Christine R. Whitcraft

REGULATION OF BENTHIC ALGAL AND ANIMAL COMMUNITIES BY SALT MARSH PLANTS: IMPACT OF SHADING

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.

Invasion of tamarisk (Tamarix spp.) in a southern California salt marsh

Exotic plants have been demonstrated to be one of the greatest threats to wetlands, as they are capable of altering ecosystem-wide physical and biological properties. One of the most problematic invaders in the western United States has been salt cedar, Tamarix spp., and the impacts of this species in riparian and desert ecosystems have been well-documented. Here we document large populations of tamarisk in the intertidal salt marshes of Tijuana River National Estuarine Research Reserve, a habitat not often considered vulnerable to invasion by tamarisk. Initial research demonstrates that there are multiple species and hybrids of Tamarix invading the estuary and that the potential impact of tamarisk within this salt marsh is significant. This highlights the need for managers and scientists to be aware of the problems associated with tamarisk invasion of coastal marine habitats and to take early and aggressive action to combat any incipient invasion.

Utilization of invasive tamarisk by salt marsh consumers

Plant invasions of coastal wetlands are rapidly changing the structure and function of these systems globally. Alteration of litter dynamics represents one of the fundamental impacts of an invasive plant on salt marsh ecosystems. Tamarisk species (Tamarix spp.), which extensively invade terrestrial and riparian habitats, have been demonstrated to enter food webs in these ecosystems. However, the trophic impacts of the relatively new invasion of tamarisk into marine ecosystem have not been assessed. We evaluated the trophic consequences of invasion by tamarisk for detrital food chains in the Tijuana River National Estuarine Research Reserve salt marsh using litter dynamics techniques and stable isotope enrichment experiments. The observations of a short residence time for tamarisk combined with relatively low C:N values indicate that tamarisk is a relatively available and labile food source. With an isotopic (15N) enrichment of tamarisk, we demonstrated that numerous macroinvertebrate taxonomic and trophic groups, both within and on the sediment, utilized 15N derived from labeled tamarisk detritus. Infaunal invertebrate species that took up no or limited 15N from labeled tamarisk (A. californica, enchytraeid oligochaetes, coleoptera larvae) occurred in lower abundance in the tamarisk-invaded environment. In contrast, species that utilized significant 15N from the labeled tamarisk, such as psychodid insects, an exotic amphipod, and an oniscid isopod, either did not change or occurred in higher abundance. Our research supports the hypothesis that invasive species can alter the trophic structure of an environment through addition of detritus and can also potentially impact higher trophic levels by shifting dominance within the invertebrate community to species not widely consumed.

Lignocellulose-responsive bacteria in a southern California salt marsh identified by stable isotope probing.

Carbon cycling by microbes has been recognized as the main mechanism of organic matter decomposition and export in coastal wetlands, yet very little is known about the functional diversity of specific groups of decomposers (e.g., bacteria) in salt marsh benthic trophic structure. Indeed, salt marsh sediment bacteria remain largely in a black box in terms of their diversity and functional roles within salt marsh benthic food web pathways. We used DNA stable isotope probing (SIP) utilizing 13C-labeled lignocellulose as a proxy to evaluate the fate of macrophyte-derived carbon in benthic salt marsh bacterial communities. Overall, 146 bacterial species were detected using SIP, of which only 12 lineages were shared between enriched and non-enriched communities. Abundant groups from the 13C-labeled community included Desulfosarcina, Spirochaeta, and Kangiella. This study is the first to use heavy-labeled lignocellulose to identify bacteria responsible for macrophyte carbon utilization in salt marsh sediments and will allow future studies to target specific lineages to elucidate their role in salt marsh carbon cycling and ultimately aid our understanding of the potential of salt marshes to store carbon.

Spatial Hedonic Valuation of a Multiuse Urban Wetland in Southern California

Most of Southern Californias wetlands have disappeared despite being critical ecosystems with many valuable attributes. Many of the wetlands that remain are in relatively urban areas, are severely degraded, and may not function properly. Using hedonic spatial error models, we measure the economic value of living near an urban multi-use wetland in Long Beach, California. Both sales prices and estimated values are used in the analysis. Results show that proximity to wetlands increases residential property values in the focus area. This analysis provides important information for policymakers to justify ongoing restoration projects and prevent further degradation of urbanized natural resources.

