Biodiversity value of remnant pools in an intermittent stream during the great California drought

Abstract

1. In many intermittent streams, remnant pools persist after flow ceases and provide refuge for aquatic organisms able to tolerate stagnant water conditions. The conservation value of these pools may be greatly under-appreciated, especially in regions with a Mediterranean climate, where perennial streams have been substantially modified or disturbed by human activities.2. Fish, amphibians, aquatic reptiles, and aquatic invertebrates were sampled from 15 remnant pools and three seeps at Coyote Creek, California, USA, in the late summer of 2014, during the height of the most intense drought that California has experienced in 500 years. Patterns of vertebrate and invertebrate species richness and community composition were compared with abiotic factors (e.g. water quality and habitat size).3. Thirteen vertebrate species and 172 invertebrate taxa were identified from remnant pools and seeps. Overall vertebrate richness and composition were not correlated with abiotic factors, but fish species richness increased with remnant pool size and depth. Invertebrate taxon richness increased with pool size. Invertebrate community composition differed by habitat type (pool versus seep) and gradients in composition were correlated with several abiotic factors (e.g. pool size, substrate, and canopy cover). Remnant pools at CoyoteCreek supported a full assemblage of native fishes and numerous imperilled taxa, including California red-legged frogs and California floater mussels. Nearly all native fishes and imperilled taxa are absent from artificially perennial and urbanized reaches of Coyote Creek just a few kilometres downstream of the study area. Remnant pools in intermittent streams should be a focus of conservation efforts inregions with a Mediterranean climate, especially during extreme droughts. Native fauna adapted to harsh intermittent flow regimes can thrive in these habitats, whereas non-native taxa may fare poorly. Furthermore, remnant pools supported by deep groundwater sources, such as those along geological faults, may provide both ecological refuge and evolutionary refugia for freshwater biota.

Variability of stream extents controlled by flow regime and network hydraulic scaling

“…For example, in California, which experiences a highly variable Mediterranean climate, future climate is projected to have an exacerbated seasonal cycle, with rapidly alternating drought and flood periods (Swain et al, 2018). This has direct implications for the ecological dynamics within these systems, where intermittency of headwater river networks is typically the norm rather than the exception, and aquatic species rely on wetted channel reach refuges during network contraction (Bogan et al, 2019; Hwan et al, 2018). Our study addresses recent calls for novel strategies to adaptively manage river ecosystems, with a focus on process based models that incorporate increasing climatic variability Tonkin et al (2019).…”

Fish Rescue during Streamflow Intermittency May Not Be Effective for Conservation of Rio Grande Silvery Minnow

“…Compared to other intermittent streams in the American Great Plains region [15,40] and around the world [41], isolated pools in the MRG are shallow (<0.6 m) and short-lived, with only a small percentage persisting > 4 days [37]. Globally, isolated pools can last for weeks to years and allow the persistence of fishes and other organisms [42][43][44]. Isolated pools that support fish can be important for fishes that inhabit seasonally intermittent streams by providing habitat patches that reduce mortality compared to areas with no surface water [45].…”

Effects of drying and orientation to perennial refuges on aquatic biodiversity across two basins differing in aridity

“…Although they are separated by ~190 km, both areas are in the same floristic and faunistic province and share a Mediterranean climate characterized by cool, wet winters (December-April) and warm, dry summers (May-September). In this region, intermittent reaches often flow from December to April in response to rainfall, but may be dry the rest of the year (Bogan et al, 2017(Bogan et al, , 2019. Generally, the environment at Pinnacles is drier than that of Point Reyes, and so we anticipated that contrasts between locations could provide insight into responses of biotic communities under these different conditions.…”

“…From surrounding riparian areas, aquatic species with terrestrial adult life stages timed to coincide with drying can deposit eggs in streams to initiate recruitment (Bogan & Boersma, 2012). Other aquatic species that moved into the hyporheic zone (Kawanishi et al, 2013; Rodríguez‐Lozano et al, 2019; Stubbington, 2012) or remnant pools (Bogan et al, 2019; Marshall et al, 2016) during dry periods can recolonize newly flowing reaches nearby. From outside of the immediate area, drift and swimming can bring colonists from upstream refuges (Brittain & Eikeland, 1988), species can swim or crawl upstream from downstream refuges (Davey & Kelly, 2007; Mackay, 1992), or terrestrial adult forms can immigrate from other parts of the river network (Bilton et al, 2001; Sánchez‐Montoya et al, 2017).…”