Benthic marine diatom deformities associated with contaminated sediments in Hong Kong

Abstract

Three thousand benthic diatoms were examined at each of twelve sites to determine the frequency of diatom deformities. Two basic types of diatom deformities were observed: 1) diatoms with deformed cell wall morphology; and 2) diatoms with deformed valve wall ornamentation. Only six deformed diatoms were observed. Deformed individuals of Fragilaria capucina and Achnanthes hauckiana displayed external cell wall deformities, while deformed individuals of Diatoma vulgare displayed valve walls with a wavy pattern of longitudinal lines in which the valve ornamentation, rather than the valve cell wall, was abnormal. The deformity frequency of Navicula rhyncocephala, Achnanthes hauckiana, Fragilaria capucina, and Diatoma vulgare was significantly lower at unpolluted sites than at polluted sites based on Fisher exact probability estimates. Cadmium reached 1.1 mg/kg dry wt. of sediment, while other levels were chromium (42 mg/kg of sediment), copper (440 mg/kg), nickel (31 mg/kg), lead (130 mg/kg), and zinc (450 mg/kg of sediment) at the most polluted site. There was a significant correlation (P < 0.05, r s = 0.652) between sediment toxicity, as reflected by the Microtox test, and benthic diatom diversity. The most polluted site exhibited the highest Microtox acute toxicity levels, the lowest diversity, and moderate diatom deformity levels. It was concluded that abnormal cell morphology of diatoms may be a valid indicator of ecosystem health. However, because the amount of time and effort required to identify a statistically meaningful number of deformed diatoms is so great, diatom deformity frequency is unlikely to become a useful tool unless an automated system of assessing diatom deformity frequency is developed.