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Classification of California estuaries based on natural closure patterns: templates for restoration and management
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... Ryan et al. [13] expanded the Australian estuary classification to seven classes based largely on the balance of forcing from waves, tides, and rivers. Classifications that focus on temporarily closed estuaries include aspects of mouth position, state, and composition [6,31]. South Africa recently reclassified its estuaries to reflect greater sensitivity to pressures; the new classification reflects estuary size, mouth state, geomorphology/shape, tidal amplitude, salinity regime, typical mixing processes, sediment stability, and relative catchment flows (mean annual runoff) [32]. ...
... This pattern of varying hydrologic function and ecological services as a function of estuary state was observed by Clark and O'Connor [17] in their investigation of intermittent estuaries along the California (USA) coast. Jacobs et al. [31] provides one of the few classification systems that account for temporal dynamics by using geologic origin, exposure to littoral process, watershed size and runoff characteristics as the basis of a conceptual model that predicts likely frequency and duration of estuary mouth opening. Their system also includes general management recommendations related to both estuary class and status. ...
... The health of estuaries is fundamentally associated with freshwater inflow, which includes the magnitude of flow, as well as the timing, frequency and duration of flow events. These dynamic aspects of flow regime play an important role in mouth closure [31], with low flows being associated with closed mouth state and high flows with open mouth state [15]. Flow alteration in the surrounding watershed from, e.g., dams, channelization, urbanization and abstraction, can have a substantial impact on estuarine mouth dynamics, which in turn can influence biotic processes and ecosystem functions and services (Table 1). ...
The science needed to inform management of environmental flows to temporarily closed estuaries and coastal lagoons is decades behind the state of knowledge for rivers and large embayments. These globally ubiquitous small systems, which are often seasonally closed to the ocean’s influence, are under particular threat associated with hydrologic alteration because of changes in atershed land use, water use practices, and climate change. Managing environmental flows in these systems is complicated by their tight coupling with watershed processes, variable states because of intermittently closing mouths, and reliance on regional scale sediment transport and littoral processes. Here we synthesize our current understanding of ecohydrology in temporarily closed estuaries (TCEs) and coastal lagoons and propose a prioritized research agenda aimed at advancing understanding of ecological responses to altered flow regimes in TCEs. Key research needs include agreeing on a consistent typology, improving models that couple watershed and ocean forcing at appropriate spatial and temporal scales, quantifying stress–response relationships associated with hydrologic alteration, improving tools to establish desired conditions that account for climate change and consider cultural/indigenous objectives, improving tools to measure ecosystem function and social/cultural values, and developing monitoring and adaptive management programs that can inform environmental flow management in consideration of other stressors and across different habitat types. Coordinated global efforts to address the identified research gaps can help guide management actions aimed at reducing or mitigating potential impacts of hydrologic alteration and climate change through informed management of freshwater inflows.
... Understanding historical conditions provides valuable context for the relationship between landscape-scale process and wetland composition and can inform decisions about appropriate restoration targets at different landscape positions. While not meant to provide a blueprint for the future, reconstructing historical patterns can inform decisions regarding restoration and management by improving understanding of both cultural and natural (i.e., geomorphic) processes that led to current conditions (Jacobs et al. 2011). Similarly, understanding how coastal wetlands will be impacted by changes in future conditions associated with sea level rise and changing runoff patterns is critical to making informed decisions regarding regional restoration planning. ...
... Intermediate estuaries, which are intermittently opening and closing estuaries or bar-built estuaries are noteworthy because they represent a significant component of coastal wetlands in Southern California (Zedler 1996). Although a distinct class, it is important to note that most other archetypes include wetlands that have seasonally closing mouths (Jacobs et al. 2011). Finally, we mapped habitat data from the National Wetlands Inventory (NWI) and the California Vegetation Classification (CalVeg) onto the clusters to produce habitat associations for each archetype. ...
... The modeling framework incorporates regionally important factors that contribute to SLR response, such as mouth dynamics, which have not been included in previous models (Swanson et al. 2014;Lentz et al. 2016). This approach may be relevant for assessing SLR response in estuaries in other Mediterranean settings across the globe, including South Estuaries and Coasts Africa and Australia, which are subject to similar processes (Jacobs et al. 2011). Based on the use of archetypes, the model should provide a regionally applicable screening tool for application to a wide range of coastal systems, which may have differential responses to SLR (Lentz et al. 2016). ...
