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Donald R Strong - One of the best experts on this subject based on the ideXlab platform.

  • Responses to salinity of Spartina hybrids formed in San Francisco Bay, California (S. alterniflora × foliosa and S. densiflora × foliosa )
    Biological Invasions, 2016
    Co-Authors: Alex K. Lee, Debra R Ayres, Mary R. Pakenham-walsh, Donald R Strong
    Abstract:

    San Francisco Bay (SFB), which supports large populations of the California native cordgrass Spartina foliosa , has been the recipient of introductions of S. alterniflora and S. densiflora. Hybrids have arisen between the native and these exotic species. Sterile F1 S. densiflora  ×  foliosa hybrids have formed numerous times in a number of marshes, while introgressing S. alterniflora  ×  foliosa hybrids are fully fertile and invaded widely in SFB, especially onto naturally-open low tidal flats by inundation-tolerant hybrids. Sarcocornia pacifica , pickleweed, dominates the mid-to-upper marsh zones where the hypersaline conditions that occur during the summer drought, characteristic of this climate, exclude S. foliosa . Here we report on two glasshouse experiments investigating the salinity tolerance of hybrid Spartina . Some hybrids of both origins grew well and flowered at high salinity levels while the parental species grew little and did not flower. Our results imply that mid-zone marshes are also vulnerable to invasion by salinity-tolerant Spartina hybrids. Herbicide control implemented over the last 10 years targeting both the exotic species and their hybrids have reduced their extent. However, efforts in monitoring and management of exotic Spartina and its hybrids must continue as vast areas of tidal marsh restoration are underway and planned in SFB; colonization by Spartina hybrids tolerant to inundation and/or salinity will greatly alter restoration trajectories. These concerns are all the more vital given projections of climate change and its effects on salinity and sea level rise in SFB salt marshes.

  • Responses to salinity of Spartina hybrids formed in San Francisco Bay, California (S. alterniflora × foliosa and S.densiflora × foliosa)
    Biological Invasions, 2016
    Co-Authors: Alex K. Lee, Debra R Ayres, Mary R. Pakenham-walsh, Donald R Strong
    Abstract:

    San Francisco Bay (SFB), which supports large populations of the California native cordgrass Spartina foliosa, has been the recipient of introductions of S. alterniflora and S. densiflora. Hybrids have arisen between the native and these exotic species. Sterile F1 S. densiflora × foliosa hybrids have formed numerous times in a number of marshes, while introgressing S. alterniflora × foliosa hybrids are fully fertile and invaded widely in SFB, especially onto naturally-open low tidal flats by inundation-tolerant hybrids. Sarcocornia pacifica, pickleweed, dominates the mid-to-upper marsh zones where the hypersaline conditions that occur during the summer drought, characteristic of this climate, exclude S. foliosa. Here we report on two glasshouse experiments investigating the salinity tolerance of hybrid Spartina. Some hybrids of both origins grew well and flowered at high salinity levels while the parental species grew little and did not flower. Our results imply that mid-zone marshes are also vulnerable to invasion by salinity-tolerant Spartina hybrids. Herbicide control implemented over the last 10 years targeting both the exotic species and their hybrids have reduced their extent. However, efforts in monitoring and management of exotic Spartina and its hybrids must continue as vast areas of tidal marsh restoration are underway and planned in SFB; colonization by Spartina hybrids tolerant to inundation and/or salinity will greatly alter restoration trajectories. These concerns are all the more vital given projections of climate change and its effects on salinity and sea level rise in SFB salt marshes.

  • responses to salinity of Spartina hybrids formed in san francisco bay california s alterniflora foliosa and s densiflora foliosa
    Biological Invasions, 2016
    Co-Authors: Alex K. Lee, Debra R Ayres, Mary R Pakenhamwalsh, Donald R Strong
    Abstract:

    San Francisco Bay (SFB), which supports large populations of the California native cordgrass Spartina foliosa, has been the recipient of introductions of S. alterniflora and S. densiflora. Hybrids have arisen between the native and these exotic species. Sterile F1 S. densiflora × foliosa hybrids have formed numerous times in a number of marshes, while introgressing S. alterniflora × foliosa hybrids are fully fertile and invaded widely in SFB, especially onto naturally-open low tidal flats by inundation-tolerant hybrids. Sarcocornia pacifica, pickleweed, dominates the mid-to-upper marsh zones where the hypersaline conditions that occur during the summer drought, characteristic of this climate, exclude S. foliosa. Here we report on two glasshouse experiments investigating the salinity tolerance of hybrid Spartina. Some hybrids of both origins grew well and flowered at high salinity levels while the parental species grew little and did not flower. Our results imply that mid-zone marshes are also vulnerable to invasion by salinity-tolerant Spartina hybrids. Herbicide control implemented over the last 10 years targeting both the exotic species and their hybrids have reduced their extent. However, efforts in monitoring and management of exotic Spartina and its hybrids must continue as vast areas of tidal marsh restoration are underway and planned in SFB; colonization by Spartina hybrids tolerant to inundation and/or salinity will greatly alter restoration trajectories. These concerns are all the more vital given projections of climate change and its effects on salinity and sea level rise in SFB salt marshes.

