Benthic ostracod diversity and biogeography in an urban semi–enclosed eutrophic riverine bay

Abstract. The benthic ecosystem has been greatly altered by environmental pressure over the past several decades. Compared to some well-studied large bays, the situation will be in populated small bay areas is still under investigated. In this study, we investigated the abundance, diversity, composition, and distribution of ostracod (a meiobenthic group) and their interactions with eutrophication and pollution through high resolution sampling of surface sediment in Deep Bay, a small semi-enclosed riverine bay adjacent to two of the world’s most populated cities. We found that ostracod abundance and diversity exhibited an inner-outer gradient in Deep Bay, shaped by eutrophication and pollution from human activities. Faunal composition was also characterized by inner-outer difference, as well as difference between Hong Kong side and Shenzhen side, where Hong Kong side was more influenced by eutrophication, Shenzhen side was more affected by metal pollution. Ostracod distribution and their environmental preference in Deep Bay were consistent with broader studies in Hong Kong, strongly supporting the idea that ostracod is a useful bioindicator of coastal benthic ecosystems. Our study emphasizes the importance of studying of uncomplicated system with finer sampling, as this approach offers a clear and direct understanding of how benthic ecosystems are shaped by distinct coastal environmental problems.