Mathematical models were used to quantify annual production of the epiphytic community on the saltmarsh cordgrass Spartina alterniflora. Hourly measurements of solar radiation and light attenuation (a function of plant canopy and tidal height) were used as forcing functions in the model. Steeper initial slopes (alpha) of photosynthesis vs. irradiance curves (P-I curves) were estimated in the summer (when the canopy was densest), indicating highest shade adaptation. Model validation showed a good agreement between actual hourly production measurements and hourly predicted net production (r(2) = 0.90). Predicted areal epiphytic community production was negative during all seasons and higher in the high marsh (short S. alterniflora zone) than in the low marsh (tall S. alterniflora zone), due to a more open canopy and less exposure to tidal waters. The results indicated that the epiphytic community on S. alterniflora in North Inlet is an energy sink (i.e. net heterotrophic community). When irradiance values were held constant at 615 mu mol photons m(-2) s(-1) (mean daily irradiance value during daylight), production values were overestimated by 11.68 to 34.77%. Therefore, building quantitative models that include hourly changes in light is key to the realistic estimation of epiphytic production in salt marshes.

ABSTRACTThe temporal and spatial variability in recruitment patterns of macroalgae were stuided by evaluating the appearace of propagules on marble tiles set over a depth gradient in a high marsh tidal creek in North Inlet Estuary, South Carolina. Ulvoids and Porphyra occurred over a wide range of depths in the intertidal zone unlike Ectocarpus and members of the Florideophycease, which grew over a more restricted zone. Ulvoid propagules were the most abundant, attaining maximum densities at 0 and ‐15 cm mean low water (MLW) at all seasons except winter. In summer, coincident with high tubbidity, ulvoid densities decreased at ‐15 cm MLW but not in other seasons. Ulvoid densities at 0 MLW were depressed in January, February was preceded with the lowest recoreded temperatures and salinities during the study period, while the decrease in July was preceded by the highest recorded temperature. The number of taxa was highest in April and September, representing winter‐spring and summer‐fall transition periods, respecitively. The biomass of adult forms was higher on the tiles than on naturally occurring substrala, perhaps due to lack of stable suitable substrata in the field. Inhibition of subsequent recruitment by initial recreuitment was evident only on tiles submerged in October. The initial recruitment pattern of Porphyra rosengurtii coll et Cox and Ectocarpus siliculosus (Dillwyn) Lyngbye seem to determine the biomass distribution of adult forms, while that of ulvoids may be altered later by other factors. The considerable decrease in the number of adult forms compared to the initial denisties of propagules indicales high juvenile mortalities.

Accurate measures of intertidal benthic microalgal standing stock (biomass) and productivity are needed to quantify their potential contribution to food webs. Oxygen microelectrode techniques, used in this study, provide realistic measures of intertidal benthic microalgal production. By dividing a salt-marsh estuary into habitat types, based on sediment and sunlight characteristics, we have developed a simple way of describing benthic microalgal communities. The purpose of this study was to measure and compare benthic microalgal biomass and production in five different estuarine habitats over an 18-mo period to document the relative contributions of benthic microalgal productivity in the different habitat types. Samples were collected bimonthly from April 1990 to October 1991. Over the 18-mo period, tall Spartina zone habitats had the highest (101.5 mg chlorophyll a (Chl a) m−2±6.9 SE) and shallow subtidal habitats the lowest (60.4±8.9 SE) microalgal biomass. There was a unimodal peak in biomass during the late winter-early spring period. The concentrations of photopigments (Chl a and total pheopigments) in the 0–5 mm of sediments were highly correlated (r2=0.73 and 0.88, respectively) with photopigment concentrations in the 5–10 mm depth interval. Biomass specific production (μmol O2 mg Chl a −1 h−1) was highest in intertidal mudflat habitats (206.3±11.2 SE) and lowest in shallow subtidal habitats (104.3±11.1 SE). Regressions of maximum production (production at saturating irradiances) vs. biomass (Chl a) in the upper 2 mm of sediment by habitat type gave some of the highest correlations ever reported for benthic microalgal communities (r2 values ranged from 0.43 to 0.73). The habitat approach and oxygen microelectrode techniques provide a useful, realistic ranged from 0.43 to 0.73). The habitat approach and oxygen microelectrode techniques provide a useful, realistic method for understanding the biomass and production dynamics of estuarine benthic microalgal communities.

