Abstract:

Aims: Oyster reefs provide crucial ecosystem services, but are being seriously degraded globally. Natural oyster resources in the Yellow River Estuary have been severely damaged in recent years due to overfishing and other threat factors. We investigate existing natural oyster resources and the diversity, community structure, and abundance of phytoplankton, zooplankton, and macrobenthos in the typical oyster distribution area of the Yellow River Estuary. Our research provides a better understanding of species composition, growth characteristics, environmental conditions of different distribution areas, and the ecological functions of oyster reefs. These findings will help develop scientific strategies for oyster reef restoration and conservation. 

Methods: The natural oyster resources investigated include Hekou District of Dongying City (HK), Zhanhua District of Binzhou City (ZH) and Wudi County (WD), in the west of the Yellow River Estuary and Kenli District of Dongying City (KL1, KL2) in the south of the Yellow River Estuary. We consider the species composition of oyster based on 16S rDNA gene sequence analysis. We employ one-way ANOVA to analyze species diversity indices across different reef and reef-free areas. The species abundance biomass comparison curve (ABC curve) is used to reveal the disturbance status of macrobenthos community in the Yellow River Estuary. 

Results: In the five study areas around the Yellow River Estuary, oysters in KL1 and KL2 are dominantly juveniles with mean shell height 6.16 ± 1.63 mm and 4.70 ± 6.86 mm, respectively. Oysters in WD are mostly adult (mean shell height 45.69 ± 22.41 mm). The largest oyster population is found in HK (mean shell height 19.68 ± 13.64 mm). We collected a total of 147 oyster specimens from the Yellow River estuary. From KL1, a total of 13 specimens with 11 identified as Crassostrea gigas and 2 Crassostrea ariakensis. Among the 39 oyster specimens from KL2, there are 4 species including 19 of C. gigas, 6 of C. ariakensis, 8 of Crassostrea talonata, and 6 of Nanostrea fluctigera. There are 8 oyster specimens from WD including 4 of C. gigas and 4 of C. ariakensis. All 87 oyster specimens from HK are identified as C. gigas. A total of 36 species are identified as belonging to 3 phyla of phytoplankton with the dominant species belonging to bacillariophyta. There are a total of 21 species belonging to 4 phyla of zooplankton. The dominant species in the reef area is jellyfish, while the dominant species in the reef-free area is Noctiluca scintillans. A total of 84 species are identified as belonging to 5 phyla of macrobenthos. The dominant species in the reef areas is crustaceans and polychaetes, while in the reef-free area mollusks and ostracods. The dominant species of crustaceans in reef areas is significantly higher than in reef-free areas (P < 0.05). The abundance curves of both reef and reef-free areas are above the biomass curves, and the statistical W value of reef area (–0.144) is higher than of the reef-free area (–0.207). 

Conclusion: Oyster reefs in various areas of the Yellow River Estuary are differ in oyster species composition, numbers of adult, and larval recruitments. The overall resource quantity is relatively low in the Yellow River Estuary when compared with other regions. The macrobenthos community structure of the Yellow River Estuary is significantly affected by environmental and human activities, but those in the reef area are less disturbed than in the reef-free area. Our results indicate oyster reefs reduce the disturbance degree to macrobenthos and play a role in maintaining the stability of biological community structure. Therefore, we suggest strengthening publicity and education is necessary to reduce human damage and interference to oyster reefs. Further, public education will be helpful in scientific restoration according to the current characteristics of oysters in different regions and improving the ecological environment of the Yellow River estuary through habitat function reconstruction.

Key words: Yellow River Estuary, oyster reef, resource status, dominance value, community structure