Assessment of ecological carrying capacity of intertidal mangrove planting-aquaculture ecological coupling system

Carrying capacity is critical for the sustainable development of fishery. Based on the data obtained from bimonthly surveys during the period from October 2008 to August 2009,a trophic model of a mangrove planting-aquaculture coupling system was constructed by using the ECOPATH model with Ecosim software. Energy flows and ecological carrying capacity( ECC) of the coupling system were analyzed and evaluated. The results showed that the constructed ECOPATH model consists of 14 functional groups,with the trophic level ranging from 1.00 to 3.05. The geometric mean of the trophic transfer efficiencies was 6.9%,with 7.2% from detritus and 6.6% from primary producers within the system. The lower efficiencies were attributable to that most energy flows back to detritus,suggesting that the food web was more dependent on detritus than on primary producers to support fishery. The ecosystem attributes statistics:TPP/TR( total primary production / total respiration) was 8.021,together with low connectivity index (CI) being 0.243,Finn’s cycling index( FCI) being 0.26 and mean path length( MPL) being 2.139,indicating this system is at a development stage according to Odum’s theory. Furthermore,we estimated the carrying capacity for tilapia( Oreochromis niloticus),grass carp( Ctenopharyngodon idellus),silver carp( Hypophthalmichthys molitrix) and bighead carp( Aristichthys nobilis),which are the main cultured species in the system. The ECC was defined as the maximum biomass that a specified environment can support without significant change of major energy fluxes or structure of the food web. The ECC of tilapia,grass carp,silver carp and bighead carp culture should be 5.82 t/hm2,1.81 t/hm2,2.62 t/hm2 and 4.76 t/hm2,respectively in the system. Furthermore,the effects of uncertainty of input parameters and sensitivity analysis of the ECOPATH were also explored.