Jeb Byers, Associate Professor of Zoology, travels to Australia

Professor James (Jeb) Byers spent the 2007-08 academic year in Australia conducting research on a highly invasive alga species

Spatial Patterns of Marine Larvae as Indicators of Incipient Invasions in Great Bay

Understanding the dynamics of coastal marine communities represents a substantial challenge, and one that is actively pursued globally. Within the United States, several sites have been designated as National Estuarine Research Reserves (NERR) with the idea that concentrated research at these sites will lead to greater understanding of the ecosystem. The Great Bay Estuary of New Hampshire is one of these sites. A wide spectrum of research is conducted within the Great Bay, and substantial financial support is committed to that research on an annual basis. To facilitate the success of these research efforts, it is particularly important to develop a working understanding of the dynamics of marine communities within the Great Bay. Invertebrate communities within the Bay and at other coastal sites are largely composed of open populations whose growth and maintenance depend on settlement of new recruits that may arrive from distant source populations. Larval monitoring programs designed to survey these incoming recruits should therefore be an important component of the research program within the Great Bay and other NERR sites. By monitoring recruitment within the Great Bay, we may begin to determine larval spatial patterns within potential habitats. This will then allow for comparison of observed larval spatial patterns and observed adult population distributions. If the two are similar, this would indicate that future adult populations can be predicted by knowledge of larval settlement. If the two are dissimilar, this indicates a need to investigate causes of post-settlement mortality that lead to discrepancies in larval and adult abundances. For example, if there is a large discrepancy between larval and adult abundances, then the Great Bay may be acting as a sink for some species whose larvae are transported into the bay, but do not survive to establish adult populations. By monitoring invertebrate recruitment into the Great Bay, we begin to establish a baseline for biotic conditions within the Bay against which future conditions can be compared. This is a crucial step in determining the effects of anthropogenically induced environmental changes, such as the introduction of nonindigenous species. Furthermore, we predict that because a sufficient influx of larvae is needed to establish a viable adult population, larvae of exotic species not currently present in Great Bay will be first detectable in the plankton, perhaps for several years before they arrive in sufficient numbers for adults to establish. This may provide an advanced warning of incipient invasions and allow managers to develop plans for eradication or mitigation in advance of the exotic species’ establishment. Here we report on a study designed to collect the baseline data necessary to establish patterns and make comparisons to future conditions. We have collected larvae on artificial settlement substrates at six sites within the Great Bay Estuary and at an adjacent coastal site during ice-free months since July 2002. This report gives a brief description of the results of this monitoring program to determine the species composition, spatial patterns, and timing of invertebrate settlement within the Great Bay. This report specifically includes data from April 2005 to June 2006, the portion of the project funded by NHEP. Data from 2002-04 are also available, but are not included in this report

Chapter 8 Comparative Biogeography of Marine Invaders Across Their Native and Introduced Ranges

Biological invasions continue to exert extensive environmental and economic impacts. Understanding why some introduced species become invasive is critical to their management. Determining the mechanisms underpinning invasion success has focussed on aspects of the ecology and physiology of the species in the introduced range. Through the application of biogeographic approaches, however, a growing body of research highlights insights that stem from studying invasion success as a biogeographic issue. In particular, a comparison of both biogeographic regions (i.e., the native and invasive ranges) allows exclusive insight into seven different major biogeographic hypotheses that we identified to explain invader success. These include the enemy release hypothesis, niche shifts, trait differences, the evolution of invasiveness, native allies, environmental matching, and genetic diversity. All imply a difference or gradient between the ranges that may mechanistically explain an invader’s differential performance. This review summarises the support for these seven different theories underpinning the biogeography of marine invasions, and also provides case studies for different theories addressing the comparative biogeography of marine invasions. Additionally, we catalogue the geographic regions of the invasive species used in biogeographic comparisons and the diversity of species, habitats and climate zones examined. Finally, we highlight critical knowledge gaps and suggest future research directions for improving our understanding the processes driving invasion success

Variable direct and indirect effects of a habitat-modifying invasive species on mortality of native fauna

