No abstract

Some dinoflagellate species within the genera Alexandrium, Gymnodinium and Pyrodinium are well-known producers of paralytic shellfish toxins (PST), which led to many poisoning incidents around the world. In the northern Yellow Sea, an important mariculture zone for scallop Patinopecten yessoensis, PST have been frequently detected from scallops. However, there is little knowledge concerning PST-producing microalgae in this region so far. In cruises carried out in 2011 and 2012, scallop and phytoplankton samples were collected from the northern Yellow Sea. PST were detected from scallops by high-performance liquid chromatography with fluorescence detection (HPLC-FLD). Toxin content and profile were remarkably different among the four tissues, i.e. viscera, adductor muscle, mantle and gonad, suggesting apparent toxin transfer and transformation in scallops. Viscera always had the highest content of PST dominated by low-potency N-sulfocarbamoyl toxins C1 and C2, which closely resembled the toxin profiles of net-concentrated phytoplankton samples in spring. Based on the morphological features, cells of Alexandrium spp. in net-concentrated phytoplankton samples were picked out and a partial sequence of the large subunit ribosomal RNA gene (LSU rDNA) was amplified using a single-cell polymerase chain reaction (PCR) method. Cells of both toxic A. tamarense species complex and non-toxic A. affine were identified from the phytoplankton samples based on the partial LSU rDNA sequence information. According to these findings, it is implied that A. tamarense species complex is the major toxic species related to PST contamination in scallops of the northern Yellow Sea. The presence of both toxic and non-toxic Alexandrium spp. in this region requires for a species-specific method to monitor the distribution and dynamics of A. tamarense species complex.

Water samples were collected to measure dissolved and particulate phosphorus species in order to examine the dynamics of phosphorus in the water column across the river–sea interface from the lower Dafengjiang River to the open Beibu Gulf. Dissolved inorganic phosphorus concentrations were as high as 0.90 ± 0.42 μM in river water but decreased dramatically to as low as 0.02 ± 0.01 μM in open coastal waters. Total dissolved phosphorus was largely measured in the form of dissolved inorganic phosphorus in river waters (58% ± 18%), whereas dissolved organic phosphorus became the predominant species (>90% on average) in open coastal waters. Total dissolved phosphorus was the dominant species, comprising 76% ± 16% of the total phosphorus, while total particulate phosphorus only comprised 24% ± 16% of the total phosphorus pool. Riverine inputs, physical and biological processes, and particulate phosphorus regeneration were the dominant factors responsible for the dynamic variations of phosphorus species in the study area. Based on a two-end-member mixing model, the biological uptake resulted in a dissolved inorganic phosphorus depletion of 0.12 ± 0.08 μM in the coastal surface water, whereas the replenishment of dissolved inorganic phosphorus in the lower river from particle P regeneration and release resulted in an increase (0.19 ± 0.22 μM) of dissolved inorganic phosphorus in the estuarine mixing region. The molar ratios of dissolved inorganic nitrogen to dissolved inorganic phosphorus and dissolved silicate to dissolved inorganic phosphorus in the open surface waters were >22, suggesting that, although the lower Dafengjiang River contained elevated concentrations of dissolved inorganic phosphorus, the northern Beibu Gulf was an overall P-limited coastal ecosystem.