I assume when you translate it you will explain that it was something I posted to the coral mailing list . I appreciate you asking. I hope that if you translate my posting you will also attach the following addendum.

Sincerely,

Julian Sprung

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From: Julian Sprung

Subject: Iron against bleaching ?

Some food for thought-

Following Martin PECHEUX's suggestion to experiment with iron fertilizing around bleached reefs I am compelled to share some ideas I have that I hope will be taken in the spirit I intend them- just ideas, a hypothesis, no ill intent, and a hope to open everyone's eyes to the POSSIBILITY that many of us (myself included) up to now have been preaching an erroneous scenario concerning mass bleaching on coral reefs. I'll get to that in a moment.

First, regarding the iron fertilization suggestion. I agree with Jim Maragos that the likely result of elevated availability of iron would be a bloom of algae (with undesirable consequences!). Iron fertilization in closed system aquariums often (but not always) produces that effect, explosively at times, the availability of phosphate and CO2 also being important in the equation.

The suggestion by Martin PECHEUX to fertilize with iron was based on the notion that bleached corals would benefit if there was a way to stimulate the growth of their lost symbionts. Here's where the possible error about mass bleaching comes in.

In general the explanation for recent mass coral bleaching and mortality events (at least as they are reported in the newspapers, dive magazines, environmental publications, etc.) is based on a story along the following lines:

1. High water temperatures STRESS corals.

4. If the corals "remain stressed" and don't regain their zooxanthellae, they starve and eventually die (or are weakened and subject to attack by disease and smothering mats of algae).

5. Other factors affect the recovery, such as pollution, eutrophication, siltation, etc.

What I am going to propose is the POSSIBILITY that this scenario is mostly wrong, based on what work done by (Toren et al., 1998) implies.

An article in a recent issue of Reef Encounter, Newsletter of the International Society for Reef Studies describes how bleaching in a species of Oculina is caused by a species of bacteria, Vibrio shiloi. The authors give an analogy to help explain the distinction between the causative environmental conditions and real "cause" of the disease (ie. the microorganism). In their example, the flu is prevalent in the winter, when weather conditions favor its activity. The cause of the flu is the microorganism, however, not winter.

In their study they showed that the way Vibrio shiloi affects the Mediterranean species Oculina patagonica is mediated by temperature. At temperatures from 16 - 20 degrees Celsius the disease does not occur, even when large numbers of the pathogen are applied to the coral. At 25 - 30 degrees, even a small quantity of V. shiloi will cause the disease. Further, they showed that at this increased temperature, when antibiotics were used to block the Vibrio, the disease did not occur.

In a separate study, (Toren et al., 1998) it was found that V. shiloi adheres to the surface of O. patagonica via a chemical receptor. The bacteria's counterpart adhesin that recognizes this receptor is not produced at lower temperatures. The elevated seawater temperature therefore is what causes the bacteria to become virulent. It effects a change in the bacteria, not the coral- the coral is not stressed.

Although the bacteria that affect tropical corals are likely to be different from V. shiloi, their basic behavior may be similar. Elevated seawater temperatures on coral reefs are known to be associated with coral bleaching. The article in Reef Encounter clearly suggests the possibility that the elevated sea surface temperatures associated with mass bleaching and mortality of corals on tropical reefs may indicate a similar process happening there, caused by bacteria, not temperature "stress" on corals.

If that is the case, then the scenario could be:

1. At elevated temperatures various strains of bacteria adhere to corals and become virulent.

2. The bacteria cause the corals to expel zooxanthellae (reason not known).

3. The bacteria destroy coral tissue (ie. the corals don't starve, they are destroyed).

Based on observations in aquaria I tend to believe the latter scenario, which I am proposing. Furthermore, I believe that there are other environmental factors that may cause various bacteria to become virulent and affect corals, temperature notwithstanding. Of course there may be as many pathogenic bacteria as there are families of corals, and different bacteria may become virulent for different reasons, not always with fatal results. In aquaria I have seen disease affect only members of one species,

genus or family, leaving other corals unharmed. Other times I've seen rapid death move through an aquarium, affecting all corals as well as other invertebrates and even fishes! I have seen diseases that cause impaired health, reduced growth, bleaching, and sensitivity to light. In many, but not all cases, treatment with antibiotics or antibacterial chemicals (iodine for example) reverses the symptoms. Such observations are anecdotal and surely need closer study. The beauty of aquariums of course is the ease with which we can control them.

Some additional remarks-

Of course I know that it can be demonstrated that changes in light intensity and spectrum effect changes in density of pigment and zooxanthellae. I also know that a variety of factors can cause corals to expel zooxanthellae, not just bacteria or disease. Please don't misconstrue what I suggest here.

Regarding stress and reduced resistance to disease, I do not doubt that a variety of diseases may affect corals more strongly when the corals are in an environment that is not ideal. However, it is important to accept that at least sometimes a rapidly fatal disease may occur suddenly in perfectly healthy corals when the disease causing organism is "switched on" by an environmental stimulus that does not stress the coral directly.

Algae mats grow on exposed coral skeletons, smother, and usually kill corals, but sometimes they offer a life-saving shade to live coral tissue on lower branches during mass bleaching events.