Habitat-modifying invasive species can influence rates of predation on native prey either directly by providing protective structure or indirectly by modifying traits of prey species responding to the habitat. The alga Caulerpa taxifolia is one of the most successful invasive species of shallow-water marine systems globally, often provisioning habitat in areas previously lacking in vegetated structure. We experimentally evaluated the direct effect of Caulerpa to provide refuge for the native clam Anadara trapezia and how this balances with its influence on two trait-mediated indirect interactions that may increase Anadara\u27s susceptibility to predators. Specifically, Caulerpa\u27s alteration of physical and chemical properties of the surrounding water and sediment deteriorate Anadara\u27s condition and predator resistance properties and also cause Anadara, though normally buried, to project from beneath the sediment, exposing it to predators. Our results show that Anadara are somewhat (but not consistently) protected from predators by living among Caulerpa. Shallow burial depth did not counteract this protective effect. However at times of year when predator activity diminishes and conducive environmental conditions develop, negative effects of Caulerpa habitat such as hypoxia and lowered flow may dominate. Under such situations, poor clam condition accentuates Anadara\u27s susceptibility to mortality. Ultimately, a slight and inconsistent positive effect of Caulerpa to protect Anadara from predators is exceeded by the strong negative effect of Caulerpa on clam mortality, which is heightened by clams\u27 weakened condition produced by chronic exposure to Caulerpa. Our results show that invasive habitat-modifying species can affect mortality of native species not simply through obvious positive direct effects of their protective structure, but indirectly through contrasting negative modification of the traits of prey species responding to the habitat

Invasive ecosystem engineer selects for different phenotypes of an associated native species

Invasive habitat-forming ecosystem engineers modify the abiotic environment and thus represent a major perturbation to many ecosystems. Because native species often persist in these invaded habitats but have no shared history with the ecosystem engineer, the engineer may impose novel selective pressure on native species. In this study, we used a phenotypic selection framework to determine whether an invasive habitat-forming ecosystem engineer (the seaweed Caulerpa taxifolia) selects for different phenotypes of a common cooccurring native species (the bivalve Anadara trapezia). Compared to unvegetated habitat, Caulerpa habitat has lower water flow, lower dissolved oxygen, and sediments are more silty and anoxic. We determined the performance consequences of variation in key functional traits that may be affected by these abiotic changes (shell morphology, gill mass, and palp mass) for Anadara transplanted into Caulerpa and unvegetated habitat. Both linear and nonlinear performance gradients in Anadara differed between habitats, and these gradients were stronger in Caulerpa compared to unvegetated sediment. Moreover, in Caulerpa alternate phenotypes performed well, and these phenotypes were different from the dominant phenotype in unvegetated sediment. By demonstrating that phenotype-performance gradients differ between habitats, we have highlighted a role for Caulerpa as an agent of selection on native species

Chapter 8 Comparative Biogeography of Marine Invaders Across Their Native and Introduced Ranges

Biological invasions continue to exert extensive environmental and economic impacts. Understanding why some introduced species become invasive is critical to their management. Determining the mechanisms underpinning invasion success has focussed on aspects of the ecology and physiology of the species in the introduced range. Through the application of biogeographic approaches, however, a growing body of research highlights insights that stem from studying invasion success as a biogeographic issue. In particular, a comparison of both biogeographic regions (i.e., the native and invasive ranges) allows exclusive insight into seven different major biogeographic hypotheses that we identified to explain invader success. These include the enemy release hypothesis, niche shifts, trait differences, the evolution of invasiveness, native allies, environmental matching, and genetic diversity. All imply a difference or gradient between the ranges that may mechanistically explain an invader’s differential performance. This review summarises the support for these seven different theories underpinning the biogeography of marine invasions, and also provides case studies for different theories addressing the comparative biogeography of marine invasions. Additionally, we catalogue the geographic regions of the invasive species used in biogeographic comparisons and the diversity of species, habitats and climate zones examined. Finally, we highlight critical knowledge gaps and suggest future research directions for improving our understanding the processes driving invasion success