  • Tidal and seasonal effects on survival rates of the endangered California clapper rail: does invasive Spartina facilitate greater survival in a dynamic environment?
    Biological Invasions, 2014
    Co-Authors: Cory T Overton, Donald R Strong, Michael L Casazza, John Y Takekawa, Marcel Holyoak
    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  ×  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.

  • Spatial and temporal genetic structure in a hybrid cordgrass invasion.
    Heredity, 2010
    Co-Authors: Christina M. Sloop, Debra R Ayres, Donald R Strong
    Abstract:

    Invasive hybrids and their spread dynamics pose unique opportunities to study evolutionary processes. Invasive hybrids of native Spartina foliosa and introduced S. alterniflora have expanded throughout San Francisco Bay intertidal habitats within the past 35 years by deliberate plantation and seeds floating on the tide. Our goals were to assess spatial and temporal scales of genetic structure in Spartina hybrid populations within the context of colonization history. We genotyped adult and seedling Spartina using 17 microsatellite loci and mapped their locations in three populations. All sampled seedlings were hybrids. Bayesian ordination analysis distinguished hybrid populations from parent species, clearly separated the population that originated by plantation from populations that originated naturally by seed and aligned most seedlings within each population. Population genetic structure estimated by analysis of molecular variance was substantial (FST=0.21). Temporal genetic structure among age classes varied highly between populations. At one population, the divergence between adults and 2004 seedlings was low (FST=0.02) whereas at another population this divergence was high (FST=0.26). This latter result was consistent with local recruitment of self-fertilized seed produced by only a few parental plants. We found fine-scale spatial genetic structure at distances less than ∼200 m, further supporting local seed and/or pollen dispersal. We posit a few self-fertile plants dominating local recruitment created substantial spatial genetic structure despite initial long-distance, human dispersal of hybrid Spartina through San Francisco Bay. Fine-scale genetic structure may more strongly develop when local recruits are dominated by the offspring of a few self-fertile plants.

Debra R Ayres - One of the best experts on this subject based on the ideXlab platform.

  • Responses to salinity of Spartina hybrids formed in San Francisco Bay, California (S. alterniflora × foliosa and S. densiflora × foliosa )
    Biological Invasions, 2016
    Co-Authors: Alex K. Lee, Debra R Ayres, Mary R. Pakenham-walsh, Donald R Strong
    Abstract:

    San Francisco Bay (SFB), which supports large populations of the California native cordgrass Spartina foliosa , has been the recipient of introductions of S. alterniflora and S. densiflora. Hybrids have arisen between the native and these exotic species. Sterile F1 S. densiflora  ×  foliosa hybrids have formed numerous times in a number of marshes, while introgressing S. alterniflora  ×  foliosa hybrids are fully fertile and invaded widely in SFB, especially onto naturally-open low tidal flats by inundation-tolerant hybrids. Sarcocornia pacifica , pickleweed, dominates the mid-to-upper marsh zones where the hypersaline conditions that occur during the summer drought, characteristic of this climate, exclude S. foliosa . Here we report on two glasshouse experiments investigating the salinity tolerance of hybrid Spartina . Some hybrids of both origins grew well and flowered at high salinity levels while the parental species grew little and did not flower. Our results imply that mid-zone marshes are also vulnerable to invasion by salinity-tolerant Spartina hybrids. Herbicide control implemented over the last 10 years targeting both the exotic species and their hybrids have reduced their extent. However, efforts in monitoring and management of exotic Spartina and its hybrids must continue as vast areas of tidal marsh restoration are underway and planned in SFB; colonization by Spartina hybrids tolerant to inundation and/or salinity will greatly alter restoration trajectories. These concerns are all the more vital given projections of climate change and its effects on salinity and sea level rise in SFB salt marshes.

