Effects of nesting waterbirds on nutrient levels in mangroves, Gulf de Fonseca, Honduras

Mangroves provide numerous ecosystem services, including biodiversity values such as nesting sites for piscivorous waterbirds. High concentrations of pisicivoirous birds are hypothesized to affect ecosystem dynamics, yet few studies have examined their effects in mangroves. We examined the effects of nutrient enrichment by colonial waterbirds at a mangrove rookery in the Gulf of Fonseca, Honduras. We compared macronutrient levels in the vegetation and soils between two sites — a small island that hosted large numbers of roosting waterbirds and a nearby control site with little evidence of waterbird activity. Nest density at the rookery was 1721 ± 469 nests ha⁻¹. Mangrove community structure and ecosystem carbon stocks were quantified by measuring above and belowground biomass, downed wood, and soil carbon. The nutrient input via bird guano deposition was quantified at each site. Rookery birds deposited 7.2 ± 3.4 g m⁻² day⁻¹ guano dry weight. This large nutrient influx contributed to substantially higher concentrations of biologically important nutrients in the soil and mangrove leaves. These results suggest that colonial waterbirds may significantly impact mangrove ecology and productivity at local scales. Further research is needed to understand the effects of avian delivered nutrients on mangrove growth rates, nutrient export to adjacent waters, invertebrate communities, and mangrove associated fisheries