To design artificial reef (ARs) structures that can provide better habitats for fish, extensive research has been conducted on the flow field effects of ARs with different structures. The evaluation indices of the flow field effects include upwelling and back vortex flow. However, there has been little quantitative analysis of these two indices. In addition, several studies have suggested that other flow field characteristics of ARs can aid in providing habitats for fish. To evaluate the flow field effects of ARs more comprehensively, the following work was conducted in this study. First, the flow field of the solid cubic AR was simulated using a computational fluid dynamics (CFD)-based software (Fluent), and based on the particle image velocimetry (PIV) approach, these simulation results were verified by flume experiments. Next, the flow fields of ARs with other structures (hollow cube, solid triangular pyramid, hollow triangular pyramid, solid truncated rectangular pyramid, and hollow truncated rectangular pyramid) were simulated using the verified numerical model. Subsequently, based on the analytic hierarchy process (AHP) approach, an evaluation model with six evaluation indices of the flow field effect of ARs (upwelling region, wake region, surface area of ARs, upper slow-flowing area, lateral slow-flowing area, and internal velocity of ARs) was established, and the weights of the evaluation indices were determined using the entropy weight method (EWM). Finally, to determine the structure of ARs with optimal flow field effects, the evaluation model was used for evaluating the flow field effects of all ARs. The superiority and ranking of the flow field effects of all ARs were calculated using the fuzzy comprehensive evaluation (FCE) method. This study provides a theoretical basis and reference for the optimization of AR structures.

Seagrass plays an important role in global coastal ecosystems but is among the least conserved marine ecosystems. The Northern Chinese Seas have abundant seagrasses. However, the limited information on their distribution and habitat suitability has hindered seagrass conservation and restoration in this area. The maximum entropy (MaxEnt) model was developed to study the distribution and habitat suitability of seagrasses. First, the model was developed using seagrass occurrence points and environmental variables data. The predictions were visualized using ArcGIS to create a map of potential seagrass distribution. Next, the Jackknife analysis tool and contribution rate were used to identify and quantify the dominant environmental variables. The predictions were analyzed to quantify the suitable range of the dominant environmental variables and determine the conditions for seagrass habitat suitability in the study area. Finally, the predictions were re-analyzed. By coupling the previous predictions and re-analysis results, the areas and suggestions for seagrass conservation and restoration were identified and recommended. The results indicated the predictions of the model were highly reliable, with a total potential seagrasses distribution area was 3,296.47 km² in the study area. The distance from the shore, transparency, substrate type, SST, and nitrate concentration were identified as the dominant environmental variables. Seagrasses habitat suitability was high in study area when the distance from the shore was < 210 m, the SST was around 11 ~ 25°C, the substrate type was sandy with high mud content, the substrate particle size was around 35 ~ 330 µm, the transparency was around 0.7 ~ 1.5 m, and the nitrate concentration was< 6.4 mol·m^-3. This was the first study in which seagrasses were investigated and predicted in the Northern Chinese Seas, and their potential distribution and suitable habitat conditions were assessed. Our work will not only provide fundamental information for coastal seagrass ecosystem management, but also serve as a method to support the conservation and restoration of seagrasses.

In this paper, a numerical model of 2D weakly compressible smoothed particle hydrodynamics (WCSPH) is developed to simulate the interaction between waves and thin structures. A new color domain particle (CDP) technique is proposed to overcome difficulties of applying the ghost particle method to thin structures in dealing with solid boundaries. The new technique can deal with zero-thickness structures. To apply this enforcing technique, the computational fluid domain is divided into sub domains, i.e., boundary domains and internal domains. A color value is assigned to each particle, and contains the information of the domains in which the particle belongs to and the particles can interact with. A particle, nearby a thin boundary, is prevented from interacting with particles, which should not interact with on the other side of the structure. It is possible to model thin structures, or the structures with the thickness negligible with this technique. The proposed WCSPH module is validated for a still water tank, divided by a thin plate at the middle section, with different water levels in the subdomains, and is applied to simulate the interaction between regular waves and a perforated vertical plate. Finally, the computation is carried out for waves and submerged twin-horizontal plate interaction. It is shown that the numerical results agree well with experimental data in terms of the pressure distribution, pressure time series and wave transmission.