The use of phytoplankton pigments for studying phytoplankton community structure and red tide occurrence in Tolo Harbour, Hong Kong

This research is to investigate the use of phytoplankton pigments for studying phytoplankton community structure and red tide occurrence in Tolo Harbour, Hong Kong. The study is divided into four parts. The first part studied the spatial and temporal structures of the marine phytoplankton during a red tide occurrence in Tolo Harbour. A red tide caused by dinoflagellate Scrippsiella trochoidea was detected in the inner part of Tolo Harbour at the end of November 2000. For temporal study, water samples were collected from a fixed station at the centre of the red tide patch for microscopic analysis of phytoplankton community composition and High Performance Liquid Chromatography (HPLC) analysis of phytoplankton pigments. At the peak of the red tide on 24 November 2000, phytoplankton was dominated by S. trochoidea at a density of ∼3.5 × 104 cells ml−1 .; In the second part, phytoplankton characteristics in the eutrophic inner Tolo Harbour was studied at monthly interval from February 2001 to April 2002. The result showed that chl a concentrations were generally high throughout the study, ranging between 2.20 and 110 ng ml−1 , especially during red tides and algal blooms (>50 ng ml−1 ). FUCO and PERI have been confirmed to be good quantitative markers of diatoms and dinoflagellates abundances, respectively.; In the third part, water samples were analysed in four different parts of Tolo Harbour (inner Tolo Harbour to outer Tolo Harbour) between November 2000 and March 2002 to study the applicability of using phytoplankton pigments for spatio-temporal phytoplankton monitoring. The phytoplankton ecology survey was also carried out to study the latest phytoplankton community structure and dynamic in the harbour. The results showed that there had been a gradual increase of phytoplankton density from outer parts of Tolo Harbour to the inner. The average phytoplankton density of diatoms and dinoflagellates in the inner Tolo Harbour was about six times higher than those in the outer one.; Finally, the feeding habits of the marine cladoceran Penilia avirostris in inner Tolo Harbour were studied during a red tide bloom in April 2001. Microscopic examination of phytoplankton assemblages in areas where discoloration of seawater was obvious indicated that the red tide was caused by blooms of the dinoflagellates Scrippsiella trochoidea (∼8.9 × 103 cells ml−1) and Prorocentrum dentatum (∼4.5 × 103 cells ml−1). (Abstract shortened by UMI.)...