Primary production by microphytobenthos in Corpus Christi Bay, Texas




MacIntyre, Hugh Logan, 1960-

Journal Title

Journal ISSN

Volume Title



The photosynthetic rates of microphytobenthos, those microalgae associated with sediment, were measured in a shallow, turbid bay on the coast of Texas. Rates were determined using a novel technique, appropriate for well-mixed sandy sediments, based on the construction of photosynthesis-irradiance (PI) curves. Photosynthesis-irradiance curves were obtained from ¹⁴C incorporation by suspensions of sediment and were normalized to chlorophyll a. Rates of photosynthesis in situ were calculated from the PI curves and from measured vertical distributions of chlorophyll a and light within the sediment. This technique describes the photosynthetic potential of the microphytobenthos, allowing direct comparison between different strata of the sediment at a single site as well as between different sites. At each site studied, there was a homogeneity of photosynthetic response and biomass that extended well below the photic zone of the sediment, suggesting that the algae in the sediment were mixed vertically. Some evidence that resuspension into the water column is responsible for this homogeneity comes from the vertical differentiation of response and biomass that occurred when sediment was trapped in situ in acrylic cores and from observed fluxes of chlorophyll a and suspended particulate matter in the water column. Because the photosynthetic capacity of the microphytobenthos was similar to that of the algae in the water column, the microphytobenthos may have an important role in net production budgets when resuspended as well as when settled. The sediment may therefore function as a reservoir of photosynthetically-competent algae. The photosynthetic potential and biomass of the microphytobenthos varied on a small spatial scale, as did the rates of photosynthesis realized. Measured hourly rates of microphytobenthic production were 6-62 mg C·m⁻²·h⁻¹. Daily rates were 95-480 mg C·m⁻²·d⁻¹