Regional approaches to coastal wetland restoration are one of the best ways to ensure that these threatened habitats persist in the face of sea level rise. Regional approaches provide a mechanism for prioritizing restoration actions in areas where future conditions will promote maximum resiliency while still providing for an appropriate composition of plant and animal habitats across the region as a whole. Developing a regional restoration strategy requires understanding historical losses relative to contemporary habitat distributions, predicting future changes due to sea level rise (and other stressors), and evaluating management actions with the potential to offset expected future losses. In this study, we present an approach to assess historical losses and future management options for more than 100 individual wetlands along the Southern California (USA) coast ranging in size from a few tenths of a hectare to over 250 ha. This analysis was conducted to support development of a regional wetland strategy that will guide restoration in Southern California for the next several decades. The approach consisted of reconstructing historical wetland distribution using US Coast and Geodetic Survey T-sheets, mapping current wetlands and classifying them into archetypes that represent different settings and processes, and predicting future distributions based on a hypsometric model of elevation changes under various sea level rise and management scenarios. Historical analysis revealed that two-thirds of the 331 wetlands present in ca. 1850 and 75% of vegetated estuarine habitat area has been lost, with most losses occurring in small to medium size wetlands. Up to 69% of the remaining marshes and flats could be lost with 1.7 m of sea level rise, with an associated increase in subtidal habitat. However, potential future losses could be largely offset, and total area could increase under scenarios of facilitated wetland migration and sediment augmentation. Although the future distribution of wetlands would likely be different from current conditions, sufficient habitat would be provided region-wide. This analysis demonstrates how regional analysis of historic, present, and likely future conditions can support a strategy that could lead to net wetland gain under future sea level rise conditions. However, immediate and decisive action is necessary.
... Despite the potential benefits of opening closed lagoons such as LPL, tidal inlets and their management are extremely complex, and mechanical opening of tidal inlets is one of the most contentious management issues associated with ICEs (Jacobs et al. 2011;Clark and O'Connor 2019;Largier et al. 2019;Stein et al. 2021). It is clear that naturally closing systems provide a variety of unique functions and services (e.g., support for anadromous fish) that artificial opening can compromise, especially when intermittent systems are made to be permanently open (Jacobs et al. 2011). ...
... Despite the potential benefits of opening closed lagoons such as LPL, tidal inlets and their management are extremely complex, and mechanical opening of tidal inlets is one of the most contentious management issues associated with ICEs (Jacobs et al. 2011;Clark and O'Connor 2019;Largier et al. 2019;Stein et al. 2021). It is clear that naturally closing systems provide a variety of unique functions and services (e.g., support for anadromous fish) that artificial opening can compromise, especially when intermittent systems are made to be permanently open (Jacobs et al. 2011). However, without mechanical opening of inlets, anthropogenically impacted lagoons such as LPL can experience unnatural, prolonged closures as well as watershed inputs that affect biota, including invertebrate communities. ...
The southern California coastline hosts low-inflow estuaries that have mouths that periodically close. Low-inflow estuaries can become hypoxic and are then often opened mechanically. The consequences of mouth closure and hypoxia (< 2 mg L ⁻¹ O 2 ) on macrobenthic densities, species richness, diversity, composition, and biological traits were evaluated for legacy data generated by the Pacific Estuarine Research Lab for Los Peñasquitos Lagoon (LPL) (1991–2006) and Tijuana Estuary (TJE) (1988–2004). LPL closed at least annually and TJE remained open during the study period. Effects were moderated by zone within the estuary (relative to the mouth) and season. Periodic closure in LPL was associated with raised macrofaunal density and diversity, especially at the mouth, and with suppressed seasonality. Closure favored soft-bodied (non-calcified) non-bioturbating, mobile, epifaunal taxa in LPL with planktotrophic development, large branchiae, and no vision. There were more spionid and capitellid polychaetes, Traskorchestia traskiana , Cerithideopsis californica , Tagelus californianus , and phoronids during closure. In contrast, hypoxia (< 2 mg L ⁻¹ ) measured during faunal sampling was associated with lower densities in LPL and different taxonomic composition, but no difference in taxon richness or diversity. There were more corophiid amphipods, small snails, tubificid oligochaetes, Palaemon macrodactylus (shrimp), and Trichorixa reticulata (insects) under hypoxic conditions, and retention of taxa with very large or small bodies and with vision. TJE densities were nearly double those of LPL; taxon richness and diversity (H’) were also higher in TJE. TJE hosted more burrowing, large-bodied, highly calcified taxa with planktotrophic development and no vision than LPL. Differences in composition and traits between the two estuaries disappeared in the middle and upper reaches, where ocean flushing was more limited. Historical long-term monitoring data for benthos, such as the data set analyzed here, offer a valuable baseline for evaluating ecosystem response to changes induced by climate, infrastructure development, contamination, or restoration.
