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1.3.4.2 Marine ERS ModelsDeveloping ERS models for the marine realm is often the most difficult of the threerealms due to the lack of data and the dynamic nature of the ocean, an environment that isconstantly moving. Assigning risk boundaries to the ocean is a complicated andperplexing task. Attempts to model coastal transport with ocean current data for assigningmarine risk distributions has been attempted by Schill (2005) using the cell-assignedvelocity from the Hybrid Coordinate Ocean Model (HYCOM) data model. The modeloperates using eastward and northward velocities on a cell-by-cell basis to compute atravel cost surface which represents the number of seconds it takes to cross a cell.Additional investigations are currently being conducting using the new network datamodel in ArcGIS Network Analyst.As with the other, ERS models,marine experts must first identify therisk elements to the marine habitats.Human activities that are riskelements can be divided into fourcategories based on their marineimpact: direct impacts (e.g.population density), contamination(e.g. coastal industry, ports/marinas),extraction (e.g. fishing and harvestingpractices), and watershed-basedsedimentation/run-off (land andmarine-based pollution). This processwas followed for the marine ERSmodels that were developed for theJamaica Ecoregional PlanningMarine Analysis (Zenny, 2006).Each risk element that was identifiedand mapped by experts was assignedan intensity value, an influencedistance, then combined to create anoverall risk surface.One idea for modeling potentialupland sedimentation on coastalenvironments is to use the flowaccumulation of the freshwater ERSmodel to gauge risk intensity atcoastal outlets. As discussed in theprevious section, the flowaccumulation function aggregates androutes risk intensities to watershedoutlets, which often empty into theThe creation of the Jamaican marine cost surface used in theMARXAN model included the combining of four riskcategories: contamination, direct impacts, flow accumulation,and extraction.TNC Protected Area Tools (PAT) Version 3.0The Nature Conservancy, August 200929