Seasonal and short-time-scale dynamics of microplankton community production and respiration in an inshore upwelling system

Abstract

An intensive study of pelagc primary production and microplankton community respiration was carried out during an entire upwehng season in the Ria de Vigo (NW Spain). From April to November measurements of oxygen production and respiration using the hght-dark bottle technique were made twice a week at the surface. l % Light depth ( l % LD, 12 r 4 m) and 40 m (8 m above sea floor) alongside routine physical, chemical and biological measurements. During the major part of the survey period intermittent intrusions of cold, nutrient-rich upwelled water were observed In the ria with a periodicity of about 2 wk. Rates of gross primary production (GPP) were high but variable averaging 37.3 + 30.7 pM O2 d-' and 3.6 + 4.8 pM O2 d-' at the surface and l % LD respectively over the period of survey (n = 50). Rates of dark community respiration (DCR) were also high and variable with maximum values being observed in the surface layer where the seasonal average was 12.2 * 9.8 pM O2 d-l. At the l % LD and 40 m, DCR averaged 5.3 + 4.4 and 2.8 * 3.0 I.IM O2 d-l respectively. Although seasonal average and maximal DCR (up to 46.5 pM 0, d-l) were among the highest reported for coastal areas, microplankton production over the period of survey was dominated by autotrophic processes. Respiration losses by the microplankton community in the euphotic zone represented on average 43 % of estimated mean seasonal water column GPP (2.1 to 2.7 g C m-' d-l). Net heterotrophy in the aphotic layer consumed the equivalent of a further 25% of estimated water column GPP. The degree of coup h g between primary production and respiration was primarily controlled by upwelling. Dunng upwelling events respiration was generally low in the water column but it increased as a linear function of chlorophyll a concentrat~on (R2 = 0.55. n = 13) and GPP (R2 = 0.47, n = 13) in the surface layer. Under such condition phytoplankton appears as the dominant component of community respiration consuming 14 % of GPP. During penods of upwelling relaxation respiration was high relative to GPP High water column respiration rates extending occasionally down to 40 m took place at the expense of organic matter trapped inside the bay. The seasonal breakdown of thermal stratification in autumn presented a relationship between surface respiration and chlorophyll a or GPP similar to that observed during upwelling events. The large excess primary production during this period was not remineralised inside the ria, suggesting that a large fraction may be exported towards the shelf.

Net ecosystem metabolism of a coastal embayment fertilised by upwelling and continental runoff

“…Despite the high renewal rate of the study volume, the net ecosystem production was elevated, 1.0-1.5 g C m -2 d -1 . It is comparable to the values obtained in the Rías Baixas during the upwelling season Moncoiffé et al, 2000;Cermeño et al, 2006;Arístegui et al, 2009) and to the gross primary production of the northern Galician coast (Bode et al, 1996;Bode and Varela, 1998). Therefore, although the nutrient levels in shelf waters (Prego et al, 1999) and the offshore Ekman transport (see section 4.1) are lower than off the Rías Baixas, the reduced dimensions of the Ría de Ares-Betanzos leads to comparable nutrient inputs and net ecosystem production rates per unit of surface area.…”

“…Pérez et al, 2000) and of most temperate coastal ecosystems (Howarth, 1988;Wollast 1993). The resulting net ecosystem production rates, 0.2-0.3 g C m -2 d -1 , can be considered representative of summer stratification in the Galician coast (Moncoiffé et al 2000;Cermeño et al, 2006) and about one half to one third the expected gross primary production under these conditions in the study area (Bode et al, 1996;Bode and Varela, 1998).…”

Net ecosystem production of dissolved organic carbon in a coastal upwelling system: the Ría de Vigo, Iberian margin of the North Atlantic

“…It increases to Ͼ250 mmol C m Ϫ2 d Ϫ1 during upwelling episodes, during which the nitrate-rich ENACW is promoted to surface waters (Moncoiffé et al 2000). Primary production rates are similar in other coastal upwelling systems of the world ocean (Wollast 1993).…”

Community metabolism, phytoplankton size ­structure and heterotrophic prokaryote production in a highly productive upwelling zone off northern Chile

“…5). A near-equi librium community ecosystem meta bolism (GPP:CR ratio of ~1) has also been observed during periods of upwelling relaxation or weak upwelling in the Ria de Vigo (Moncoiffé et al 2000). On 2, 4, 6 and 8 February 2007, large cells were dominant (>86%), and the water column presented cold, nutrient-rich conditions identified by shallow thermoclines and oxyclines (Fig.…”