Cadmium and phosphate variability during algal blooms of the dinoflagellate Lingulodinium polyedrum in Todos Santos Bay, Baja California, Mexico

摘要

Dinoflagellate algal blooms (DABs), with lingulodinium polyedrum as the dominant species, have increased over the past few years in coastal areas off Baja California, Mexico. Vertical and temporal variability of paniculate cadmium (Cd_p), dissolved Cd (Cd_d), PO_4~(3-) and Cd_d/PO_4~(3-) were investigated during two intense DABs of L. polyedrum that occurred during the fall of 2011 and 2012 in Todos Santos Bay. Results were then, compared with data gathered in the absence of algal blooms during the autumn of 2013. In both algal blooms, L. polyedrum tended to be concentrated near the surface throughout the duration; however, during DAB 2011 the number of cells was twice as abundant ([10.0 ± 8.0] × 10~5 cells L~(-1)) as in DAB 2012 ([5.0 ± 4.4] × 10~5 cells L~(-1)). During DAB 2011, Cdp increased significantly (up to 1.02 ± 0.99 nmol kg~(-1)) and was positively correlated with the cell abundance of L. polyedrum, suggesting that this dinoflagellate is able to assimilate and concentrate Cd_d. Likewise, Cd_d (up to 0.71 ± 0.17 nM) increased in the days of highest cell abundance, which could be attributed to uptake and subsequent regeneration of Cd_d resulting from the remineralization of organic paniculate matter produced during the bloom, as well as with the presence of organic ligands secreted by L. polyedrum that could keep Cd_d in solution. During DAB 2011, dissolved Cd_d/PO_4~(3-) ratios exhibited high vertical and temporal variability in the upper 5 m of the water columa but remained virtually constant near the bottom, suggesting a depth-dependent decoupling between these two dissolved components during the bloom development. Given the observed differences in the vertical and temporal variability of Cd_d, Cd_p, and PO_4~(3-) between these two intense DABs, we propose the existence of an abundance threshold of approximately 10~6 cells L~(-1) of L. polyedrum above which Cd and PO_4~(3-) significantly increased due to remineralizan'on in coastal waters during the bloom development.