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Contrasting metabolic patterns among seagrass and sand-bottom habitats: relative roles of plankton and benthic metabolism
Citation:
Murrell, M., Jim Hagy, J. Caffrey, D. Marcovich, AND D. Yates. Contrasting metabolic patterns among seagrass and sand-bottom habitats: relative roles of plankton and benthic metabolism. CERF 2015, Portland, OR, November 08 - 12, 2015.
Impact/Purpose:
This abstract summarizes an SSWR study to be presented in a contributed session at the CERF 2015 conference
Description:
Human activities can alter the ecological function of estuaries, affecting the ecosystem metabolic balance, which in turn dictates the magnitude and mode of organic matter accumulation. Because human perturbations can cause a loss of seagrass habitat, seagrasses can be a sensitive indicator of overall ecosystem health. In this study, we examined ecosystem metabolism in shallow subtidal waters in Pensacola Bay, comparing a Thalassia testudinum seagrass bed with a nearby deep, bare-bottom site. Over a 6 month period in 2013, we deployed continuous water quality monitors at each site, and conducted 40 plankton production-respiration bottle experiments. Continuous data were used to calculate ecosystem metabolism rates using Odum’s open water method, whereas plankton metabolism rates were derived from the bottle experiments; benthic metabolic rates were inferred by difference. At the deep site, plankton and ecosystem metabolism rates (production and respiration) were similar, implying a minor benthic role in total ecosystem metabolism. In contrast, at the shoal site, ecosystem metabolic rates were ~ 7-fold larger than corresponding plankton metabolic rates, indicating a strong benthic contribution. Midway through the study, high river flow lowered the salinity at study sites, which affected plankton and ecosystem metabolic rates differently. In general, plankton net metabolism increased following the freshwater inflow, becoming net autotrophic, whereas ecosystem metabolic rates showed no definitive trend. The flow event decreased water transparency reducing light to the seagrass bed by ~20%. Despite these changes caused by intrusion of low salinity water, the effect on net ecosystem metabolism was small with near balanced net metabolism persisting at both sites. These complex response patterns underscore the importance of improving integrated process rate measurements to help predict ecosystem responses to environmental variability in estuarine environments.