Effects Of Temperature Stress On Symbiodinium Spp. From Selected Scleractinians
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Date
2018-09
Authors
Nadthikphorn Kamphol
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
Symbiodinium is described as a coccoid yellow-brown endo-symbiont, which inhabits coral tissues and provides photosynthetic products necessary for corals. However, under stressful conditions such as temperature change, the symbiotic relationship between Symbiodinium and corals may collapse and result in coral bleaching. Hence, this study was conducted to record coral species found in Pulau Songsong, Pulau Kendi and Pulau Redang, and to investigate the effects of temperature increased on the Symbiodinium cell density and health among coral species. Ten families with a total of 21 coral species were recorded. Diving-Pulse Amplitude Modulation (PAM) was used to determine the maximum quantum yield values (dark-adapted) (Fv/Fm), which is an indicator that helps to assess the current health status of corals. The in-situ Fv/Fm value of Porites somaliensis, Porites lutea, Goniopora cellulosa, Turbinaria mesenterina, Oulastrea crispata, Cyphastrea chalcidicum, Goniastrea retiformis and Pavona danai indicated that these corals were healthy and had adapted to maximum bottom light condition (600μmol quanta m-2s-1) during sampling day. Massive meandroid coral colonies like Coelastrea aspera and Goniopora cellulosa recorded high in its zooxanthellae density, 0.258±0.134x10-5cm-2, and 0.224±0.229x10-5cm-2, respectively, in 40-60mg/L total suspended solids (TSS) of turbid water area. Moreover, thermal stress experiments were conducted to investigate how the zooxanthellae thrive at 31°C to 37°C of water temperature. Results obtained indicated that every coral expelled two forms of Symbiodinium morphology, which were healthy and degraded cells, and the ratios of these forms differ depending on the exposed temperature. Corals expelled healthy and degraded Symbiodinium cells in the ratio 4:6 when exposed to 30°C -33°C. In contrast, when the temperature was increased to 33°C-37°C, the expulsion rate drastically increased, except Goniopora cellulosa, where almost 80% of the expelled populations exhibited healthy Symbiodinium cells. This result indicated that under non-stress conditions, the corals regulate Symbiodinium density by expelling degraded cells. This function will break down under high temperature, leading to extensive loss of healthy but photosynthetically damaged Symbiodinium cells as their Fv/Fm value was gradually decreased. It was found that Porites lutea, the massive meandroid coral is the most resistant coral species towards the turbid water and high temperature. In conclusion, corals could adapt to stress condition through the action of photoprotective mechanisms such as increasing or decreasing its photo-protective pigments to gain maximum light capture or controlling its Symbiodinium density inhibit within coral polyps.
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Keywords
Symbiosis