  • Responses to salinity of Spartina hybrids formed in San Francisco Bay, California (S. alterniflora × foliosa and S.densiflora × foliosa)
    Biological Invasions, 2016
    Co-Authors: Alex K. Lee, Debra R Ayres, Mary R. Pakenham-walsh, Donald R Strong
    Abstract:

    San Francisco Bay (SFB), which supports large populations of the California native cordgrass Spartina foliosa, has been the recipient of introductions of S. alterniflora and S. densiflora. Hybrids have arisen between the native and these exotic species. Sterile F1 S. densiflora × foliosa hybrids have formed numerous times in a number of marshes, while introgressing S. alterniflora × foliosa hybrids are fully fertile and invaded widely in SFB, especially onto naturally-open low tidal flats by inundation-tolerant hybrids. Sarcocornia pacifica, pickleweed, dominates the mid-to-upper marsh zones where the hypersaline conditions that occur during the summer drought, characteristic of this climate, exclude S. foliosa. Here we report on two glasshouse experiments investigating the salinity tolerance of hybrid Spartina. Some hybrids of both origins grew well and flowered at high salinity levels while the parental species grew little and did not flower. Our results imply that mid-zone marshes are also vulnerable to invasion by salinity-tolerant Spartina hybrids. Herbicide control implemented over the last 10 years targeting both the exotic species and their hybrids have reduced their extent. However, efforts in monitoring and management of exotic Spartina and its hybrids must continue as vast areas of tidal marsh restoration are underway and planned in SFB; colonization by Spartina hybrids tolerant to inundation and/or salinity will greatly alter restoration trajectories. These concerns are all the more vital given projections of climate change and its effects on salinity and sea level rise in SFB salt marshes.

  • responses to salinity of Spartina hybrids formed in san francisco bay california s alterniflora foliosa and s densiflora foliosa
    Biological Invasions, 2016
    Co-Authors: Alex K. Lee, Debra R Ayres, Mary R Pakenhamwalsh, Donald R Strong
    Abstract:

    San Francisco Bay (SFB), which supports large populations of the California native cordgrass Spartina foliosa, has been the recipient of introductions of S. alterniflora and S. densiflora. Hybrids have arisen between the native and these exotic species. Sterile F1 S. densiflora × foliosa hybrids have formed numerous times in a number of marshes, while introgressing S. alterniflora × foliosa hybrids are fully fertile and invaded widely in SFB, especially onto naturally-open low tidal flats by inundation-tolerant hybrids. Sarcocornia pacifica, pickleweed, dominates the mid-to-upper marsh zones where the hypersaline conditions that occur during the summer drought, characteristic of this climate, exclude S. foliosa. Here we report on two glasshouse experiments investigating the salinity tolerance of hybrid Spartina. Some hybrids of both origins grew well and flowered at high salinity levels while the parental species grew little and did not flower. Our results imply that mid-zone marshes are also vulnerable to invasion by salinity-tolerant Spartina hybrids. Herbicide control implemented over the last 10 years targeting both the exotic species and their hybrids have reduced their extent. However, efforts in monitoring and management of exotic Spartina and its hybrids must continue as vast areas of tidal marsh restoration are underway and planned in SFB; colonization by Spartina hybrids tolerant to inundation and/or salinity will greatly alter restoration trajectories. These concerns are all the more vital given projections of climate change and its effects on salinity and sea level rise in SFB salt marshes.

  • Spatial and temporal genetic structure in a hybrid cordgrass invasion.
    Heredity, 2010
    Co-Authors: Christina M. Sloop, Debra R Ayres, Donald R Strong
    Abstract:

    Invasive hybrids and their spread dynamics pose unique opportunities to study evolutionary processes. Invasive hybrids of native Spartina foliosa and introduced S. alterniflora have expanded throughout San Francisco Bay intertidal habitats within the past 35 years by deliberate plantation and seeds floating on the tide. Our goals were to assess spatial and temporal scales of genetic structure in Spartina hybrid populations within the context of colonization history. We genotyped adult and seedling Spartina using 17 microsatellite loci and mapped their locations in three populations. All sampled seedlings were hybrids. Bayesian ordination analysis distinguished hybrid populations from parent species, clearly separated the population that originated by plantation from populations that originated naturally by seed and aligned most seedlings within each population. Population genetic structure estimated by analysis of molecular variance was substantial (FST=0.21). Temporal genetic structure among age classes varied highly between populations. At one population, the divergence between adults and 2004 seedlings was low (FST=0.02) whereas at another population this divergence was high (FST=0.26). This latter result was consistent with local recruitment of self-fertilized seed produced by only a few parental plants. We found fine-scale spatial genetic structure at distances less than ∼200 m, further supporting local seed and/or pollen dispersal. We posit a few self-fertile plants dominating local recruitment created substantial spatial genetic structure despite initial long-distance, human dispersal of hybrid Spartina through San Francisco Bay. Fine-scale genetic structure may more strongly develop when local recruits are dominated by the offspring of a few self-fertile plants.

