Factors controlling primary production and photosynthetic characteristics of intertidal microphytobenthos

Abstract

Microphytobenthlc 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. 14C uptake values obtained from incubations In a photosynthetron were used for the construction of P-I (photosynthesis-irradiance) curves. Annual averages indicate that both sediments were equally productive (34.5 * 23.6 mg C m-' h-' and 41.1 2 11.6 mg C m-' h-' 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, (light saturation) were correlated with temperature. I, showed seasonal changes, suggesting that algae adapted to the seasonal light conditions but there was not a significant correlation between the Ik 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 sedirnents, 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 llrnitation of production due to nutrients and/or carbon is not frequent in the microphytobenthos of the Westerschelde.

Variability and control of carbon consumption, export, and accumulation in marine communities

“…These results indicate that the influence of primary production on export, by setting an upper limit to the magnitude of organic matter than can be carried out of the community, is blurred by more influential factors, such as the buoyancy of autotrophic material (Zieman et al 1979;Alongi 1998) or exposure to physical energy (Bach et al 1986;Barranguet et al 1998), when communities of diverse or the same type, other than microalgal communities, are compared. Differences in refractory accumulation across types are also poorly associated with those in primary pro-duction.…”

Microphytobenthic primary production in the Bodden estuaries, southern Baltic Sea, at two study sites differing in trophic status

“…Barranguet et al 1998) or within microbial mats (e.g. Oren et al 1995) provided very detailed information on the spatial and temporal heterogeneity of light, photosynthetic activity and oxygen within the sediment itself.…”

“…Thus, benthic primary production rates in KB sediments were well within the range of data for highly productive diatom associations in the Wadden Sea. Colijn & de Jonge (1984) and Barranguet et al (1998) determined benthic gross production rates of 10 to 115 mg C m -2 h -1 and 11 to 58 mg C m -2 h -1 in the tidal zone, respectively, depending on season. Moreover, the photosynthetic rates in KB sediments at light intensities up to 350 µE m -2 s -1 were 1.5 times higher than in biofilms along an eutrophication gradient in Bodden waters (34.4 to 94.5 mg C m -2 h -1 at radiation levels of 100 to 800 µE m -2 s -1 , Meyer-Reil & Neudörfer 1998).…”

“…Since temperature and light were comparable at the sediment surface of both study sites, no significant differences in the physiological adaptations of the 2 algal communities would be expected. Nevertheless, the parameters of the P/E curves such as photosynthetic capacity (P max ), photosynthetic efficiency (α) and light saturation (E k ), should indicate general adaptations of the benthic algae to, for example, low light regimes when data from both study sites are compared with data in the literature (Kohl & Nicklisch 1988, Pickney & Zingmark 1991, Falkowski & Raven 1997, Barranguet et al 1998.…”

“…Hence the calculations of the underwater light field and corresponding production rates (especially with regard to the different trophic status of the 2 study sites) achieved further precision in the present study. Possible physiological adaptations of the benthic algae to prevailing light conditions were examined using photosynthesis/irradiance (P /E) curves with data on maximum photosynthetic capacity (P max ), photosynthetic efficiency (α) and the light saturation coefficent (E k ) (Kohl & Nicklisch 1988, Pickney & Zingmark 1991, Falkowski & Raven 1997, Barranguet et al 1998. To examine possible effects of eutrophication on the benthic microalgal community (Sundbäck & Snoeijs 1991), the species composition of the phytoplankton and microphytobenthos was determined microscopically at the 2 study sites.…”