Photosynthesis vs. irradiance (P‐I) curves usually express production in terms of production per unit biomass. However, for benthic microalgal communities, the depth of the sediment photic zone as well as the amount of biomass exposed to light varies as a function of incident irradiance. We examined the photosynthetic responses of intertidal benthic microalgal communities from different light environments with traditional depth‐integrated methods as well as the percent Pmax and fixed‐depth interval methods. P‐I curve parameters (α, Ik, Im) change depending on the method used. With the depth‐integrated biomass‐specific method, microalgae in unshaded mudflats have a higher α (0.261±0.016) than microalgae in shaded tall Spartina habitats (0.161±0.014), suggesting that mudflat microalgae are more shade‐acclimated than tall Spartina microalgae. However, if curves are constructed with measurements obtained at a fixed depth (surface) in the sediment, tall Spartina microalgae exhibit a significantly higher α (0.260±0.020) than mudflat microalgac (0.175±0.006). With the latter method, tall Spartina surface microalgae appear more shade‐acclimated than mudflat surface microalgae. We conclude that the fixed‐depth interval method provides a more realistic representation of the photophysiological responses of benthic microalgal communities.

ABSTRACTThe purpose of this study was to develop and validate a habitat‐specific production simulation model to quantify annual benthic microalgal production in North Inlet estuary, South Carolina. Using hourly measurements of incident irradiance during 1990–1991 as the forcing function, the simulation model was used to obtain hourly estimates of areal benthic microalgal gross primary production in five habitat types. The model, which was validated using actual measurements of production, showed good (r2= 0.63, P < 0.001) agreement between observed and predicted production in the short Spartina alterniflora Loisel zone habitats showed the highest mean hourly production (61.1 mg C m−2 h−1) while intertidal mudflats had the maximum hourly rate (166.9 mg C m−2 h−1). Daily production was highly variable, primarily due to daily fluctuations in irradiance. Annual estimates of habitat‐specific production were multiplied by the mates of habitat‐specific production were multiplied by the known area of each habitat type to determine total microalgal production for the estuary (3.423 × 109 g C yr−1). Short Spartina zone habitats provided 45% of total microalgal annual production, followed by intertidal mudflats (22%), tall Spartina zones (18%), shallow subtidal (13%) and microalgal production exceeds phytoplankton and microalgal production but is less than Spartina production.

The in situ metabolism of an oyster reef in North Inlet, South Carolina, was observed for 1 yr using a portable plastic tunnel technique. The fluxes of oxygen, Chl a and ammonium to and from the reef were determined every 10.2 days (33 tidal cycles) for 1 yr and the technique of regression estimation was used to compute annual estimates. The oyster reef took up 6.5 kg·m−2 of oxygen and 23.7 g·m−2 of Chl a over the year. Ammonium release was 124.8 g·m−2 for the same period. The O:N ratio of the fluxes on the reef was ≈ 30:1, indicating carbohydrate and lipid catabolism. Because of the high rates of Chl a and oxygen uptake and ammonium release observed with the in sity tunnel technique, oyster reefs should be considered even more important components in estuarine processes than previously thought.

A synthesis of a comprehensive annual study of material processing in the Bly Creek marsh-estuarine basin is described. The project design provides statistical estimates of material fluxes for the water column, salt marsh, and oyster reef subsystems. Fluxes from a freshwater stream, groundwater, and rain are also presented. Material processing by the Bly Creek marsh-estuarine basin is constituent- and subsystem-specific. Inflows of material via rain, streamwater, and groundwater are small and relatively unimportant compared to tidal fluxes. The salt marsh dominates the basin in aerial extent and in terms of net material fluxes. Most constituents exhibit significant net annual import to the salt marsh. Only DON is exported from the marsh and from the basin at significant levels. The salt marsh appears to recycle most of the nitrogen and phosphorus needed for marsh grass primary production. Sufficient inorganic particulate material is imported to allow the salt marsh to maintain its elevation with respect to ongoing sea-level rise. As a result of metabolic processes, the oyster reef imports particulate materials and releases dissolved nutrients. The reef is a significant consumer of chl a and produces enough dissolved inorganic nitrogen and phosphorus to support water column primary production. The N:P ratio of Bly Creek dissolved inorganic nutrients is lower than that of North Inlet or ocean waters and implies nitrogen conservation or mobilization of particulate phosphorus into orthophosphate. In contrast to human-impacted coastal systems, this pristine basin reduces the N:P ratio as water passes through it. Differences in the N:P ratio are probably the result of DON export, denitrification, and phosphorus import by the basin.