... Other studies document the genetic connectivity of estuarine populations on the Pacific coast as a result of habitat expansion as sea level rose (Dolby et al., 2016(Dolby et al., , 2018(Dolby et al., , 2020Stiller et al., 2021). Sea level rise would also lead to the formation and broad distribution of lagoons following maturation of the coast (Jacobs et al., 2011;Masters, 2006). ...
... open to the ocean during heavy rain events (Jacobs et al., 2011). The complex coastal geomorphology and hydrology of lagoons probably created dispersal opportunities that help explain the cohesion of the OC group, a pattern consistent with G. aculeatus worldwide where marine fish tend to show genetic uniformity across large geographic distances (Mäkinen et al., 2006). ...
Habitat loss, flood control infrastructure, and drought have left most of southern California and northern Baja California’s native freshwater fish near extinction, including the endangered unarmored threespine stickleback (Gasterosteus aculeatus williamsoni). This subspecies, an unusual morph lacking the typical lateral bony plates of the G. aculeatus complex, occurs at arid southern latitudes in the eastern Pacific Ocean and survives in only three inland locations. Managers have lacked molecular data to answer basic questions about the ancestry and genetic distinctiveness of unarmored populations. These data could be used to prioritize conservation efforts. We sampled G. aculeatus from 36 localities and used microsatellites and whole genome data to place unarmored populations within the broader evolutionary context of G. aculeatus across southern California/northern Baja California. We identified three genetic groups, with none consisting solely of unarmored populations. Unlike G. aculeatus at northern latitudes, where Pleistocene glaciation has produced similar historical demographic profiles across populations, we found markedly different demographies depending on sampling location, with inland unarmored populations showing steeper population declines and lower heterozygosity compared to low armored populations in coastal lagoons. One exception involved the only high elevation population in the region, where the demography and alleles of unarmored fish were similar to low armored populations near the coast, exposing one of several cases of artificial translocation. Our results suggest that the current ‘management‐by‐phenotype’ approach, based on lateral plates, is incidentally protecting the most imperiled populations; however, redirecting efforts toward evolutionary units, regardless of phenotype, may more effectively preserve adaptive potential.
... This thesis will provide the most upto-date understanding of what has been found in the Cayucos area with the intention of producing a foundation of general information about an area which has not yet been summarized by scholars and which can be built upon by future researchers. (Jacobs et al. 2010). ...
... This may have allowed the estuary located at VillaCreek to form, during a time of mega floods opened wetlands, after 200 year-long megadroughts. Combined factors during the last 5,000 years or so likely influenced the current formation of the Villa Creek Estuary, which is classified as a hydraulic estuary and can be episodic during climate fluctuations(Jacobs et al. 2010).Between 2600 and 1400 BP, evidence indicates there was seismic event or events that caused a sudden deepening of Estero Bay and sea level rise(Gallagher 1996). This would likely result in habitat upheaval; however, it appears that general brackish conditions prevailed.as ...
Located on the Central Coast, within the northern portion of Estero Bay, Cayucos remains an under-investigated area, and with over 8,000 years of human occupation there, it has the potential to inform about local and regional precontact history. Though relatively few archaeological investigations have occurred in Cayucos, by synthesizing studies in the area, a baseline of information emerges to build upon. This thesis reviews every recorded archaeological site with a precontact component, in the vicinity of Cayucos. These records, along with other relevant studies and theoretical framework, provide clues about the past associated with local settlement, technology, and the environment. Sources of information have been culled from site records and studies, authored by a variety of experts and non-experts including avocationalists, rock art scholars, residents, local CRM archaeologists, and others. One source of information comes from the orphaned Cayucos Bench Collection. Produced in the 1960s by the San Luis Obispo County Amateur Archaeologists, the collection is associated with 11 archaeological sites along the Estero Bluffs and includes site and artifact records, photographs, and a report. The collection is important because it represents the only artifact collection associated with the bluffs, a major portion of the research area. An aspect of this research includes comparative analysis of Cayucos with the Morro Bay Estuary, just south of Cayucos, in order to establish the relationship between these areas and identify regional patterns. The findings of this research begin to fill in the research gap remaining in the northern portion of Estero Bay.
