The protection of the biological diversity and the maintenance of the regional ecological integrity for the Huanghe (Yellow River) Estuary and its adjacent areas are practically significant and valuable. However, frequent human activities and natural climate changes have caused vigorous disturbances on the ecosystem in these sea areas. An objective assessment on the benthic habitat quality (BHQ) of the Huanghe Estuary and its adjacent areas is conducted, using AZTI's Marine Biotic Index (AMBI) and multivariate AMBI (M-AMBI) based on the data of macrobenthos in May and August 2011. The results show that both the indices do not correlate significantly, and their assessment results are greatly different. All of the samples assessed using the AMBI were "high" or "good", because the ecological group I (EGI) and the ecological group II (EGII) were dominant macrobenthic ecological groups in the research area. Owing to a low species' richness and a high individual abundance in some samples, the BHQ levels using the M-AMBI were worse than those of the AMBI. Significant correlations are observed between the M-AMBI, water depth, bottom water salinity and dissolved inorganic nitrogen, thus the M-AMBI could sensitively respond to environmental changes and distinguish influences from uninfluenced stations, but the AMBI could not. The consistent results between the AMBI and the M-AMBI mainly appeared in the uninfluenced (undisturbed or slightly disturbed) stations. Therefore, the M-AMBI is more effective than the AMBI in assessing the benthic habitat quality in the Huanghe Estuary and its adjacent areas. Using the M-AMBI to assess the BHQ of the Huanghe Estuary and its adjacent areas, the results show that 3% of the stations are undisturbed and the BHQs are "high", and 61% of the stations are slightly disturbed and those of the BHQ are "good", and the rest are meanly disturbed and those of the BHQ are "moderate".

Multivariate AZTI's Marine Biotic Index (M-AMBI) was designed to indicate the ecological status of European coastal areas. Based upon samples collected from 2009 to 2012 in the Bohai Bay, we have tested the response of variations of M-AMBI, using biomass (M-BAMBI) in the calculations, with different transformations of the raw data. The results showed that the ecological quality of most areas in the study indicated by M-AMBI was from moderate to bad status with the worse status in the coastal areas, especially around the estuaries, harbors and outfalls, and better status in the offshore areas except the area close to oil platforms or disposal sites. Despite large variations in nature of the input data, all variations of M-AMBI gave similar spatial and temporal distribution patterns of the ecological status within the bay, and showed high correlation between them. The agreement of new ecological status obtained from all M-AMBI variations, which were calculated according to linear regression, was almost perfect. The benthic quality, assessed using different input data, could be related to human pressures in the bay, such as water discharges, land reclamation, dredged sediment and drilling cuts disposal sites. It seems that M-BAMBI were more effective than M-NABMI (M-AMBI calculated using abundance data) in indicating human pressures of the Bay. Finally, indices calculated with more severe transformations, such as presence/absence data, could not indicate the higher density of human pressures in the coastal areas of the north part of our study area, but those calculated using mild transformation (i.e., square root) did.

Taxonomic sufficiency (TS) refers to identifying taxa to a taxonomic level sufficient to detect community changes in stressed environments and may provide a cost-effective approach in routine monitoring programs. However, there is still limited information regarding the seasonal impact of applying TS and its implications for the ecological quality evaluation in the estuarine ecosystem. This study investigated the relationship between the multivariate-AZTI’s Marine Biotic Index (M-AMBI) and environmental variables in three seasons (i.e., spring, summer, and autumn) in the Liaohe River Estuary. We tested the reliability of TS for simplifying the M-AMBI methodology. The results showed that family and genus level data could reproduce the spatial-temporal patterns of community structure at the species level. The M-AMBI values showed a consistent spatial distribution pattern in all sampling seasons, with a decreasing trend with the increasing distance from the estuary mouth. Both genus and family level data performed nearly as well as species level in detecting the seasonal variations of pollutants (i.e., nutrients and total organic content). The family level M-AMBI was feasible to discern stress in the Liaohe River Estuary because of the high aggregation ratios at different taxonomic levels in all sampling seasons. These findings suggest that applying taxonomic sufficiency based on the M-AMBI provides an efficient approach for evaluating ecological quality in the Liaohe River Estuary.

