Sea-level rise, habitat loss, and potential extirpation of a salt marsh specialist bird in urbanized landscapes.

Jordan A Rosencranz,John Y Takekawa,Karen M Thorne,Robert T Patton,Tara E Stewart,Kevin J Buffington,Ryan F Hechinger,Richard F Ambrose,Glen M Macdonald,Kevin D Lafferty,Jeff A Crooks,Mark A Holmgren

doi:10.1002/ece3.4196

Abstract

Sea‐level rise (SLR) impacts on intertidal habitat depend on coastal topology, accretion, and constraints from surrounding development. Such habitat changes might affect species like Belding's savannah sparrows (Passerculus sandwichensis beldingi; BSSP), which live in high‐elevation salt marsh in the Southern California Bight. To predict how BSSP habitat might change under various SLR scenarios, we first constructed a suitability model by matching bird observations with elevation. We then mapped current BSSP breeding and foraging habitat at six estuarine sites by applying the elevation‐suitability model to digital elevation models. To estimate changes in digital elevation models under different SLR scenarios, we used a site‐specific, one‐dimensional elevation model (wetland accretion rate model of ecosystem resilience). We then applied our elevation‐suitability model to the projected digital elevation models. The resulting maps suggest that suitable breeding and foraging habitat could decline as increased inundation converts middle‐ and high‐elevation suitable habitat to mudflat and subtidal zones. As a result, the highest SLR scenario predicted that no suitable breeding or foraging habitat would remain at any site by 2100 and 2110. Removing development constraints to facilitate landward migration of high salt marsh, or redistributing dredge spoils to replace submerged habitat, might create future high salt marsh habitat, thereby reducing extirpation risk for BSSP in southern California.

Highlights

Salt marshes shift their distributions in response to sea-level rise (SLR) through vertical accretion, landward inundation, and retreat to formerly dryland sites (Donnelly & Bertness, 2001)
This is of particular concern in areas such as southern California (USA), where small, “urban” salt marshes are hotspots and refugia for sensitive endemic species (Zedler, 1982), including the state endangered Belding’s savannah sparrow (Passerculus sandwichensis beldingi; BSSP)
Our models suggest that under all projected SLR scenarios, and without adaptation by BSSP or accommodation by humans, near complete loss of BSSP habitat is likely throughout the Southern California Bight (SCB) under high SLR scenarios

Summary

| INTRODUCTION

Salt marshes shift their distributions in response to sea-level rise (SLR) through vertical accretion, landward inundation, and retreat to formerly dryland sites (Donnelly & Bertness, 2001). Along the Pacific Coast, recent modeling efforts have predicted a complete loss of coastal salt marshes in California (Thorne et al, 2018) This is of particular concern in areas such as southern California (USA), where small, “urban” salt marshes are hotspots and refugia for sensitive endemic species (Zedler, 1982), including the state endangered Belding’s savannah sparrow (Passerculus sandwichensis beldingi; BSSP). Salt marsh sparrows (Ammodramus caudacutus) on the USA east coast declined by 9% annually, from 1998 to 2012, primarily due to reductions in habitat availability Such losses could be compounded by SLR, with studies predicting extirpation by 2035 (Field et al, 2017) or 2050 (Correll et al, 2016). Maxent can calculate objective threshold values (e.g., 10-percentile threshold) to generate species distribution maps (Liu, Berry, Dawson, & Pearson, 2005; Wakie, Evangelista, Jarnevich, & Laituri, 2014)

| MATERIALS AND METHODS

| DISCUSSION

Findings

CONFLICT OF INTEREST