Morphological, molecular and toxigenic characteristics of Namibian Pseudo-nitzschia species - including Pseudo-nitzschia bucculenta sp. nov.

A field study was undertaken to investigate the occurrence and toxin production of species in the diatom genus Pseudo-nitzschia in Namibian waters, in the extremely productive Benguela upwelling system. From surveys conducted on the R/V Mirabilis and the R/V !Anichab, 52 strains were morphologically determined to species level, supported by nuclear ITS rDNA data. Seven species were identified; P. australis, P. decipiens, P. dolorosa, P. fraudulenta, P. plurisecta, P. pungens var. cingulata, and the new species P. bucculenta F. Gai, C. K. Hedemand, N. Lundholm & Ø. Moestrup sp. nov. Molecular and morphological diversity of the Namibian Pseudo-nitzschia species is discussed. Most importantly, P. bucculenta is both morphologically and phylogenetically most similar to P. dolorosa differing mainly in valve width and densities of striae, poroids and band striae as well as by four hemi-compensatory base changes in the ITS2. Morphological and molecular differences among the strains of P. decipiens suggest a temperate and a warm water subdivision. The geographical and toxigenic characteristics of the identified Pseudo-nitzschia species are described and compared to previous studies. Initial tests of toxin production in all seven species revealed production of domoic acid (DA) in two species: one strain of P. australis (0.074 pg DA cell-1) and two strains of P. plurisecta (0.338 pg DA cell-1 and 0.385 pg DA cell-1).

Use of Highly Specific Molecular Markers Reveals Positive Correlation between Abundances of Mesodinium cf. major and Its Preferred Prey, Teleaulax amphioxeia, During Red Water Blooms in the Columbia River Estuary.

In a previous study, Teleaulax amphioxeia-the preferred prey of Mesodinium in the Columbia River estuary-were undetectable within intense annual blooms, suggesting blooms are prey-limited or prey are acquired outside of bloom patches. We used a novel molecular approach specifically targeting the prey (i.e., Unique Sequence Element [USE] within the ribosomal RNA 28S D2 regions of T. amphioxeia nucleus and nucleomorph) in estuarine water samples acquired autonomously with an Environmental Sample Processor integrated within a monitoring network (ESP-SATURN). This new approach allowed for both more specific detection of the prey and better constraint of sample variability. A positive correlation was observed between abundances of M. cf. major and T. amphioxeia during bloom periods. The correlation was stronger at depth (> 8.2 m) and weak or nonexistent in the surface, suggesting that predator-prey dynamics become uncoupled when stratification is strong. We confirmed exclusive selectivity for T. amphioxeia by M. cf. major and observed the incorporation of the prey nucleus into a 4-nuclei complex, where it remained functionally active. The specific biomarker for T. amphioxeia was also recovered in M. cf. major samples from a Namibian coastal bloom, suggesting that a specific predator-prey relationship might be widespread between M. cf. major and T. amphioxeia.