Size distribution of chlorophyll a biomass and primary production in a temperate estuary (Southampton Water): the contribution of photosynthetic picoplankton

Abstract

Size-fractionated chlorophyll a (chl a) biomass and primary production rate (>3 pm, 1-3 pm and < l pm) and picophytoplankton abundance (both prokaryotic and eukaryotic) were investigated in Southampton Water (south coast of England), with routine sampling at 2 stations, representative of conditions in the mid and outer estuary. In the mid estuary the cycle of chl a biomass in the >3 pm size fraction was characterized by a small spring peak and a more intense summer peak. In the outer estuary a chl a maximum in the >3 pm size fraction occurred in spring; phytoplankton in this size fraction may have been nutrient limited in summer at this station. Phycoerythrin-containing picocyanobacteria, eukaryotic picophytoplankton cell numbers, and chl a biomass and primary production rate by the < l pm size fraction all showed a positive correlation with temperature and peaked during summer at both stations. The 1-3 and < l pm size fractions contributed around 14 and 6%, respectively, to the estimated annual rate of depth-integrated plankton community primary production. These results suggest that the impact of the photosynthetic picoplankton diminishes in an increasing eutrophication gradient, from offshore (>50%) to coastal (ca 20%) and estuarine waters (<10%). This pattern in relation to a eutrophication gradient was also apparent on a seasonal basis, the < l pm fraction having its maximum significance at times of lowest overall chl a concentration. It is thus suggested that factors limiting growth and accumulation of larger phytoplankton are the primary cause of an increase in the relative significance of picophytoplankton.

Phytoplankton Biomass and Production in Subtropical Hong Kong Waters: Influence of the Pearl River Outflow

“…Furthermore, during fall and winter, the chl a-specific photosynthetic rate for the small size fraction (<5 μm) is higher than the large size fraction (>5 μm) at all stations. The same results were obtained in other coastal and oceanic waters (Howard and Joint 1989;Iriarte and Purdie 1994). This was likely due to the physiological advantages of a higher efficiency of photon absorption and nutrient uptake for the small-sized phytoplankton under low light and nutrient conditions (Raven 1986).…”

Quantitative relationships between phytoplankton, bacteria and protists in an Aegean semi-enclosed embayment (Maliakos Gulf, Greece)

“…In most systems, after the winter or spring bloom (usually consisting of large diatom cells) collapses, smaller cells (pico-and nanoplankton) tend to dominate (Nielsen & Richardson 1989, Andersson & Rudehall 1993, Iriarte & Purdie 1994, Rodriguez & Guerrero 1994, Brussaard et al 1995, Malej et al 1995. Such a shift, with the potential subsequent development of the microbial loop, seems to be the routine source of fixed carbon to pelagic food webs, if we accept that net phytoplankton blooms (i.e.…”

“…Additionally, mesozooplankton directly interact with the microbial loop food web by grazing upon heterotrophic protists, especially when small phytoplankton dominate the autotrophic community or under oligotrophic conditions . Summer nutrient depletion, which is also considered as evidence for the dominance of pico-and nanoplanktonic organisms (Anderson & Rudehall 1993, Iriarte & Purdie 1994, Malej et al 1995, has been observed in Maliakos Gulf (Kormas et al unpubl.). According to Krupatkina (1990), oligotrophic waters seem to be a most favourable environment for smaller organisms due to more efficient utilisation of near to analytical zero concentration of nutrients, higher photosynthetic activity and practically zero sinking rate.…”

Importance of the Viral Shunt in Nitrogen Cycling in Synechococcus Spp. Growth in Subtropical Western Pacific Coastal Waters

“…In oligotrophic oceans, Synechococcus spp. contribute up to > 50% of the total photosynthetic carbon fixation (Iriarte and Purdie 1994). Furthermore, during warm seasons, Synechococcus spp.…”