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.

The so-called unarmoured dinoflagellates are not a “natural” (phylogenetic) group but they lack thecal plates, share fragility and possess relatively few morphological characters that can be positively identified. This study depicts the species composition of unarmoured dinoflagellates collected from sites along the coasts of the Gulf of Mexico and the Mexican Pacific and includes their descriptions and illustrations. We identified a total of 25 species belonging to 13 genera and six families that were studied through various techniques using light and scanning electron microscopy. Seven new records for the Mexican Pacific are annotated here that include

In 2010, we surveyed 42 sampling locations at 11 sites along the Mexican part of the Mesoamerican Reef System, including eight protected natural areas of the coastal state of Quintana Roo, to determine the richness of benthic-epiphytic dinoflagellates in the area. At each site, the host macroalgae of the genera Dictyota, Halimeda, Laurencia, Sargassum, and Stypopodium were manually collected. A total of 383 samples were analyzed microscopically using transmitted light, epifluorescence with calcofluor staining, and scanning electron microscopy. A total of 24 dinoflagellate species distributed among the genera Amphidinium, Bysmatrum, Coolia, Gambierdiscus, Ostreopsis, Prorocentrum, Plagiodinium, and Sinophysis were identified. Prorocentrum is the most diverse genus in the benthic-epiphytic environment with 13 species. This work also includes 15 new records of species from the Mexican Caribbean.

The chemical characteristics and hydrogeochemical processes that govern the groundwater in the sinkholes ring of the Yucatan Peninsula were assessed. The groundwater of the area studied is of the Ca–Mg–HCO3 type. Local geology (abundance of dolomite) determines Mg2+ enrichment relative to Ca2+. The absence of seawater intrusion was established. Sinkhole water chemistry is controlled by carbonate rock dissolution, with dominance of Ca2+, Mg2+ and HCO3–. The dynamic and controlling factors of trace elements were determined in sediments of the southern part of Mexico. The order of mean concentrations of trace elements in sediments is Sr>Pb>Cu>Zn>Cr>> Cd. With regard to the sequential extraction procedure, the potential importance of fractions in sediments is in the order residual>organic matter>carbonates>exchangeable>water soluble, confirming that sinkhole sediments works as a sink of trace elements, and that no anthropogenic pressure exists in the groundwater of the hydrogeological reserve area. Trace element stability in sediments decreased as follow: Cd>Pb>Zn>Cr>Cu>Sr. The study results describe the groundwater and sediment condition of the hydrogeological reserve area, and provide insights for stakeholders and authorities. Growing population and economic activities may be major threats to the groundwater in coming decades.

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