Phaeocystis globosa Scherffel,a harmful microalga,and its production of dimethylsulfoniopropionate

The production of dimethylsulfoniopropionate （DMSP） and its cleavage products （DMS） are well studied in phytoplankton worldwide. However, less is known about their sources, distributions, and impacts in the coast of China. We examined the production of DMSP and DMS in Phaeocvstis globosa Scherffel and other benthic macroalgae from the South China coast in relation to environmental conditions. P. globosa was a harmful marine microalgal species and its bloom took place in the eutrophic waters along the South China Sea frequently. It also produced high content of DMSP at different growth stages, with the highest concentration usually observed in the stationary period. Moreover, the production of DMSP in P. globosa was significantly affected by salinity and temperature with the highest contents associated with high salinity （e.g. 40） and low temperature （e.g. 20℃）. In field benthic macroalgae, there was also a marked difference in the DMSP of various species or different samples of the same species. Chlorophyll a contents were also determined for each macroalgal species. The highest chlorophyll a （238.7 ng/g fresh weight） was recorded in Chlorophyta Ulva lactuca at Guishan Island （Zhuhai）, while the lowest value （1.5 ng/g fresh weight） was found in Rhodophyta Gracilaria tenuistipitata in Zhanjiang. Further correlation analysis indicated that there was no significant relationship between the content of DMSP and chl-a in macroalgae samples （P〉 0.05）. All the results suggested that the production of DMSP in marine algae was not only species- and stage-related, but also greatly affected by various environmental factors.

Negative effects of Phaeocystis globosa on microalgae

The potential allelopathic effects of the microalga,Phaeocystis globosa Scherffel,on three harmful bloom algae,Prorocentrum donghaiense Lu,Chattonella marina(Subrahmanyan) Hara et Chihara and Chattonella ovata Hara et Chihara were studied.The growth of C.marina and C.ovata was markedly reduced when the organisms were co-cultured with P.globosa or cultured in cell-free spent medium.Haemolytic extracts from P.globosa cells in the senescence phase had a similar inhibitory effect on the three harmful bloom algae.However,P.globosa had less influence on the brine shrimp,Artemia salina.These results indicate that P.globosa may have an allelopathic effect on microalgae,which would explain the superior competitive abilities of P.globosa.Because the addition of the haemolytic toxins from P.globosa had similar effects on algae as spent media,these compounds may be involved in the allelopathic action of P.globosa.

Distribution and germination of viable diatom resting stage cells in sediments of the East China Sea

The abundance and temporal patterns of viable diatom resting stage cells in sediments of the East China Sea in 2006 have been investigated.The abundance of viable resting stages was enumerated with the most probable number（MPN） technique.Overall,25 diatom species（including varieties） belonging to 16 genera were detected.Viable resting stage cells were common,on the order of 103 to 106 cells/g dry mass.The abundant taxa included Skeletonema marina,S.dohrnii,Chaetoceros curvisetus and Thalassiosira spp.,with Skeletonema accounting for 83.3% of the cell.The effects of temperature（10,15,20,25 ℃）,salinity（20,25,30,35 psu） and light intensity（0,300,4 000,8 000 lux） on the germination of resting stages in sediment samples were also determined.The results showed that light intensity had a significant positive effect on the germination of diatom resting stage cells（p 〈0.01） and that diatoms could not germinate in darkness.Temperature and salinity had no noticeable effects on the germination.The present study suggests that there are abundant diatom resting cells in sediments of the East China Sea,which could serve as a ＂seed bank＂ in the phytoplankton population succession and contribute to the initiation of algal blooms.