|Other Abstract||This thesis aimed to solve the following questions: understanding the long-term impact of Penglai 19-3 oil spill event on benthic ecosystem and its present quality in Bohai Sea; studying the exact variation process of macrobenthic community under different degrees of diesel oil disturbances at intertidal flats, and observing the recovery time of macrobenthic assemblages in consideration of species number, abundance and biomass. The main results were shown as bellows.
The macrobenthic community was quantitatively researched based on data carried out at 27 sampling stations from August to September in 2014, Bohai Sea. 191 macrobenthic species in total were obtained in present work, most of the them belong to Polychaeta (83), Mollusca (42), Crustacea (40) and Echinodermata (15). The dominant species was molluscan Musculus senhousei, as a disturbance tolerant species, which could affect the stability of macrofauna community. The total mean abundance was 676.88 ind/m², varied from 15 ind/m2 to 11555 ind/m2, which was lower than the value of survey results before the oil spill happened; the total mean biomass of this area reached 30.77 g/m², varied from 0.09 g/m2 to 141.55 g/m2, which was higher than the previous level before the oil spill happened. The main contributor to the biomass value belonged to Echinodermata, while Mollusca contributed the most to abundance value. Comparing to previous studies, the trend of macrobenthic miniaturization in body size seemed to slow down. The mean value of Shannon-Wiener diversity index, richness index and evenness index were respectively 3.11±1.20, 2.89±1.40 and 0.82±0.22.
Abundance Biomass Comparison Curves indicated that the macrofauna communities in the research region had been suffered from good to moderate disturbance. The results of AMBI and M-AMBI indices showed that the benthic health at oil spill accident area was good, and the benthic environment in the sea area of oil spill had been restored to a healthy condition three years after the oil spill.
In order to investigate the structure changes of macrobenthic fauna under different degrees of oil spill stress and its specific community succession process, the oil spill simulation experiment was carried out in 2015 in the intertidal zone of Laizhou, Shandong province, using multivariate before and after/control and impact (M-BACI) experimental design method. The results showed that there was no significant difference in the sediment grain size, and the content of petroleum hydrocarbon decreased and then slightly increased within the temporal scale in this experiment. In total, 35 macrobenthos were obtained at the sampling intertidal zone, among which Mollusca was the most abundant taxon with 16 species (45.71%), followed by Polychaeta with 12 species (34.29%). Crustaceans comprised 17.14% of the total fauna with 6 species, and 1 Nemertea took the least composition. Five species were identified as the dominant species according to their dominant values (Y>0.02), including 2 mulluscs Batillaria cumingi and Moerella iridescens; 2 polychates Armandia intermedia and Neanthes japonica; 1 crustacean Diastylis tricincta. The abundance values of Batillaria cumingi witnessed an increasing in all impact groups after the experimental oil spill, while the abundance of which remained steady in control group with in the sampling time scale. Armandia intermedia and Diastylis tricincta experienced a dramatic raise two days after the oil spill, yet gradually disappear in the subsequent sampling dates. Moerella iridescens and Neanthes japonica existed in all of the control and impact groups before oil spill interference, while both of them had underwent a decrease tendency in impact groups after oil spill experiment with stable quantity in control groups.
The SIMPER analysis showed that the main contributor to the community similarity before the oil spill were Moerella iridescens, Armandia intermedia, Batillaria cumingi and Diastylis tricincta, while only Batillaria cumingi after the oil spill. The ANOSIM analysis showed that the macrobenthic assemblages differed significantly before and after the oil spill. In the 2D plot of n-MDS, remarkable discrepancy could also be detected before and after the oil impact. The ANOVA and PERMANOVA analysis indicated that the macrobenthic assemblages showed significant variations in abundance, biomass, and species number under different degrees of oil impact across two experimental periods.
The main conclusions in thesis were, i) After 3 years of Penglai 19-3 oil spill accident, the benthic communities affected by oil spill had been restored to different degrees, and there was no significant difference in species composition, dominant species, biomass, abundance and species diversity between benthic communities and peripheral control points in adjacent sea waters; ii) The macrobenthos reacted diversely to various degrees of oil spill impacts at intertidal zone in Laizhou Bay. At the spatial and temporal scales in this experiment, the macrobenthic communities were significantly influenced by the oil contaminants. Some of the species were resilient to the oil spill impact, yet some were sensitive to the planned oil spillage. The community gradually recovered at low concentration oil polluted areas, but not recolonized at high concentration zone.|