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Threshold is defined as the point where small changes in an environmental driver produce large responses in the ecosystem. Generalized additive models (GAMs) were used to estimate the thresholds and contribution of key dynamic physical variables in terms of phytoplankton production and variations in biomass in the tropical‐subtropical Pacific Ocean off Mexico. The statistical approach used here showed that thresholds were shallower for primary production than for phytoplankton biomass (pycnocline < 68 m and mixed layer < 30 m versus pycnocline < 45 m and mixed layer < 80 m) but were similar for absolute dynamic topography and Ekman pumping (ADT < 59 cm and EkP > 0 cm d−1versus ADT < 60 cm and EkP > 4 cm d−1). The relatively high productivity on seasonal (spring) and interannual (La Niña 2008) scales was linked to low ADT (45–60 cm) and shallow pycnocline depth (9–68 m) and mixed layer (8–40 m). Statistical estimations from satellite data indicated that the contributions of ocean circulation to phytoplankton variability were 18% (for phytoplankton biomass) and 46% (for phytoplankton production). Although the statistical contribution of models constructed with in situ integrated chlorophyll aand primary production data was lower than the one obtained with satellite data (11%), the fits were better for the former, based on the residual distribution. The results reported here suggest that estimated thresholds may reliably explain the spatial‐temporal variations of phytoplankton in the tropical‐subtropical Pacific Ocean off the coast of Mexico. We statistically estimated the thresholds of physical dynamic variables on phytoplanktonThe mixed layer thresholds were shallower for primary production than for integrated chlorophyll aThe contributions of ocean circulation to phytoplankton production and biomass variability were 46% and 18%

This investigation reports, for the first time, results of CO2system variables in the Gulf of Tehuantepec, located in the Mexican tropical Pacific. We quantified the post‐Tehuano concentration of dissolved inorganic carbon (DIC) and pH (April 2013). These values were used to calculate pCO2, aragonite saturation (ΩAr), and air‐sea CO2fluxes (FCO2). The intense vertical stratification was found to contribute to the biogeochemical processes in surface waters (<70 m). However, in post‐Tehuano conditions, high pCO2 (∼1000 µatm) and DIC concentrations (2200 µmol kg−1), as well as low ΩAr(∼1.1) and pH (∼7.5), remain in surface waters for a few days after Tehuano winds have weakened. We identified four oceanographic areas: (a) a highly mixed region due to previous Tehuano events; (b) coastal upwelling in the western region; (c) mesoscale eddies; (d) a poleward surface coastal current. The first three promoted the influence of Subtropical Subsurface Water in the chemistry of surface waters, whereas the coastal current contributed to the horizontal advection of DIC. The calculated CO2fluxes ranged from −2.3 mmol m−2d−1in areas with stratified waters to over 25 mmol m−2d−1for mixed areas. Positive values indicate an ocean‐to‐atmosphere flux. Our findings suggest that the Gulf of Tehuantepec is a major source of CO2into the atmosphere. The aragonite saturation horizon is close to the surface near the coastReported air‐sea CO2fluxes are the largest observed to date in the Mexican Pacific

AbstractThe distribution of phyllosoma of California spiny lobster Panulirus interruptuswas investigated in relation to the seasonal variability of hydrographic conditions off the west coast of the Baja California Peninsula between 2006 and 2008. Early larval stages were recorded mostly from summer to fall, immediately following the reproductive period. The duration of larval development in plankton is variable (8–12 months), and hence, larvae are found at different times of the year; thus, intermediate and late stages did not show a well-defined seasonal pattern. The highest phyllosoma density was associated with the relatively warm transitional water mass. However, the peak frequency of occurrence was observed in the colder subarctic water mass. A canonical correspondence analysis identified two distinct seasonal periods: (1) a warm period (summer–autumn), when the abundance of early and intermediate stages was highly correlated with a higher sea surface temperature, and (2) a cold period (winter–spring), when the most advanced stages were associated with a lower water temperature and higher dissolved oxygen. The distribution of larvae and the geostrophic flow patterns suggest that transport by the California Current and mesoscale eddies are the primary dispersal and retention mechanisms from the various breeding centers along the peninsula: northern (Ensenada–Punta Baja), central (Punta Eugenia), and southern (Golfo de Ulloa). In contrast, the data obtained suggest that the recruitment of late larval stages and pueruli in settlement areas might be regulated by the formation of meanders and poleward currents, in addition to the ability of pueruli (self-recruitment) to reach settlement areas via swimming.Received January 21, 2015; accepted July 13, 2015

The distribution of phyllosoma of California spiny lobster Panulirus interruptuswas investigated in relation to the seasonal variability of hydrographic conditions off the west coast of the Baja California Peninsula between 2006 and 2008. Early larval stages were recorded mostly from summer to fall, immediately following the reproductive period. The duration of larval development in plankton is variable (8–12 months), and hence, larvae are found at different times of the year; thus, intermediate and late stages did not show a well-defined seasonal pattern. The highest phyllosoma density was associated with the relatively warm transitional water mass. However, the peak frequency of occurrence was observed in the colder subarctic water mass. A canonical correspondence analysis identified two distinct seasonal periods: (1) a warm period (summer–autumn), when the abundance of early and intermediate stages was highly correlated with a higher sea surface temperature, and (2) a cold period (winter–spring), when the most advanced stages were associated with a lower water temperature and higher dissolved oxygen. The distribution of larvae and the geostrophic flow patterns suggest that transport by the California Current and mesoscale eddies are the primary dispersal and retention mechanisms from the various breeding centers along the peninsula: northern (Ensenada–Punta Baja), central (Punta Eugenia), and southern (Golfo de Ulloa). In contrast, the data obtained suggest that the recruitment of late larval stages and pueruli in settlement areas might be regulated by the formation of meanders and poleward currents, in addition to the ability of pueruli (self-recruitment) to reach settlement areas via swimming.