In order to study the spatial and temporal distribution patterns of meiofauna in Jiaozhou Bay and its influencing environmental factors, two field samplings were carried out in the waters inside and outside Jiaozhou Bay in January and April 2021. The taxon composition, abundance, biomass, community structure, horizontal and vertical distribution of meiofauna, and their relationship with the environmental factors were investigated. The results showed that 12 taxa of meiofauna were identified in the study area. The average abundance of meiofauna in winter and spring was (769.6±184.8) and (683.3±173.3) ind./10 cm², respectively. The average biomass of meiofauna in winter and spring was (587.0±78.0) and (426.7±67.4) μg/10 cm², respectively. Free-living marine nematode was the most dominant taxon, accounting for 87.60% and 92.36% of the total abundance of meiofauna, in winter and spring, respectively. Other important taxa included copepods, rotifers and nauplius. There were significant differences in seasonal distribution of meiofauna community structure. Results of BioEnv analysis showed that the best combination of environmental factors explaining the variation of meiofaunal community structure was water depth, bottom water temperature, sediment water content and median grain size. In terms of horizontal distribution, there were no significant differences in the community structure of meiofauna community inside and outside of Jiaozhou Bay between the two seasons, but the lowest abundance values in each season appeared in the mouth of the bay, which might be related to the sediment median grain size and bottom water temperature. The average abundance of meiofauna in the study area was lower than other areas, which was caused by the offshore human activities. The high values of N/C ratio indicated that there was organic pollution in the study area, which may be due to the bivalve bottom aquaculture in Jiaozhou Bay, resulting in the accumulation of organic matter in sediment environment.

In order to reveal the characteristics of macrofaunal communities and evaluate the benthic ecological quality in the coastal waters of Qingdao, macrofaunal samples were collected at 12 sampling sites in this area in June and October, 2021. A total of 110 macrofaunal species were found, including 50 species of polychaetes, 40 species of crustaceans, 13 species of mollusks, 4 species of echinoderms, 1 species of nemerteans, 1 species of hemichordates and 1 species of chordates. Polychaetes, crustaceans and mollusks were the three dominant groups. Prionospio queenslandica (polychaete) was the most dominant species in the 2 sampling seasons. Both abundance and biomass of macrofauna showed a decreasing trend from the northwest nearshore area to the southeast offshore area. CLUSTER analysis showed that the macrofaunal communities in summer and autumn in the study area could be divided into two groups and one independent site. BIOENV analysis showed that the combination of salinity and sediment water content, as well as the combination of bottom water dissolved oxygen and sediment median particle size, were the best combinations of environmental variables to explain the structure of macrofaunal communities in summer and autumn, respectively. Results of the Shannon-Wiener diversity index and abundance-biomass comparison curves showed that the benthic ecological environment in the coastal waters of Qingdao was greatly disturbed. The benthic ecological quality in the study area was poor, and it was worse in autumn than that in summer.

In order to characterize the species composition, abundance, biomass and community structure of zooplankton in Qiongzhou Strait and their influencing environmental factors, field samplings were conducted with vertical net in June (rainy season) and November (dry season), 2022. A total of 62 species of zooplankton were identified, including 34 species of arthropods, 14 species of Cnidaria, 9 species of larvae, 3 species of Chaetognatha, 1 species of Chordata and 1 species of Mollusca. The dominant species in rainy season were Subeucalanus subcrassus, Euchaeta plana and Canthocalanus pauper. The dominant species in dry season were Subeucalanus subcrassus, Flaccisagitta enflata and Canthocalanus pauper. The average values of abundance and biomass of zooplankton in the rainy season were 66.32 ind./m³ and 359.9 mg/m³, and those in the dry season were 93.0 ind./m³ and 163.4 mg/m³, respectively. The average diversity index (H′) was 2.20, the average evenness index (J′) was 0.79, and the average richness index (d) was 5.41. The average diversity index (H′), evenness index (J′) and richness index (d) of the dry season were 2.33, 0.81 and 6.75, respectively. The community structure of zooplankton was mainly correlated with nutrients, suspended solids and water temperature. Overall, the zooplankton community structure in Qiongzhou Strait was greatly influenced by water temperature, water flow velocity and terrestrial inputs from rivers.