... Artificial breaching of closed estuaries and coastal lagoons is a common practice worldwide, used to offset flow reduction, prevent flooding, and improve fisheries and water quality [18][19][20][21]. In Central and Southern California, many historically closed estuaries have been permanently opened using groins, levees, and regular dredging [22], practices that can have unforeseen negative environmental impacts. TCEs can have high biodiversity importance and productivity. ...
... This has resulted in changes to habitat types because the closed state is essential to normal estuarine function. For an activity to be restorative, it should follow natural hydrological and sediment dynamic regimes [22]. ...
Temporarily closed estuaries require seasonal opening to tidal flows to maintain normal ecological processes. Each estuary has specific environmental flow (EFlow) requirements based on the relationship between freshwater inflow, coastal dynamics, rate of sandbar formation, and the open/closed state of the mouth. Key abiotic processes and ecosystem services linked to mouth state were highlighted. We reviewed completed EFlow requirement studies for temporarily closed estuaries in South Africa and found that the formulation of these requirements should consider the timing and magnitude of flows in relation to the morphology of an estuary, its mouth structure, catchment size, and climate. We identified ten key principles that could be adapted to similar systems in equivalent climatic settings. Principle 1 recognizes that each estuary is unique in terms of its EFlow requirements because size, scale, and sensitivity of core elements to freshwater inflow are specific for each system; EFlows cannot be extrapolated from one estuary to another. Principle 2 highlights the importance of baseflows in keeping an estuary mouth open because a small reduction in flow can cause the mouth to close and alter essential ecological processes. Principle 3 outlines the role of floods in resetting natural processes by flushing out large volumes of sediment and establishing the equilibrium between erosion and sedimentation. Principle 4 emphasizes the need for open mouth conditions to allow regular tidal flushing that maintains water quality through reducing retention times and preventing the onset of eutrophic conditions. Principle 5 advises artificial breaching to be practiced with caution because execution at low water levels encourages sedimentation that reduces the scouring effect of flushing. Principle 6 holds that elevated inflow volumes from wastewater treatment works or agricultural return flows can increase the frequency of mouth opening and cause ecological instability. Principle 7 states that water released from dams to supply the environmental flow cannot mimic the natural flow regime. Principle 8 specifies the need for short-and long-term data to increase the confidence levels of EFlow assessments, with data to be collected during the open and closed mouth states. Principle 9 advocates the implementation of a monitoring program to track the achievement of EFlow objectives as part of a strategic adaptive management cycle. Finally, Principle 10 recommends the adoption of a holistic catchment-to-coast management approach underpinned by collaboration with regulatory authorities and stakeholders across a range of sectors. These principles can be used to guide the formulation and management of EFlows, an essential strategy that links the maintenance of estuarine ecological integrity with social well-being.
... Overall, we do not believe the effects of uplift would bias our overarching conclusions, but these considerations would be important for local interpretations in some areas. Third, we do not account for many environmental or climatic processes that are known to influence the distribution of species (Jacobs et al., 2011;Kench, 1999;Wolfe and Kjerfve, 1986). It was previously noted that because estuaries have highly variable abiotic properties (salinity, temperature, pH, turbidity, dissolved oxygen, dissolved organic matter, etc.), that not only is it likely that their inhabitants can sustain a range of abiotic conditions, but also it is not possible to include this abiotic detail in our models. ...
... Work is particularly needed in strike-slip (transform) coastlines, which we expect to exhibit narrow shelves similar to fore-arc settings. While it is established that estuaries predominantly inhabit low-gradient regions (Jacobs et al., 2011), measuring the sensitivity and specificity of these models on present-day habitat could develop more sophisticated paleo-estuarine models as well as modeling approaches for other types of coastal habitats. Detailed seismic stratigraphy data could be used to ground-truth such estimates (Bastos et al., 2015;Berton et al., 2019;Lee et al., 2017;Roach, 2017;Zaremba et al., 2016). ...
