2.1 Sampling sites and environmental data
In Hong Kong, the Tolo Harbour (TH; 22°43’ N, 114° 22’ W) is characterised by a gradient of chemical pollution that has profound implications for the diversity and distribution of benthic organisms, from corals (Duprey et al., 2016) to microbial communities in the sediments (J. Chen et al., 2019). For our experimental design, we first assessed environmental parameters along the pollution gradient in the Channel Water Control Zone of TH. This information was obtained from the marine water quality database of the Hong Kong Environmental Protection Department (EPD) (available from: https://cd.epic.epd.gov.hk/EPICRIVER/marine/). Parameters such as salinity, total phosphorus, total nitrogen, total Kjeldahl nitrogen, nitrite, nitrate, ammonia, chlorophyll-a, dissolved oxygen, and 5-day Biological Oxygen Demand (BOD) on the surface water across ten years (2010-2020) were used for comparisons. Based on this information, we established three experimental localities, including Starfish Bay (SFB) (22° 26’ 3.0” N, 114° 14’ 45.6” E), Lai Chi Chong (LCC) (22° 27’ 22.4” N, 114° 17’ 59.4” E) and Tung Ping Chau (TPC) (22° 32’ 34.1” N, 114° 26’ 6.5” E) (Figure 1). A principal component analysis (PCA) was conducted to visualize the differentiation of water quality between the experimental sites along the pollution gradient in TH.