Motile benthic diatoms exhibit rhythmic vertical migrations that are influenced by tidal and light cycles. As a consequence of these periodic migrations, corresponding periodicities in benthic microalgal production should occur. Using oxygen microelectrodes, hourly measurements of microalgal production were obtained from subaerially exposed cores collected from low-intertidal muddy sediments in North Inlet estuary, South Carolina, USA. Microalgal productivity at low tide was twice that at high tide (mean difference 52%) and was significantly correlated with diurnal and tidal periodicities (r2 = 0.41; p < 0.0001). Production values ranged from 28.0 to 460.5-mu-mol O2 mg chl a-1 h-1 and maximum rates were achieved during mid-afternoon low tides. A curvilinear regression equation was constructed to simulate daily and monthly benthic microalgal production based on tidal and light cycles. Comparisons between predictions of the curvilinear equation and published data sets showed a reasonable agreement (r2 = 0.77), suggesting similar phenomena in other estuaries. Current benthic microalgal production models do not account for hourly variability in productivity, leading to potentially large errors when measurements are extrapolated over monthly and annual time scales. Although other physiological and abiotic factors also influence benthic microalgal productivity, much of the short-term variability in production rates may be simply attributed to migratory rhythms within estuarine sediments.

Bacterial abundance, biomass, and rates of secondary production were measured at three locations along a transect extending from stream-input areas to near-ocean areas at the North Inlet salt-marsh ecosystem. Bacterial abundances, biomass, and growth rates were low in stream areas compared to abundances, biomass, and growth rates in high-marsh and near-ocean marsh. This general pattern was influenced by tidal events. Bacteria were more abundant and had higher growth rates during low tides than during high tides at high-marsh and near-ocean marsh sites. This pattern was reserved in stream input areas where bacterial abundance and growth rates were higher during high tides than during low tides. Estimates of bacterial secondary production ranged between 1.8 × 107 and 4.5 × 107 cells·1−1·h−1 and significantly covaried with salinity. Covariance of growth rates and salinity suggested that bacterial growth rates were more closely associated with a given water mass than with a particular landscape segment or the characteristics of that landscape segment.

Intertidal reef communities dominated by filter feeding organisms (such as the American oyster Crassostrea mrginjca) are a prominent feature of some marsh-estuarine systems of the southeaste m United States.Such reef communities may be considered as major components in the coupling of aquatic and benthic systems within the marsh.The ability of the reef community to remove suspended microbial biomass (as ATP) was investigated through the use of a 10 m long plexiglas tunnel that covered 7.9 m2 of reef surface.Generally, there was a net loss of suspended microbial biomass as water flowed over the reef.Microbial biomass levels were lower at the output from the tunnel than at the input to the tunnel for 61 % of flood tides and 76 '10 of ebb tides.Determinations of net transport revealed that total microbial biomass was imported to the reef on 26 of 33 flood-tide phases and 27 of 33 ebb-tide phases.Import rates ranged between 0.1 1 and 5.39 pg ATP S-' during flood tides and between 0.46 and 18.20 pg ATP S -' during ebb tides.Annually 55 g ATP were imported to the reef community.T h s import rate corresponded to an equivalent carbon flow of 1750 g C m-' yr.'The net flow of microbial carbon into the reef community was 20 times greater than reported estimates of particulate organic carbon flow from the entire marsh system to the ocean.

Results of data analyses from multispectral scanning data are presented. The data was collected in July 1977 for concentration of chlorophyll in benthic microalgae (mainly diatoms) on an estuary mudflat.

ABSTRACTCultures of freshwater algae, representing three algal divisions, Synura petersenii Korshikov; Chlamydomonas sp.: and Nitzschia sp., were subjected to four different mercury‐temperature shock interactions to demonstrate synergistic effects between mercury and temperature. Algal growth, measured by temporal changes in vivo fluorescence of chlorophyll was used to ascertain the effects. Mercury addition and temperature shock had various inhibitory effects on algal growth. Prior environmental conditions influence the effect of subsequent treatments. Growth of S. petersenii was severely inhibited by mercury in all experiments. Control cultures would not grow at 30 C and died when shacked at this temperature. Chlamydomonas sp. cultures initially inhibited by mercury were able to recover under most conditions after a period of reduced growth. Nitzschia sp. was resistant to mercury except when simultaneously shocked with temperature. Mercury analyses showed that Nitzschia cells at 25 C and 30 C contained a high percentage of the mercury initially added to the cultures. There was a significant loss of mercury at the end of each experiment from all cultures, probably due to volatilization.

Six species of benthic diatoms and a natural benthic diatom community were cultured in flasks on a variety of sediments. Diatom species which secreted large quantities of mucilage were effective sediment stabilizers. These mucilage-secreting species significantly reduced resuspension and retarded laminar flow of the sediments when the culture flasks were agitated. Diatom species which secreted little or no mucilage were not effective sediment stabilizers. These non-mucilage-secreting species did not significantly effect resuspension or laminar flow of the sediments when the culture flasks were agitated. A sediment stabilizing mechanism based on the secretion of mucilage by pennate benthic diatoms is proposed. The effect such a process may have on distributional patterns of benthic invertebrates in areas where extensive diatom or other microalgal films occur is discussed.