Nutrients: species, absolute exposure and heat matter
Montipora digitata · Xenia umbellata
Names as reported by the authors; no accepted-taxon or specimen-identity claim.
Reading the evidence
These records describe traits and results under specific study conditions. They do not establish recommended aquarium settings.
What the study tells us
A nominal N:P ratio does not isolate a ratio effect from phosphate concentration. Increased symbiont density is not equivalent to improved host survival. There is no concurrent cool control through the warming phase.
Study conditions
Five weeks; twelve tanks with 40 L seawater, four tanks per nutrient treatment. First two weeks at 26 degrees C, then 2-degree weekly increments to 32 degrees C. Nominal nitrate 37 micromolar in both enriched groups, phosphate 8 or 2 micromolar (named 5:1 and 19:1 N:P); unenriched control. Light 108 ± 14 micromol photons m−2 s−1, 12:12 light:dark; fragments acclimatized before exposure. Daily mortality plus pulsation, symbiont counts and chlorophyll.
Methods and evidence class
controlled captive experiment
Daily survival counts; sampled pulsation, symbiont density and chlorophyll; Kaplan–Meier/log-rank survival comparisons with Holm–Bonferroni adjustment and nonparametric endpoint tests.
Findings
obs-pmc12619941-01
After two weeks at 26 degrees C, the 5:1 enriched group showed a 113% increase in Montipora symbiont density (p=0.021) without mortality, while Xenia pulsation fell to zero relative to control (p=0.01). These endpoints differ by organism and do not define beneficial nutrient targets.
Under enrichment followed by warming to 32 degrees C, all Montipora in the 5:1 group died before the experiment ended; Xenia survival probability in that group declined to 13%. Both differed from controls with p less than 0.001.
Measurements and uncertainty
{"group": "5:1 plus warming", "metric": "Xenia survival probability", "uncertainty": "p<0.001 versus control", "unit_as_published": "%", "value_as_published": "13%"}
Where to find it in the paper
Results / Combined effect of nutrient enrichment and temperature increase | ./body/sec[3]/sec[3]/p[1]
Results / Combined effect of nutrient enrichment and temperature increase | ./body/sec[3]/sec[3]/p[2]
Results / Differences between coral species | ./body/sec[3]/sec[4]/p[3]
Temperature increases with time for all treatments; there is no concurrent 26-degree control throughout the heated phase. Time and heat are not fully separable.
Changing N:P changes absolute phosphate at fixed nitrate; this design does not isolate a universal ratio effect from concentration effects.
Treatment pH means differ (Table 1). Late surviving samples are reduced; no 5:1 Montipora survivors and only two Xenia samples remain for some day-35 assays.
Different methods passages give the baseline temperature as 25 and 26 degrees C; this discrepancy remains unresolved.
Both species and all nutrient/temperature endpoints belong to the same 12-tank experiment. Xenia stock from Bremen/northern Red Sea overlaps provenance of PMC10472534; shared stock is not independent-population confirmation.
Evidence family: study-pmc12619941
Method passage locators
Materials & Methods / Study organisms | ./body/sec[2]/sec[1]/p[1]
Materials & Methods / Study organisms | ./body/sec[2]/sec[1]/p[2]