Relationship of \u3cem\u3eSphaeroma quoianum\u3c/em\u3e to Sediment Characteristics and Invertebrate Community

Many important wetland functions are tied to sediment dynamics, which are influenced by infaunal invertebrate communities. These communities are sensitive to changes in sediment structure and to colonization by non-native species. In a southern California salt marsh, the non-native isopod Sphaeroma quoianum has created dense networks of burrows within the marsh banks. Since this isopod increases erosion in many areas and can change local invertebrate communities, its possible contribution to habitat loss in this already-scarce southern California ecosystem is an important issue. To determine the relationship of S. quoianum to invertebrate community and sediment characteristics, three burrowed transects and one unburrowed transect were surveyed and sampled for invertebrate and sediment cores. This study tested the association between burrows and grain size distribution, sediment carbon content, respiration rates, and invertebrate community composition. Sphaeroma quoianum burrows were correlated with altered invertebrate community composition, decreased carbon content, and steep marsh bluffs. These results highlight the potential susceptibility of salt marsh habitat with steep edges to invasion by non-native species. These results also suggest that S. quoianum invasion of salt marsh habitats can alter native communities and ecosystem functions; thus, incipient invasions should be of concern to managers and ecologists alike

Seed Collection and Germination Strategies for Common Wetland and Coastal Sage Scrub Species in Southern California

There is a need for a consolidated source of information on native vegetation seed collection and germination strategies in southern California. Published literature on these methods is often experimental, species-specific, and widely scattered throughout online and print media. Planting and restoration strategies may need to be site-specific; however, similar methodological approaches are often utilized allowing for the development of general strategies for seed collection, storage, and germination methods. A better understanding of species-specific seed attributes and growth processes will help restoration ecologists collect high-quality, viable seed, thereby increasing the potential success of the restored vegetation community by reducing plant mortality, project costs, and effort. This paper synthesizes seed collection and germination strategies for native vegetation common to southern California estuarine wetland, coastal dune, and coastal sage scrub systems

Recovering Ecosystem Functions in a Restored Salt Marsh by Leveraging Positive Effects of Biodiversity

Natural and managed ecosystems provide a variety of ecological, economic, and cultural benefits; yet most have been altered by human activity such that they exhibit deficits in both biodiversity and functionality. Identifying factors accelerating the recovery of key species and associated functions in degraded systems is therefore a global priority. We tested the hypotheses that explicitly incorporating biodiversity into restoration design will lead to greater ecosystem function and that positive effects of diversity will strengthen over time due to an increase in the importance of complementarity relative to selection effects. We did this by manipulating salt marsh plant species richness across a tidal elevation gradient as part of a coastal wetland restoration project in southern California. Overall, diversity enhanced biomass accumulation in experimental plots, with the magnitude of the effect strengthening from one to three years post-restoration due to a combination of decreasing performance in monocultures and increasing performance in multispecies mixtures over time. Positive diversity effects were initially due exclusively to selection, as mixtures were dominated by species also exhibiting high performance in monoculture, although the identity of the highest performing species varied across tidal elevations and over time. By the end of the study, complementarity, indicative of niche partitioning and/or positive interactions among species, contributed to productivity at least as much as selection effects. Our study provides real-world support for a recent theoretical model predicting strong positive biodiversity effects when functionally different species coexist in a heterogeneous landscape. Incorporating biodiversity into restoration designs can result in net gains in ecosystem function especially in low diversity systems, yet shorter experiments lacking broad environmental and species trait variability may both underestimate the strength of and misidentify the mechanisms underlying positive diversity effects

Patterns of carbon processing at the seafloor: the role of faunal and microbial communities in moderating carbon flows

