in dem von Hajo zitierten Artikel heißt es weiter: "The pathogenesis of the disease is favored by the suspectibility of the biovalves, but external stress factors, as poor water quality, high organic matter and other stressors faciliate the progagation of potential pathegenic bacteria. So in many episodes mortalities can resulted from the overgrowth of opportunist bacteria."
In diesem Zusammenhang ist noch eine andere Studie sehr interessant: Metabarcoding reveals distinct microbiotypes in the giant clam Tridacna maxima
"The microbiome of giant clams is particularly interesting because clams are exposed to an extreme abundance and diversity of microbes through filter feeding, and because they live in symbiosis with dinoflagellate algae. We showed that the presence of the coral Acropora cytherea in an assemblage negatively affects the health of the giant clam Tridacna maxima and that this effect is amplified under temperature stress. Our results showed that nearly all clams with compromised health were characterized by a distinct microbiome in which the Vibrionaceae family was enriched. (...)"
"When Acropora cytherea was present in the assemblage (PAT and AT), clam mortality increased. This pattern was particularly striking for PAT under increased temperature. Since all aquariums were filled with seawater from the same pipe and some healthy giant clams in T assemblages harbored the Vibrionaceae species at a lower proportion, the prevalent hypothesis is an increased susceptibility of infection due to the presence of corals. (...)"
"Corals compete either by direct physical contact or via the production and secretion of secondary metabolites that can weaken or kill neighboring organisms [65,66,67,68,69,70]. These metabolites are produced by the coral host itself or by their associated microorganisms, some of which are known to synthetize toxic compounds [67, 71]. Other than the direct effect of a toxic metabolite potentially produced by A. cytherea or by its associated organisms, the decline and subsequent death of giant clams could also be the consequence of anti-inflammatory molecules produced by corals [72, 73], reducing the immune response of clams against microbial pathogens. An immune depression associated with the reproductive period and/or increase of water temperature has also been linked to vibriosis in poikilotherm organisms, including mollusks. (...)"
"As nearly all dying clams harbored a typical microbiome mainly composed of Vibrionaceae (Catenococcus spp. or an unclassified genus), we hypothesize that the combined effect of secondary metabolites from Acropora corals and increased water temperature may have weakened the clams’ defenses against Vibrio infection. Interestingly, the microbiome of two healthy clams, from T assemblage under thermal stress, showed similarities to that of dying clams."
Zusammenfassend: "Our results led to three major conclusions. First, the health status of giant clams depended on the composition of the benthic species assemblages. Second, we discovered distinct microbiotypes in the studied T. maxima population, one of which was disproportionately dominated by Vibrionaceae and directly linked to clam mortality. Third, neither the increase in water temperature nor the composition of the benthic assemblage had a significant effect on the composition of the Symbiodiniaceae and bacterial communities of T. maxima."
Ich weiß nicht, ob man das auf alle Trinacda Arten übertragen kann. Auf jeden Fall scheint es deutlich komplexer zu sein. Ein Rumdrehen an einzelnen Stellschrauben wird wohl kaum zum Erfolg führen.
Neben unterschiedlichen Mikrobiomtypen spielt in dieser Studie die umgebende Mikro- und Makrofauna eine entscheidende Rolle und zudem Stressfaktoren wie Hitze. Hier kann man sicherlich auch annehmen, dass schwankende Wasserwerte, geringe Calicumkonzentrationen, zu viel oder zu wenig Jod, Kupfer usw. das ihrige dazu beitragen, Muscheln zu schwächen, was meist ein Absterben zur Folge hat.