Microzooplankton grazing impact on the phytoplankton community at a coastal upwelling

Abstract

Microzooplankton grazing impact on the phytoplankton community at a coastal upwelling station off northern Baja California, MexicoImpacto del pastoreo del microzooplancton sobre la comunidad fitoplanctónica en una estación de surgencia costera localizada en la región norte de Baja California, México ABSTRACT. Experiments were carried out at a coastal upwelling site (ENSENADA station) off northern Baja California (México) during autumn 2015 (OCT-15) and spring 2016 (APR-16) to estimate phytoplankton daily growth (µ o ) and mortality (m) rates and to assess microzooplankton grazing impact (m:µ o ) on the phytoplankton community and specific autotrophic groups. In accordance with regional seasonality and under an environmental warming scenario due to the El Niño 2015-2016 event, significant differences in both hydrographic conditions and the growth-mortality dynamics of the phytoplankton community were observed between the 2 study periods. The µ o and m estimates were, respectively, 0.120 ± 0.012 d -1 and 1.145 ± 0.049 d -1 for OCT-15 and 1.186 ± 0.002 d -1 and 0.409 ± 0.086 d -1 for APR-16. The results of this study suggest that the effects of the anomalous warming on the phytoplankton community were more evident in OCT-15. During that period, growth of the larger autotrophic components (diatoms) was severely controlled by the environmental limitation of nutrients caused by the sinking of the thermocline that resulted from the entrance of warm water to the region. Furthermore, microzooplankton exerted active grazing pressure on phytoplankton biomass (72% of chlorophyll a [Chla]) and primary production (PP = 0.20 µg Chla·L -1 ·d -1 ), with grazing impact >100% of PP. In APR-16, when the ecosystem apparently started returning to the spring conditions, a high value for PP (3.73 µg Chla·L -1 ·d -1 ) was estimated, with only one third of it being consumed by microzooplankton (34% of PP). The results of this research evidence the high dynamism of multivorous food webs coupled to the seasonal and interannual variability of coastal upwelling systems.RESUMEN. En un sitio de surgencia costera (estación ENSENADA) frente a la región norte de Baja California (México) se realizaron experimentos durante el otoño de 2015 (OCT-15) y la primavera de 2016 (ABR-16) para estimar las tasas diarias de crecimiento (µ o ) y mortalidad (m) del fitoplancton, que permitieron evaluar el impacto (m:µ o ) que genera el pastoreo diario del microzooplancton sobre la comunidad de fitoplancton y grupos autótrofos específicos. Acorde con la estacionalidad de la región y bajo el escenario de un calentamiento ambiental debido al evento El Niño 2015-2016, se observaron notables diferencias en las condiciones hidrográficas y en la dinámica de crecimiento y mortalidad de la comunidad de fitoplancton entre los 2 periodos de estudio. Las estimaciones de µ o y m fueron, respectivamente, 0.120 ± 0.012 d -1 y 1.145 ± 0.049 d -1 para OCT-15 y 1.186 ± 0.002 d -1 y 0.409 ± 0.086 d -1 para ABR-16. Los resultados de este estudio sugieren que los efectos del calenta...

The Effect of Cold and Warm Anomalies on Phytoplankton Pigment Composition in Waters off the Northern Baja California Peninsula (México): 2007–2016

“…Many of these investigations [14,25,26,28] reported the effect of these warm anomalies on sea surface temperature and phytoplankton biomass from the SCC southern region using information obtained from remote sensors. However, off the Baja California Peninsula, only the work of Linacre et al [30] and Jiménez-Quiróz et al [31] reported results regarding phytoplankton biomass and its taxonomic composition in consideration of field data from the entire water column; however, their work was based on a reduced number of cruises and a short period of time.…”

Impacts of the 2014–2015 Warm‐Water Anomalies on Nutrients, Chlorophyll‐a and Hydrographic Conditions in the Coastal Zone of Northern Baja California

“…In other words, was there a top‐down or bottom‐up control on the phytoplankton size‐structure in that period? Underlying factors invoked in modulating size‐structure in marine environments, include temperature (López‐Urrutia & Morán, 2015), sinking and grazing (Acevedo‐Trejos et al., 2015; Linacre et al., 2012, 2017) and changes in nutrient supply (Finkel et al., 2010; Marañon et al., 2012, 2014, and references therein). In the case of temperature, it is well known that this variable regulates the metabolic response of phytoplankton (e.g., Lewandowska et al., 2014; Sherman et al., 2016); however, phytoplankton metabolic rates increase with temperature only when nutrients are abundant (Marañon et al., 2012, 2014, 2018).…”

“…On the other hand, zooplankton grazing "pushes" the phytoplankton community toward larger cell sizes (Acevedo-Trejos et al, 2013, and the apparent dominance of smaller size cells throughout the study (Figures 3c-3f) might suggest that zooplankton grazing was not a factor controlling size-structure of phytoplankton during the 2014-HW and El Niño events (Lavaniegos et al, 2019). However, in an experiment carried out in October 2015 (i.e., El Niño), Linacre et al (2017) reported that microzooplankton exerted an intense grazing pressure on phytoplankton biomass (>70% [Chl-a]) and daily primary production (>100% PP). Thus, their data suggest that the low Chl-a recorded during El Niño 2015 could also be explained by microzooplankton grazing, and thereby, this process cannot be completely ruled out.…”

“…The latter period was characterized by an increase of Prochlorococcus, a distinctive cyanobacteria thriving in oligotrophic and highly stratified waters (Gonzalez-Silvera et al, 2020;Hirata et al, 2011;Lewandowska et al, 2014). Similarly, Linacre et al (2017) studied the temporal variability of picoplankton carbon-biomass at a station located 5 km southeast of our station 6, during March and October 2015. They recorded an increase in carbon-biomass of the cyanobacterial populations, Prochlorococcus and Synechococcus, linked with the appearance of unusually warm water in nBC in 2015.…”

“…The first anomalously warm condition was initially observed during the winter of 2013–2014, when the waters off the coast of Alaska showed anomalously high temperatures (Gentemann et al., 2017). Then, during 2014, the patch of warm water (hereafter 2014‐HW for heatwave) appeared along the coast of Baja California in the southernmost part of the CCS (Avila‐Lopez et al., 2016; Di Lorenzo & Mantua, 2016; Durazo et al., 2017; Gómez‐Ocampo et al., 2017, 2018; Rudnick et al., 2017). Such thermal anomaly in surface waters of the northeastern Pacific was due to a persistent high‐pressure ridge that inhibited winter mixing, preventing typical cooling of surface waters (Bond et al., 2015; Siedlecki et al., 2016), and enhanced northward surface ocean transport by anomalous easterly winds (Freeland & Whitney, 2014; Peterson et al., 2015).…”