Uncovering the Ocean’s Past

The ocean has a history. Over the past hundreds, thousands, and millions of years the ocean and life within it have evolved and changed. This history determines the ocean’s present state and shapes its path into the future. We cannot understand how the ocean functions today without knowing its ecological history. Likewise, we cannot predict future changes without knowing the origin, cause, and trajectory of change in the past. Finally, we cannot effectively restore degraded marine populations, communities, or ecosystems without historical baselines to use as reference points.

Invasive plant ecosystem engineer facilitates community and trophic level alteration for brackish marsh invertebrates

Wetland habitats are becoming increasingly scarce worldwide while experiencing exceptionally high levels of plant invasion. Invasive plant species affect ecosystems through numerous avenues, including acting as ecosystem engineers, contributing unique plant functional traits, and altering trophic dynamics. We examined the impacts of the invasive weed Lepidium latifolium on soil-dwelling and canopy-dwelling invertebrate communities in a brackish marsh of northern California. Invertebrate abundance, species richness, diversity, and community composition were measured in both invaded and non-invaded areas of the marsh in four time periods that correspond with different L. latifolium phenologic phases. We observed these different stages of L. latifolium, and we recorded alterations in the habitat structure provided by L. latifolium as the plant entered senescence. L. latifolium had differential impacts on the two invertebrate communities studied. The presence of L. latifolium increased abundance of soil-dwell...

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

Abstract 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.

Diversity of Desulfobacteriaceae and Overall Activity of Sulfate-Reducing Microorganisms in and Around a Salt pan in a Southern California Coastal Wetland

Sulfate-reducing bacteria (SRB) are key mediators of anaerobic carbon cycling in coastal salt marsh sediments and have been shown to be important decomposer communities even in hypersaline habitats. Understanding how SRB function in various salt marsh habitats (vegetated, salt pans) is crucial to advancing our knowledge of salt marsh function. We compare overall sulfate reducing activity and the diversity of a subset of SRB (Desulfobacteriaceae) in two hypersaline sediments (salt pan and nearby area with desiccated vegetation) with a regularly inundated control site within the Huntington Beach Wetlands (HBW). Biological activity was quantified using radiotracer studies to measure sulfate reduction rates (SRR) with and without carbon amendment. All sites showed enhanced SRR under carbon amendment, suggesting short-term carbon limitation. Unique communities of Desulfobacteriaceae were found in all three sites with increased incidence of halotolerant genotypes in the salt pan. These findings indicate that, despite reduced anaerobic respiratory activity, highly diverse and functional deltaproteobacterial communities exist in salt pan and surrounding hypersaline habitats in coastal salt marshes in southern California.

Does Estuary Restoration Design Alter the Fine Scale Movements of Grey Smoothhounds (Mustelus californicus) in Southern California

Abstract Restored estuaries in southern California are limited in size and shape by fragmentation from human development, which can in turn restrict habitat use. Thus, it is important to assess how habitat design affects how fish use restored estuaries. Acoustic telemetry tracking from prior studies revealed that Gray Smoothhounds (Mustelus californicus) used primarily the eelgrass ecotone and warm interior waters in Bolsa Chica Full Tidal Basin (BCFTB), a 1.48 km2 open-format marine dominated estuary. In this study, M. californicus utilized the Channel in Huntington Beach Wetlands Complex (HBWC), a smaller creek estuary. The Channel had more eelgrass than other available habitats but was also the coolest microhabitat, with temperatures below what M. californicus was found to select in BCFTB. Individuals may behaviorally thermoregulate by moving upstream, away from the HBWC Channel, during periods of incoming, cooler ocean water. Mustelus californicus translocated to different microhabitats within the HBWC selected the Channel habitat after the translocation regardless of where animals were released. Despite the large difference in available subtidal habitat between HBWC and BCFTB, no differences in patch size utilization distributions of M. californicus were observed. While individuals seem to shift between microhabitats based on temperature and eelgrass availability, the area size used by M. californicus appears to be the same within both sites despite the differences in overall size between sites. These results suggest that differences in microhabitat use may influence distribution patterns of M. californicus within each site, and therefore, shark abundance may vary with the restoration design (e.g. basin versus channel) and the size of the estuarine habitat. This information on habitat selection will be critical to planning future restorations on the Southern California coast.