Macrophyte life forms shape macroinvertebrate composition more than richness: implications for urban stream wetland conservation

The aesthetic value of macrophytes has been considered in priority in the re-vegetation of urban wetlands. Aquatic vegetation can simultaneously act as nurses and support the biodiversity of other aquatic organisms such as benthic macroinvertebrates. However, the ecosystem service of macrophytes in biological conservation has been usually neglected in the traditional landscape design of urban blue space. The present study investigated the diversity and composition of benthic macroinvertebrates associated with different life forms of macrophytes including two submerged plants - Elodea nuttallii (Planch.) H.St.John and Hydrilla verticillata (Linnaeus f.) Royle, and two floating-leaved plants - Nymphaea alba Linnaeus and Nymphoides peltata (S. G. Gmelin) Kuntze in the Licang Stream Wetland Park, Qingdao, China. We found that the life form of macrophytes discriminated the phylum-, genus- and functional feeding group (FFG) composition rather than the richness of benthic macroinvertebrates. Notably, the phylum-level composition of benthic macroinvertebrates remained uniform beneath the floating-leaved vegetation and in the unvegetated bare sites, despite a variance in the dominant macroinvertebrate genus between the substrates of N. alba and N. peltata. Conversely, the submerged vegetation appeared to "attract" a greater abundance of Arthropoda and predators, predominantly species of Cercion (damselflies). Therefore, if the biological conservation of benthic macroinvertebrates is considered as the central goal of urban wetland re-vegetation, the restoration of submerged vegetation may be more significant since they function as spawning bed and hatchery for Arthropoda. The effects of urbanization on freshwater diversity of macrophytes and macroinvertebrates need further study.