Potentially toxic diatoms belonging to the genus Pseudo-nitzschia were observed for the first tiem in plankton samples fromHong Kong collected in 1996. To determine whether potentially toxic diatoms had become more common during the last six decades, three gravity cores were taken from the anaerobic sediments of Kowloon Bay in Victoria Harbour. Anaerobic sediments are thought to be ideal for palaeoecological reconstructions because their vertical stratigraphy is undisturbed by bioturbidation. Analysis of the Kowloon bay sediment cores indicated that very few individual diatoms belonged to the genus Psuedo-nitzschia, even though Pseudo-nitzschia was found in abundance in many of the plankton samples taken from a nearby site. The relative absence of Pseudo-nitzschia frustules was interpreted as indicating that these thin walled, poorly silicified, planktonic diatoms failed to preserve in the saline (32-34 per sounsand), slightly alkaline (pH 7.6-7.8), anaerobic sediments of Kowloon Bay.
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