All good points! And to your main point, I agree, not all microbial species we introduce into our systems (whether in a bottle or on a rock) persist. Interestingly, studies suggest that even among the microbiota that live in or on wild corals, diversity actually
decreases over the life of the colony.
I don't speak for manufacturers of other so-called bacteria-in-a-bottle products. As far as I'm aware, nobody (at least in the States) offers a product that is anything like ours. We deal exclusively in purple non-sulfur bacteria (for more details refer to the video linked at the beginning of the thread), including
Rhodopseudomonas,
Rhodospirillum and
Rhodobacter. These are
shown to be extremely abundant on wild reefs; however, according to
findings published by Aquabiomics, this group is absent from what Dr. Meyer calls the 'core aquarium microbiome' (note that not all Rhodobacteraceae are purple non-sulfurs). Purple non-sulfur bacteria are extraordinarily adaptable and hardy, so a plausible explanation for their scarcity in captive environments is competitive exclusion (in this case by other bacteria that are, for some reason, better suited to typical aquarium conditions). Given that these microbes are naturally abundant on healthy reefs, and that they perform important ecological roles there, we believe that adding them to aquaria makes good sense not simply
despite the fact that that tend not to persist, but precisely
because they tend not to persist. In other words, we see them as a re-set button that (at least in part) restores the microbiome to something more like what we'd expect to see on a wild reef.
All that aside, we consider our products primarily to be live microplanktonic foods. And, studies demonstrate that corals do consume these bacteria in the wild. Their nutritional content (which is extensively characterized in the scientific literature) is excellent. Though superficially similar to phytoplankton, they are comparatively higher in protein and certain fatty acids that tend to lacking in many other sources (e.g., oleic acid). They are also more digestible than phyto. They're not perfect (no single food ever seems to be): Studies do show that they are lacking in certain essential fatty acids. For this reason, the findings in one study indicate that
Rhodopseudomonas and phyto are nutritionally complementary and thus provide better nourishment together than either provides by itself. Altogether, these bacteria known to be a valuable source of nutrition to corals and other marinelife in Nature, including fishes (as a probiotic).
The microbiome, whether in an aquarium or in the wild, is a numbers game. That's why I went at length to emphasize firstly that the main use of these products (at least PNS ProBio and PNS YelloSno) are as a food. As with phytoplankton and zooplankton, many aquarists must introduce microplankton (i.e., bacterioplankton) since populations within the tank are insufficient to meet the dietary needs of many planktivores (of course the degree to which this is an issue varies from system to system). So yeah, the point here is to add a concentrated feed containing a known nutritious and harmless bacterioplankter (by the way, many if not most biologists claim that bacterioplankton, not zooplankton or phytoplankton, make up the majority of most corals' planktonic diet). Many might say in reply that they they've done just fine without adding live microplanktonic foods; to that I'd say, that's perfectly fine, I believe you, and that's totally cool. We simply believe a coral (and other bacteriovores for that matter) are healthier with the addition of a microbial food source generally--and with these bacteria in particular.
I'll address one more thing from your statements though, if I may. It's true that various types of bacteria will find their way into an aquarium (the air, hands, allow with new animals, etc.). It's interesting that you mention spores; these are non-sporiform species, which could be one reason they do not as readily appear/persist in aquaria. I never thought of that, but it could account for at least some part of their typical scarcity. But I do know from bringing microbial samples back from overseas that some of these microbes die off simply because they don't travel well. That, I believe, could contribute to a massive loss of microbiotic diversity on live rock--maybe another reason certain microbes don't show up in our tanks, even if they're abundant in the wild. (Another potential plus for certain bottled products?) By the way, don't get me wrong, I LOVE live rock and lament that its availability is a joke compared to what it was in the mid-late 90s. I just don't think that bottled products and live rock are mutually exclusive. Live rock is great for adding overall diversity, and also complete microbial guilds (i.e., groups of unrelated species that benefit from or even depend on each other), whereas bottled products introduce massive populations of highly desirable species (particularly if they tend not to thrive captivity) or of course as a natural live food.
Sorry that was long, but you made a lot of great points. Thanks!
