The Huangmao Island dumping area is adjacent to the Pearl River Estuary in the South China Sea. From its first dumping activity in 1986 to 2017, 6750 × 10⁴ m³ dredged materials were dumped in this dumping area. Sediment pollution levels, ecological risk, and benthic communities in 2011–2017 were evaluated; the results showed that the concentrations of the heavy metals (HMs; except Hg) in surface sediments of the dumping area met the class I standard of marine sediment quality (GB 18668-2002). HMs in the surface sediments were relatively high in the northern and central areas but relatively low in the south of the dumping area. Speculation was that the spatial variation in HM concentrations might be caused by dumping activities. The Nemerow index implied that the contaminated area was mainly in the north of the dumping area (S1, S2, and S3), where the dumping amount was the largest. The potential ecological risk (Eⁱ_r) indices of Zn, As, Cu, and Pb indicate that these metals posed a low risk to the ecosystem of the dumping area, whereas Cd and Hg posed a high risk at some stations. The geoaccumulation indices (I_geo) of Zn, As, Cu, and Pb specified no pollution or light pollution in the study area, whereas those of Cd and Hg in most years indicated mild contamination levels. Benthic organisms in the study area were arthropods, chordates, annelids, mollusks, echinoderms, nemertinean, coelenterate, and echiuran, among which arthropods were the most abundant. The abundance of taxa and density of benthic organisms had a little difference among the stations within the dumping area, but were significantly lower than those of the stations outside the dumping area. In addition, non-metric multidimensional scaling analysis confirmed that the observed patterns separated the stations within the dumping area from stations outside the dumping area. The evaluation results of the HMs revealed that the dumping area with a large dumping amount was more severely polluted. Dumping dredged materials seemed to have a negative impact on the benthic community in the dumping area.

Taking the coral communities of the Xuwen coral reef in 2020 as the research object, we analyzed the species composition, diversity, and interspecific Spearman correlation of the scleractinian coral communities, investigated the features and spatial distribution of the scleractinian coral community, and discussed the correlation between the community composition and environmental factors to identify the affecting factors and their sources. These results showed that (1) compared with the survey in 2004, the coverage of corals in 2020 had significantly decreased, while the dominant genera were still Goniopora and Porites. The coral morphology was massive, and the diversity of the coral community (Shannon–Wiener index, H’) was 2.87. The distribution of coral was uneven. The competition among some dominant species of coral was intense. (2) The mass coral bleaching event in the NSCS in August 2020 did not cause severe coral death in the short term on the Xuwen coral reef. (3) The growth of the coral community in 2020 might be greatly affected by high suspended solids and nutrient levels, which were related to the current, mariculture, and coastal erosion. (4) Anthropogenic activities such as coastal aquaculture and fishing were the major factors leading to the reduction in coral coverage on Xuwen coral reef in the past 10 years.

This study aimed to investigate the acute and chronic toxic effects of two thermodynamic inhibitors (methanol and ethylene glycol) widely used in deep-sea oil and gas operations on two typical marine fish species, the medaka (Oryzias melastigma) and the yellowstripe goby (Mugilogobius chulae), to assess their potential ecological risks in marine environments. The 96-h median lethal concentration (LC₅₀) was determined through acute toxicity tests. A 56-day chronic toxicity test was conducted to evaluate the effects on fish growth (body length) and the antioxidant defense system, specifically the activities of superoxide dismutase (SOD) and catalase (CAT). The results revealed marked species-specific differences. In terms of acute toxicity, medaka exhibited exceptionally high sensitivity to ethylene glycol (LC₅₀ 15.77 g/L), while the yellowstripe goby showed greater tolerance (LC₅₀ 22.17 g/L). Chronic exposure led to concentration-dependent growth inhibition in both species, and medaka showed significantly higher mortality than yellowstripe goby. Under methanol exposure, medaka exhibited significantly higher mortality (30–45%) than yellowstripe goby (5–20%). When exposed to ethylene glycol, medaka showed markedly high mortality (55–85%), while yellowstripe goby mortality remained below 15%. At the molecular level, both chemicals induced oxidative stress, but the response patterns of the antioxidant enzymes (SOD and CAT) were species-specific, indicating differences in toxic mechanisms and detoxification capacities. Methanol and ethylene glycol pose non-negligible ecotoxicological risks to marine fish, and the toxicity intensity is influenced by species specificity, exposure concentration, and the effectiveness of the antioxidant defense system. This study emphasizes that environmental risk assessments for such chemicals must fully account for species differences and sublethal effects, providing critical scientific evidence for formulating precise environmental safety standards for marine hydrocarbon exploitation.