The copepod Eurytemora americana showed in this year the maximal population abundance registered for the estuary over the last decade ( Berasategui et al., 2009 and Hoffmeyer and Prado Figueroa, 1997). Light availability, although may have played a significant role in bloom initiation, was not a determining factor of bloom Selleckchem Apitolisib duration as underwater light penetration remained high over the next two months after the event ended. Dissolved nutrient concentrations were high

all-year round, except during the blooming season (see Fig. 2c). This annual pattern is relatively constant in the inner zone of the Bahía Blanca Estuary, where the nutrients notably decrease in the water column during late winter-early spring in relation to microalgae consumption (Guinder et al., 2010 and Popovich et al., 2008). In the present study, the estimation of nutrient ratios (data not shown) indicated a limitation (Popovich et al., 2008 and references therein) in phosphate (N:P >20–30) and in nitrogen (N:P <10 and Si:N >1) in some dates toward the end of the blooming season. The beginning of the winter bloom was dominated by small diatom species like Chaetoceros

sp. (3–8 μm) and Cyclotella sp. (5–12 μm), which showed a peak of abundance in June–July. The abrupt population decrease of these diatoms in July–August could be related with predation by microzoopankton ( Barria de Cao et al., 2005 and Pettigrosso and Popovich, 2009) and nauplii of E. americana ( Berasategui et al., 2012). Although this small-sized copepod stage was not considered in this study, as we used a net of 200-μm mesh ( Berasategui et al., 2012 and Grice, 1970), it Cabozantinib cost is well known that in the Bahía Blanca Estuary, hatching of resting eggs of E. americana occurs between May–July under conditions of low temperature, high salinity

and high chlorophyll levels and nauplii feed on small sized-phytoplankton ( Berasategui et al., 2012 and Berasategui et al., 2013). The adult stage of E. americana feeds preferentially on large species of the phytoplankton winter assemblage, i.e. Thalassiosira spp. Phosphoribosylglycinamide formyltransferase ( Hoffmeyer and Prado Figueroa, 1997). The selective grazing of the adult of E. americana on large cells might reduce the relative abundances of these diatoms in the mid-late winter bloom. In this study, no fixatives were added to the containers in order to evaluate the accumulation of particulate matter near the bottom over time, embracing also natural processes of production and decomposition (Schloss et al., 1999 and Varela et al., 2004). On the one hand, not using preservatives eliminates the risk of overestimating the sedimentation due to swimmer contamination (i.e. vertically migrating phototrophic micro-organisms) (Heiskanen and Leppänen, 1995 and Heiskanen et al., 1998). On the other hand, when fixatives are not used, the actual sedimentation of organic matter can be slightly underestimated (e.g.