  • Sexual reproduction of cordgrass hybrids (Spartina foliosa x alterniflora) invading tidal marshes in San Francisco Bay
    Diversity and Distributions, 2007
    Co-Authors: Debra R Ayres, Christina M. Sloop, Katherine Zaremba, Donald R Strong
    Abstract:

    We genetically analysed cordgrass plants and seedlings throughout the San Francisco, California, USA, estuary and found that hybrids between exotic Spartina alterniflora and native Spartina foliosa are the principal cordgrass invaders and colonizers. We hypothesized that this was due to higher seed set and siring ability by hybrids relative to the native species; too few alien parents remained in San Francisco Bay for our comparative studies. Hybrid seed comprised 91% to 98% of that set in the marsh study plants over the 2 years of the study. Total viable pollen production by hybrid plants was 400 times that of the native plants. Seed and pollen production were highly skewed towards a few hybrid genotypes. In addition to seed produced by hybrid plants, hybrid seed was produced by S. foliosa due to hybrid backcrossing. While the greatest advantage for hybrids was in pollen and seed production, hybrid seeds germinated, and seedlings survived and grew as well or better than the native species. As native S. foliosa becomes increasingly rare, hybrid seed floating on the tides will predominate, overwhelming recruitment sites and resulting in further colonization by hybrids. In an evolutionary context, hybrids with exceptional pollen and seed production will be initially favoured by natural selection, leading to the evolution of even more fertile hybrid genotypes.

Edwin D. Grosholz - One of the best experts on this subject based on the ideXlab platform.

  • Appendix C. 15N signatures of macrofauna exposed to different parts of 15N-labeled Spartina foliosa in litter bags for 50 days.
    2016
    Co-Authors: Lisa A Levin, Carlos Neira, Edwin D. Grosholz
    Abstract:

    15N signatures of macrofauna exposed to different parts of 15N-labeled Spartina foliosa in litter bags for 50 days

  • Appendix C. Height–weight regressions used to calculate biomass of Spartina foliosa and Salicornia virginica for each site and treatment in San Francisco Bay.
    2016
    Co-Authors: Anna Christina Tyler, John G. Lambrinos, Edwin D. Grosholz
    Abstract:

    Height–weight regressions used to calculate biomass of Spartina foliosa and Salicornia virginica for each site and treatment in San Francisco Bay

  • ORIGINAL PAPER Influence of invasive Spartina growth stages on associated macrofaunal communities
    2013
    Co-Authors: Edwin D. Grosholz, Æ Guillermo Mendoza, C. Neira, L. Levin A. G. Mendoza, E. D. Grosholz
    Abstract:

    Abstract In coastal wetlands, invasive plants often act as ecosystem engineers altering flow, light and sediments which, in turn, can affect benthic animal communities. However, the degree of influence of the engineer will vary significantly as it grows, matures and senesces, and surprisingly little is known about how the influence of an ecosystem engineer varies with ontogeny. We address this issue on the tidal flats of San Francisco Bay where hybrid Spartina (foliosa · alterniflora) invaded 30 years ago. The invasion has altered the physico-chemical properties of the sediment habitat, which we predicted should cause changes in macrofaunal community structure and function. Through mensurative and manipulative approaches we investigated the influence of different growth stages of hybrid Spartina on macrobenthos and the underlying mechanisms. Cross-elevation sampling transects were established covering 5 zones (or stages) of the invasion, running from the tida

  • Influence of invasive Spartina growth stages on associated macrofaunal communities
    Biological Invasions, 2007
    Co-Authors: Carlos Neira, Lisa A Levin, Edwin D. Grosholz, Guillermo Mendoza
    Abstract:

    In coastal wetlands, invasive plants often act as ecosystem engineers altering flow, light and sediments which, in turn, can affect benthic animal communities. However, the degree of influence of the engineer will vary significantly as it grows, matures and senesces, and surprisingly little is known about how the influence of an ecosystem engineer varies with ontogeny. We address this issue on the tidal flats of San Francisco Bay where hybrid Spartina ( foliosa ×  alterniflora ) invaded 30 years ago. The invasion has altered the physico-chemical properties of the sediment habitat, which we predicted should cause changes in macrofaunal community structure and function. Through mensurative and manipulative approaches we investigated the influence of different growth stages of hybrid Spartina on macrobenthos and the underlying mechanisms. Cross-elevation sampling transects were established covering 5 zones (or stages) of the invasion, running from the tidal flat (pre-invasion) to an unvegetated dieback zone. Additionally, we experimentally removed aboveground plant structure in the mature (inner) marsh to mimic the ’unvegetated areas’. Our results revealed four distinct faunal assemblages, which reflected Spartina -induced changes in the corresponding habitat properties along an elevation gradient: a pre-invaded tidal flat, a leading edge of immature invasion, a center of mature invasion, and a senescing dieback area. These stages of hybrid Spartina invasion were accompanied by a substantial reduction in macrofaunal species richness and an increase in dominance, as well as a strong shift in feeding modes, from surface microalgal feeders to subsurface detritus/ Spartina feeders (mainly tubificid oligochaetes and capitellid polychaetes). Knowledge of the varying influence of plant invaders on the sediment ecosystem during different phases of invasion is critical for management of coastal wetlands.

