Leaf-consumption levels in subtropical mangroves of Paranaguá Bay (SE Brazil)

Abstract

The objective of this study was to measure leaf consumption levels, mainly by insect herbivores and the tree-dwelling crab Aratus pisonii (H. Milne Edwards, 1837), in mangrove forests of a large subtropical estuarine system in the South Atlantic Ocean, to determine if patterns of herbivory varied with forest structure, tree species and marked seasonal differences in rainfall and temperature. We analyzed three structurally different mangroves located in the euhaline high-energy sector of Paranagua Bay, all of them with known values of annual litter fall. Consumption levels varied from 2.2–5.4% of total leaf area considering each site as a whole, and from 2.0–6.0% considering each tree species separately. No significant differences in consumption levels were found between summer and winter samples, but significant differences were found among sites and among tree species. Leaves from Laguncularia racemosa were most consumed. The site with lower consumption levels was the one covered with dwarf trees, a condition usually caused by low nutrient availability in the soil. Analysis of nitrogen and phosphorus levels revealed lower amounts of both nutrients in soils and of phosphorus in leaves from this site when compared to the ones containing more developed trees. This result suggests a relationship between herbivory and nutrient availability in the plants.