Picoplankton dynamics during contrasting seasonal oceanographic conditions at a coastal upwelling station off Northern Baja California, Mexico

Abstract

The exception was an intense algal bloom (.25 mg Chl a L 21) during La Niña-intensified upwelling conditions in April 2008, during which biomass and production estimates of picophytoplankton were at their lowest levels, suggesting that the smallest primary producers were being replaced by larger cells. Thus, for most of the environmental circumstances encountered during our study, our results supported the recent "rising tide" hypothesis that improved growth (nutrient) conditions benefit all size classes, including picophytoplankton. Under extreme conditions of upwelling, however, the picophytoplankton declined abruptly, despite seemingly strong (average) growth rates. Future studies need to provide a better mechanistic understanding of the physical (advection), physiological (nutrient uptake and temperature) and ecological (food web) factors that result in this dramatic nonlinearity in picophytoplankton response to system forcing and richness.

Effects of coastal upwelling on picophytoplankton distribution off the coast of Zhanjiang in South China Sea

“…Upwelling can transport bottom/subsurface water to the surface, and rich deep sea water can stimulate phytoplankton growth. Several studies have focused on changes in the phytoplankton community induced by upwelling (Rodriguez et al 2003, Linacre et al 2010, van Dongen-Vogels et al 2012. These studies showed that the vertical location, magnitude, and composition of the maximum chlorophyll content can be highly affected by changes in the vertical nutrient transport and pycnocline oscillations, which are associated with coastal upwelling.…”

Temporal dynamics of carbon flow through the microbial plankton community in a coastal upwelling system off northern Baja California, Mexico

“…Based on in situ fluorescence profiles, seawater for the experiments was collected in 5 l Niskin bottles from the euphotic zone at the subsurface chlorophyll maximum (SCM) and from the depths above and below the SCM. Details of the experimental design are described by Linacre et al (2010a). Briefly, dilution treatments (10, 30 and 100% of natural plankton density) were prepared in clear polycarbonate bottles (2 l), mixing a whole seawater fraction with water directly filtered from the Niskin bottles using a peristaltic pump, silicone tubing and an in-line Suporcap filter capsule.…”

“…For enumeration of picophytoplankton and heterotrophic bacteria, 2 ml samples were preserved (in 0.5% paraformaldehyde, final concentration), flash frozen and stored in liquid nitrogen until analysis. Samples were analyzed with a BeckmanCoulter Altra cytometer following the approach described by Linacre et al (2010a) and Taylor et al (2011). The cell abundances of hetero trophic bacteria (H-Bact), Prochlorococcus spp.…”

“…According to these calculations, the ranges in cell carbon estimates were 16 to 24 (H-Bact), 34 to 47 (Pro), 64 to 119 (Syn) and 608 to 1421 fg C cell −1 (P-Euks). For size structure assessments, we assumed that the largest 'pico' sized cells were 2 µm in diameter, although some in the enumerated P-Euks category may have been larger than this formal cut-off (Linacre et al 2010a). …”

“…Instantaneous rates of phytoplankton growth (μ) and mortality loss (m) due to protistan grazers were estimated from dilution incubations in accordance with Landry & Hassett (1982), using the abbreviated 3-treatment dilution protocol described by Linacre et al (2010a). Initial pigment concentrations and population abundances (C 0 ) from HPLC and FCM analyses, respectively, were determined for each dilution treatment from measured concentrations in the unfiltered seawater (100%) and the proportion of unfiltered (D i ) seawater in the treatment i.…”