Shallow marine ecological degradation in Hong-Kong: a palaeoecological approach using ostracods

Abstract

Hong Kong is one of the largest and most rapidly developing cities in Asia. It is known that the marine ecosystems of Hong Kong have been seriously influenced by a variety of anthropogenic factors, including eutrophication, bottom trawling, coastal reclamation, pollution, etc. However, little is known about long-term history of human-induced marine ecological degradation in Hong Kong. Here we use microfossil ostracods as a model system and reconstruct marine ecological degradation history in Hong Kong, using grab samples from 55 sites covering almost entire Hong Kong's shallow marine areas and a long (42m) sediment core covering almost entire Holocene from offshore Lantau Island. The grab samples were subsampled from surface (0–1cm) and subsurface (1–20cm), representing present and past assemblages, respectively. Based on the ostracode census data obtained from these grab and core samples, Bray-Curtis similarity, cluster analysis, nonmetric multidimensional scaling (MDS), and regression models were used to investigate biogeographic distribution and temporal changes in Hong Kong marine ostracode fauna and diversity and their controlling factors. Preliminary results of grab samples show that the common species are Sinocytheridea impressa, and Neomonoceratina. Species diversity was not significantly different between present (i.e., surface) and past (subsurface) assemblages. Pairwise comparison of Bray-Curtis similarity between present and past assemblages indicated lower similarity in Tolo Harbour and Victory Harbour sites, i.e., city sites, compared with other sites. Although this lower similarity in city sites may indicate recent ecological degradation in urban areas, further investigation is needed to understand the underlying mechanism. On the basis of MDS analysis, ostracod assemblages are similar within Western, Central and Eastern waters while no cluster is clearly identified in Southern waters. The long sediment core indicates changes of ostracode assemblage for the past ~9000 years. Both absolute abundance (number of specimens/10g dry sediment) and species diversity increased since ~8000 cal yr BP. Three biofacies were identified in the core, using Q-mode cluster analysis based on Bray-Curtis index. Although these ostracode changes are likely related to Holocene sea-level changes, further investigation and analysis is needed. Full results will be shown at the presentation.