[Coral-List] Coral bleaching and light levels
RichardPDunne at aol.com
Sat Feb 14 09:13:03 EST 2009
I have seen a great deal of poor work submitted to scientific journals
over the years, some of which has unfortunately survived peer review and
appeared in print. In some cases I have questioned in print the quality
of those publications, as several authors can bear testament to. So you
are incorrect to assume that I am not careful and critical of published
Unpublished work such as your own is quite impossible to assess - so I
am right to be highly sceptical of its value. I hope that I am not being
personal in suggesting that a little less time writing to Coral List and
a little more time spent researching and publishing would I am sure
greatly benefit all of us. Anecdotes are best left to the dinner table
Richard P Dunne
Thomas Goreau wrote:
> I think you are missing my point.
> We have for at least half a century from experimental work that
> extreme changes of light in either direction can stimulate bleaching
> (these are well known to aquariasts) and no one disputes that doldrum
> calm, cloudless, sunny conditions make bleaching happen faster when
> the temperature is above the threshold. But you are not willing to
> accept that light is key secondary stressor and insist it be regarded
> as a PRIMARY stressor, that is to say, sufficient BY ITSELF IN THE
> ABSENCE OF HIGH TEMPERATURE TO EXPLAIN MASS BLEACHING IN THE FIELD.
> But every known mass bleaching event (discounting local events which
> could have been caused by freshwater, sediments, or other local
> stresses, which are only a few percent of all reported events) has
> been predicted FROM TEMPERATURE ALONE. There is no evidence that
> average light exposure is increasing globally in reefs (although of
> course it fluctuates strongly and this is highly relevant to local
> bleaching patterns, as has been well known since the 1980s), and there
> is excellent and unambiguous data that ocean cloudiness is INCREASING.
> I am simply saying that there are no known mass bleaching events at
> temperatures below the threshold temperatures which could be
> attributed to high light.
> I used neutral grey filters to reduce all light using full sunlight,
> half sunlight, and quarter sunlight in tanks at various temperatures.
> Peter Glynn used both neutral grey filters with and without UV
> specific filters. You seem to believe (almost) everything you see on
> paper and nothing that experienced observers have personally seen! I
> did not get around to publishing my data, so you will naturally
> discard that evidence no matter how strong it is.
> On Feb 14, 2009, at 5:23 AM, Richard Dunne wrote:
>> 1. I am sure that Brown or her co-workers were not confused in their
>> descriptions of bleaching if that is what you mean, nor that aerial
>> exposure is always required, nor that these were "extreme" low tides
>> (they occur every month). A re-read of those papers would help to
>> clarify your interpretation. Your term "blanching" is semantic and
>> 2. "*Sudden* changes in light level" are not a prerequisite to coral
>> bleaching. It is a complex combination of dose and irradiance, as
>> well as spectral composition.
>> 3. The light and temperature interaction does not necessarily require
>> the presence of "high temperatures". At normal or slightly elevated
>> sea temperature high light can cause bleaching. It is the interaction
>> that is important. The fact that no-one can directly attribute
>> incidences of "mass bleaching" to light is more a factor of the lack
>> of adequate light data (cf the ease with which temperature data can
>> be collected). Absence of evidence is not evidence of absence. The
>> words of Glynn (Global Change Biology 1996 495-509) are still
>> pertinent: "a lack of long term in situ physical data and systematic
>> monitoring of coral health have frequently frustrated efforts to link
>> unequivocally mass bleaching events with extreme environmental
>> anomalies". For light data, that problem still persists.There are
>> also papers where elevated temperature bleaching did not occur
>> because of reduced light (e.g. Mumby et al MEPS).
>> 4. Surface light is not just the important factor as far a corals are
>> concerned - it is the underwater light field modified by a host of
>> physical factors which changes not only the power, angular
>> distiribution, but also the spectral power distribution in a very
>> complex way.
>> 5. The shorter wavelengths of UV are and have always been a largely
>> irrelevant factor in the bleaching of adult corals in the natural
>> environment. Gleason & Wellington's 993 Nature paper started an
>> unfortunate hare running but was in error (comment by Dunne Nature
>> 1994). This is a very complicated area but there are many subsequent
>> publications some of which, regrettably, continue to muddy the water.
>> UV experimentation for corals is fraught with problems, hence the
>> lack of quality data.
>> 6. Light does not just contribute to the "small scale patterns".
>> Regional changes in meterology (as I mentioned before) can result in
>> effects at scales of thousands of square kilometers (e.g., the change
>> in the timing of the onset of the monsoon over the entire SE Asia).
>> Similarly, sea level changes induced by effects such as the Indian
>> Ocean Dipole affect whole ocean basins including large areas of
>> shallow fringing reefs that predominate in SE Asia.
>> 7. I am aware of Glynn's work with UV filters (Glynn et al 1992 Proc
>> 7th Int Coral reef Symp) but not the PAR filter work to which you
>> refer. In his UV paper he purported to find effects due to UV but
>> there are problems with the experimentation which I wrote to him
>> about in 1994. It would be most helpful to have the reference for
>> the PAR filter work in case I have overlooked it.
