Input of various nitrogen species by large amplitude internal waves (LAIW) and intake by Pocillopora verrucosa


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Gertraud.Schmidt [ at ] awi.de

Abstract

Spatial distribution of nitrogen species across the Similan Islands chain from west to east directions were investigated during a low and high large amplitude internal waves (LAIW) season in December 2010 and March 2011. Periodic water sampling was performed on the west side Similan reef in a depth of about 15-17 meter together with an in situ temperature logged CTD. Temporal samplings were carried out to determine the dominant nitrogen species in the soliton water reaching the Similan island chain. The major inorganic nitrogen species were chosen in order to determine dissolved inorganic nitrogen (DIN) uptake in screlactenian corals. Pocillopora verrucosa (Ellis & Solander, 1786) was assigned as experimental species because of its common presence on both, west and east sides of the Similan Islands and Racha Island. 40 coral nubbins were collected in situ and reared in the PMBC aquarium for the experimental approaches. The corals were incubated in a Red Sea Salt® solution to control the organic and inorganic nutrient background. Normal warm reef temperature (28°C) and cold LAIW temperature (20°C) were applied in the incubations with different DIN concentrations (control N, 20 μM NO3 -, 6 μM NH4 +20 and 20 μM NO3 - & 6 μM NH4 +) under both dark and light conditions. The incubation period was 2 hours but the water samples were taken as time series after 0, 10, 30, 60, 90 and 120 minutes respectively. The DIN uptake rates were calculated per coral surface area and time period. Additionally, in order to get information on the micro scale of inorganic nitrogen uptake, labeled 15NO3 - and 15NH4 + were used in a further incubation run. Nitrate was found to be the dominant DIN in the soliton waters approaching the reefs at the Similan Islands. The NO3 - uptake experiments under low temperature conditions revealed a significant negative effect on the nitrate uptake rate in both light and dark. However, the concentration-dependent uptake behavior was found in both NH4 + and NO3 - enriched experiments. The concentration of DIN present in water had a higher effect on the uptake rates than temperature. High NH4 + concentration was shown to limit NO3 – uptake. NH4 + was more favorable to P.verrucosa than NO3 -. Light independent uptakes were discovered in both NH4 + and NO3 - enriched experiments. The highest uptake rates were found at the beginning of the incubation experiments (10 minutes after the start) in both NH4 + and NO3 - enriched experiments. The labeled DIN experiments showed that the symbiotic algae are the terminal station for both NO3 - and NH4 +. Delta 15N enrichment exhibits similar results in temperature dependence and concentration dependence as found in normal DIN uptake experiments. Interestingly, a higher uptake rate of NH4 + was found in the zooxanthellae under enriched NH4 + & NO3 - combined with low temperature conditions. LAIW seem to be favorable for the symbiotic corals in the Similans with a high inorganic nutrient supply. Even though the low temperature entrained by the LAIW to the reefs suppresses the optimum uptake the higher abundance of DIN has a greater effect on the corals. This denotes differences in the uptake behavior of corals growing on the exposed side of the Similan Islands (west) and the sheltered sides (east). With this study a possible explanation might be visualized to the differences of the framework formations found on the LAIW exposed and sheltered reefs.



Item Type
Thesis (Master)
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Not peer-reviewed
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Published
Eprint ID
32391
Cite as
Noowong, A. (2011): Input of various nitrogen species by large amplitude internal waves (LAIW) and intake by Pocillopora verrucosa , Master thesis, Bremen University.


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