Photosynthetic characteristics of the phytoplankton in the Scheldt estuary: community and single-cell fluorescence measurements

Abstract

Estuaries present a very dynamic environment for phytoplankton with large changes in salinity occurring over relatively short distances, usually with high turbidity. We investigated the photosynthetic characteristics of phytoplankton in the Scheldt estuary (Belgium and the Netherlands) along a salinity gradient using community and single-cell fluorescence measurements. Single-cell fluorescence measurements offer the opportunity to study differences between species that were formerly possible only using uni-algal cultures. The objective was to study differences in the photochemical efficiency of photosystem II (F v /F m ) between different species or different genera (when identification to the species level was not possible) and to investigate the effect of salinity on individual species. The difference in F v /F m between species was small, but often significant (ANOVA, p < 0.05), and was found to be a true characteristic of species, as opposed to being caused by stochastic processes affecting cells of all species more or less equally. High algal mortality is implied by a large decline of biomass from freshwater towards higher salinity, as well as a complete change in the phytoplankton composition. Nevertheless, cells with low F v /F m , which would indicate decreased health, were rare. F v /F m of 93% of the measured cells was between 0.5 and 0.8. There was no obvious relation between F v /F m and species abundance. In laboratory studies, green algae are often reported to have a higher F v /F m than diatoms, but we found no indication of this in the Scheldt estuary.

Mapping Phytoplankton Community Physiology on a River Impacted Continental Shelf: Testing a Multifaceted Approach

“…Some studies indicate that changes in phytoplankton community structure may lead to differential response to FRRF (Moore et al 2005;Suggett et al 2009a); therefore, such information would have improved the interpretation of our findings. On the other hand, other studies have shown that there are only small differences in F v /F m between different species in estuarine settings (Dijkman and Kronkamp 2006).…”

Temporal variation of caspase 3-like protein activity in cultures of the harmful dinoflagellates Karenia brevis and Karenia mikimotoi

“…However, the maintenance of high F v /F m values even during the decline phase of the cultures is unexpected and surprising since F v /F m is commonly used as an indicator of the physiological state of cells, which responds mostly to nutrient limitation and high irradiance (Kolber and Falkowski, 1993). Because large proportions of dead "but intact and pigment-containing" cells are now known to be present in phytoplankton communities (Veldhuis et al, 2001;Agustí 2004), Franklin et al (2009) (Dijkman and Kromkamp, 2006).…”

Combined effect of high light and high salinity on the regulation of photosynthesis in three diatom species belonging to the main growth forms of intertidal flat inhabiting microphytobenthos

“…Surprisingly, changes in salinity have been less studied in benthic diatoms, while in planktonic diatoms it is known to induce modification of community species diversity (Dijkman and Kromkamp, 2006;Muylaert et al, 2009;Petrou et al, 2011;Thessen et al, 2005), and of growth and photosynthesis (Dijkman and Kromkamp, 2006;Petrou et al, 2011;Thessen et al, 2005). Salinity often co-varies with other environmental gradients like light and temperature in the case of high salinities (due to pore-water evaporation in the upper-layer of the sediment) and with nutrient concentrations in the case of low salinities (due to the discharge of estuarine rivers) (Admiraal and Peletier, 1980;Thornton et al, 2002;Underwood and Provot, 2000).…”