>> Thankfully, we are now seeing useful wider geographic datasets and
>> work on light emerging (e.g. the work of Hendee and others) which may
>> help us to better understand wide scale bleaching patterns. And as
>> the photophysiologists unravel the mechanisms of bleaching at the
>> cellular level it appears that the normal modus operandii of
>> temperature is likely to be damage to the mechanisms of photorepair
>> in PSII, in otherwords light is required to be present at sufficient
>> irradiances in the first place to cause the photodamage. Certainly,
>> extreme temperatures alone can cause other forms of cellular
>> disruption, but it is debatable that this is happening in most
>> examples of widespread bleaching.
>> I do not seek to downplay the important role of sea temperature in
>> coral bleaching, but light is an equally important consideration,
>> albeit less easy to manipulate experimentally and more complex to
>> Whilst I appreciate the historical anecdotal information that you
>> post to Coral List , it is the published science on which I prefer to
>> rely, and I have doubts that this is in agreement with the views you
>> often express.
>> all the best
>> Richard P Dunne
>> Thomas Goreau wrote:
>>> It has been well known for about 50 years from direct
>>> experimentation for at least that sudden changes in light level,
>>> both high and low, can induce bleaching. I do not at all deny that
>>> high light exacerbates the rate of bleaching at high temperatures,
>>> which I measured directly 20 years ago. But I do not think anyone
>>> can seriously claim that increased light has caused the mass
>>> bleaching that we have seen in the last three decades, although it
>>> was obvious that it was a contributing factor from field evidence in
>>> the very first mass bleaching events, but it plays a secondary role,
>>> not a primary one. You should not confuse "blanching" (what happens
>>> to corals that are exposed to full sunlight at extreme low tides)
>>> with "bleaching" sensu strictu as Brown does.
>>> The question is whether light levels have changed at the surface in
>>> a way that could explain mass bleaching apart from changes in
>>> temperature. Variations in cloudiness are not new, although they are
>>> becoming more extreme. But there is a strong and clear tendency to
>>> increased cloudiness over the oceans, so this is resulting in
>>> reduced light stress, not more!
>>> There is in fact a large literature on changes in global surface
>>> irradiation, and the results have shown that solar output is
>>> essentially unchanged but that changes in atmospheric transparency
>>> have had a global impact. This was stimulated by the widespread
>>> prediction that decreases in the ozone layer caused by increases in
>>> atmospheric nitrous oxide and halocarbon gases should result in
>>> increases in surface UV. But the long term data conclusively showed
>>> the opposite, that UV had been decreasing for decades. The same
>>> turned out also to be true for surface visible light, and also for
>>> total irradiation as measured by global meteorological pan
>>> evaporation rates. The explanation was global dimming caused by
>>> sulfur and nitrogen aerosols generated from combustion. As
>>> industrial pollution has begun to be controlled, global dimming has
>>> decreased, allowing a slight increase in surface irradiation in
>>> recent years. This is a double whammy because global dimming had
>>> masked an appreciable portion of the global warming caused by CO2 in
>>> the short term, so that now that these pollutants are reduced,
>>> global warming rates will greatly accelerate. Increased pollution
>>> has been proposed by some as a devil's bargain to geo-engineer
>>> against global warming, but this is a fool's errand because the CO2
>>> remains in the atmosphere absorbing heat for centuries, but the
>>> aerosols are rained out in days to weeks (or a year or so in the
>>> stratosphere) so you would need to pollute with aerosols at
>>> exponentially increasing rates just to stay even. There are many
>>> excellent papers on this, but Meinrat Andreae provides the clearest
>>> recent explanation.
>>> At any rate, light cannot explain the large scale spatio-temporal
>>> bleaching patterns we see, although it clearly contributes to the
>>> small-scale patterns. Juvenile corals, which prefer to settle in
>>> dark undersides, are protected for that reason. Peter Glynn did
>>> excellent work with various filters in which he showed that it was
>>> photosynthetically active radiation was causing the increased rate
>>> of bleaching in high light exposed corals above the bleaching
>>> threshold temperature, and that UV increases made no difference.
>>> This is as would be expected by the very high levels of UV screening
>>> pigments. Charlie Mazel and I dived on severely bleached reefs at
>>> night in 1990 measuring UV absorbance and fluorescence of bleached
>>> corals, and we found that even totally bleached corals were
>>> completely opaque to UV light. So increased UV cannot be the cause
>>> of the large scale field bleaching, even though it can be an
>>> experimental cause of bleaching.
>>> I'm fully aware of the microphysical patterns you mention discussing
>>> light attenuation and scattering. But the reason I do not think they
>>> are relevant is because what I have seen is that waters in most
>>> reefs are far more turbid than they used to be and light penetration
>>> is greatly reduced. In many places I see large areas of deep reef
>>> 100-200 feet down that used to be healthy and are now dead because
>>> they are no longer getting the light they used to, for example in
>>> Jamaica and Panama. In places where as a boy I would watch my father
>>> diving 300 feet below from the surface, the waters that used to be
>>> clear and blue are now dark and green. The whole reef light looks
>>> completely different. So I am sure that increased light exposure is
>>> not the cause of mass bleaching.