... A typology of Californian estuaries distinguished eight closed-mouth states based on berm elevation and tidal exchange where river inflow rather than tidal influence controls mouth opening. This scheme recognised that mouth states prevail over multiyear to multidecadal periods (Jacobs et al. 2010). Over the past six decades estuary classification studies have therefore evolved from relatively simple "topology" schemes (defining estuary types based on a key process or feature), to more complex regional ecosystem-level classification schemes (regional schemes that include elements of climatic/biogeography, estuarine processes and biological responses). ...
For nearly three decades, the Whitfield (1992) characterisation scheme served as a reference framework to type South African estuaries. We outline a revised ecosystem classification scheme that incorporates biogeographicalzonation and introduces new types. Coastal outlets were re-categorised as estuaries or micro-systems. For functional estuaries, the Estuarine Lakes, Estuarine Bays and Predominantly Open Estuary types were largely retained. New types are Estuarine Lagoons and Arid Predominantly Closed Estuaries. The numerically dominant, temporarily open/closed category was subdivided into Small and Large Temporarily Closed Estuaries, with a total habitat area of 15 ha, serving as threshold separating these two subdivisions. River mouths were renamed Fluvially Dominated Estuaries and divided into large and small size categories to reflect dissimilar catchment influences. Micro-systems were separated into micro-estuaries, micro-outlets, and waterfalls. South Africa’s 290 estuaries were classified into 22 estuarine ecosystem categories arising from nine estuary types occurring across four
biogeographical zones. In addition, 202 micro-systems were classified into nine ecosystem types, of which only the micro-estuaries (42) share possible functionality with estuaries. Estuaries subjected to functional shifts were also identified. The classification system provides a framework that integrates biogeography and the range of biophysical parameters evident in South Africa, and can be used for red listing of ecosystem types and determining estuarine sensitivity to pressures.
... In estuaries with low or intermittent river outflow and/or small watersheds and tidal areas, wave-driven sediment accumulation can exceed tidal/fluvial erosion leading to the formation of a sill or barrier berm at the estuary mouth that separates the estuary from the ocean (e.g., Largier et al. 1992;Elwany et al. 1998; Morris and Turner 2010;Behrens et al. 2009;Behrens et al. 2013;Rich and Keller 2013;Orescanin and Scooler 2018). A common feature globally, estuaries that close intermittently have been referred to by many names (Tagliapietra et al. 2009), including intermittently closed and open lakes and lagoons (ICOLL, Roy et al. 2001), temporarily opening and closing estuaries (TOCE, Whitfield 1992), intermittently open estuaries (IOE, Jacobs et al. 2010 In developed regions such as Southern California, many ICEs fail to re-open naturally due to adjacent beach nourishment , reduced tidal prism, structurally impeded inlet migration, and altered fluvial inputs (Hastings and Elwany 2012). This results in environmental concerns, including flooding of low-lying development, undesirable water quality and impacts to fish and other marine organisms that require management attention (Largier et al. 2019 Largier et al. 2019), there remain several critical questions as to how these systems will respond to rising sea levels and a changing climate, including if marsh accretion rates will keep pace with sea level and how elevation and formation of barrier berms will change. ...
The 2015–2016 El Niño provided insight into how low-inflow estuaries might respond to future climate regimes, including high sea levels and more intense waves. High waves and water levels coupled with low rainfall along the Southern California coastline provided the opportunity to examine how extreme ocean forcing impacts estuaries independently from fluvial events. From November 2015 to April 2016, water levels were measured in 13 Southern California estuaries, including both intermittently closed and perennially open estuaries with varying watershed size, urban development, and management practices. Elevated ocean water levels caused raised water levels and prolonged inundation in all of the estuaries studied. Water levels inside perennially open estuaries mirrored ocean water levels, while those inside intermittently closed estuaries (ICEs) exhibited enhanced higher-high water levels during large waves, and tides were truncated at low tides due to a wave-built sand sill at the mouth, resulting in elevated detided water levels. ICEs closed when sufficient wave-driven sand accretion formed a barrier berm across the mouth separating the estuary from the ocean, the height of which can be estimated using estuarine lower-low water levels. During the 2015–2016 El Niño, a greater number of Southern California ICEs closed than during a typical year and ICEs that close annually experienced longer than normal closures. Overall, sill accretion and wave exposure were important contributing factors to individual estuarine response to ocean conditions. Understanding how estuaries respond to increased sea levels and waves and the factors that influence closures will help managers develop appropriate adaptation strategies.