  • effect of native and invasive cordgrass on macoma petalum density growth and isotopic signatures
    Estuarine Coastal and Shelf Science, 2007
    Co-Authors: Elizabeth D. Brusati, Edwin D. Grosholz
    Abstract:

    Abstract Ecosystem engineers can influence community and ecosystem dynamics by controlling resources, modifying the flow of energy or biomass, or changing physical characteristics of the habitat. Invasive hybrid cordgrass ( Spartina alterniflora × Spartina foliosa ) is an ecosystem engineer in salt marshes in San Francisco Bay, California, U.S.A. that raises intertidal elevations and may be either increasing C 4 plant carbon input into food webs or tying up carbon in a form that is not usable by consumers. A manipulative experiment compared abundance, growth, and stable isotope (δ 13 C and δ 15 N) composition of the clam Macoma petalum (= M. balthica ) among native marsh, hybrid Spartina , and mudflats in central San Francisco Bay. We found higher densities (individuals m −2 ) of M. petalum on mudflats compared to either native or hybrid Spartina ( p Macoma petalum shell growth was significantly greater in mudflats than in either vegetation type in 2002 ( p  = 0.005) but not 2003. Differences in shell growth between native and hybrid Spartina were not significant. Stable isotope results showed differences between habitats in δ 13 C but not δ 15 N. Carbon signatures of M. petalum placed in Spartina were much more depleted than the isotopic signature of Spartina . Neither native nor hybrid Spartina appears to be a significant carbon source for M. petalum in San Francisco Bay, and we found no evidence that hybrid Spartina contributes carbon to M. petalum beyond what is provided by S. foliosa , despite the hybrid's much greater biomass. Our results show that loss of mudflat habitat, rather than increased input of C 4 carbon, is the greatest effect of the invasion of hybrid Spartina on M. petalum .

Joy B Zedler - One of the best experts on this subject based on the ideXlab platform.

  • Accelerating the Restoration of Vegetation in a Southern California Salt Marsh
    Wetlands Ecology and Management, 2006
    Co-Authors: Erin L. O’brien, Joy B Zedler
    Abstract:

    Re-establishing plant cover is essential for restoring ecosystem functions, but revegetation can be difficult in severe sites, such as salt marshes that experience hypersalinity and sedimentation. We tested three treatments (adding tidal creeks, planting seedlings in tight clusters, and rototilling kelp compost into the soil) in a site that was excavated to reinstate tidal flows and restore salt marsh. The magnitude of responses was the reverse of expectations, with tidal creeks having the least effect and kelp compost the most. On the marsh plain, kelp compost significantly increased soil organic matter (by 17% at 0–5 cm; p  = 0.026 and 11.5% at 5–20 cm; p  = 0.083), total Kjeldahl nitrogen (45% at 5–8 cm; p < 0.001) and inorganic nitrogen (35% at 5–8 cm; p < 0.006), and decreased bulk density (16% at 0–5 cm; p < 0.001 and 21% at 5–8 cm depth; p < 0.001) compared to control plots. Survivorship of kelp compost treated plantings increased, along with growth (> 50% increase in a growth index at 20 months after planting; p < 0.0001). In Spartina foliosa plots, kelp compost did not affect soil organic matter, but plants were taller (by ~11 cm; p  = 0.003) and denser (47% more stems; p  = 0.003). Planting seedlings 10-cm apart in tight clusters on the marsh plain increased survivorship by 18% (compared to 90-cm apart in loose clusters; p  = 0.053), but not growth. Tidal creek networks increased survivorship of Batis maritima and Jaumea carnosa by ≥20% ( p  = 0.060 and 0.077, respectively). Kelp compost had a strong, positive influence on vegetation establishment by ameliorating some of the abiotic stress.

