Production of DMS and DMSP in different physiological stages and salinity conditions in two marine algae

Dimethylsulfide(DMS) and dimethylsulfoniopropionate(DMSP) production by Scrippsiella trochoidea and Prorocentrum minimum was investigated to characterize the effects of physiological stage and salinity on DMS and DMSP pools of these two marine phytoplankton species.Axenic laboratory cultures of the two marine algae were tested for DMSP production and its conversion into DMS.The results demonstrated that both algal species could produce DMS,but the average concentration of DMS per cell in S.trochoidea(12.63 fmol/L) was about six times that in P.minimum(2.01 fmol/L).DMS and DMSP concentrations in algal cultures varied significantly at different growth stages,with high release during the late stationary growth phase and the senescent phase.DMS production induced by three salinities(22,28,34) showed that the DMS concentrations per cell in the two algal cultures increased with increasing salinity,which might result from intra-cellular DMSP up-regulation with the change of osmotic stress.Our study specifies the distinctive contributions of different physiological stages of marine phytoplankton on DMSP and DMS production,and clarifies the influence of salinity conditions on the release of DMS and DMSP.As S.trochoidea and P.minimum are harmful algal bloom species with high DMS production,they might play an additional significant role in the sulfur cycle when a red tide occurs.

A COMPARISON OF EASTERN AND WESTERN HONG KONG PHYTOPLANKTON FROM WEEKLY SAMPLES (1997-1999)

Weekly phytoplankton samples were taken from western Hong Kong (Lamma) from Jan. 1997 to Dec. 1999 and from Port Shelter in Eastern Hong Kong from January 1998 to December 1999. During that time diatom blooms occurred repeatedly at both sites but never in synchrony. One species would bloom at one site and then weeks later it or another species would bloom at the other site; while the 1998 red tide of the mucus producing dinoflagellate Gymnodinium mikimotoi occurred at both sites. It first occurred at the Port Shelter site in March and did not appear at the Lamma site until April. With the single exception of this species, no other dinoflagellate reached bloom concentrations at the Lamma site. In addition, dinoflagellate abundance at the Lamma site was significantly lower (P <0.05) than that at the Port Shelter site. This was correlated with a significantly higher turbidity (i.e. low Secchi transparency) and higher turbulence (stronger currents) at the Lamma site. Annual variation in surface temperature correlated with total surface phytoplankton abundance at both our sample sites. Phytoplankton abundance increased in spring as water temperatures warmed. In fall, as surface water temperatures began to decline and the monsoon rains became less frequent there was a reduction in phytoplankton abundance associated with the reduction in temperature and light. Because so many variables co-occur with temperature (e.g. the amount of rainfall, light intensity and light duration etc.) it is not possible to cite temperature as the causal factor associated weth controlling phytoplankton abundance at our two sample sites. Our data support the rather controversial notion that percentage-wise, there are relatively more harmful bloom forming species in nutrient-rich coastal waters than there are in the world’s oceans. 16% of the dinoflagellate species and 10.3% of the diatom species observed at our two sample sites were classed as harmful. These percentages were higher than those cited by Sournia (1995) for the worlds oceans (9.6% and 6.8% respectively). This raises the possibility that there are relatively more toxic species in the nutrient-rich coastal waters of the world than there are in the mid ocean nutrient-poor areas of the world. Some reasons for this are briefly discussed.

New desmids material from Donghu Lake,Wuhan,China

This paper reports two new species, one new variety and fourteen taxa new to China in three genera of the phytoplankton desmids from Donghu Lake, Wuhan, China.

Effect of Anthracene on the Interaction Between Platymonas helgolandica var. tsingtaoensis and Heterosigma akashiwo in Laboratory Cultures

Two species of marine phytoplankton, Platymonas helgolandica var. tsingtaoensis and Heterosigma akashiwo, were cul- tivated in bi-algal cultures to investigate the effect of anthracene （ANT） on the interaction between them. Without ANT, H. akashiwo out-competed P. helgolandica at low initial biomass ratios （P. helgolandica （P）： H. akashiwo （H） = 1：4 and 1 ： 1）, but not at the highest （P：H=4：I）. This observation was consistent with the description in Lotka-Volterra two species competition model. It was found that P. helgolandica was excluded at low initial biomass ratios, while the unstable equilibrium between two species was predicted at the highest. For both species, carrying capacity and maximal specific growth rate decreased in bi-algal cultures compared to those in monocultures. H. akashiwo exhibited a higher sensitivity to ANT than P helgolandica. This resulted markedly in a reduced cell den- sity of H. akashiwo but an increased cell density ofP. helgolandica. Carrying capacity ofP. helgolandica was consistently higher in bi-algal cultures with ANT than those without ANT, suggesting that ANT, through the elimination of H. akashiwo, generated the dominance of P helgolandica independently of initial biomass ratios. This study showed a density-dependent effect of harmful alga （H. akashiwo） on dietary alga （P helgolandica）, and indicated that ocean pollutant ANT could induce the succession of marine phytoplankton.

Harmful algal blooms in fresh and marine water systems： The role of toxin producing phytoplankton

In this paper, we have investigated a model with three interacting species： non-toxic phy- toplankton, toxic phytoplankton and zooplankton with Holling type II and III functional responses over the space and time. The role of toxin producing phytoplankton （TPP） has been studied. We have presented the theoretical analysis of pattern formation in spatially distributed population with local diffusion. The paper highlights the hetero- geneity of HABs over space and time. The choice of parameter values and the functional response is important to study the effect of TPP, also it would depend more on the non- linearity of the system. With the help of numerical simulations, we have observed the spatial and spatiotemporal patterns for plankton system. This study demonstrates that TPP plays an important role in controlling the dynamics. We have observed that prey＇s anti-predator efforts promote predator switching. It has been found that high predation of TPP helps for the coexistence of toxic, non-toxic phytoplankton and zooplankton population.