Effects of Decomposing Rhizophora apiculata Leaves on Larvae of the Shrimp Penaeus monodon

We studied the effects of different concentrations of decomposing Rhizophora apiculata leaves and their leachates on larvae of the shrimp Penaeus monodon under laboratory conditions. Shrimp mortality was highly dependent on the concentration of oxygen in the water, which in turn was strongly correlated to the amount of decomposing leaves in the same water. Shrimps died after 5 min when placed in water containing the highest concentration of mangrove leachates (15 g l−1) tested in our experiments. Shrimp survival and biomass decreased significantly when the shrimp were cultured at the relatively higher concentrations of leaves and leachates (10 and 15 g l−1); in contrast, moderate amounts of leaves or their leachates (2.5–5 g l−1) had positive effects on shrimps. The survival and biomass of shrimps cultured with plastic leaves was lower than those of shrimps cultured with mangrove leaves, indicating that food derived from mangrove leaves contributed to a higher shrimp survival and biomass. These results have important implications for the culture of shrimps in extensive mangrove-shrimp systems. While litter may promote shrimp production, high leaf concentrations may have negative effects due to the drop in the oxygen concentration. Water circulation may help to prevent low oxygen conditions and reduce local accumulations of mangrove leaves.