... The native populations occurring in this region have a variety of distinctive behavioral, physiological, and genetic traits warranting their designation as distinct population segments (DPSs) by the national marine fisheries service (NMFS 2012(NMFS , 2013. Because of large, interannual variation in lagoon sand berm breaching, some steelhead spawners do not have access in dry years to their natal streams, where they typically spawn, so they can disperse to nearby streams where adequate flows allow access (Boughton et al. 2006, Clemento et al. 2009, Bell et al. 2011, Jacobs et al. 2011. Steelhead populations in this region also show unusual tolerances to low flow, high temperatures, and low oxygen levels, with juveniles often oversummering in isolated or semi-isolated pools with temperatures sometimes exceeding 25°C (occasionally approaching 30°C) and oxygen levels occasionally dropping to <3 mg/L, outside tolerances reported for steelhead in other regions (Carter 2005, Richter and Kolmes 2005, Spina et al. 2005, Spina 2007, Bell et al. 2011, Sloat and osterback 2013. ...
The Pacific coast population of Western Snowy Plovers (Charadrius alexandrinus nivosus) is a federally listed threatened species, having experienced significant and pervasive population declines within its range in California, Oregon, and Washington.
Recovery of the species depends on the effective use of management resources because human- associated disturbance is a key factor in reducing or eliminating nesting habitat. Within the large extensive tracts of potential habitat, managers must decide where to pursue conservation actions and weigh the benefits of those actions against the costs of implementation. Geographic Information Systems (GIS)-based predictive habitat modeling is an approach that can identify and rank nesting habitats for Western Snowy Plover. We implemented a series of habitat models for the central coast of California (Recovery Unit 5 in the U.S. Fish and Wildlife Service Recovery Plan for the species).
Recovery Unit 5 (RU5) encompasses roughly 700 km of coastline in San Luis Obispo, Santa Bar- bara, and Ventura counties. It has remarkable geographic diversity, with predominantly west- facing beaches in San Luis Obispo County and south-facing beaches in much of Santa Barbara and Ventura Counties. The recovery unit also includes the northern California Channel Islands of San Miguel, Santa Rosa, Santa Cruz, Anacapa, Santa Barbara, and San Nicolas. An average of 1,000 Western Snowy Plovers nest in RU5, which is approximately half of the population of the Pacific Coast. A broad array of management actions is taken for Western Snowy Plover in RU5, ranging from nothing to intensive management.
We took two approaches to develop habitat suitability models for Western Snowy Plover.
The first is a deductive method, where environmental variables to predict habitat were selected based on the existing scientific literature and its description of the habitat preferences of the species. Such preferred habitat includes sand spits, dune-backed beaches, estuary and lagoon salt pans, beaches at creek and river mouths, bluff- backed beaches, dry salt ponds, and sand and gravel bars in rivers.
We consulted the literature to identify variables that could best describe optimal habitats, with our final models including elevation; slope gradient; distance from the coast; distance from streams and estuaries; distance from major rivers; landward boundary (e.g. dune, bluff); beach substrate (e.g. sand, gravel); beach width plus adjacent sand dunes/river sand bars; wave height; wind speed; and air/sea temperature. We intentionally excluded vegetation, presence of beach wrack, and other factors that could be influenced by management. Data were obtained or calculated from existing sources or developed for this purpose from remotely sensed information (e.g., description of landward boundary, beach width, and beach substrate from aerial photography). The continuous variables were standardized using fuzzy-logic linear or nonlinear functions with inflection points based on recorded species’ preferences before being used in the deductive models. Habitat suitability models were calculated from the continuous and categorical variables using Idrisi multi-criteria evaluation procedures.
Inductive models are built from species occurrence data and the modeling procedure selects those environmental variables and their values that best predict existing occurrences to extrapolate to potential habitat. We used nest site data obtained from beach managers to run the Maxent model with the same environmental variables as our deductive models, while keeping some nest site data aside to check the accuracy of the predictions.
