Studies on the Trophic Relationship in an Integrated Agriculture- Aquaculture system

Abstract- Integrated agriculture- aquaculture ecosystem containing complex food web and it is interconnected to multitude of organism present in different trophic levels. A mass balanced model constructed for understanding trophic interactions of the different components in the Pokkali field, model gave a total system throughput of 11924 t km-2 year-1. Paddy has the lowest ecotrophic efficiency (0.049) the group was not fully consumed or under exploited, and its contribution to the total biomass to the detritus box is prominent. Various parameters, TPP/TR (4.911), NSP (4120.782 t.km-2yr-1), TPP/TB (9.311), TB/Throughput (0.047), CI (0.410), and SOI (0.187) proved that Pokkali farming is not attained maturity. This is due to replenishment of organic matter in the system due to the rotation of crop.

In commercially important group present in the Pokkali field, Etroplus spp. showing more P/Q (0.287), it indicates that better growth of the Etroplus spp. comparing to other group mainly shrimps. The FtD for the Pokkali field was computed as 5171.403 t km-2yr-1. Net efficiency of benthos (0.53) and Etroplus spp. (0.36) was high due to excessive consumption of biomass of detritus originated from paddy and subsequent development of microbes which fall in food web. Highest omnivory index (OI) in the Pokkali system was observed for the omnivorous and detritivorous fishes (0.457), indicating that this group effectively exploit the niches available in the ecosystem. Total net primary production of Pokkali field is 5174.494 t .km-2year-1.

A flow diagram was constructed to illustrate the trophic interactions, which explained the biomass flows in the ecosystem with reference to shrimps. The trophic interaction is very dynamic in the ecosystem with production exceed net consumption, The detritus based food chain and primary and secondary consumers in that food chain shows higher assimilation which denotes immense food production in the system other than the autotrophic primary production. Etroplus spp. and prawns which derive energy or consumes from different trophic levels seem to have higher net efficiency. The Pokkali culture system supports these components very much and thus higher productivity from the system. The parameters obtained after the mass balanced optimizations provide a better understanding of the system and justified the higher production from the system in quantitative terms.