PRELIMINARY STUDIES OF DENITRI F ICAT ION ON A CORAL REEF 



Sybil P. Seitzinger 



and 



Christopher F. D'Elia 1 



Division of Environmental Research 



Academy of Natural Sciences of Philadelphia 



Philadelphia, Pennsylvania 19103 



ABSTRACT 



This preliminary study presents evidence that coral reefs may be the sites 

 of potentially high rates of denitrification. Qualitative evidence for the 

 existence of denitrification in dead coral heads and in sediments from a sea 

 grass community were obtained using the acetylene blockage technique and by 

 measuring the rate of nitrate reduction occurring in sediment slurries incubated 

 under anaerobic conditions. The degree to which this denitrification offsets 

 nitrogen fixation is unknown and awaits quantification with better techniques, 

 but from rough approximation it appears to be considerable. 



INTRODUCTION 



Many studies on coral reefs have shown that while standing stocks for N 

 species are low, rates of transformations of N species are rapid (Szmant 

 Froelich, 1983). Coral reefs typically exhibit high rates of nitrogen fixation 

 (Wiebe, et a! . , 1975; Mague and Holm-Hansen, 1975; Bunt, et al . , 1970; Capone 

 and Taylor, 1977), the process by which atmospheric N2 gas is chemically 

 transformed into "combined" nitrogen forms (e.g., ammonia) that can be utilized 

 as nutrients by autotrophs. Indeed, some of the highest rates of N2 fixation 

 for any ecosystem have been reported for coral reef areas. However, denitrifi- 

 cation, the process by which combined nitrogen is chemically transformed back 

 to atmospheric N2 gas, has received much less attention in reef environments. 

 Denitrification represents a potential removal mechanism for combined N both on 

 the reef and in lagoons behind reefs. _Recent reports of substantial rates of 

 nitrification (ammonia oxidation to NO2 and NO3) on coral reefs (Webb and Wiebe, 

 1975; LIMER Expedition, 1977) indicate that a potential exists for denitrifica- 

 tion to occur. 



This paper presents preliminary measurements of denitrification on a coral 

 reef in Abrahams Bay, Mayaguana, Bahamas, and from sediments behind the reef 

 in a lagoon with Thalassia beds. We used techniques suitable for qualitative 

 determination of denitrification under field conditions. This work was carried 

 out on the R/V MARSYS RESOLUTE with the cooperation and support of Dr. Walter 

 Adey of the Marine Systems Laboratory of the Smithsonian Institution. Additional 

 support also was provided by the Ruth Patrick Foundation at the Academy of 

 Natural Sciences of Philadelphia. 



^Present address: Chesapeake Biological Laboratory, Solomons, Maryland 

 20688. 



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