Marine sediments, particularly those located in estuarine and coastal zones, are key locations for the burial of organic carbon (C). However, organic C delivered to the sediment is subjected to a range of biological C-cycling processes, the rates and relative importance of which vary markedly between sites, and which are thus difficult to predict. In this study, stable isotope tracer experiments were used to quantify the processing of C by microbial and faunal communities in two contrasting Scottish estuarine sites: a subtidal, organic C rich site in Loch Etive with cohesive fine-grained sediment, and an intertidal, organic C poor site on an Ythan estuary sand flat with coarse-grained permeable sediments. In both experiments, sediment cores were recovered and amended with 13C labelled phytodetritus to quantify whole community respiration of the added C and to trace the isotope label into faunal and bacterial biomass. Similar respiration rates were found in Loch Etive and on the Ythan sand flat (0.64 ± 0.04 and 0.63 ± 0.12 mg C m−2h−1, respectively), which we attribute to the experiments being conducted at the same temperature. Faunal uptake of added C over the whole experiment was markedly greater in Loch Etive (204 ± 72 mg C m−2) than on the Ythan sand flat (0.96 ± 0.3 mg C m−2), and this difference was driven by a difference in both faunal biomass and activity. Conversely, bacterial C uptake over the whole experiment in Loch Etive was much lower than that on the Ythan sand flat (1.80 ± 1.66 and 127 ± 89 mg C m−2, respectively). This was not driven by differences in biomass, indicating that the bacterial community in the permeable Ythan sediments was particularly active, being responsible for 48 ± 18 % of total biologically processed C. This type of biological C processing appears to be favoured in permeable sediments. The total amount of biologically processed C was greatest in Loch Etive, largely due to greater faunal C uptake, which was in turn a result of higher faunal biomass. When comparing results from this study with a wide range of previously published isotope tracing experiments, we found a strong correlation between total benthic biomass (fauna plus bacteria) and total biological C processing rates. Therefore, we suggest that the total C-cycling capacity of benthic environments is primarily determined by total biomass

Wetland Plant Influence on Sediment Ecosystem Structure and Trophic Function

Vascular plants structure wetland ecosystems. To examine mechanisms behind their influence, plants were studied under different scenarios of change: experimental manipulation of cover, invasion, and response to flushing regimes. I tested the hypothesis that wetland plants alter benthic communities through modification of abiotic factors, with cascading effects on microalgae and invertebrate communities. Major plant effects were observed in all systems studied, but the magnitude of, mechanisms behind, and exact consequences of plant alterations depended on the particular combination of physical and biological stresses within the habitat along the marine to terrestrial continuum. Manipulation of plant cover and light regime, combined with natural abundance isotope studies in a mid-elevation salt marsh of Mission Bay, CA revealed how two dominant plants, Spartina foliosa and Sarcocornia pacifica (formally Salicornia virginica ), regulate light, temperature, and moisture, thereby influencing the abundance of benthic diatoms and the relative importance of microalgal-feeding invertebrates. Tamarisk ( Tamarix spp.), normally a freshwater invader that has recently colonized the salt marsh in Tijuana Estuary, was studied in 3 marsh zones with mensurative benthic assessment techniques and stable isotope enrichment experiments. Results demonstrate that this plant has (1) impacted the mid-marsh environment most, (2) accelerated salt marsh succession towards a more terrestrial environment by creating drier, less organic-rich sediments and an altered macroinvertebrate community (decreased densities of gastropods and marine oligochaetes, more insects) and (3) entered the food web through a broad range of invertebrate consumers. Using similar approaches, the ephemeral seagrass, Ruppia maritima , abundant in lagoons during periods of inlet closure, was also shown to play a key trophic role in structuring wetlands in southern California. Results of faunal characterization and isotope enrichment studies within San Dieguito Lagoon suggest that food webs in these environments are driven by detrital and epiphytic production. Increased representation of detritivores in R. maritima habitats relative to unvegetated mudflat appears linked to animal feeding preferences and the ability of consumers to utilize R. maritima . In summary, this research developed several experimental methods by which to isolate structuring mechanisms of vascular plants in wetlands and allowed us to make generalizations across abiotic gradients in salt marsh ecosystems

