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Abstract

NUTRIENT OVER-ENRICHMENT DIFFERENTIALLY AFFECTS GROWTH AND HERBIVORY IN MANGROVE FORESTS ALONG LATITUDINAL AND TIDAL GRADIENTS

Ilka C. Feller¹ and Catherine E. Lovelock^2
1Smithsonian Environmental Research Center
²University of Queensland
Bio

Mangroves form complex marine ecosystems with spatial differences in structural complexity, biodiversity, biogeochemistry, and hydrology that vary at local and regional scales. Although mangroves provide critical ecosystem goods and services, they are threatened globally by human activities including nutrient over-enrichment. Our goal was to determine if enrichment with nitrogen (N) or phosphorus (P) interacts with forest structure and latitude to alter growth, nutrient dynamics, and patterns of herbivory. We established a series fertilization experiments across more than 2000 km and 18º of latitude from the Indian River Lagoon (IRL), Florida to Twin Cays, Belize to Bocas del Toro, Panama. At each site, we fertilized individual trees with one of three treatment levels (control, +N, +P) in two zones (fringe, dwarf) along transects perpendicular to shorelines and measured their responses at 6-mo intervals for 4 yr. Growth was measured as shoot elongation, and herbivory was measured as a function of folivory, loss of yield, and tissue mining. Results showed that all sites were nutrient limited, but patterns of nutrient limitation varied by zone and latitude. At IRL, growth was N-limited from the fringe to the dwarf forest; at Twin Cays, the fringe was N-limited, but the dwarf forest was P-limited; at Bocas del Toro, the fringe was N-limited, but the dwarf forest was both N- and P-limited. Nutrient enrichment had dramatic effects on herbivory that varied by treatment, zone, latitude, and species. Our studies show that responses to eutrophication of mangrove ecosystems will depend on site characteristics, the species considered, and the nature of nutrient limitation. Predicting how herbivores respond to nutrient over-enrichment requires an assessment of spatial heterogeneity coupled with feeding strategies and species-specific behavior measured on multiple scales of response.