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 threats. We aim to 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.

Methods: The natural oyster resources investigated include Hekou District (HK) of Dongying City, Zhanhua District (ZH) and Wudi County (WD) of Binzhou City, in the western Yellow River Estuary and Kenli District (KL1, KL2) of Dongying City in the southern Yellow River Estuary. We considered the species composition of oyster based on 16S rDNA gene sequence analysis. We employed one-way ANOVA to analyze species diversity indices across different reef and reef-free areas. The species abundance biomass comparison curve (ABC curve) was 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 were dominantly juveniles with mean shell height 6.16 ± 1.63 mm and 4.70 ± 6.86 mm, respectively. Oysters in WD were mostly adults (mean shell height 45.69 ± 22.41 mm). The largest oyster population was 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 were 4 species including 19 of C. gigas, 6 of C. ariakensis, 8 of Crassostrea talonata, and 6 of Nanostrea fluctigera. There were 8 oyster specimens from WD including 4 of C. gigas and 4 of C. ariakensis. All 87 oyster specimens from HK were identified as C. gigas. A total of 36 species were identified as belonging to 3 phyla of phytoplankton with the dominant species belonging to bacillariophyta. There were a total of 21 species belonging to 4 phyla of zooplankton. The dominant species in the reef area was jellyfish, while the dominant specie in the reef-free area was Noctiluca scintillans. A total of 84 species were identified as belonging to 5 phyla of macrobenthos. The dominant species in the reef areas was crustaceans and polychaetes, while in the reef-free area mollusks and ostracods. The dominant species of crustaceans in reef areas was significantly more than in reef-free areas (P< 0.05). The abundance curves of both reef and reef-free areas were above the biomass curves, and the statistical W value of reef area (-0.144) was higher than of the reef-free area (-0.207).

Conclusion: Oyster reefs in different areas of the Yellow River Estuary vary in oyster species composition, numbers of adults, 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 areas 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 public education to reduce human damage and interference to oyster reefs. According to the current characteristics of oysters in different regions, scientific restoration should be carried out to rebuild the habitat functions and improve the ecological environment of the Yellow River Estuary.

Key words: Yellow River Estuary, oyster reef, resources, dominance value, community structure, ecological function, habitat restoration