Impacts of submerging and emerging shorelines on various biota and indigenous Alaskan harvesting patterns

Background/Question/Methods - Southeast Alaska has some of the greatest rates of isostatic rebound (post-glacier retreat land uplift) found anywhere in the world. Our study examined effects of coastal change on shoreline biota and Alaskan Native harvesting pattern. Future alongshore benthic species shoreline lengths undergoing both sea level rise and relative sea level lowering (associated with 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 with nearshore bathymetry and measures of mean global-level rise along with local GPS information of isostatic rebound rate. Student interns in 14 communities led 223 community discussions to discuss species collected and harvested and summarize community concerns.

Results/Conclusions - Given up to 1.8 m of sea level lowering, up to 30% decreases in estuary shoreline lengths are predicted one-hundred years into the future. 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). Predicted - and field verified - changes in shorelines may exacerbate community concerns. Students found > 80% of people collect or harvest, 80% described seasonal nature of harvesting, and nearly 30% noted climate change impacts. At least 85% rely on berry and salmon harvests and over 50% collect black seaweed, butter clams, gum boots, and/or cockles. Summarized community concerns include pollution, shellfish poisoning, overharvest and sea otter predation.