From a dataset of macrobenthos obtained from 18 cruises from 2004 to 2013 in the Huanghe (Yellow River) Estuary and its adjacent areas, the composition and characteristics of macrobenthos were analyzed, and the applicability of the Shannon-Wiener Index (H'), AZTI's Marine Biotic Index (AMBI) and multivariate AMBI (M-AMBI) for assessing benthic habitat quality was compared. The results showed a total of 203 macrobenthos in the study area. The macrobenthos were dominated by polychaetes, followed by mollusks and crustaceans. The macrobenthic ecological groups were dominated by EGI, EGII and EGIII, which respectively accounted for 31.5%, 36.0% and 21.2% of the total. There were significant differences between the evaluation results of the three indices. The ecological quality status (EQS) levels given by the AMBI were greater than those given by the H'and M-AMBI. The AMBI could not reflect the differences between 11 sites but the H'and M-AMBI could do. Moreover, the three indices responded well to the variations in salinity (S) and dissolved oxygen (DO) in the waters. The H' and M-AMBI also responded sensitively to the differences in physical parameters, such as water depth and sediment texture. The correlation between M-AMBI and environmental pressure gradient data was the strongest. The M-AMBI could effectively distinguish degraded conditions from undegraded but the H' and AMBI could not. Therefore, the M-AMBI reflected benthic habitat health well in the study areas. However, the objectivity of evaluation results of M-AMBI needs further verification by physical, chemical and biological methods. The thresholds also need further discussion.

To understand the ecological status and macrobenthic assemblages of the Xin'an River Estuary and its adjacent waters, a survey was conducted for environmental variables and macrobenthic assemblage structure in September 2012 (Yantai, China). Several methods are adopted in the data analysis process:dominance index, diversity indices, cluster analysis, non-metric multi-dimentional scaling ordination, AMBI and M-AMBI. The dissolved inorganic nitrogen and soluble reactive phosphorus of six out of eight sampling stations were in a good condition with low concentration. The average value of DO ((2.89±0.60) mg/L) and pH (4.28±0.43) indicated that the research area faced with the risk of ocean acidification and underlying hypoxia. A total of 62 species were identified, of which the dominant species group was polychaetes. The average abundance and biomass was 577.50 ind./m² and 6.01 g/m², respectively. Compared with historical data, the macrobenthic assemblage structure at waters around the Xin'an River Estuary was in a relatively stable status from 2009 to 2012. Contaminant indicator species Capitella capitata appeared at Sta. Y1, indicating the animals here suffered from hypoxia and acidification. AMBI and M-AMBI results showed that most sampling stations were slightly disturbed, which were coincided with the abiotic measurement on evaluating the health conditions. Macrobenthic communities suffered pressures from ocean acidification and hypoxia at the research waters, particularly those at Stas Y1, Y2 and Y5, which displays negative results in benthic health evaluation.

As an important part of the Bohai economic rim, the Laizhou Bay has been stressed by serious eco-environmental problems in recent years. In this study, the Shannon-Wiener index (H′), AZTI’s marine biotic index (AMBI) and the multivariate AMBI (M-AMBI) were used to assess the ecological quality status (EQS) of the Laizhou Bay according to macrobenthos data collected annually in August 2011–2014. The results showed that the overall benthic habitat quality in the Laizhou Bay was assessed as “Good”. However, 25% of the samples were classified as “Moderate”, “Bad” or “Poor” status under degraded conditions. Ecological group III (EGIII) species which had a certain tolerance to environmental disturbances had a higher proportion in each station, and most of them had appeared the pollution indicator species Capitella capitata. This indicated that the benthic habitat in the Laizhou Bay had been disturbed and polluted to some extent. The comparison of the three indices evaluation result and the RDA analysis showed that the H′ and M-AMBI were more suitable when the relative abundance of the single species was high and the macrobenthic community was significantly imbalanced; when the relative abundance of opportunistic species (EGIV and EGV) was high, the AMBI and M-AMBI could reflected the EQS objectively; in an undisturbed and polluted environment, all the three indices could indicate the benthic habitats quality. In summary, the better correlation between the three indices and environmental factors showed that they were well responsive to the tendency of the benthic habitats quality in the Laizhou Bay.