>>> You may think that the changes global atmosphere patterns are
>>> "simplistic" and not "scientific" with regard to microphysical water
>>> measurements, but I can assure you that they are well documented in
>>> the atmospheric literature (having degrees in Planetary Physics
>>> (MIT), Planetary Astronomy (Caltech), and Atmospheric
>>> Biogeochemistry (Harvard) and having worked on these issues from the
>>> top down as well as the coral's bottom up view).
>>> Thomas J. Goreau, PhD
>>> President, Global Coral Reef Alliance
>>> Coordinator, United Nations Commission on Sustainable Development
>>> Partnership in New Technologies for Small Island Developing States
>>> 37 Pleasant Street, Cambridge MA 02139
>>> goreau at bestweb.net <mailto:goreau at bestweb.net>
>>> On Feb 13, 2009, at 12:25 PM, Richard Dunne wrote:
>>>> It is wrong to state so unequivocally that light is "a secondary
>>>> factor". It can be a primary factor as publications have shown (e.g
>>>> Brown et al - plenty of pubs). It is much more scientific and
>>>> accurate to say that it is an interplay between light and
>>>> temperature - see the diagram and discussion in the Fitt et al.
>>>> Review in Coral Reefs. Sometimes light is more important and
>>>> sometimes temperature.
>>>> It is also incorrect to say that "light levels are basically
>>>> unchanged". Changes in regional meterology occur as a result of
>>>> climate change which can lead to coral reefs being exposed to much
>>>> higher seasonal irradiance which can tip the balance between corals
>>>> bleaching or not. In addition, changes in sea level can be a very
>>>> important factor, particularly for shallow reefs. The underwater
>>>> light field is a lot more complicated, and affected by many
>>>> physical parameters (e.g., cloud cover, water surface roughness,
>>>> sediment levels, water depth, bottom type, zenith angle of the
>>>> light field, differential spectral attentuation, etc). Your
>>>> statement about surface light going down (evidence?) is far too
>>>> simplistic to be accurate.
>>>> I know this is just Coral List but please can we be a bit more
>>>> Richard P Dunne
>>>> Thomas Goreau wrote:
>>>>>> From: Thomas Goreau <goreau at bestweb.net>
>>>>>> Date: February 13, 2009 10:11:18 AM EST
>>>>>> To: billraymond10 at yahoo.com
>>>>>> Subject: Re: [Coral-List] Coral bleaching and ocean acidification
>>>>>> Dear Bill,
>>>>>> Absolutely! But it is a secondary factor.
>>>>>> 20 years ago I did a bunch of experiments in Jamaica with corals in
>>>>>> tanks at different temperatures and light level combinations.
>>>>>> Bleaching took place only above a certain temperature, but the more
>>>>>> light the faster it happened. Peter Glynn did similar experiments in
>>>>>> Okinawa and reached the same conclusions. The reason I did this was
>>>>>> our field observations in the first Caribbean bleaching event in
>>>>>> 1987, where shaded corals were much less bleached, in fact where
>>>>>> they were shaded by overhangs you could see the shadow, and we've
>>>>>> seen that everywhere in the Indian Ocean and Pacific since too.
>>>>>> But the discussion was about bleaching versus acidification, so I
>>>>>> did not get into secondary factors affecting bleaching. And
>>>>>> temperature has been rising worldwide whereas light levels are
>>>>>> basically unchanged because solar radiation variations are so small.
>>>>>> In fact surface light has been going down for decades because of
>>>>>> atmospheric pollution, but now starting to rise slowly as
>>>>>> atmospheric sulfur and nitrogen pollution are controlled.
>>>>>> Hans Creek is an interesting area, and you may know that I proposed
>>>>>> it as a coral reef restoration site. I still hope this is possible,
>>>>>> but it really depends on blocking the marina and golf course. Which
>>>>>> I guess is still a pending issue. There is a small chance that I may
>>>>>> get back to BVI later this year.
>>>>>> Best wishes,
>>>>>> Thomas J. Goreau, PhD
>>>>>> President, Global Coral Reef Alliance
>>>>>> Coordinator, United Nations Commission on Sustainable Development
>>>>>> Partnership in New Technologies for Small Island Developing States
>>>>>> 37 Pleasant Street, Cambridge MA 02139
>>>>>> goreau at bestweb.net
>>>>>> On Feb 13, 2009, at 9:57 AM, Bill Raymond wrote:
>>>>>>> Tom Goreau:
>>>>>>> Don't you consider solar intensity a factor in coral bleaching? In
>>>>>>> Tortola I found bleached corals in late October, offshore, but
>>>>>>> mangrove-shaded Siderastreas in warm Hans Creek
>>>>>>> were not bleached.
>>>>> Coral-List mailing list
>>>>> Coral-List at coral.aoml.noaa.gov
> Thomas J. Goreau, PhD
> President, Global Coral Reef Alliance
> Coordinator, United Nations Commission on Sustainable Development
> Partnership in New Technologies for Small Island Developing States
> 37 Pleasant Street, Cambridge MA 02139
> goreau at bestweb.net <mailto:goreau at bestweb.net>
More information about the Coral-List