Pepperweed's Ecosystem Impacts in Suisun Marsh: Methods for Control

Perennial pepperweed (Lepidium latifolium) is an aggressive, non-native herbaceous weed displacing native vegetation in marshes, floodplains, prairies and rangeland throughout California. You can even find it growing along roadsides and highways. But does the plant’s ubiquity really mean it is an ecological problem warranting costly eradication efforts

Development of Novel Stable Isotope Approaches to Evaluate Carbon Flow in a Restored Coastal Wetland in Southern California

We hypothesized there would be differences in the microbial and infaunal communitiesprimarily responsible for degrading macrophyte vs. microalgal carbon. Specifically we predicted that: The invertebrate community degrading macrophyte-derived carbon will be significantly different from those degrading algal-derived carbon. The microbial communities (bacteria and fungi) degrading macrophyte-derived carbon will be significantly different from those not using this carbon source

Wetland plant influence on sediment ecosystem structure and trophic function

Vascular plants were studied under different scenarios of change: experimental manipulation of cover, invasion, and response to flushing regimes. I tested the hypothesis that wetland plants alter benthic communities through modification of abiotic factors, with cascading effects on microalgae and invertebrate communities. Major plant effects were observed in all systems studied, but the magnitude of, mechanisms behind, and exact consequences of plant alterations depended on the particular combination of physical and biological stresses within the habitat along the marine to terrestrial continuum. Manipulation of plant cover and light regime, combined with natural abundance isotope studies in a mid-elevation salt marsh of Mission Bay, CA revealed how two dominant plants, Spartina foliosa and Sarcocornia pacifica (formally Salicornia virginica), regulate light, temperature, and moisture, thereby influencing the abundance of benthic diatoms and the relative importance of microalgal-feeding invertebrates. Tamarisk (Tamarix spp.), normally a freshwater invader that has recently colonized the salt marsh in Tijuana Estuary, was studied in 3 marsh zones with mensurative benthic assessment techniques and stable isotope enrichment experiments. Results demonstrate that this plant has (1) impacted the mid-marsh environment most, (2) accelerated salt marsh succession towards a more terrestrial environment by creating drier, less organic- rich sediments and an altered macroinvertebrate community (decreased densities of gastropods and marine oligochaetes, more insects) and (3) entered the food web through a broad range of invertebrate consumers. Using similar approaches, the ephemeral seagrass, Ruppia maritima, abundant in lagoons during periods of inlet closure, was also shown to play a key trophic role in structuring wetlands in southern California. Results of faunal characterization and isotope enrichment studies within San Dieguito Lagoon suggest that food webs in these environments are driven by detrital and epiphytic production. Increased representation of detritivores in R. maritima habitats relative to unvegetated mudflat appears linked to animal feeding preferences and the ability of consumers to utilize R. maritima. In summary, this research developed several experimental methods by which to isolate structuring mechanisms of vascular plants in wetlands and allowed us to make generalizations across abiotic gradients in salt marsh ecosystem

Evaluating the Functional Recovery of Restored Coastal Wetland in Southern California

Within the Huntington Beach Wetlands (HBW), we hypothesized that Brookhurst and Magnolia Marshes (marsh areas isolated from tidal influence for approximately 100 years) would have significantly different physical characteristics (salinity, temperature, moisture, sediment parameters), more terrestrial plant, algal, invertebrate and microbial communities and altered food web structure from neighboring Talbert Marsh (a marsh area whose tidal connect was restored 20 years ago). In addition, we hypothesized that once Brookhurst Marsh was restored (Summer 2009), these differences would decrease and with time, resemble those of Talbert Marsh. This restoration of structure and function will occur on differing time scales; we predicted that physical parameters would quickly become similar while algal, invertebrate and microbial communities would begin to change on a month-year time scale. Changes to the plant community and the food web structure are anticipated to occur on a year-decadal time scale (beyond the funding cycle for this project)