In order to realize the spatiotemporal variations of benthic macrofaunal communities at the “Amphioxus Sand” habitat, six surveys including four seasons and three consecutive summers (i.e., 2014, 2015 and 2016) were conducted in two core sites, i.e., Huangcuo (HC) and Nanxian-Shibaxian (NX), in the Xiamen Amphioxus Nature Reserve in China. A total of 155 species of macrofauna were recorded, therein, polychaetes were dominant in terms of species number and density. Significant spatiotemporal variations of macrofaunal communities were observed. The density of polychaetes and the biomass of molluscs in the HC site were higher than those in the NX site. Macrofauna were more diverse and abundant in the cold seasons (winter and spring) than that in the warm seasons (summer and autumn). The annual variations of macrofaunal communities may be attributed to the changes in sediment texture among the three years of the survey. The variations in macrofaunal communities were mainly related to the proportion of polychaetes within the community. In addition, the density of amphioxus (include Branchiostoma japonicum and B. belcheri) was negatively correlated to that of polychaetes, bivalves, and crustaceans. Amphioxus was less likely to be found in the sediments with higher silt and clay content. Five biotic indices including Margaref’s richness index (d), Peilou’s evenness index (J′), Shannon-Wiener diversity index (H′), AMBI and M-AMBI were calculated in the present study. AMBI seems suitable in assessing benthic health at the “Amphioxus Sand” habitat, and a potential risk of ecological health in Xiamen Amphioxus Nature Reserve should be aware.

A three-dimensional isopycnic-coordinate internal tidal model is employed to investigate the generation, propagation, vertical structure and energy conversion of M₂ internal tides in the Luzon Strait (LS) with mooring observations. Simulated results, especially the tidal current amplitudes, agree well with observations, demonstrating the reasonability and accuracy of the model. Results indicate that M₂ internal tides mainly propagate into three directions horizontally, i.e., eastward towards the western Pacific Ocean, westward towards the Dongsha Island and southwestward towards the South China Sea Basin. In the horizontal direction, tidal current amplitudes decrease as distance increases away from the LS; in the vertical direction, they show an obvious decreasing tendency with depth. Between the double ridges of the LS, a clockwise gyre of M₂ baroclinic energy flux appears, which is caused by reflections of M₂ internal tides at supercritical topographies, and resonance of M₂ internal tides happens along 19.5° and 21.5°N due to the heights and separation distance of the double ridges. The total energy conversion in the LS is about 14.20 GW.

Based on the z-coordinate ocean model HAMSOM, we introduced the internal-tide viscosity term and applied the model to numerically investigate the M2 internal tide generation and propagation in the Luzon Strait (LS). The results show that (1) in the upper 250 m depth, at the thermocline, the maximum amplitude of the generated internal tides in the LS can reach 40 m; (2) the major internal tides are generated to the northwest of Itbayat Island, the southwest of Batan Island and the northwest of the Babuyan Islands; (3) during the propagation the baroclinic energy scattering and reflection is obvious, which exists under the effect of the specific topography in the South China Sea (SCS); (4) the westward-propagating internal tides are divided into two branches entering the SCS. While passing through 118°E, the major branch is divided into two branches again. The strongest internal tides in the LS are generated to the northwest of Itbayat Island and propagate northeastward to the Pacific. However, to the east of 122°E, most of the internal tides propagate southeastward to the Pacific as a beam.

A simple three-dimensional tidal model is used to examine the M₂ tidal current distribution in a northeastern part of the East China Sea, especially the vertical variation of the current in the region. Computed M₂ current is compared with observations available and found to be in good agreement.
Main features of the calculating method in this study are:(1) Vertical variation of the tidal current is taken as a funetion of the depth-mean velocity:(2) the method is applicable to a variety of the vertical eddy viscosities; (3) it has a fine vertical resolution, especially near the sea bootom. So, this method not only enables us to get a steady state solution easily but also depicts effects of the friction on the vertical variation of the current much better.