In September and November 2016, eight marine sampling sites along the coast of the southeastern Gulf of Mexico were monitored for the presence of lipophilic and hydrophilic toxins. Water temperature, salinity, hydrogen potential, dissolved oxygen saturation, inorganic nutrients and phytoplankton abundance were also determined. Two samples filtered through glass fiber filters were used for the extraction and analysis of paralytic shellfish toxins (PSTs) by lateral flow immunochromatography (IFL), HPLC with post-column oxidation and fluorescent detection (FLD) and UHPLC coupled to tandem mass spectrometry (UHPLC-MS/MS). Elevated nutrient contents were associated with the sites of rainwater discharge or those near anthropogenic activities. A predominance of the dinoflagellate Pyrodinium bahamense was found with abundances of up to 10⁴ cells L⁻¹. Identification of the dinoflagellate was corroborated by light and scanning electron microscopy. Samples for toxins were positive by IFL, and the analogs NeoSTX and STX were identified and quantified by HPLC-FLD and UHPLC-MS/MS, with a total PST concentration of 6.5 pg cell⁻¹. This study is the first report that confirms the presence of PSTs in P. bahamense in Mexican waters of the Gulf of Mexico.

Allelopathy between phytoplankton species can promote cellular stress and programmed cell death (PCD). The raphidophyte Chattonella marina var. marina, and the dinoflagellates Margalefidinium polykrikoides and Gymnodinium impudicum have allelopathic effects on Gymnodinium catenatum; however, the physiological mechanisms are unknown. We evaluated whether the allelopathic effect promotes cellular stress and activates PCD in G. catenatum. Cultures of G. catenatum were exposed to cell-free media of C. marina var. marina, M. polykrikoides and G. impudicum. The mortality, superoxide radical (O₂^●−) production, thiobarbituric acid reactive substances (TBARS) levels, superoxide dismutase (SOD) activity, protein content, and caspase-3 activity were quantified. Mortality (between 57 and 79%) was registered in G. catenatum after exposure to cell-free media of the three species. The maximal O₂^●− production occurred with C. marina var. marina cell-free media. The highest TBARS levels and SOD activity in G. catenatum were recorded with cell-free media from G. impudicum. The highest protein content was recorded with cell-free media from M. polykrikoides. All cell-free media caused an increase in the activity of caspase-3. These results indicate that the allelopathic effect in G. catenatum promotes cell stress and caspase-3 activation, as a signal for the induction of programmed cell death.

Harmful algal blooms (HABs) can produce a variety of noxious effects and, in some cases, the massive mortality of wild and farmed marine organisms. Some HAB species produce toxins that are released into seawater or transferred via food webs (particulate toxin fraction). The objective of the present study was to identify the toxicological effects of subacute exposure to saxitoxin (STX) during embryonic and early larval stages in Seriola rivoliana. Eggs were exposed to dissolved 19 STX (100 μg L⁻¹). The toxic effects of STX were evaluated via the hatching percentage, the activity of three enzymes (protein and alkaline phosphatases and peroxidase), and the expression of four genes (HSF2, Nav1.4b, PPRC1, and DUSP8). A low hatching percentage (less than 5%) was observed in 44 hpf (hours post fertilization) embryos exposed to STX compared to 71% in the unexposed control. At this STX concentration, no oxidative stress in the embryos was evident. However, STX induced the expression of the NaV1.4 channel α-subunit (NaV1.4b), which is the primary target of this toxin. Our results revealed the overexpression of all four candidate genes in STX-intoxicated lecithotrophic larvae, reflecting the activation of diverse cellular processes involved in stress responses (HSF2), lipid metabolism (PPRC1), and MAP kinase signaling pathways associated with cell proliferation and differentiation (DUSP8). The effects of STX were more pronounced in young larvae than in embryos, indicating a stage-specific sensitivity to the toxin.

Gambierdiscus is a marine benthic dinoflagellate genus that currently contains 19 species; some of them are toxigenic, producing ciguatoxins, maitotoxins, and other toxic compounds. The objective of this study was to document the morphological and molecular identification (ITS, 5.8S and 28S of the rDNA) of two strains of Gambierdiscus from La Gaviota Island, Gulf of California, Mexico, and a toxicity test. The shape of the 2′ plate varied between hatchet-shaped and rectangular, that complicated the differentiation between G. carpenteri and G. toxicus. Molecular markers of the three rDNA regions allowed confirmation of the taxonomic identity of G. carpenteri, separating this species from other congeners with high phylogenetic affinity, such as G. excentricus, G. toxicus and G. caribaeus. Studies of the morphological taxonomy of G. carpenteri are scarce; therefore, due to the similarity between species, the combination of morphological and molecular tools is recommended for the identification of species, such as G. carpenteri, G. excentricus, G. toxicus and G. caribaeus. The mouse bioassay showed that the examined isolate was toxic, and it is a potential etiology of ciguatera fish poisoning cases in the region. This study provides the first reliable report and ribosomal sequences of G. carpenteri for the Gulf of California, as well as data on mouse bioassay toxicity.

We describe five new isolates of two Gambierdiscus species from Bahía de La Paz in the southern Gulf of California. Batch cultures of Gambierdiscus were established for morphological characterization using light microscopy (LM) and scanning electron microscopy (SEM). Pigment and amino acid profiles were also analyzed using high-performance liquid chromatography (HPLC-UV and HPLC-DAD). Finally, toxicity (CTX-like and MTX-like activity) was evaluated using the Artemia salina assay (ARTOX), mouse assay (MBA), marine fish assay (MFA), and fluorescent receptor binding assay (fRBA). These strains were identified as Gambierdiscus cf. caribaeus and Gambierdiscus cf. carpenteri. Toxicity for CTX-like and MTX-like activity was confirmed in all evaluated clones. Seven pigments were detected, with chlorophyll a, pyridine, Chl2, and diadinoxanthin being particularly noteworthy. For the first time, a screening of the amino acid profile of Gambierdiscus from the Pacific Ocean was conducted, which showed 14 amino acids for all strains except histidine, which was only present in G. cf. caribeaus. We report the presence of Gambierdiscus and Fukuyoa species in the Mexican Pacific, where ciguatera fish poisoning (CFP) cases have occurred.

Allelopathy in phytoplankton species can modify the community structure by growth inhibition, organelle damage, cellular stress, metabolic modifications, and by inducing programmed cell death (PCD). In this study, the allelopathic responses of G. catenatum, a paralytic toxin harmful algal bloom (HAB) forming species, towards the raphidophyte C. marina var. marina and the dinoflagellate Gymnodinium impudicum were evaluated. Gymnodinium catenatum was cultivated during 72 h in mixed cultures with and without direct cell contact with C. marina and G. impudicum. Growth, cell morphology, toxin profile, and caspases 3/7 activity were registered. Growth of G. catenatum exposed to C. marina and G. impudicum with and without direct cell contact was significantly reduced, toxin content decreased, and caspases 3/7 activity increased. Changes in the toxin profile were also observed, in general, with a higher content of gonyautoxin-2,3 (GTX2, 3), decarbamoyl gonyautoxin-2,3 (dcGTX2,3) and B1 analogs. In all cases the highest response was observed in direct cell contact with C. marina. These results allow new insights of the allelopathic responses of G. catenatum towards co-occurring HAB species confirming growth limitation and evidencing metabolic changes in the toxin content, as well as the induction of PCD.