Primary Production by Phytoplankton and Microphytobenthos in Estuaries

From 1976 through 1978 primary production of microphytobenthos was measured at 6 stations on intertidal flats in the Ems-Dollard estuary using the 14C method. The purpose of the measurements was to estimate the annual primary production at different sites in the estuary and to investigate the factors that influence the rates of primary production. Therefore benthic chlorophyll a and a set of environmental factors were measured. Only primary production correlated sigruficantly with chlorophyll a concentration in the superficial (0.5 cm) sediment layer; other factors (temperature. in situ irradiance) did not correlate with primary production, primary production rate or assimilation number. Annual primary production ranged from ca. 50 g C m-' to 250 g C m-2 and was closely related to elevation of the tidal flat station. However, highest values were also recorded at the station closest to a waste water discharge point in the inner part of the estuary. Annual primary production can be roughly estimated from the mean annual content of chlorophyll a in the sediment. Use of different calculation methods results in annual primary production values that do not differ greatly from each other. Also productivity rates did not differ much over most of the estuary, except at the innermost station which showed a high production rate in combination with high microalgal biomass; this could not be explained by the high elevation of the station alone. A hypothesis is offered to explain the limited primary production of microphytobenthic vegetations.

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Primary production of microphytobenthos in the Ems-Dollard Estuary

Published data on production of natural populations of benthic organisms were used to derive allometric equations relating annual production per unit biomass (P: B ratio) to mean individual body mass (time and biomass weighted) in the population on which production was measured. Separate equations were derived for meiofauna and macrofauna. Since no published data on production and size-structure in natural bacterial populations were found, P:B ratios for bacteria were calculated by extrapolation from an all-inclusive regression. In situ respiration was then calculated from production assuming the two to be approximately equal over an annual cycle for bacteria and benthc microalgae, and using an empirical relation between annual respiration and production in marine benthic animals for meiofauna and macrofauna. Monthly observations of benthic biomass spectra at Pecks Cove, an intertidal site in the upper Bay of Fundy, were used to estimate production and respiration in bacteria, microalgae, meiofauna, and macrofauna from the allometric equations. These estimates compared well with measured production for Corophjum volutator and Macoma balthjca, the 2 dominant macrofaunal species, and w ~ t h gross primary production by benthic microalgae, but not with total community respiration as measured by sediment oxygen consumption. Calculated values for production by bactena were of an expected magnitude ~f between 1 and 10 O/O of the total biomass was assumed to be active. The contribution of meiofauna and macrofauna to total community production (8 to 19 %, depending on the assumphon for bacterial achvity) was d~sproportionately small compared to their relahve biomass (47 to 52 %, also depending on what proportion of bacterial biomass was considered to be actlve). Estimates of respiration were much higher than measured rates of sediment oxygen consurnphon (2.5 to 5.5 times), although both followed closely sirmlar seasonal trends. Bacterial produchon in nature must be directly measured before the validity of our calculations can be assessed. However, we conclude that it 1s possible to obtain reasonable estimates of annual production and its distribution among slze groups in natural benthic comn~unities of eukaryotic organisms using allometric P : B scal~ng.

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Partitioning of production and respiration among size groups of organisms in an intertidal benthic community

The contributions of the planktonic unicellular algae [phytoplankton), the benthic unicellular algae [microphytobenthos) and the benthic multicellular algae (macrophytobenthos) to the primary production of the world ocean are evaluated, together with the respective limitations regarding data, concepts and methods. The use of “free-water” methods (e.g. in situ oxygen or CO2 budgets) is recommended in complement to the more specific measurements on enclosed organisms. For phytoplankton, a previous estimate of 30 . lo9 t C y-’ is retained as a minimal estimate. Earlier estimates of the world benthic production have been based on indirect calculations; revised estimates are suggested here which still lack precision but rely on the actual measurements available at present. Primary production of the micro- and macrobenthic algae amount to 50 and 375 g C m-? y-’ respectively as averages for the whole photic layer they can colonize, and total 2.9 . 10‘ t C y-’ for the world ocean. Thus, benthic algae contribute some 10% of the total marine primary production. On the continental shelf alone, the contributions of benthic and planktonib algae are commensurate and nearly equivalent.

https://horizon.documentation.ird.fr/exl-doc/pleins_textes/pleins_textes_5/b_fdi_31-32/34226.pdf

The comparative estimation of phytoplanktonic, microphytobenthic and macrophytobenthic primary production in the oceans

Microphytobenthic primary production and biomass were studied in an intertidal flat located in the Westerschelde (SW Netherlands) with a vertical resolution of 1 mm. Short-term variability of primary production and photosynthetic characteristics were compared during low tide in 2 types of sediment: sandy and muddy sands. The changes observed were compared with abiotic factors and the biomass abundance, which was dominated by benthic diatoms. C-14 uptake values obtained from incubations in a photosynthetron were used for the construction of P-I (photosynthesis-irradianee) curves. Annual averages indicate that both sediments were equally productive (34.5 +/- 23.6 mg C m(-2) h(-1) and 41.1 +/- 11.6 mg C m(-2) h(-1) for the sands and muddy sands respectively), but production rates were highly variable on monthly time scales and were regulated by different mechanisms. Light and temperature played an important role in determining the production rates, especially in the muddy sediments, where changes in I-k (light saturation) were correlated with temperature. I-k showed seasonal changes, suggesting that algae adapted to the seasonal light conditions but there was not a significant correlation between the I-k and PAR (photosynthetic available radiation) at any of the stations. Vertical migration of the algae, as followed by spectroradiometric measurements, probably accounted for a general absence of photoinhibition. In the sandy sediments, production appeared to be limited by the low biomass of algae, due to resuspension and export. The fact that gross oxygen production rates measured on intact cores using microelectrodes were not lower than potential production obtained from 14C fixation suggests that short-term limitation of production due to nutrients and/or carbon is not frequent in the microphytobenthos of the Westerschelde. [KEYWORDS: microphytobenthos; photosynthetic characteristics; primary production; tidal flats Benthic microalgal production; ems-dollard estuary; natural assemblages; incident irradiance; production dynamics; short-term; light; bay; phytoplankton; communities]

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Factors controlling primary production and photosynthetic characteristics of intertidal microphytobenthos

Primary production by microalgae on intertidal sediments during ebb tide at two sites in Cumberland and Minas Basin, Bay of Fundy, amounted to 47–83 g C∙m−2∙yr−1 Phytoplankton production measured during flood tide over intertidal sediments in Cumberland Basin varied from 4–10 g C∙m−2∙yr−1 with respiration in the water column between 6 and 12 g∙C∙m−2∙yr−1 depending on concentrations of suspended matter. Respiration by undisturbed sediments (47–62 g C∙m−2∙yr−1) was measured at both locations to estimate aerobic metabolic consumption of organic matter.Maximum rates of benthic primary production occurred during early and late summer at both locations but Values at the Cumberland Basin sites were two to three times greater than those observed in Minas Basin; Chlorophyll a in surface sediments was also lower at the stations in Minas Basin where coarser grained deposits reflect extensive sediment transport. Annual benthic respiration at the two stations in Cumberland Basin, however, was only slightly greater tha...

B. T. Hargrave

Papers

Primary Production and Respiration in Pelagic and Benthic Communities at Two Intertidal Sites in the Upper Bay of Fundy