Nutrient Controls on Biocomplexity of Mangrove Ecosystems

<strong>Nutrient</strong> <strong>Controls</strong> on Biocomplexity of Mangrove EcosystemsMangrove EcosystemsMangrove forests are important coastal ecosystems thatprovide a variety of ecological and societal services. Theseintertidal, tree-dominated communities along tropical coastlinesare often described as “simple systems,” compared to othertropical forests with larger numbers of plant species andmultiple understory strata; however, mangrove ecosystemshave complex trophic structures, and organisms exhibit uniquephysiological, morphological, and behavioral adaptationsto environmental conditions characteristic of the land-seainterface. Biogeochemical functioning of mangrove forestsis also controlled by interactions among the microbial, plant,and animal communities and feedback linkages mediated byhydrology and other forcing functions. Scientists with the U.S.Geological Survey (USGS) at the National Wetlands ResearchCenter are working to understand more fully the impact ofnutrient variability on these delicate and important ecosystems.Worldwide, there are about 50 mangrove species, but speciesrichness in any particular forest stand may vary. In Florida andthe Caribbean region, the most common species is Rhizophoramangle (red mangrove) (fig.1), which typically dominates theshorelines of islands and low-lying regions along continentalmargins. Red mangrove may occur with two other species;Avicennia germinans (black mangrove), and Lagunculariaracemosa (white mangrove), in addition to a number ofmangrove associates such as Conocarpus erectus (buttonmangrove) and Batis maritima (maritime saltwort). In the Indo-West Pacific realm, forests may have over 30 mangrove speciesplus additional numbers of associates. Some mangrove forestsmay exhibit low structural complexity, but others may contain avariety of forbs, ferns, vines, and epiphytes such as orchidsand bromeliads.What is Biocomplexity?The study of biocomplexity is a rapidly developing area ofresearch that seeks to better understand the emergent propertiesof ecosystems and how they may be affected as underlyingmechanisms or external forcing functions change. Habitatstability is an emergent property of ecosystems that arisesas a consequence of many processes interacting at differentspatio-temporal scales and at different levels of biologicalorganization. For mangroves, habitat stability is primarilyRhizophora mangle (red mangrove) Avicennia germinans (black mangrove) Laguncularia racemosa (white mangrove)Figure 1.Dominant mangrove species occurring in Florida and the Caribbean region.U.S. Department of the InteriorU.S. Geological SurveyFact Sheet 2004-3124March 2006

whole—even destabilizing the delicate balance between bioticand abiotic processes controlling soil elevations and habitatstability in peat-forming mangroves.A global comparison of nutrient limitations to mangrove growthis essential to an understanding of how coastal eutrophicationmay impact these important ecosystems—in the United States,as well as in other countries. Collaboration between theUSGS and the Smithsonian Environmental Research Center inEdgewater, Maryland has led to the establishment of multipleexperimental sites in mangrove forests located in Florida,Louisiana, Belize, Honduras, Panama, Australia, and NewZealand (fig. 3). Research in different geographic areas will leadto more accurate models to predict global change impacts onmangrove ecosystems and better management plans fortheir conservation.References CitedFeller, I.C., McKee, K.L., Whigham, D.F., and O’Neill, J.P., 2003,Nitrogen vs phosphorus limitation across an ecotonal gradient in amangrove forest: Biogeochemistry, v. 62, p. 145-175.Feller, I.C., Whigham,D.F., McKee, K.L., and Lovelock, C.E., 2003,Nitrogen limitation of growth and nutrient dynamics in a disturbedmangrove forest, Indian River Lagoon, Florida: Oecologia, v. 134,no. 3, p. 405-414.McKee, K.L., Feller, I.C., Popp, M., and Wanek,W., 2002, Mangroveisotopic fractionation (δ 15 N and δ 13 C) across a nitrogen versusphosphorus limitation gradient; Ecology, v. 83, no. 4, p. 1065-1075.For more information, contactKaren L. McKeeU.S. Geological SurveyNational Wetlands Research Center700 Cajundome Blvd.Lafayette, LA 70506337-266-8500http://www.nwrc.usgs.govRookery Bay,Florida, USAIndian River Lagoon,Florida, USAPort Douglas, AustraliaPort Fourchon,Louisiana, USAHinchinbrook, AustraliaTwin Cays, BelizeCape Ferguson, AustraliaBay Island & Gulf of Fonseca,HondurasBocas del Toro, PanamaWaikopua Creek,New ZealandFigure 3. Location of multiple experimental sites where USGS scientists are studying nutrient controls on mangroveecosystem structure and function.