Beta diversity is an important way to analyze community assembly mechanisms in different habitats or along environmental gradients. However, research on marine fish assemblages around islands has lagged, especially for functional beta diversity. In this study, we evaluated taxonomic and functional beta diversity change of island fish assemblages along the coast in two seasons and revealed its relationship with environmental factors and geographical distance. Taxonomic and functional beta diversity were both dominated by turnover (over 80% and 60%), while the contribution of nestedness on functional beta diversity was significantly increased. Environmental factors such as temperature and dissolved oxygen were important drivers of beta diversity rather than geographical distance. Fish assemblages around islands that are far away from mainlands or affected greatly by anthropogenic activities usually have higher beta diversity. These results indicated that environmental filtration is the primary factor driving the mechanism of fish community assembly. Our study revealed the importance of the integrated application of two facets of biodiversity to investigate beta diversity. The findings can provide theoretical support for the protection of marine fish and the planning of marine protected areas in the future.

Fish-aggregating devices play a significant role in tuna purse fisheries. The severe marine environment and the large number of non-biodegradable fish-aggregating devices impact structural safety and cause marine litter. Therefore, hydrodynamic performance and the use of biodegradable materials are crucial issues for ensuring the sustainability of fish-aggregating devices. In this study, a type of virtual biodegradable drifting fish-aggregating device (Bio-DFAD) was designed. Numerical simulations were conducted to investigate the motion responses and relative velocities of Bio-DFADs in regular waves (first- and fifth-order waves). The numerical model was applied based on unsteady Reynolds-averaged Navier–Stokes equations with the realizable k–ε model. For different scenarios of modeling, various conditions were modeled, including the relative length, wave steepness, and diameter of the balsa wood, to analyze their effects on the hydrodynamic response of the Bio-DFADs. The results indicated that the increased relative length, wave steepness, and diameter of balsa wood had a significant influence on the motion response amplitude operators (RAOs) and relative velocity of Bio-DFADs. The results suggested that a relative length (L_F/B = 1.5) and smaller diameter (D_F = 30 mm) were recommended for fewer motion responses and relative velocity. The obtained results provide insight for practical engineering applications of the hydrodynamic design of Bio-DFADs.