Sunlight and sediment improve the environment of a litter biofilm-based shrimp culture system

In silvofishery, where shrimp culture is integrated with mangrove trees, the mangrove leaf litter may modify the environment in these culture systems. This study tested the potential of submerged leaf litter of Rhizophora mucronata and associated biofilm in providing a favorable environment for postlarval shrimp Penaeus monodon. Litter decomposition and assembly of microalgae and epifauna were assessed under exposure to sunlight or shade, and presence or absence of sediment. Litter incubated with sediment and exposed to sunlight was rapidly decomposed and supported the highest biomass and diversity of microalgae and epifauna. The litter also supported the highest abundance of diatoms, polychaetes and nematodes during the 4th week of decomposition. Cyanobacteria of the genus Microcystis dominated litter incubated without sediment, in sunlight, after decom position for 5 wk. Under shaded conditions, diatoms of the genus Navicula and the Cyanobacteria Anabaena spp. and Oscillatoria spp. continued to grow at high total ammonium nitrogen, low dissolved oxygen, low temperature and low pH. Our study illustrates synergy between sediment and direct sunlight in promoting diversity of microalgae and polychaetes (of dietary benefit to shrimps), inhibiting growth of Cyanobacteria and maintaining water quality at levels favorable to culture of post- larval shrimp. Our findings support 4 practices for a healthy environment in fish ponds: (1) locating ecological shrimp culture in less forested areas, (2) promoting sediment conditions in artificial shrimp culture systems, (3) exposing litterderived bio film within ponds to sunlight and incubating with sediment to maintain favorable water quality and control Cyanobacteria blooms, and (4) minimizing the use of pond liners and related sludge removal.