Mass fish die-off during a diatom bloom in the Bahía de La Paz, Gulf of California

An unusual fish die-off occurred during a bloom of diatoms from June 10th July 3rd 2006 in Bahía de La Paz in the Gulf of California. The prevalent organisms were Pseudo-nitzschia spp. (2.4 × 106 cells L1), Thalassiosira eccentrica (2.3 × 106 cells L1) and Chaetoceros spp. (9.65 x 105 cells L1). Three toxic species were identified: P. pseudodelicatissima-complex, P. fraudulenta, and P. pungens. Fucoxanthin was the dominant pigment during the bloom, peaking at 9.3 ?g L1. Sea surface temperature dramatically increased from 19.0 °C to 27.0 °C during the bloom, with inorganic nitrogen (1.0 ± 0.6 ?M) and Si(OH)4 (15.5 ± 8.0 ?M). Low content of domoic acid measured by HPLC-UV from net samples ranged from 24.0 to 52.0 ng per filter and tissue of the chocolate clam Megapitaria squalida (0.55 ?g g1) and the white clam Dosinia ponderosa (0.06 ?g g1). Domoic acid analysis of dead fish tissues was negative. Fish necropsy indicated that death by asphyxia was probably caused by Thalassiosira eccentrica and Chaetoceros spp. Alternate mixing processes and instability of the water column, as well as sudden changes of both temperature and nutrients created conditions for proliferation of the diatoms

Toxicogenomic Effects of Dissolved Saxitoxin on the Early Life Stages of the Longfin Yellowtail (<i>Seriola rivoliana</i>)

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

Presence of Cyanotoxins in a Mexican Subtropical Monomictic Crater Lake

Microcystins (MCs) produced by cyanobacteria are a ubiquitous worldwide problem because some MCs can cause tumor formation and are hepatotoxic. In the Santa Mar&iacute;a del Oro crater lake, Mexico, plankton scums are recurrent during most of the year and are associated with cyanobacteria of the genera Microcystis spp. and Lyngbya spp. As some of these species are associated with the production of MCs and paralytic shellfish toxins (PSTs), samples from these scums and particulate matter were collected and analyzed for the main bloom species and toxins by a ultrahigh performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS) and high performance liquid chromatography with fluorescence detection (HPLC-FLD). Results showed that the main bloom-forming species were Limnoraphis robusta and Microcystis aeruginosa, the presence of at least seven MC congeners and the absence of PSTs in the algae scums. The MCs identified were MC-WR, MC-LR, MC-LA, MC-HilR, MC-LF, MC-YR, and MC-LY. On a dry mass weight basis, MC concentrations were low and ranged between 0.15 and 6.84 &mu;g/kg. Toxin profiles were dominated by MC-WR, MC-LR, and MC-LA, representing 94.5% of the total sample, with each analog contributing 39.8%, 38.1% and 16.5% by relative concentration, respectively. Two of the more hazardous congeners, MC-LR and MC-LA, represented 54.6% of the total MC concentration. MCs in particulate matter along the depth profile were not detected. The MC profile is linked to M. aeruginosa, and it represents the first quantitative MC congener description for this species from a Mexican water ecosystem. Since these mats are recurrent yearly, their effects on humans and wild fauna, and the possible role of anthropogenic activities that favor their presence and proliferation, need to be evaluated