  • Accelerating the restoration of vegetation in a southern California salt marsh
    Wetlands Ecology and Management, 2006
    Co-Authors: Erin L. O’brien, Joy B Zedler
    Abstract:

    Re-establishing plant cover is essential for restoring ecosystem functions, but revegetation can be difficult in severe sites, such as salt marshes that experience hypersalinity and sedimentation. We tested three treatments (adding tidal creeks, planting seedlings in tight clusters, and rototilling kelp compost into the soil) in a site that was excavated to reinstate tidal flows and restore salt marsh. The magnitude of responses was the reverse of expectations, with tidal creeks having the least effect and kelp compost the most. On the marsh plain, kelp compost significantly increased soil organic matter (by 17% at 0–5 cm; p = 0.026 and 11.5% at 5–20 cm; p = 0.083), total Kjeldahl nitrogen (45% at 5–8 cm; p 50% increase in a growth index at 20 months after planting; p < 0.0001). In Spartina foliosa plots, kelp compost did not affect soil organic matter, but plants were taller (by ~11 cm; p = 0.003) and denser (47% more stems; p = 0.003). Planting seedlings 10-cm apart in tight clusters on the marsh plain increased survivorship by 18% (compared to 90-cm apart in loose clusters; p = 0.053), but not growth. Tidal creek networks increased survivorship of Batis maritima and Jaumea carnosa by ≥20% (p = 0.060 and 0.077, respectively). Kelp compost had a strong, positive influence on vegetation establishment by ameliorating some of the abiotic stress.

  • Episodic colonization of an intertidal mudflat by native cordgrass (Spartina foliosa) at Tijuana Estuary
    Estuaries, 2003
    Co-Authors: Kristen M. Ward, John C. Callaway, Joy B Zedler
    Abstract:

    Following heavy winter storms and sedimentation in 1993,Spartina foliosa (Pacific cordgrass) clones established on a 6.5-ha mudflat in Tijuana Estuary, with over 80 new clones counted by 1997. El Nino Southern Oscillation (ENSO) storms in 1993 apparently facilitated the habitat conversion through river flooding, which caused a temporary reduction in soil salinity and delivered large volumes of sediment. Extreme sedimentation likely raised mudflat elevations enough to allowSpartina establishment. We hypothesized that clones, once established, increased sedimentation in a positive feedback loop leading to accelerated habitat conversion. We collected data on elevation,Spartina expansion, and sediment accretion in two consecutive years (1998–1999). The elevation range of the mudflats in 1998 (0.5–0.83 m NGVD) was within the elevation range ofSpartina at this site (0.39–0.83 m NGVD), indicating that remaining mudflats are at elevations suitable for further expansion. Sediment accretion ranged from 4.0–12.7 cm between 1997–1998 (ENSO conditions), but was close to long-term averages (˜ cm yr−1) in 1998–1999 (nonflood year) indicating how susceptible Tijuana Estuary is to sedimentation from episodic storms. Although accretion rates were similar withinSpartina clones and on bare mudflats over the ENSO winter, clones were typically dome-shaped suggesting higher sediment retention rates within clones. The radial expansion rates of clones (1.31±0.25 m in 1998; 1.12±0.07 m in 1999) approximated the maxima reported for this species and were not related to clone size or vigor. Conditions on the mudflat appear ideal forSpartina growth, masking differences that might otherwise be observed. Given the likelihood of sedimentation-driven habitat conversion in southern California and other Mediterranean-type estuaries, management efforts are needed to address sedimentation issues on a watershed scale. We recommend that wetland restoration projects in southern California include large areas of intertidal mudflat, both to maintain habitat for shorebird feeding and to allow colonization by salt marsh vegetation.

  • WETLAND RESTORATION THRESHOLDS: CAN A DEGRADATION TRANSITION BE REVERSED WITH INCREASED EFFORT?
    Ecological Applications, 2003
    Co-Authors: Roberto Lindig-cisneros, Katharyn E Boyer, Julie Desmond, Joy B Zedler
    Abstract:

    Previous attempts to reverse the degradation of a coastal wetland and restore nesting habitat for an endangered bird showed that adding nitrogen could temporarily increase the height of Spartina foliosa, but not produce self-sustaining tall canopies. We asked if increased effort (up to five years of N fertilization) would shift canopy attributes across the hypothesized threshold. Thirty plots were treated with 0–5 yr of urea addition, and all were followed for 5 yr. Canopies were robust while urea was being added, but Spartina reverted to short stature soon after fertilization ended, supporting R. J. Hobbs and D. A. Norton's concept of an irreversible transition. However, specific outcomes depended on the choice of response variable (six comparisons), the choice of reference data (initial conditions, same-year data, and pooled data), and the choice of statistical design (repeated measures vs. complete design), indicating the need to assess experiments thoroughly before making strong recommendations for ma...

