Production-respiration relationships at different timescales within the Biosphere 2 coral reef biome

Abstract

Temporal relationships between organic carbon production and respiration are not well understood in coral reef ecosystems. We monitored dissolved oxygen (O2) concentrations within the Biosphere 2 coral reef biome over a 3-yr period (1 January 1997-1 January 2000), to calculate daily rates of gross production (P), community respiration (R), and net community production (NCP). P averaged 170 mmol O2 m-2 d-1, and R averaged 173 mmol O2 m-2 d-1, which yielded a mean NCP of only -3 mmol O2 m-2 d-1, or a difference of only 2%. This long-term balance between P and R reflects the closed-system design of the biome. The SD of P, however, was ±56 mmol O2 m-2 d-1; that of R was ±47 mmol O2 m-2 d-1; and that of NCP was ±26 mmol O2 m-2 d-1 or ±15% of mean P. To better resolve the behavior of P, R, and NCP at different timescales, each of these time series were spectrally decomposed into four frequency bands that corresponded to four timescales: <1 week, 1 week-1 month, 1-3 months (subseasonal), and >3 months (seasonal to annual). At timescales >1 month, the variance of P was not different from the variance of R. At timescales of <1 month, the variance in P was significantly greater than the variance in R (P < 0.01). Furthermore, the correlation between changes in P and changes in R became weaker with decreasing timescale. We suggest that changes in P and R become well matched at timescales that coincide with the turnover of carbon by the dominant macroalgae within the biome (1-3 months). In addition, we conclude that measurements of NCP based on daily or weekly data sets are not good indicators of the long-term net metabolic performance of coral reefs.