Stress Of The Main Environmental Factors On Poritidae

In this research, two dominant species of coral （Porites lutea and Gonioporastutchburyi） in Xuwen Coral Reef National Nature Reserve Poritidae were collected assamples; the stress test was designed in terms of temperature, salinity, pH and Cu²⁺, PO₄^3-on four different levels. What kind of impact these five environmental factors will have onPorites lutea and Goniopora stutchburyi as well as the tolerability. Besides, the status ofrecovery of the two corals after the stress test and the experiment of lethal conditions.Theresults showed that:1. Different temperatures had influence on the coral stress testWhen the temperature was above25°C, Porites lutea and Goniopora stutchburyistart to react; While raising the temperature in the range of28°C, the density of two kindsof coral zooxanthellae and the content of chlorophyll a intended to increase, which showeda certain degree of temperature resistance mechanism; when the temperature was above28°C, coralline algae continues to proliferate, but the discharge rate was higher than theproliferation rate. With the increasing temperature, the density of symbiotic algae reducedand continued to decline when it reached the level at the beginning; when the temperatureraised to about34°C, coral would bleach to death. Therefore, coral could only survive inthe most appropriate ranch of temperature. Otherwise coral symbiotic algae system wouldbe damaged. Coral would eventually die with the increasing pressure.2. Different salinity had influence on the coral stress testwhen the salinity was from35to30, the number of zooxanthellae and chlorophyll a ofPorites lutea in each square meter did not change significantly. When the salinity was lessthan30, the number of zooxanthellae and chlorophyll a in each square meter drasticallyreduced. In particularly, Goniopora stutchburyi reacted more sensitively. The number ofzooxanthellae and chlorophyll a in each square meter drastically reduced when the salinityreduced from30to20, and eventually died. Therefore, the low-salt could affect thedistribution of corals.The tolerability of Porites lute and Goniopora stutchburyi varied inthe low-salted condition, which manifest the difference in the tolerability within the samecoral division.3. Different pH had influence on the coral stress testThe environment for the normal growth of zooxanthellae of coral symbiotic wasalkaline. For the coral, alkaline environmental change as a pressure on the environmentwould affect both the coral activities; pH between8.0and6.5, the two corals had a certain reaction, but showed normal growth conditions. When the pH was below6.5, it broke thecoral symbiotic algae to optimize the system. As the pressure continued, the coralseventually die, but Goniopora stutchburyi tolerability was weak compared with Poriteslutea. Therefore, the pH was within a certain range, coral had tolerance for the declining ofpH, and different genera of corals within the same division had a different level oftolerability.4. Different concentration of Cu²⁺had influence on the coral stress testThe change of the Cu²⁺concentration, the density of zooxanthellae and Chlorophyll aon the surface of two corals rapidly increased in4μg/L.When it reached the highest point,it then decreased. Heavy metals were so common in nature that was essential materials totrace amounts in vivo, but once the percentage of heavy metal exceeds in the environment,it would bring about toxic effects on organisms. What most serious was that it not onlyleads to acute toxic effects on organisms but lead the rapid death of organisms. Therefore,once the Cu²⁺concentration exceeded a certain threshold, photosynthesis of thezooxanthellae, under the toxic effects, was suppressed. The coral itself would be exhaustedfrom being poisoned zooxanthellae.5. Different PO₄^3-concentration had influence on the coral stress testWith the increase of phosphate concentration, the density on the surface of theorganization Porites lutea of zooxanthellae and the number of Chlorophyll a showed firstlyincreased to a peak and then decreased. This might be in the case of the added lowconcentrations of phosphate. Phosphate could benefit the photosynthesis of zooxanthellae,which made the number of zooxanthellae increase temporarily, but after the phosphateconcentration increased to a certain point, they started to negatively affect the coralzooxanthellae. In addition, the maximum tolerable phosphate concentration of theGoniopora stutchburyi was30μmol/L, while the maximum tolerable phosphateconcentration of Porites lutea was20μmol/L. Obviously, different genera of corals in thesame family are on different level of tolerability of phosphate. This was related to thenumber and species of zooxanthellae within the coral tissue and the different bodystructure of coral tissue..