It's a lot more complex than just "toxins" From my post in this
thread on "Stability"
"Maybe our definition of "stability" is wrong or at least very inadequate :/. As I see it the typical assumptions about stability don't take into account any of the following:
From the research I've read the microbial processes in any reef ecosystem are likely in constant flux.
The different fluorescing and chromo proteins corals make are to cope with less than ideal environmental conditions
(1) (2) (3) (4) (5). (colorful is not necessarily healthy.)
The different clades of simbodinium simbionts require different conditions and corals usually host more than one clade. Environmental changes (like differences between tanks) have the potential of changing the clade numbers and altering the photobiology
(1)
Corals have "decadal" memory and the same two specimens of the same species/genotype or even in different parts of the same colony may react differently to the same conditions
(1) (2).
Corals are influencing the bacteria in the water around them
(1).
Each coral species has it's own unique microbiome (see Rohwer's "Coral Reefs in the Microbial Seas") which also includes components essential for it's immunity.
Immunity within a species varies significantly at the genotype level
(1)
"Healthy" looking corals may not be.
(1) (2) An excerpt from this paper -
"Critical to coral disease transmission – or resistance – is the coral's surface mucus layer,
which is produced in part by the coral's endosymbionts [12]. The mucus layer hosts a complex
microbial community, referred to hereafter as the surface microbial community (SMC). Because
the mucus environment is rich in nutrients, microbial population densities there are orders of
magnitude higher than in the surrounding water column [20]. Most established and emerging
pathogens are endemic to the ecosystem and typically present at low numbers in the SMC.
When stressed, the SMC can switch rapidly from a community associated with healthy corals to
diseased corals. In field studies during the 2005 summer bleaching event, Ritchie [28] observed
that "visitor" bacteria (bacterial groups otherwise not dominant) became the predominant
species in mucus collected from apparently healthy Acropora palmata.""