Parasites Alter Community Structure

Parasites often play an important role in modifying the physiology and behavior of their hosts and may, consequently, mediate the influence hosts have on other components of an ecological community. Along the northern Atlantic coast of North America, the dominant herbivorous snail Littorina littorea structures rocky intertidal communities through strong grazing pressure and is frequently parasitized by the digenean trematode Cryptocotyle lingua. We hypothesized that the effects of parasitism on host physiology would induce behavioral changes in L. littorea, which in turn would modulate L. littorea\u27s influence on intertidal community composition. Specifically, we hypothesized that C. lingua infection would alter the grazing rate of L. littorea and, consequently, macroalgal communities would develop differently in the presence of infected versus uninfected snails. Our results show that uninfected snails consumed 40% more ephemeral macroalgal biomass than infected snails in the laboratory, probably because the digestive system of infected snails is compromised by C. lingua infection. In the field, this weaker grazing by infected snails resulted in significantly greater expansion of ephemeral macroalgal cover relative to grazing by uninfected snails. By decreasing the per-capita grazing rate of the dominant herbivore, C. lingua indirectly affects the composition of the macroalgal community and may in turn affect other species that depend on macroalgae for resources or habitat structure. In light of the abundance of parasites across systems, we suggest that, through trait-mediated indirect effects, parasites may be a common determinant of structure in ecological communities

Responses of an oyster host (Crassostrea virginica) and its protozoan parasite (Perkinsus marinus) to increasing air temperature

Background Changes in climate are predicted to influence parasite and pathogen infection patterns in terrestrial and marine environments. Increases in temperature in particular may greatly alter biological processes, such as host-parasite interactions. For example, parasites could differentially benefit from increased reproduction and transmission or hosts could benefit from elevated immune responses that may mediate or even eliminate infections. In the southeastern United States, the Eastern oyster, Crassostrea virginica, is infected by the lethal protozoan parasite, Perkinsus marinus. Under field conditions, intertidal (air-exposed) oysters have been found to have significantly higher P. marinus infection intensity and marginally higher infection prevalence than subtidal (submerged) oysters. During summer, air temperatures are much warmer than water and this exposure of intertidal oysters to higher temperatures is a suggested mechanism for increased infection intensity. Methods We simulated intertidal exposure using controlled laboratory experiments to determine how host traits (survival and immune response) and parasite infection intensity will respond to elevated air temperature ranging from 27 °C to 53 °C during emersion at low tide. In Georgia, where our work was conducted, the average summer water temperature is 29 °C and the average maximum high air temperature in July is 33 °C (though oysters have been shown to survive at much higher air temperatures). Results Host survival declined as temperature increased, with a definitive drop-off between 39–43 °C. Negative effects of air temperature on host immune response (phagocytic activity) were detectable only at extremely high temperatures (47–50 °C) when hosts were suffering acute mortality. Parasite infection intensity peaked at 35 °C. Discussion Our results suggest that an increase in average summer air temperature to 35 °C or higher could affect oyster survival directly through temperature-related impacts in the short-term and indirectly through increased P. marinus infection intensity over the long-term

Quantitative LSPR Imaging for Biosensing with Single Nanostructure Resolution

AbstractLocalized surface plasmon resonance (LSPR) imaging has the potential to map complex spatio-temporal variations in analyte concentration, such as those produced by protein secretions from live cells. A fundamental roadblock to the realization of such applications is the challenge of calibrating a nanoscale sensor for quantitative analysis. Here, we introduce a new, to our knowledge, LSPR imaging and analysis technique that enables the calibration of hundreds of individual gold nanostructures in parallel. The calibration allowed us to map the fractional occupancy of surface-bound receptors at individual nanostructures with nanomolar sensitivity and a temporal resolution of 225 ms. As a demonstration of the technique’s applicability to molecular and cell biology, the calibrated array was used for the quantitative LSPR imaging of anti-c-myc antibodies harvested from a cultured 9E10 hybridoma cell line without the need for further purification or processing

Development and characterization of microsatellite loci for the haploid–diploid red seaweed Gracilaria vermiculophylla

Microsatellite loci are popular molecular markers due to their resolution in distinguishing individual genotypes. However, they have rarely been used to explore the population dynamics in species with biphasic life cycles in which both haploid and diploid stages develop into independent, functional organisms. We developed microsatellite loci for the haploid–diploid red seaweed Gracilaria vermiculophylla, a widespread non-native species in coastal estuaries of the Northern hemisphere. Forty-two loci were screened for amplification and polymorphism. Nine of these loci were polymorphic across four populations of the extant range with two to eleven alleles observed. Mean observed and expected heterozygosities ranged from 0.265 to 0.527 and 0.317 to 0.387, respectively. Overall, these markers will aid in the study of the invasive history of this seaweed and further studies on the population dynamics of this important haploid–diploid primary producer