title: Watershed- and island wide-scale land cover changes in Puerto Rico (1930s-2004) and their potential effects on coral reef ecosystems.
abstract: Anthropogenically enhanced delivery of sediments and other land-based sources of pollution represent well-recognized threats to nearshore coral reef communities worldwide. Land cover change is commonly used as a proxy to document human-induced alterations to sediment and pollutant delivery rates to coral reef bearing waters. In this article, land cover change was assessed for a 69-km(2) watershed in Puerto Rico between 1936 and 2004 by aerial photograph interpretation. Forests and sugar cane fields predominated from 1936 through the late 1970s, but while cropland dipped to negligible levels by 2004, net forest cover doubled and built-up areas increased tenfold. The watershed-scale land cover changes documented here mimicked those of the entire Puerto Rican landmass. Sediment yield predictions that rely on the sort of land cover changes reported here inevitably result in declining trends, but anecdotal and scientific evidence in the study watershed and throughout Puerto Rico suggests that sediment and pollutant loading rates still remain high and at potentially threatening levels. The simultaneous reduction in living coral cover that accompanied reforestation and urbanization patterns since the 1970s in our study region is discussed here within the context of the following non-mutually exclusive potential explanations: (a) the inability of land cover change-based assessments to discern spatially-focused, yet highly influential sources of sediment; (b) the potentially secondary role of cropland and forest cover changes in influencing nearshore coral reef conditions relative to other types of stressors like those related to climate change; and (c) the potentially dominant role that urban development may have had in altering marine water quality to the extent of reducing live coral cover. Since identification of the causes for coral reef degradation has proven elusive here and elsewhere, we infer that coral reef management may only be effective when numerous land- and marine-based stressors are simultaneously mitigated.
authors.affiliation: Department of Geography & the Environment and Lozano Long Institute of Latin American Studies, 305 E. 23rd Street, CLA 3.306, A3100, The University of Texas, Austin, TX 78712, United States; Island Resources Foundation, Washington, DC, United States. Electronic address: cramos@austin.utexas.edu.
authors.forename: Carlos E
authors.initials: CE
authors.lastname: Ramos-Scharrón
authors.affiliation: Sinoptica Sistemas de Informação Ltda., Av. João Machado, 849 S. 709 58013-520 João Pessoa, PB, Brazil.
authors.forename: Damaris
authors.initials: D
authors.lastname: Torres-Pulliza
authors.affiliation: Center for Applied Tropical Ecology and Conservation, Coral Reef Research Group, PO Box 23360, University of Puerto Rico, San Juan 00931-3360, Puerto Rico.
authors.forename: Edwin A
authors.initials: EA
authors.lastname: Hernández-Delgado
mesh_terms: D000383:Agriculture / Q000639:trends; D057231:Climate Change; D003247:Conservation of Natural Resources; D057894:Coral Reefs; D004784:Environmental Monitoring; D019015:Geologic Sediments / Q000032:analysis; D011647:Puerto Rico; D014507:Urbanization / Q000639:trends
keywords: Coastal development; Coral reef management; Erosion; Land cover change; Runoff; Urbanization