
    sudden decline in calcification is unprecedented in at least the past 400 years.” Again, there is no observational bias – your bias here is that you are citing a paper that’s 14 years old and ignoring more recent literature. Note that Lough is a co-author on both papers.

    • OveHG says:

      Thanks Thomas, I neglected to mention that key facts about the Lough and Barnes paper. You are absolutely correct … the data in the paper that Marc H clings to only goes up to 1982-1991 (with the growth trend ending in 1982). Pity Marc is picking the wrong cherries – doesn’t help the credibility of his arguments!

Leave a Reply

Your email address will not be published. Required fields are marked *


*

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>

Set your Twitter account name in your settings to use the TwitterBar Section.