A trophic model of a sandy barrier lagoon at Chiku in southwestern Taiwan

Using the ECOPATH 3.0 software system, a balanced trophic model of a sandy barrier lagoon with intensive fishery activities at Chiku in tropical Taiwa n was constructed. The lagoon model comprised 13 compartments. Trophic leve ls of the compartments varied from 1.0 for primary producers and detritus t o 3.6 for piscivorous fish. Hanging-cultured oysters accounted for 39% of t he harvestable fishery biomass and were the most important fishery species. The most prominent group in terms of biomass and energy flow in the lagoon was herbivorous zooplankton. Manipulations of the biomass of herbivorous z ooplankton would have a marked impact on most compartments. Both total syst em throughput and fishery yield per unit area were high when compared to ot her reported marine ecosystems. This appears mainly due to high planktonic primary production, which is probably promoted by enriched river discharges draining mangroves and aquaculture ponds. Consequently, more than half of the total system throughput originates from primary producers in the lagoon . Although half of the primary production was not immediately used by upper trophic levels and flowed into the detrital pool, most of the detritus was directly consumed, passed up the food web and was exported to the fishery. Thus only a small proportion of energy was recycled through detritus pathw ays. This mechanism produces short pathways with high trophic efficiencies at higher trophic levels. The high fishery yield in the lagoon is due to hi gh primary production and short pathways. This is the first model of a trop ical sandy barrier lagoon with intensive fishery activities and thus may se rve as a basis for future comparisons and ecosystem management. (C) 1999 Ac ademic Press.