Mandy Man Yee Tsoi

Qualitative and quantitative changes in marine biofilms as a function of temperature and salinity in summer and winter

This study examined quantitative (dry weight, chlorophyll a content and C:N ratio) and qualitative (community compositions of bacteria and diatoms) changes in marine biofilms as a function of season (summer 2003 and winter 2004), temperature (16, 23 and 30 ◦ C) and salinity (20‰ ,2 7‰ and 34‰) underlaboratoryconditions.Biofilmswereallowedtodevelopfor20daysinthe laboratory,usingnaturalseawatercollectedfromPortShelter,HongKong.The following results were obtained: (1) biofilm dry weight was greater in summer than in winter, and greater at 34‰ than at 20‰; (2) biofilm chlorophyll a content was affected by all three factors (season, temperature and salinity), with significant interactive effects among the three factors; and (3) C:N ratio was affected by season (winter >summer) and temperature (30 ◦ C >16 ◦ Ci n summer), but not by salinity. Bacterial community composition was analyzed by terminal restriction-fragment length polymorphism of polymerase chain reaction-amplified 16S rRNA genes. In summer, community compositions of both bacteria and diatoms were strongly affected by salinity. In addition, natural summer biofilms that developed at three field sites, where different salinities were found, harbored appreciably different bacterial and diatom community compositions. In contrast, in winter, temperature exerted a major influence on community compositions. The present study adds to the growing evidence that environmental factors are important determinants of both the quality and quantity of marine biofilms.

Temporal variation of coastal surface sediment bacterial communities along an environmental pollution gradient

Terminal restriction fragment length polymorphism analysis (T-RFLP) was used to track the changes of bacterial community compositions (BCC) in coastal surface sediments along an environmental pollution gradient between 2004 and 2006. BCC in the chronically contaminated sites showed the largest deviation from those in the adjacent sites. Surprisingly, BCC at two contrasting environments (oceanic vs. river-influenced) were more similar. Unexpectedly, the BCC did not recover (when compared to oceanic control site) even after 5 years of pollution abatement initiatives in Victoria Harbour, Hong Kong. On the other hand, disposal of treated sewage for 5 years in one of the sites did not significantly affect the BCC. A striking seasonal variation in the BCC was observed at only the polluted sites. Although factors other than pollution gradients may explain the observed BCC patterns, the information presented here can be useful in predicting long-term effects of pollution on BCC. Furthermore, this study suggests that BCC analysis using T-RFLP is a faster, reliable and easier approach to monitor microbenthic community response to environmental pollution gradient in coastal sediments.