Our deductive habitat models were also tested using nest site data and performed well. Beaches identified in the Recovery Plan as recovery sites encompassed high habitat suitability values as would be expected. For most beaches, our habitat suitability values for nest sites were statistically greater than at non-nest sites within recovery beaches. In instances where this was not true, a lack of management at high suitability value areas was the obvious and overwhelming explanation. For example, at Coal Oil Point in Santa Barbara County, which is intensively managed for Western Snowy Plovers, nest sites are concentrated in areas with high suitability values. By contrast, nest sites on the Morro Bay Strand in San Luis Obispo County are also found at some locations with high habitat suitability values, but are conspicuously absent from others. This reflects the different patterns of ownership and associated level of management.
With uneven management effort, nest sites are located in high suitability sites within managed areas, but also within lower habitat suitability sites that are intensively managed. Sites without management, despite having high suitability values defined by physical variables in the model, are not used for nesting.
Our inductive models were not as useful. They returned high suitability values for areas with nest site data, but did not return generalized rules that were able to extrapolate such high values to areas with known high habitat value but no nest point data.
We conclude a deductive approach provides a number of advantages for conservation planning in a heavily human-dominated landscape, even though it does depend on the existence of a well-developed natural history for the species in question. With this information, however, it can extrapolate the ideal conditions to locations where the species is no longer present and indeed is useful for identifying locations that would be excellent habitat if appropriate management were undertaken. Such sites are simply not ranked highly by inductive models when the training data are geographically clustered and the actual potential range is large.
Our model results should be useful for identifying, accurately delimiting, and assessing critical habitat for the species within RU5. Our deductive model gives gradations of habitat suitability within (and outside) existing recovery sites that might be used both to concentrate efforts within those sites and to reconfigure them during future recovery planning efforts.
By comparing the models that we developed with existing survey data we provide convincing evidence that many sites are indeed nesting habitat for western snowy plover, but it is only ongoing beach disturbance that consistently and chronically interferes with nesting. The model results, validated by the nest site and historic data, provide the basis for strong argument that “take,” as defined under the Endangered Species Act, is regularly occurring at high habitat suitability value sites that have wintering populations of Western Snowy Plovers but are not managed for the species.
The Los Angeles coastal prairie was an herbaceous plant community with high concentrations of annual forbs, similar to coastal prairie described for northern California, interspersed with a network of vernal pools with their associated specialized flora. Unfortunately, the unique community was lost before it could be studied in detail. The prairie covered about 95 km2 of coastal Los Angeles County, extending north-south from the crest of the Ballona Bluffs to the Palos Verdes peninsula and inland for 3–7 km from the lee of the El Segundo sand dunes. We present (1) historical accounts and photographs of the prairie, (2) a description of the vegetation, including a list of plants native to the prairie assembled from herbarium accessions, botanical literature, and recent surveys of a highly degraded 12-ha fragment, and (3) a review of the mammals, birds, reptiles and amphibians that were once found on the prairie. The description of the Los Angeles coastal prairie and its vernal pools should inform restoration efforts in the area, and aid in the potential identification of previously overlooked fragments of these habitats in the urban mosaic.
This document is part of the Habitat Suitability Index (HSI) Model Series [Biological Report 82(10)] which provides habitat information useful for impact assessment and habitat management. Several types of habitat information are provided. The Habitat Use Information Section is largely constrained to those data that can be used to derive quantitative relationships between key environmental variables and habitat suitability. This information provides the foundation for the HSI model and may be useful in the development of other models more appropriate to specific assessment or evaluation needs. The HSI Model Section documents the habitat model and includes information pertinent to its application. The model synthesizes the habitat use information into a framework appropriate for field application and is scaled to produce an index value between 0.0 (unsuitable habitat) and 1.0 (optimum habitat). The HSI Model Section includes information bout the geographic range and seasonal application of the model, its current verification status, and a list of the model variables with recommend measurement techniques for each variable.
Spring tidal flows and stream stormflows are effective at scouring littoral sediment from inlets and restoring inlet stability. The inlets were most unstable and occasionally closed when high waves coincided with neap tide conditions. Inlets with cobble-size bed sediment tend to be less stable than those with sandy beds due to bed armouring. -from Authors
All generally available navigation charts and tidal data were critically examined for 48 tidal inlets, lagoons, and bays along the coasts of California, Oregon, and Washington to determine the tidal prism and throat area of the inlets. Twenty-five of the inlets yielded data which were considered reliable, and a relationship between tidal prism and inlet area was formulated.
Considers the overall stability with particular reference to the bar section and its combined flow and sediment conditions. Certain practical conclusions on improvements for navigation are drawn. -from Author