  • evaluating the progress of restored cordgrass Spartina foliosa marshes belowground biomass and tissue nitrogen
    Estuaries, 2000
    Co-Authors: Katharyn E Boyer, John C. Callaway, Joy B Zedler
    Abstract:

    We report the first data on belowground tissue mass and nitrogen (N) concentration forSpartina foliosa in southern California, assessing one natural and two constructed marshes on San Diego Bay. Biomass at the natural marsh was low compared to that of otherSpartina spp., but higher than values reported forS. foliosa in northern California. In sandy constructed marshes planted 5 and 10 years before this study,S. foliosa had lower belowground tissue N, lower N crop (%N×biomass), and shallower roots than in the adjacent natural marsh. We took advantage of a 2-yr, large-scale fertilization project being performed in the older constructed marsh and examined biomass and N storage after N additions. Although there was a trend toward N accumulation with fertilization, N crop remained at approximately 50% of natural marsh levels, unlike the large aboveground responses to N addition in our previous studies. Lower belowground reserves help to explain poor aerial growth in the created marshes and suggest the need for finer sediments (with greater potential for holding and supplying nutrients) to sustain (S. foliosa. While fine sediments are beginning to accumulate on the surface of the created marshes, vertical accretion is more likely to shift the plant community toward other species than to enhanceS. foliosa growth. We suggest salvaging and importing fine, organic marsh sediments or providing organic amendments to establish proper substrate conditions. Overexcavating and allowing fine sediments to accumulate remains an option, although the time scale is unpredictable due to the stochasticity of accretion events.

Lisa A Levin - One of the best experts on this subject based on the ideXlab platform.

  • Appendix C. 15N signatures of macrofauna exposed to different parts of 15N-labeled Spartina foliosa in litter bags for 50 days.
    2016
    Co-Authors: Lisa A Levin, Carlos Neira, Edwin D. Grosholz
    Abstract:

    15N signatures of macrofauna exposed to different parts of 15N-labeled Spartina foliosa in litter bags for 50 days

  • Benthic food-web succession in a developing salt marsh
    Marine Ecology Progress Series, 2014
    Co-Authors: Marie C. Nordström, Christine R Whitcraft, Theresa Sinicrope Talley, Carolyn A. Currin, Lisa A Levin
    Abstract:

    Ecological succession has long been a focal point for research, and knowledge of underlying mechanisms is required if scientists and managers are to successfully promote recov- ery of ecosystem function following disturbance. We addressed the influence of bottom-up pro- cesses on successional assemblage shifts in salt marshes, ecosystems with strong physical gradi- ents, and how these shifts were reflected in the trophic characteristics of benthic fauna. We tracked the temporal development of infaunal community structure and food-web interactions in a young, created salt marsh and an adjacent natural marsh in Mission Bay, California, USA (1996−2003). Macro faunal community succession in created Spartina foliosa habitats occurred rapidly, with infaunal densities reaching 70% of those in the natural marsh after 1 yr. Community composition shifted from initial dominance of insect larvae (surface-feeding microalgivores) to increased dominance of oligo chaetes (subsurface-feeding detritivores) within the first 7 yr. Iso- topic labeling of microalgae, N2-fixing cyanobacteria, S. foliosa and bacteria revealed direct links (or absence thereof) between these basal food sources and specific consumer groups. In combina- tion with the compositional changes in the macroinvertebrate fauna, the trophic patterns indi- cated an increase in food-web complexity over time, reflecting resource-driven marsh succession. Natural abundance stable isotope ratios of salt marsh consumers (infaunal and epifaunal macroin- vertebrates, and fish) initially reflected distinctions in trophic structure between the created and natural marsh, but these diminished during successional development. Our findings suggest that changing resource availability is one of the important drivers of succession in benthic communi- ties of restored wetlands in Southern California.

  • Wetland response to sedimentation and nitrogen loading: diversification and inhibition of nitrogen‐fixing microbes
    Ecological applications : a publication of the Ecological Society of America, 2010
    Co-Authors: S. M. Moseman-valtierra, K. Armaiz-nolla, Lisa A Levin
    Abstract:

