Response of primary producers to the hydrographic variability in the southern region of the California Current System

Jushiro Cepeda-Morales,Eduardo Millán-Núñez,Ramon Sosa-Ávalos,Luis Soto-Mardones,Reginaldo Durazo,Martín De La Cruz-Orozco,Gilberto Gaxiola-Castro,Teresa Leticia Espinoza-Carreón

doi:10.7773/cm.v43i2.2752

Abstract

The response of primary producers to seasonal and interannual variabilities in the hydrographic conditions observed between 1997 and 2012 is analyzed for the southern portion of the California Current System (CCS). The analysis uses the optimum rate of primary productivity (PP) normalized by units of chlorophyll (Chla) in the water column (PBopt) and Chla concentration. In situ PP estimations using the 14C method were obtained as part of the seasonal cruises conducted by the Investigaciones Mexicanas de la Corriente de California program. Supplementary data included sea surface temperature (SST) as measured by the AVHRR sensor from 1985–2009. We found the mean value of PBopt to be at 5.1 ± 3.3 mg C·(mg Chla)–1·h–1, with maximum ranges of 0.5 and 17.5 mg C·(mg Chla)–1·h–1. The relationship between PBopt and SST suggested a phytoplankton community change at around 19 ºC, which characterized the transitional nature of the southern portion of the CCS. SST data suggested, on the one hand, that on average the 19 ºC isotherm is located in the vicinity of Punta Eugenia and, on the other, that its spatial variability defined the alternating cool–warm conditions. At the seasonal scale, this isotherm showed a marked latitudinal displacement (from 24ºN to 32ºN), which was observed to be even out of this range during interannual events associated with El Niño/La Niña. Under both cool-warm hydrographic conditions, the phytoplanktonic community showed large PBopt rates (~6 mg C·(mg Chla)–1·h–1). At the interannual scale, changes were associated to changes in the abundance and composition of nano-microphytoplankton. Additionally, data suggested that high PP rates during warm periods could be attributed to an enhanced picoplankton contribution.

Highlights

The California Current System (CCS) is one of the most productive ecosystems in the world (Carr 2006)
Off Baja California, the CCS is characterized by upwelling favorable conditions (Linacre et al 2010), the formation of mesoscale eddies (Espinosa-Carreón et al 2012), and the influence of interannual (El Niño and La Niña) and decadal events
Physical depths were calculated by using the Beer law: Z = ln(Eo/Ez)/Kd, where Z is depth, Eo is surfce irradiance, Ez is irradiance at depth Z, and Kd is the mean diffuse attenuation coefficient, which was estimated by using depth measurements from the Secchi disc (Zd) and applying the ratio for oceanic waters Kd =1.7/Zd

Summary

Introduction

The California Current System (CCS) is one of the most productive ecosystems in the world (Carr 2006). Off Baja California, the CCS is characterized by upwelling favorable conditions (Linacre et al 2010), the formation of mesoscale eddies (Espinosa-Carreón et al 2012), and the influence of interannual (El Niño and La Niña) and decadal events These factors control primary productivity (PP) and productivity in the pelagic ecosystem (EspinosaCarreón et al 2004). Since 1997, the Investigaciones Mexicanas de la Corriente de California program (Mexican Research Program of the California Current; IMECOCAL, for its acronym in Spanish) has conducted in situ measurements of phytoplankton PP These measurements have allowed us to identify temporal variations in PP at seasonal and interannual scales (Gaxiola-Castro et al 2010), as well as significant differences in variations of integrated PP between summer and autumn (Aguirre-Hernández et al 2004). Evidence indicates that the decrease in biomass and PP in the region is a consequence of interannual variations, such as the one associated with the anomalous intrusion of subarctic water (Espinosa-Carreón et al 2015)

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