Dissertation/Thesis Abstract

The Interaction of Nutrient Loading and Biological Invasions in a Benthic Estuarine Community
by Weiskel, Heidi Shelburne Williams, Ph.D., University of California, Davis, 2012, 155; 3555446
Abstract (Summary)

For this dissertation, I investigated a key assumption of invasion biology, namely, that nutrients facilitate invasion, in a benthic estuarine habitat (Chapter 1). Following on this work in the estuarine systems in northern California, I investigated a related question about the potential merits and feasibility of attempting the restoration of a native snail (Chapter 2), and simultaneously documented the earliest stages of two invasive snail populations in the same systems (Chapter 3). I found that the nutrient-invasion dynamic breaks down at higher trophic levels, that consumer species restoration appears feasible, and that documenting the earliest invasion demographics is valuable in understanding and responding to that critical transition period between an introduced and an established invasive population. Going forward, we should expand our focus beyond nutrients to other factors that may drive invasion success, consider a broader spectrum of species for restoration, and focus our efforts on understanding what characteristics of a population enable a species to transition into a successful long term invader. My work with my collaborators is described below for each chapter.

The effects of nutrient loading on the success of biological invasions are best understood in terrestrial systems, where studies have generally shown that increased nutrients facilitate the spread of invasive plants. To date, these relationships have remained largely unexamined in marine systems and at higher trophic levels. We conducted studies to examine the effects of nutrient loading on interactions between the invasive mud snail, Ilyanassa obsoleta and the sympatric native mud snail Cerithidea californica, in San Francisco Bay, California, USA. We experimentally manipulated densities of C. californica and I. obsoleta, as well as nutrient levels, at two tidal elevations (high, unvegetated marsh; low mudflat) to investigate the interaction of nutrients and consumer effects in this system. Fertilization increased benthic chlorophyll a as diatom biomass in the marsh. Snail growth was not strongly affected by fertilization but the invasive species suffered high mortality in the marsh in the fertilized treatments, suggesting that nutrients may not universally facilitate invasions at higher trophic levels.

Restoration efforts in marine systems are usually reserved for species that are "high-profile," (i.e., charismatic or commercially valuable). However, recent snail invasions in northern CA estuaries have prompted interest in investigating whether "low-profile" species that serve as prey items or cycle nutrients, such as snails, may also have restoration value in marine ecosystems. We conducted three studies on C. californica under various scenarios to test its suitability for restoration efforts: 1) an in situ survival study across habitats; 2) a laboratory predation experiment with the invasive crab predator Carcinus maenas and I. obsoleta, and 3) laboratory tests of C. californica and I. obsoleta behavioral responses to sediments and microalgal communities from different habitats. We found the highest C. californica survivorship in the Spartina foliosa meadows, where C. maenas and I. obsoleta abundance was low. The predation trials demonstrated lower survivorship for C. californica than for I. obsoleta. The behavioral trials revealed that the invasive snail spent more time on mudflat sediments than did C. californica and was consistently more likely to be moving v. still than the native snail throughout the experiment. Based on our results, we suggest that under certain conditions it may be valuable to reestablish consumers in their historic ranges.

New invasions are an increasingly frequent occurrence in many habitats. Nevertheless, data describing the early stages of invasion are rare in marine systems and valuable for understanding the dynamics of the transition from the introduced to the established stage. We discovered populations of Batillaria attramentaria, a mud snail native to Japan, in SFB and Bodega Harbor, CA (BH), respectively, at the initial stages in their invasions. The discoveries offered an opportunity to investigate simultaneous early establishment patterns of a detrimental species. We gathered demographic data and measured sediment properties for several years to assess early population trajectories and ecosystem impacts for both new populations and compared them to a decades-old invasion in Tomales Bay, CA (TB). In SFB, population size and densities grew rapidly and mostly stayed contained. In BH, population size and densities grew moderately but the distribution expanded considerably. In the recent introductions, the size class frequency patterns of both populations shifted towards smaller snail sizes and parasite prevalence increased faster than expected. Both SFB and TB invaded mudflats had lower sediment organic matter than the uninvaded mudflats nearby, suggesting the potential for snail-sediment or snail-infauna interactions in the system that merit further inquiry.

Indexing (document details)
Advisor: Grosholz, Edwin D.
Commitee: Carlton, James T., Lawler, Sharon P., Sanford, Eric D.
School: University of California, Davis
Department: Ecology
School Location: United States -- California
Source: DAI-B 74/07(E), Dissertation Abstracts International
Subjects: Ecology
Keywords: Batillaria attramentaria, Cerithidea californica, Ilyanassa obsoleta, Initial invasion dynamics, Nutrient impacts on marine invasions in estuaries, Restoration of benthic consumers
Publication Number: 3555446
ISBN: 978-1-267-97007-7
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