Bahia Magdalena is a coastal lagoon with an enormous biological and fishing wealth; it is located in the Pacific coast of Baja California (Mexico), a transitional zone between tropical and temperate regions which is strongly affected by the global-scale climate phenomena. The objective of this work was to determine the impact of the unusual and consecutive warming events known as The Blob (TB2013–2015) and the 2015–2016 El Niño on the hydrological characteristics and plankton communities, the lower levels of the trophic web, from January 2015 to December 2017. This coastal lagoon lacks river runoff and primary producers depend on the upwelling’s nutrient supply. The environmental variables analyzed were the upwelling index (PFEL-NOAA), the air and sea temperature, salinity, nutrients, and chlorophyll-a. The species composition, species richness and the Shannon-Weiner diversity index were used to describe some aspects of the phytoplankton community structure and its phenology. The biomass and mortality of zooplankton also were analyzed. The seasonal pattern of hydrology was described with data collected in nine sampling stations. An alternative approach used with both biological and environmental datasets was to select representative sampling stations located in the vicinity of the inlet and in the interior of the lagoon. Chla-fluorescence imagery collected by the MODIS-Aqua satellite was used as an indicator of phytoplankton abundance. Statistical analyses included bi- and multivariate parametric and non-parametric tests. Principal component analysis was used to describe the seasonality of hydrological data and the canonical correlation analysis to relate environmental and biological datasets. The increase of temperature at a global and local scale in 2015 had as consequence an atypical increase in the water temperature in the fall of 2015, coincident with the abrupt diminishing of upwelling strength and input of nutrients advected from the ocean. A recovery of these two variables was recorded in 2016 at the end of the El Niño. The most abundant group of phytoplankton species were diatoms. Algal blooms were composed by species adapted to high temperatures and nutrients depletion in 2015, while in 2016 and 2017 were composed by ruderal-strategist species and they were boosted by the nutrient pulses associated with the spring upwellings. The fall algal bloom, typical of subtropical coastal lagoons, was observed only in 2016 and it was confined to the interior of the lagoon where there are local inputs of nutrients. In 2015 and 2016 there was a succession of diatoms and dinoflagellates related to the rising of temperature while in 2017 this pattern changed because of the strong upwellings. The relationships of water temperature and silicate with a ratio of diatoms’ cell abundance, was analyzed using generalized additive models (GAMs), showing significant correlations but different trends in some years. The species richness of diatom blooms was high; on the other hand, species diversity increased at the end of spring and early summer. The seasonal pattern of zooplankton biomass showed changes along the 3 years, but the most noticeable was an increase during winter and early spring 2015 and the lack of the usual high values of June–July in 2017. The seasonal pattern of the phytoplankton abundance was different in comparison with the 1982–1983 El Niño while the zooplankton was similar among the three strongest El Niño. The changes we observed strongly suggest that the warming caused by those phenomena highly affected the upwelling strength, the length of the temperate and warm seasons and the hydrology. Phenology of phytoplankton and zooplankton changed after the strong perturbation under the El Niño, and possibly The Blob. The recovery of phytoplankton biomass began in 2017, but its taxonomic composition was not adequate to support the zooplankton recovery.
The Oxygen Minimum Zone (OMZ) of the Tropical South Eastern Pacific (TSEP) is one of the most intensely deoxygenated water masses of the global ocean. It is strongly affected at interannual time scales by El Niño (EN) and La Niña (LN) due to its proximity to the equatorial Pacific. In this work, the physical and biogeochemical processes associated with the subsurface oxygen variability during EN and LN in the period 1958–2008 were studied using a regional coupled physical-biogeochemical model and in situ observations. The passage of intense remotely forced coastal trapped waves caused a strong deepening (shoaling) of the OMZ upper limit during EN (LN). A close correlation between the OMZ upper limit and thermocline depths was found close to the coast, highlighting the role of physical processes. The subsurface waters over the shelf and slope off central Peru had different origins depending on ENSO conditions. Offshore of the upwelling region (near 88°W), negative and positive oxygen subsurface anomalies were caused by Equatorial zonal circulation changes during LN and EN, respectively. The altered properties were then transported to the shelf and slope (above 200 m) by the Peru-Chile undercurrent. The source of nearshore oxygenated waters was located at 3°S−4°S during neutral periods, further north (1°S−1°N) during EN and further south (4°S−5°S) during LN. The offshore deeper (< 200–300 m) OMZ was ventilated by waters originating from ~8°S during EN and LN. Enhanced mesoscale variability during EN also impacted OMZ ventilation through horizontal and vertical eddy fluxes. The vertical eddy flux decreased due to the reduced vertical gradient of oxygen in the surface layer, whereas horizontal eddy fluxes injected more oxygen into the OMZ through its meridional boundaries. In subsurface layers, remineralization of organic matter, the main biogeochemical sink of oxygen, was higher during EN than during LN due to oxygenation of the surface layer. Sensitivity experiments highlighted the larger impact of equatorial remote forcing with respect to local wind forcing during EN and LN.
Understanding the interactive effects of multiple stressors on pelagic mollusks associated with global climate change is especially important in highly productive coastal ecosystems of the upwelling regime, such as the California Current System (CCS). Due to temporal overlap between a marine heatwave, an El Niño event, and springtime intensification of the upwelling, pteropods of the CCS were exposed to co-occurring increased temperature, low Ωar and pH, and deoxygenation. The variability in the natural gradients during NOAA’s WCOA 2016 cruise provided a unique opportunity for synoptic study of chemical and biological interactions. We investigated the effects of in situ multiple drivers and their interactions across cellular, physiological, and population levels. Oxidative stress biomarkers were used to assess pteropods’ cellular status and antioxidant defenses. Low aragonite saturation state (Ωar) is associated with significant activation of oxidative stress biomarkers, as indicated by increased levels of lipid peroxidation (LPX), but the antioxidative activity defense might be insufficient against cellular stress. Thermal stress in combination with low Ωar additively increases the level of LPX toxicity, while food availability can mediate the negative effect. On the physiological level, we found synergistic interaction between low Ωar and deoxygenation and thermal stress (Ωar:T, O2:T). On the population level, temperature was the main driver of abundance distribution, with low Ωar being a strong driver of secondary importance. The additive effects of thermal stress and low Ωar on abundance suggest a negative effect of El Niño at the population level. Our study clearly demonstrates Ωar and temperature are master variables in explaining biological responses, cautioning the use of a single parameter in the statistical analyses. High quantities of polyunsaturated fatty acids are susceptible to oxidative stress because of LPX, resulting in the loss of lipid reserves and structural damage to cell membranes, a potential mechanism explaining extreme pteropod sensitivity to low Ωar. Accumulation of oxidative damage requires metabolic compensation, implying energetic trade-offs under combined thermal and low Ωar and pH stress. Oxidative stress biomarkers can be used as early-warning signal of multiple stressors on the cellular level, thereby providing important new insights into factors that set limits to species’ tolerance to in situ multiple drivers.
Frontiers in Pharmacology
Artificial Intelligence for Translational Pharmacology