Effects of seawall revetment surface modifications on marine biodiversity: A case study in China

Traditionally paved seawalls impede biological migration and dispersal, and degrade habitat serviceability, which negatively impacts coastal ecosystems. To promote the intertidal biodiversity of coastal construction, in this study, we conducted a design improvement experiment on seawall revetment blocks in a coastal zone in Zhejiang Province, Eastern China. Ten surface treatments were established on the seawall blocks, including surface roughening, pitting, and oyster shell embedment with a non-treatment control. The effects of different revetment treatments on marine biodiversity were investigated. Over a period of 12 months from spring to winter after block installation on the intertidal coastline, 18 marine species (incl. 3 sessile species and 15 mobile species) were observed on the experimental blocks, comprising mollusks, arthropods, and algae. Total 11, 7, 16, and 14 attached species were recorded in spring, summer, autumn, and winter, respectively. A wide range of organism abundance from 33.4 to 760.6 individuals m⁻² exhibited seasonal characteristics specific to the study area. The abundance and diversity of organisms attached on blocks with pits and oyster shells were significantly higher than those of other types of blocks. The Shannon–Wiener diversity index of benthic organisms on pitted (0.13 −1.92) and on shell-embedded blocks (0.11 −1.63) was higher than that on surface-roughened (0.07 −1.53) and blank blocks (0 −1.15). Blocks with high water-holding ability was more effective in enhancing the abundance of both sessile and mobile species than blocks with increased surface roughness. Although pitted blocks can attract most marine species for attachment, we also found that oyster shell-embedded blocks could maintain a high level of biodiversity and richness indices. Therefore, this type of safe biogenic material is recommended for constructing nature-based seawall revetments. The findings have provided empirical evidence and a technical demonstration of the ecological improvement of traditionally paved seawalls.