Sea-level rise and refuge habitats for tidal marsh species: Can artificial islands save the California Ridgway's rail?

Abstract

Invasive species frequently degrade habitats, disturb ecosystem processes, and can increase the likelihood of extinction of imperiled populations. However, novel or enhanced functions provided by invading species may reduce the impact of processes that limit populations. It is important to recognize how invasive species benefit endangered species to determine overall effects on sensitive ecosystems. For example, since the 1990s, hybrid Spartina (Spartina foliosa 9 alterniflora) has expanded throughout South San Francisco Bay, USA, supplanting native vegetation and invading mudflats. The endangered California clapper rail (Rallus longirostris obsoletus) uses the tall, dense hybrid Spartina for cover and nesting, but the effects of hybrid Spartina on clapper rail survival was unknown. We estimated survival rates of 108 radio-marked California clapper rails in South San Francisco Bay from January 2007 to March 2010, a period of extensive hybrid Spartina eradication, with Kaplan-Meier product limit estimators. Clapper rail survival patterns were consistent with hybrid Spartina providing increased refuge cover from predators during tidal extremes which flood native vegetation, particularly during the winter when the vegetation senesces. Model averaged annual survival rates within hybrid Spartina dominated marshes before eradication (Ŝ = 0.466) were greater than the same marshes posttreatment (Ŝ = 0.275) and a marsh dominated by native vegetation (Ŝ = 0.272). However, models with and without marsh treatment as explanatory factor for survival rates had nearly equivalent support in the observed data, lending ambiguity as to whether hybrid Spartina facilitated greater survival rates than native marshland. Conservation actions to aid in recovery of this endangered species should recognize the importance of available of high tide refugia, particularly in light of invasive species eradication programs and projections of future sea-level rise.

Population ecology of the snail Melampus bidentatus in changing salt marsh landscapes

“…reticulatum (Smith, ). Salt marsh vegetation changes and increased inundation can have negative impacts on marsh‐dependent birds (Bayard & Elphick, ; Overton et al., ). Changing salt marsh landscape characteristics may also affect nekton populations (Hitch, Purcell, Martin, Klerks, & Leberg, ; Torio & Chmura, ).…”

Endangered species management and ecosystem restoration: finding the common ground

“…California rail populations increased with the spread of invasive Spartina across SF Bay from the 1990s through 2008, and research suggests that the bird thrives in the habitat created by this invasive species (Overton et al , 2015. During the latter part of this period, many of the largest populations of California rails occurred in marshes heavily impacted by invasive Spartina.…”

“…Biological control may be a suitable method of invasive species control (Dudley and DeLoach 2004) where closely related native congeners do not exist. Within SF Bay, these recommendations have been implemented and augmented with large-scale restoration, the installation of artificial and earthen island habitats to replace tidal refuge and nesting cover for California rail (Overton et al 2015;California State Coastal Conservancy, personal communication), supplemental native plantings, and herbicide-based seed suppression (Kerr and Grijalva 2012). These specific strategies may be useful to ameliorate conflicts once they become apparent, but compensating for the effects of management actions is not as efficient as preventing unintended consequences in the first place.…”

Control and consequences of Spartina spp. invasions with focus upon San Francisco Bay

“…Experimental elevation of tiny islands planted with native vegetation has produced encouraging results. These elevated islands could provide protection from predators at very high tides (Overton et al 2015).…”