Effects of feeding frequency and symbiosis with zooxanthellae on nitrogen metabolism and respiration of the coral Astrangia danae |
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Authors: | A Szmant-Froelich M E Q Pilson |
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Institution: | (1) Rosenstiel School of Marine and Atmospheric Science, University of Miami, 33149 Miami, Florida, USA;(2) Graduate School of Oceanography, University of Rhode Island, 02882 Narragansett, Rhode Island, USA |
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Abstract: | Colonies of the temperate coral Astrangia danae occur naturally with and without zooxanthellae. Basal nitrogen excretion rates of nonsymbiotic colonies increased with increasing feeding frequency average excretion rate was 635 ng-at N (mg-at tissue-N)-1 h-1]. Reduced excretion rates of symbiotic colonies were attributed to N uptake by the zooxanthellae. Nitrogen uptake rates of the zooxanthellae averaged 8 ng-at N (106 cells)-1 h-1 in the dark and 21 ng-at N (106 cells)-1 h-1 at 200 Ein m-2 s-1. At these rates the zooxanthellae could provide 54% of the daily basal N requirement of the coral if all of the recycled N was translocated. Basal respiration rates were 172 nmol O2 cm-2 h-1 for starved colonies and 447 nmol O2 cm-2 h-1 for colonies fed three times per week. There were no significant differences between respiration rates of symbiotic and nonsymbiotic colonies. N excretion and respiration rates of fed (symbiotic and nonsymbiotic) colonies increased greatly soon after feeding. N absorption efficiencies decreased with increasing feeding frequency. A N mass balance, constructed for hypothetical situations of nonsymbiotic and symbiotic (3×106 zooxanthellae cm-2) colonies, starved and fed 15 g-at N cm-2wk-1, showed that the presence of symbionts could double the N growth rate of feeding colonies, and reduce the turnover-time of starved ones, but could not provide all of the N requirements of starved colonies. Rates of secondary production, estimated from rates of photosynthesis and respiration were similar to those estimated for reef corals. |
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