    Anthropogenic inputs of nutrients and sediment simultaneously impact coastal ecosystems, such as wetlands, especially during storms. Independent and combined effects of sediment and ammonium nitrate loading on nitrogen fixation rates and diversity of microbes that fix nitrogen (diazotrophs) were tested via field manipulations in Spartina foliosa and unvegetated zones at Tijuana Estuary (California, USA). This estuary is subject to episodic nitrogen enrichment and sedimentation associated with rain-driven flooding and slope instabilities, the latter of which may worsen as the Triple Border Fence is constructed along the U.S.–Mexico border. Responses of diazotrophs were assessed over 17 days using acetylene reduction assays and genetic fingerprinting (terminal restriction fragment length polymorphism [T-RFLP]) of nifH, which codes for dinitrogenase reductase. Sulfate-reducing bacteria performed ~70% of nitrogen fixation in Spartina foliosa rhizospheres in the absence of nitrogen loading, based on sodium molybdate inhibitions in the laboratory. Following nutrient additions, richness (number of T-RFs [terminal restriction fragments]) and evenness (relative T-RF fluorescence) of diazotrophs in surface sediments increased, but nitrogen fixation rates decreased significantly within 17 days. These responses illustrate, within a microbial community, conformance to a more general ecological pattern of high function among assemblages of low diversity. Diazotroph community composition (T-RF profiles) and rhizosphere diversity were not affected. Pore water ammonium concentrations were higher and more persistent for 17 days in plots receiving sediment additions (1 cm deep), suggesting that recovery of diazotroph functions may be delayed by the combination of sediment and nutrient inputs. Nitrogen fixation constitutes a mechanism for rapid transfer of fixed N to S. foliosa roots and a variety of primary consumers (within 3 and 8 days, respectively), as determined via 15N2 enrichment studies with in situ microcosms of intact marsh sediment. Thus, long-term declines in nitrogen fixation rates in response to increasingly frequent nutrient loading and sedimentation may potentially alter nitrogen sources for vascular plants as well as trophic pathways in wetland ecosystems.

  • Influence of invasive Spartina growth stages on associated macrofaunal communities
    Biological Invasions, 2007
    Co-Authors: Carlos Neira, Lisa A Levin, Edwin D. Grosholz, Guillermo Mendoza
    Abstract:

    In coastal wetlands, invasive plants often act as ecosystem engineers altering flow, light and sediments which, in turn, can affect benthic animal communities. However, the degree of influence of the engineer will vary significantly as it grows, matures and senesces, and surprisingly little is known about how the influence of an ecosystem engineer varies with ontogeny. We address this issue on the tidal flats of San Francisco Bay where hybrid Spartina ( foliosa ×  alterniflora ) invaded 30 years ago. The invasion has altered the physico-chemical properties of the sediment habitat, which we predicted should cause changes in macrofaunal community structure and function. Through mensurative and manipulative approaches we investigated the influence of different growth stages of hybrid Spartina on macrobenthos and the underlying mechanisms. Cross-elevation sampling transects were established covering 5 zones (or stages) of the invasion, running from the tidal flat (pre-invasion) to an unvegetated dieback zone. Additionally, we experimentally removed aboveground plant structure in the mature (inner) marsh to mimic the ’unvegetated areas’. Our results revealed four distinct faunal assemblages, which reflected Spartina -induced changes in the corresponding habitat properties along an elevation gradient: a pre-invaded tidal flat, a leading edge of immature invasion, a center of mature invasion, and a senescing dieback area. These stages of hybrid Spartina invasion were accompanied by a substantial reduction in macrofaunal species richness and an increase in dominance, as well as a strong shift in feeding modes, from surface microalgal feeders to subsurface detritus/ Spartina feeders (mainly tubificid oligochaetes and capitellid polychaetes). Knowledge of the varying influence of plant invaders on the sediment ecosystem during different phases of invasion is critical for management of coastal wetlands.

  • regulation of benthic algal and animal communities by salt marsh plants impact of shading
    Ecology, 2007
    Co-Authors: Christine R Whitcraft, Lisa A Levin
    Abstract:

    Plant cover is a fundamental feature of many coastal marine and terrestrial systems and controls the structure of associated animal communities. Both natural and human-mediated changes in plant cover influence abiotic sediment properties and thus have cascading impacts on the biotic community. Using clipping (structural) and light (shading) manipulations in two salt marsh vegetation zones (one dominated by Spartina foliosa and one by Salicornia virginica), we tested whether these plant species exert influence on abiotic environmental factors and examined the mechanisms by which these changes regulate the biotic community. In an unshaded (plant and shade removal) treatment, marsh soils exhibited harsher physical properties, a microalgal community composition shift toward increased diatom dominance, and altered macrofaunal community composition with lower species richness, a larger proportion of insect larvae, and a smaller proportion of annelids, crustaceans, and oligochaetes compared to shaded (plant removal, shade mimic) and control treatment plots. Overall, the shaded treatment plots were similar to the controls. Plant cover removal also resulted in parallel shifts in microalgal and macrofaunal isotopic signatures of the most dynamic species. This suggests that animal responses are seen mainly among microalgae grazers and may be mediated by plant modification of microalgae. Results of these experiments demonstrate how light reduction by the vascular plant canopy can control salt marsh sediment communities in an arid climate. This research facilitates understanding of sequential consequences of changing salt marsh plant cover associated with climate or sea level change, habitat degradation, marsh restoration, or plant invasion.