Primary production, biomass and abundance of phototrophic picoplankton in the Mediterranean Sea: a review

Abstract

In the Mediterranean Sea, the contribution of picophytoplankton to primary product~on varies from 31 % (Straits of Messina, with an average total production of 0.18 mg C m-3 h-') to 9 2 % (Ionian Sea, with an average of 1.64 mg C m-3 h-'). Although studies have used different methodologies, the contribution of this small phototrophic fractlon to whole " C assimilation seems to be more important in oligotrophic off-shore waters (71 %) compared to the neritic ones (44 %). Diluting effects of fluvial waters (Adriatic Sea) and hydrodynamic phenomena (Straits of Messina) probably influence the physiologic activity of these populations. Picophytoplankton contribution to primary production in brackish and eutrophic environment is clearly lower than in marine waters both in terms of chl a and of 14C assimilation. Reports of cellular abundance (Cyanobactena and eucaryotic cells) ranged from 105to 10' cells 1-' with a mean value of 10' showing no difference between seasons and suggesting a state of particular equilibrium for this population in the planktonic community. Recent data on prochlorophyte cellular density are of the same order of magnitude (107 cells 1-l) of other picophytoplanktonic procaryotic and eucaryotic organisms.

Assessing the role of dust deposition on phytoplankton ecophysiology and succession in a low-nutrient low-chlorophyll ecosystem: a mesocosm experiment in the Mediterranean Sea

“…In association with picoeukaryotes, both genera might be considered the major contributors of biomass and primary production in oligotrophic environments (Morel et al, 1993;Partensky et al, 1999). Picophytoplankton relevant contribution to total phytoplankton biomass and production is also well known in the Mediterranean Sea (Magazzù and Decembri, 1995;Casotti et al, 2003;Brunet et al, 2006Brunet et al, , 2008.…”

Nutrient and temperature control of the contribution of picoplankton to phytoplankton biomass and production

“…The wealth of data on picoplankton abundance and production in the sea has led to the conclusion that these organisms play a much greater role in oligotrophic waters (Stockner and Antia 1986;Raimbault et al 1988;Peña et al 1990;Chisholm 1992;Magazzù and Decembrini 1995;Li 1998). This dominance would be based on their small cell size associated to small diffusion boundary layers and large surface area per unit volume (Raven 1986).…”

Accumulation of DOC in Low Phosphate Low Chlorophyll (LPLC) area: is it related to higher production under high N:P ratio?

“…In addition, variation in cellular abundance of phytoplankton is relatively small suggesting a state of particular equilibrium for this functional group (Magazzu and Decembrini, 1995). For heterotrophic bacteria, the close coupling between bacterial production and predation by higher trophic levels, suggests a similar pattern (Christaki et al, 2001).…”

“…In this study, we investigate a simple dynamical mechanistic model that includes both competition for inorganic nutrients and commensalism (through DOC exudation and re-mineralization) between pico-phytoplankton and heterotrophic bacteria. During summer, a tight balance between growth limitation by nutrients and control of cell abundances by predation results in relatively stable populations of both group of osmotrophs (Magazzu and Decembrini, 1995;Christaki et al, 2001). In this context, we chose to look at the steady state results assuming constant cell abundance and a conservative amount 934 R. Mauriac et al: Accumulation of DOC in LPLC area: is it related to high N:P ratio?…”