Multiple effects of a typhoon strike and wastewater effluent on benthic macrofaunal communities in a mangrove estuary

We examined the multiple effects of a typhoon strike and agricultural wastewater effluent on benthic faunal communities at the mangrove estuary in Nagura Lagoon, Ishigaki Island, Okinawa, Japan. Environmental parameters and benthic macrofaunal community structures were compared at wastewater-impacted and intact reference sites (which were nested in canopy-covered forests and fringing mudflats), before and after the typhoon strike. Most physical and chemical factors were not affected by wastewater loading, typhoon strikes, or habitat differences; however, organic parameters (food resource environment) were changed; wastewater input raised amounts of microphytobenthos and mangrove litter, while a typhoon strike significantly increased phytoplankton biomass. Wastewater effluent also increased the numerical abundance and species richness of benthic macrofauna; however, a typhoon strike did not induce such changes. Species compositions were clearly divided into pre-and post-typhoon periods at the reference site, but were classified into the same cluster at the wastewater site, regardless of the typhoon. The typhoon-induced compositional shift is caused by the removal of vulnerable arboreal species and facultative opportunistic species recruitment. However, wastewater that causes organic-rich conditions would lock such community dynamics by enhancing the predominance of species that prefer and tolerate eutrophic conditions. Overall, the impact of anthropogenic wastewater could outweigh those of natural typhoon disturbances on benthic faunal communities in mangrove estuaries.