Coral Reefs Conclusion and Assessment to Experiment

Coral Reefs

Conclusion and Assessment to Experiment

The experiment as described provides strong support for the idea that temperature directly affects coralline health and that even relatively small rises in temperature can have devastating effects on corals (and coral reefs) because such a shift in temperature has the effect of destroying the relationship between the corals and small symbionts that live in the corals. Rising temperatures drive the symbionts out of the corals, and it is this fleeing of the small co-habitants of the coral reefs that producing the lightening of "bleaching" effect that is a definitive indicator of coral harm or death.

The experimental data provided indicate that at 26 degrees and 28 degrees Celsius, there was no colour change in the coral (Catalaphyllia jardinei). This met the expectations of the experiment, given that this temperature is within the temperature tolerance for this coral and its symbionts. Since the temperature was such that it allowed the symbiosis to continue, the coral should have retained its typical brown/green colour. As noted in the background for the experiment: "These two coral specimens are surrounded by water replicating their optimum living conditions and therefore will remain healthy and maintain their natural colour."

The prediction for the coral in the tank with water temperature at 30 degrees Celsius was not as accurate as for the first two tanks. While the hypothesis that this temperature would lead to bleaching was confirmed, the timescale of this event was not accurate. While the hypothesis had predicted that bleaching would not occur until the seventh (that is, the last) day of the experiment, in fact it occurred by the fourth day. Moreover, the degree of bleaching was greater than had been predicted, with the final color values being E3 and D4 rather than E3 and D5.

The hypothesized reactions of the coral in a tank with water maintained at 32 degrees Celsius also failed fully to be supported by the results. While the pre-experiment model predicted that the coral in this tank would begin to show signs of bleaching before the coral in the tank with a sustained temperature of 30 degrees Celsius, in fact the corals in both tanks showed bleaching at four days.

The predicted final color values were also lighter for this tank than predicted: As in the tank held at 30 degrees Celsius, both brown and green segments of the coral bleached to one designation higher than predicted.

The hottest of the tanks -- held at 34 degrees Celsius did indeed, as predicted, show evidence of bleaching on the first day. The final results were more dramatic (and drastic) than predicted. While the predicted final values were E2 and D4 on the Coral Watch Chart, the actual (experimental) final values were E1 and D2.

In all three of the warmer tanks, there was a non-linear relationship between the bleaching of the green and the brown sections of the coral. This was not suggested by the original parameters of the experiment, which predicated that both of the symbionts in the coral (one of which is responsible for the brown color, the other of which produces the green color) would be equally affected.

Table Assessing Experimental Design

Strengths

The experiment provided clear and convincing support for the detrimental effects of even small temperature rises on coral health