Global warming and ocean acidification affect coral calcification. Nevertheless, there is not enough information regarding the growth parameters of the main reef-building coral species in marginal growth areas such as the Pacific coast of southern Mexico. In order to fill this gap, coral growth parameters of 8 hermatypic coral species (massive species: Porites panamensis, Porites lobata, Pavona gigantea, and Pavona varians; branching species: Pocillopora meandrina, Pocillopora damicornis, Pocillopora verrucosa, and Pocillopora capitata) were estimated in 2 areas of the southern Mexican Pacific. Branching coral species had a higher calcification rate (2.99–5.23 g CaCO3 cm–2 yr–1) than massive species (0.34–1.13 g CaCO3 cm–2 yr–1). A significant relation between sea surface temperature (SST) and skeletal density was observed in all massive coral species. Also, 2 massive species (P. gigantea and P. varians) showed a significant relation between SST and calcification rate. Upwelling in the Gulf of Tehuantepec transports deep water with low pH and low aragonite saturation, and may be affecting the calcification rate of stony corals in the studied area.

This investigation reports, for the first time, results of CO₂ system 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 (Ω_Ar), and air‐sea CO₂ fluxes (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 Ω_Ar (∼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 CO₂ fluxes ranged from −2.3 mmol m⁻² d⁻¹ in areas with stratified waters to over 25 mmol m⁻² d⁻¹ for mixed areas. Positive values indicate an ocean‐to‐atmosphere flux. Our findings suggest that the Gulf of Tehuantepec is a major source of CO₂ into the atmosphere.

In the Midriff Islands region (MIR) of the Gulf of California (Mexico), tidal mixing plays a very important role in the distribution of chemical properties. Although the temporal variability of the water masses is linked to the ocean dynamics of this region, its importance has not been considered. This work estimates the effect of water mass dynamics on the spatial distribution and seasonal variation of dissolved inorganic carbon (DIC) in the region, with special emphasis on the Ballenas Channel, during winter 2002, spring 2003, and summer 2004. Gulf of California Water (GCW) was found throughout the area in the first 100 m. Below, Subtropical Subsurface Water (SSW) filled the Delfín, Salsipuedes, and Tiburón basins, while to the southeast it was found between 150 and 350 m. Pacific Intermediate Water did not cross the sills. SSW enriches the surface water of the MIR with DIC when it increases in volume and when mixed with GCW by tidal effects. This contribution decreases towards summertime, when SSW sinks and the volume of GCW increases. In winter, GCW had three water types associated with oceanographic mixing processes and in combination with the presence of SSW. There was a strong DIC vs temperature relationship, which can be applied to analyze the carbon dynamics in the MIR, both at the surface using satellite imagery and vertically to simulate physical processes.

Seasonal variations of the CO₂ system in seawater for coral reefs are often controlled by both chemical‐biological processes and by regional oceanographic features in combination with the residence time of adjacent water. This study reports the seasonal variability of the CO₂ system along a year though dissolved inorganic carbon and pH measurements in Cabo Pulmo, a fringing reef from the Mexican Pacific. Two conditions were found on the reef: summer with the presence of Tropical Surface Water (TSW), characterized by high temperature, lower DIC levels, and a higher aragonite saturation (Ω_arag); and winter with Gulf of California Water (GCW), when the opposite occurred. This seasonal variation was due to the horizontal advection of two surface water masses: Gulf of California water during winter and Tropical Surface Water the rest of the year as a result of the ocean circulation at the entrance of the Gulf of California. Therefore, the reef is significantly influenced by open ocean waters, where the depth is less than 20 m. The seasonal variability in Ω_arag between months with the presence of GCW and TSW is one of the largest ranges reported in coral reefs (ΔΩ_arag = 0.5 units). Our results suggest that the reef community cannot modify the aragonite or pH of incoming ocean water. This might be the case in other fringing reefs, where the use of ocean acidification forecast models is suitable.

Providing reliable instrumentation that enables collection of high-​quality, comparable data is one of the most challenging aspects of establishing ocean acidification monitoring programs. This is especially true for under-resourced countries, where such data are mostly unavailable. In 2016, The Ocean Foundation (TOF) worked with international bodies, including the International Atomic Energy Agency’s Ocean Acidification International Coordination Centre and the Global Ocean Acidification Observing Network (GOA-ON), and subject matter experts to develop a set of equipment known as the “GOA-ON in a Box” kit (The Ocean Foundation, 2017). This comprehensive kit provides researchers with everything needed—down to specialized rubber bands—to obtain weather-quality carbonate system measurements as defined by GOA-ON (Newton et al., 2015). Data are generated from spectrophotometric measurements of pHT and manual titrations for total alkalinity from discrete samples as well as in situ sensors, the iSAMI-pH and a CTD. The kit’s modular design, composed of nearly 100 unique items, makes it much less expensive than comparable integrated systems and allows for easier troubleshooting and replacement of supplied spare components.