Browsing by Subject "Microphytobenthos"

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Primary production by microphytobenthos in Corpus Christi Bay, Texas
(1988) MacIntyre, Hugh Logan, 1960-; Cullen, John J.
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
Spatial and temporal variations in benthic bivalve stable isotopic composition in the Chukchi Sea, Arctic Ocean
(2018-01-25) Nguyen, Hoang Minh; Black, Bryan A.; Dunton, Kenneth H.
The Chukchi Sea is one of the most productive marine ecosystems in the world. Around 10% of its net primary production originates from sea ice algae, much of which falls ungrazed to a relatively shallow (40 - 50 m) shelf. The chlorophyll α derived from sinking ice algae is thought to support a robust macrobenthic faunal community, dominated by bivalves, which in turn supports higher trophic organisms such as Pacific walrus (Odibenus rosmarus divergens), and bearded seal (Erignathus barbatus). However, reductions in sea ice extent and earlier break-up could reduce epontic ice algal production and enhance the contribution by phytoplankton, decreasing the relative proportion of ice algal carbon delivery to benthic consumers. To address this question, we examined the stable isotope composition of ten common benthic bivalve taxa, collected in summer and spring between 2002 and 2016, to determine if their spatial and temporal variability revealed changes in diet with respect to sea ice conditions and to identify any differences among feeding guilds. The results showed no interannual variations but revealed a significant northeast to southwest increase in δ¹³C values. Benthic bivalves across feeding guilds also appear to assimilate a greater proportion of isotopically heavier carbon in locations with earlier ice break-up. The findings indicate high level of diet fidelity among the selected taxa and suggest there exists a ‘food bank’ in the Chukchi Sea sediments that is highly enriched in ¹³C. This sedimentary food bank could serve as a buffer to protect benthic bivalve community from changes in the delivery of ice algal carbon in response to shifting ice conditions. However, long-term changes in the delivery of reduced ice algal carbon to the seabed could result in changes in benthic community structure and production that could eventually cascade to higher trophic levels.