METABOLISM OF INTERREEF SEDIMENT COMMUNITIES 



John T. Harrison, III 

 Mid-Pacific Research Laboratory 

 P. 0. Box 1346, Kaneohe, Hawaii 96744 



ABSTRACT 



Metabolic and nutrient fluxes of lagoon sediment communities at 

 Enewetak, Marshall Islands, were measured using hemispheric incuba- 

 tion chambers. Simultaneous determination of oxygen and carbon 

 dioxide fluxes allowed empirical derivation of an RQ value of 1.5 and 

 a PQ of 0.8. More carbon is respired by the sediment community than 

 is produced, and both production and respiration are closely correl- 

 lated with depth. Biotic and functional comparisons between Enewetak 

 and Kaneohe Bay, Hawaii, suggest metabolic and structural similar- 

 ities between these physiographically disparate coral reef systems. 



INTRODUCTION 



Ecosystem analysts increasingly are turning to coral reefs as foci 

 for studies of community metabolism. However, most researchers have 

 concentrated on the conspicuous and highly productive perimeters of 

 reef systems; with a few exceptions (Sournia, 1976; Kinsey, 1979; 

 Harrison, 1981), interreef areas have been largely ignored, despite 

 the fact that these regions usually comprise the substantial areal 

 majority of the coral reef ecosystem. Lagoon floor communities have 

 long been regarded as sinks for the excess production of fringing 

 reef crests. However, neither sediment community metabolic charac- 

 teristics nor overall dimensions of the functional relationship 

 between organic sources and sinks within reef systems have been ade- 

 quately described. 



Enewetak Atoll in the northern Marshall Islands has been the site 

 of numerous pioneering investigations into coral ecosystem dynamic 

 processes. Perhaps more than any other major system, Enewetak pro- 

 vides an opportunity to achieve an empirical synthesis of all the 

 main components of coral reef ecosystems for an overall budgetary 

 analysis of organic metabolism. There remain only two major system 

 compartments needing detailed description: the lagoon water column, 

 and the lagoon benthos. In this report, I intend to provide suffi- 

 cient data to characterize the latter compartment, and I further hope 

 to provide impetus to encourage pursuit of the final area of uncer- 

 tainty, the lagoon planktonic community. 



METHODS AND RESULTS 



Clear acrylic hemispheres (domes) with a radius of 0.5 meters were 

 used to isolate sample areas for metabolic and dissolved inorganic 

 nutrient fluxes. Oxygen concentrations were measured polarographic- 

 ally; carbon dioxide fluxes were calculated from temperature, pH , 

 and alkalinity measurements (Smith and Kinsey, 1978). Preliminary 

 alkalinity determinations confirmed Smith and Harrison's (1977) sug- 

 gestion that net CaC0 3 production of the sand-rubble component of the 

 Enewetak marine environment is effectively zero. Thus, the majority 

 of C0 2 calculations were based on temperature and pH measurements 

 alone. Dissolved inorganic nutrient concentrations were determined 



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