Harmful Algal Blooms (HABs) are becoming an increasing problem to human health and environment (including effects on natural and cultured resources, tourism and ecosystems) all over the world. In Mexico a number of human fatalities and important economic losses have occurred in the last 30 years because of these events. There are about 70 species of planktonic and non-planktonic microalgae considered harmful in Mexican coasts. The most important toxin-producing species are the dinoflagellates Gymnodinium catenatum and Pyrodinium bahamense var. compressum, in the Mexican Pacific, and Karenia brevis in the Gulf of Mexico, and consequently the poisonings documented in Mexico are Paralytic Shellfish Poisoning (PSP) and Neurotoxic Shellfish Poisoning (NSP). Although there is evidence that Amnesic Shellfish Poisoning (ASP), Diarrhetic Shellfish Poisoning (DSP) and Ciguatera Fish Poisoning (CFP) also occur in Mexico, these problems are reported less frequently. The type of phytoplankton and epiphytic microalgae, their toxins and harmful effects as well as current methodology used to study these phenomena are presented in this paper. As an experienced group of workers, we include descriptions of monitoring and mitigation programs, our proposals for collaborative projects and perspectives on future research.
Warming Effects on a Mexican Coastal Lagoon diatoms. Algal blooms were composed by species adapted to high temperatures and nutrients depletion in 2015, while in 2016 and 2017 were composed by ruderalstrategist 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.
A new record of Azadinium spinosum (Dinoflagellata) from the tropical Mexican PacificAbstract.-The species Azadinium spinosum, a small thecate dinoflagellate, originally and recently described from the North Sea, was found for the first time in the tropical Pacific coast of Mexico. Description by light and scanning electron microscopy and abundance data are here provided. The morphology of the species agrees with the original description, including size, shape, presence of posterior spine and tabulation details. Less than 300 cells L -1 were found in one station in the Pacific coast of Mexico. This species has been recognized as a producer of azaspiracid toxins (AZAs) in the North Sea, although no toxin analysis has been made as yet in Mexican waters.
Sixteen monthly cruises were carried out at a station 6.5 km to the NW of the mouth of Magdalena Bay (Mexico) to study the temporal variability of phytoplankton biomass and primary production rates, and the response of phytoplankton to the prevailing hydrographic characteristics. During each cruise, temperature and salinity were measured in the water column, and discrete samples were collected to measure inorganic nutrient concentrations (nitrate, phosphate, and silicate) and chlorophyll a content (as a proxy for phytoplankton biomass); in addition, in situ incubations were performed to estimate primary production (PP) rates using the 14 C technique. During spring and early summer (March-July), the water column at the study site was cold (14.4 ºC at 80 m depth and 17.7 ºC at the surface) and well mixed, with high nutrient concentrations (nitrate = 6.39 μM, phosphate = 0.91 μM, and silicate = 11.87 μM) at the surface, typical of intense upwelling systems. On the contrary, from August to February the water column was stratified (23.5 ± 3.2 ºC above the thermocline and 17.0 ± 1.7 ºC at 80 m depth) and had low nutrient concentrations (nitrate = 3.90 μM, phosphate = 0.47 μM, and silicate = 10.30 μM) at the surface. Phytoplankton abundance, chlorophyll a concentration, and PP rates in the euphotic zone were higher during the upwelling season, with maximum cell density of 1.7 × 10 6 cells•L-1 (nanoplankton fraction), integrated chlorophyll a content of 231 mg•m-2 , and integrated PP rates of 553 mg C•m-2 •h-1). Abundance of cells <20 μm, as determined by flow cytometry, revealed the importance of the nanoplankton and picoplankton fractions in this region. This study showed the seasonal variability of phytoplankton communities (biomass and productivity) in waters off Magdalena Bay and the coupling of phytoplankton to environmental variability. Seasonal variability was similar to that observed for other typical coastal upwelling regions, that is, higher phytoplankton abundances and PP rates in spring and summer and lower values in autumn and winter.
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