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Future alongshore benthic species shoreline lengths undergoing both sea level rise and relative sea level lowering (postglacial isostatic rebound) where SE Alaska Natives regularly conduct traditional and cultural harvests were approximated. From 30-km radii of six community centers, shorelines were examined by merging relevant portions of the NOAA ShoreZone database (utilizing alongshore bioband length segments as accounting units) with nearshore bathymetry and measures of mean global sea-level rise along with local GPS information of isostatic rebound rate. For this analysis, adjustments for the year 2108 were made by using 9868 alongshore length units (totaling 3466 km), each unit having uniform substrate and biologic type, by conducting geometric analysis of shoreline attributes. Given up to 1.8 m of sea level lowering, up to 30% decreases in estuary shoreline lengths are predicted. Trends, verified with both archeologic and land ownership records, confirm utility of simple geometric-based assessments (bathtub approach), particularly for low-energy bays with minimal stream input and bedrock/sediment-dominated shorelines and sites dominated by either isostatic rebound, sea level rise, or both. Predicted changes have implications for traditional and cultural gathering, food webs, and ocean carbon sequestration rates. For example, greater change in shoreline length segments is predicted for protected low-slope gradient bays and estuaries dominated by eelgrass (Zostera marina) and inferred butter clam (Saxidomus gigantean) habitats than for exposed, rocky, steep-gradient peninsulas with red foliose algae, including dulce (Palmaria sp.) and bull kelp (Nereocystis luetkeana).