Benthic macrofauna of the mangrove swamp treated with municipal wastewater

Benthic macrofauna and possible effects on community structure of discharging municipal wastewater to Futian National Mangrove Reserve, the People's Republic of China, were investigated. Eighty-four species of ground-dwelling fauna belonging to 7 Phyla, 9 Classes, 46 Families and 65 Genera were identified. Abundant families were Assimineidae, Melanidae, Potamididae, Ocypodidae, Grapsidae and Periophthalmidae. Between April 1991 to January 1993, no obvious seasonal fluctuation in species composition occurred. Total biomass also remained unchanged. However, total density showed peaks in January and July (both in section A and B), probably due to the molluscs. A selected site of the mangroves was treated with municipal wastewater (60 m³ per week for 16 consecutive months). In comparison to a control site, the effect of wastewater discharge on total mean biomass and density (particularly of molluscs and crustaceans) appeared non-significant (P>0.05). The community structure remained unchanged although some saprobic species emerged and total biomass in the area close to the wastewater front increased slightly. Multivariate analysis indicated that there probably was an initial inhibition period and a subsequent recovery period for benthic fauna in response to the discharged wastewater in the mangrove swamp. The study confirms that the benthic macrofauna within mangroves is low in species diversity and high in population counts in comparison with a frontal mudflat. Longitudinal zonation of the fauna from landward to seaward will also be discussed.