Comparison of short-term toxicity of 14 common phycotoxins(alone and in combination)to the survival of brine shrimp Artemia salina

Toxic harmful algal blooms(HABs)can cause deleterious effects in marine organisms,threatening the stability of marine ecosystems.It is well known that different strains,natural populations and growth conditions of the same toxic algal species may lead to different amount of phycotoxin production and the ensuing toxicity.To fully assess the ecological risk of toxic HABs,it is of great importance to investigate the toxic effects of phycotoxins in marine organisms.In this study,the short-term toxicity of 14 common phycotoxins(alone and in combination)in the marine zooplankton Artemia salina was investigated.The 48 h LC_(50)of the 14 phycotoxins varied from 0.0193µg/mL to 2.415µg/mL.The most potent phycotoxin was azaspiracids-3(AZA3;with a LC_(50)of 0.0193µg/mL),followed by azaspiracids-2(AZA2;0.0226µg/mL),pectenotoxin-2(PTX2;0.0460µg/mL)and dinophysistoxin-1(DTX1;0.0818µg/mL).For the binary exposure,okadaic acid(OA)induced potential additive effects with DTX1,probably due to their similar structure(polyether fatty acid)and mode of action(attacking the serine/threonine phosphoprotein phosphatases).On the other hand,OA showed potential antagonistic effects with PTX2,which might be accounted for by their activation on the detoxification activity of cytochrome P450 activity.In addition,DTX1 induced potential synergetic effects with saxitoxin(STX),yessotoxin(YTX)or PTX2,suggesting the hazard potency of the mixtures of DTX1 and other phycotoxins(like STX,YTX and PTX2)with regard to the ecological risk.These results provide valuable toxicological data for assessing the impact of phycotoxins on marine planktonic species and highlight the potential ecological risk of toxic HABs in marine ecosystems.

Nutrient Structure of the Taiwan Warm Current and Estimation of Vertical Nutrient Fluxes in Upwelling Areas in the East China Sea in Summer

Based on field data for nutrients collected on the continental shelf of the East China Sea(ECS) during summer 2006, the structure and variations of nutrients in every water mass related to the Taiwan Warm Current(TWC) were analyzed. The supplementary effect of nutrient of upwelling on harmful algal blooms(HABs) in the ECS was also estimated, based on upwelling data. Then the maintenance contribution of nutrient of upwelling to HABs was assessed. The results showed that N/P ratio is fairly low in both surface and deep layers of the TWC, which possibly controls nutrient structure of the HABs-frequently-occuring areas. In upwelling areas, the rate of phosphate(PO4-P) uptake exceeds that of nitrate(NO3-N) of the TWC. The TWC may relieve PO4-P limitation during the process of HABs. Furthermore, upwelling plays an important role in providing nutrients to HABs. After estimating nutrient fluxes(NO3-N, PO4-P, Si O3-Si) in the upwelling areas along a typical section(S07), the results showed that the nutrient uptake rate is the greatest at 10-20 m below euphotic zone, sustaining the ongoing presence of HABs. The uptake rate of PO4-P is the highest among dissolved inorganic nutrients. Therefore, upwelling is most likely the main source of PO4-P supply to HABs.

An estimation of nutrient fluxes to the East China Sea continental shelf from the Taiwan Strait and Kuroshio subsurface waters in summer

According to historical mean ocean current data through the field observations of the Taiwan Ocean Research Institute during 1991–2005 and survey data of nutrients on the continental shelf of the East China Sea（ECS） in the summer of 2006, nutrient fluxes from the Taiwan Strait and Kuroshio subsurface waters are estimated using a grid interpolation method, which both are the sources of the Taiwan Warm Current. The nutrient fluxes of the two water masses are also compared. The results show that phosphate（PO4-P）, silicate（SiO3-Si） and nitrate（NO3-N） fluxes to the ECS continental shelf from the Kuroshio upwelling water are slightly higher than those from the Taiwan Strait water in the summer of 2006. In contrast, owing to its lower velocity, the nutrient flux density（i.e., nutrient fluxes divided by the area of the specific section） of the Kuroshio subsurface water is lower than that of the Taiwan Strait water. In addition, the Taiwan Warm Current deep water, which is mainly constituted by the Kuroshio subsurface water, might directly reach the areas of high-frequency harmful alga blooms in the ECS.