Corals on reef flats are routinely exposed to temperatures far above those associated with mass coral bleaching. What gives these corals the ability to tolerate this? Is it just duration of exposure? Intense UV affecting potential pathogens?

Changes in their surface chemistry? Production of antibacterial substances?

I have for years been bothered by the blurriness in reports of coral bleaching with respect to the distinction between white-but-alive and white-without-tissue. At one time I wanted to suggest that new terminology needs to be adopted to clarify the distinction. The term "bleaching" is truly a poor choice since the curio trade uses bleach to clean coral skeletons, so the public perception is that "bleached" corals are dead. In general, scientists referring to bleaching really refer to corals that have expelled their zoox's but are still alive. Taking into consideration the possibility (of mass bleaching events caused by disease) proposed here, then the distinction between the two conditions ("bleached" vs. dead) in the case of a mass bleaching event may just be a matter of time only, as the cause is the same. Bleaching caused by shading or other factors is of course something different. Do we need more terminology?

Finally, if some mass bleaching events are caused by bacteria, can we do something about it? That gets back to the original intention of Martin PECHEUX, which is in principal very worthwhile- even if idealistic- to come up with a way of reducing the loss of corals by intervening when a mass bleaching event ocurs. Treatment with antibiotics is of course out of the question, but what about iodine or other substances that hinder bacteria? Alternatively, is it possible to immunize corals? Is it possible to chemically block the adhesion of bacteria to the coral?

I hope that this post stimulates active exchange of ideas in a positive direction to further understanding of the mechanisms behind coral bleaching and disease. I don't mind if I am wrong. I hope others feel the same way.

Sincerely,

Julian Sprung

Rosenberg, E. and Y. Loya. 1999. Vibrio Shiloi is the Etiological (Causative) Agent of Oculina Patagonica Bleaching: General Implications. Reef Encounter.

Toren A., Laundau L., Kushmaro A, Loya Y, and E. Rosenberg (1998) Effect of Temperature on the adhesion of Vibrio AK-1 to Oculina patagonica and coral bleaching. Appl. Environ. Microbiol. 64: 1379 - 1384.

After my posting I have been communicating with Dr Ove Hoegh-Guldberg, who is a researcher studying the mechanisms of coral bleaching. He offers an additional explanation for the death after bleaching in corals and the effect of light enhancing the severity of the problem, to which I alluded.

To review Dr. Hoegh-Guldberg's explanation see the following reference and abstract of the paper below.

Jones, R, Hoegh-Guldberg, O, Larkum, AWL and Schreiber, U. (1998) Temperature induced bleaching of corals begins with impairment of dark metabolism in zooxanthellae. Plant Cell and Environment.

It is clear to me that not all incidences of sudden coral death after bleaching are due to disease. Sometimes disease is the cause, but often it is not. What is certain, however, is that the "story" commonly reported in the news that corals quickly starve to death after they bleach is wrong.

I believe I have witnessed in aquaria the effect described in the above-mentioned paper, or a similar one, since temperature was not a causative factor. Sudden sensitivity to light, leading to bleaching and death, is a problem that occasionally affects anemones, corallimorpharia, and corals. It appears to be associated with the slow loss of Goniopora stokesii as well. It remains to be demonstrated whether the cause is physiologically and environmentally grounded or the result of a pathogenic organism. It is highly likely that the same symptoms can be produced by a wide variety of factors including purely environmental ones and purely pathogenic ones.

Abstract:

by: Jones, R, Hoegh-Guldberg, O, Larkum, AWL and Schreiber, U. (1998)

The early effects of heat stress on the photosynthesis of zooxanthellae within the tissues of a reef-building coral were examined using Pulse-Amplitude-Modulated (PAM) chlorophyll fluorescence and photo-respirometry. Exposure of Stylophora pistillata to 33 and 34(C for 4 h

resulted in (1) the development of strong non-photochemical quenching (qN) of the chlorophyll fluorescence signal, (2) marked decreases in photosynthetic oxygen evolution, and (3) decreases in optimal quantum yield (Fv/Fm) of photosystem II (PSII). Quantum yield decreased to a greater extent on the illuminated surfaces of coral branches rather than lower (shaded) surfaces, and also when high irradiances intensities were combined with elevated temperature (33(C as opposed to 28(C). qN collapsed in heat-stressed samples when quenching analysis was conducted in the absence of oxygen. Collectively, these observations are interpreted as the initiation of photoprotective dissipation of excess absorbed energy as heat (qN) and O2-dependent electron flow through the Mehler-Ascorbate-Peroxidase cycle (MAP-cycle) following the point at which the rate of light-driven electron transport exceeds the capacity of the Calvin cycle. A model for coral bleaching is proposed whereby the primary site of heat damage in the S

pistillata is carboxylation within the Calvin cycle, as has been observed in

the higher plants. Damage to PSII and a reduction in Fv/Fm (cf photoinhibition) is a secondary effect following the overwhelming of photo-protective mechanisms by light, a secondary factor that aggravates the

effect of the primary variable temperature. Potential restrictions of electron flow in heat-stressed zooxanthellae are discussed with respect to Calvin cycle enzymes and the unusual status of the zooxanthellar Rubisco. Significant features of the model are that (1) damage to PSII is not the initial step in the sequence of heat stress in zooxanthellae, and (2) light plays a key secondary influence.