Primary production by suspended and benthic microalgae in a turbid estuary: Time-scales of variability in San Antonio Bay, Texas
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The within-day, between-day and month-to-month variability of light attenuation and microalgal chlorophyll a (chl a) and photosynthetic response was measured in San Antonio Bay, Texas, USA. Waters were shallow (<2 m) and turbid (attenuation coefficients of 0.7 to 15.3 m(-1), yet daily rates of primary production (0.1 to 2.5 g C m(-2) d(-1)) were comparable to those in much deeper and clearer estuaries. Chl a concentrations in the sediment (459 to 7837 mg m(-3) in the surficial millimeter) were much higher than those in the water column (4 to 48 mg m(-3)). The benthic assemblages were photosynthetically competent, but daily benthic primary productivity was low (0.00 to 0.09 g C m(-2) d(-1); an average of 2 % of productivity in the water column) because of the very low irradiances at the sediment-water interface. The high rates of production by the suspended microalgae were largely due to high chlorophyll-specific light-saturated rates of photosynthesis, P-m(chl) [3.0 to 24.4 g C (g chl a)(-1) h(-1)], which were correlated positively with temperature and inversely with the mean irradiance in the water column. The between-day and temperature-independent variation in P-m(chl) was also correlated with F(v)Chl(-1), an index of the proportion of functional photosystem II reaction centers. In turn, within-day variability in F(v)Chl(-1) was inversely correlated with the mean irradiance in the water column in 8 of 10 observations, a pattern consistent with photoinhibition. A depression of P-m(chl) caused by photoinhibition throughout the water column may therefore be responsible for the inverse trend of P-m(chl) with mean irradiance in the water column. Short-term (h) variability in suspended chl a and turbidity was high (coefficient of variation = 13 to 75 %), but estimates of daily productivity could be predicted with reasonable fidelity (mean error 27 %) from a single midday determination of chl a, the photosynthesis versus irradiance response and the attenuation coefficient, along with daily incident radiation. The predictive power of a single observation was due to coherence in the variation of chl a, P-m(chl) and the attenuation coefficient in the water column: the decrease in mean irradiance caused by resuspension was compensated for by concomitant increases in P-m(chl) and suspended chl a. Between-day variability in productivity of 15 to 52% approached month-to-month differences, so the optimal use of resources in monitoring productivity would be to take single samples daily.
MacIntyre, HL, and JJ Cullen. 1996. "Primary production by suspended and benthic microalgae in a turbid estuary: Time-scales of variability in San Antonio Bay, Texas." Marine Ecology Progress Series 145(1-3): 245-268. doi:10.3354/meps145245