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search.filters.applied.f.advisor: Hay, Mark E. × End date: 2019 × Start date: 2010 ×

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Now showing 1 - 10 of 11
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Developing appropriate methodology for assessing anti-pathogen properties of mucus-enriched water from corals

2019-05 , Jarvis, Simone

Global coral reef health is in rapid decline. A major contributor to this trend is warming ocean temperatures. As ocean temperature increases, corals become more susceptible to diseases that lead to bleaching and tissue mortality. Vibrio coralliilyticus is one of the few documented coral bleaching pathogens. Previous studies developed methods to quantify V. coralliilyticus metabolism and developed culturing procedures to test the anti-Vibrio potency of mucus-enriched water from numerous coral species. However, the best way to collect and process mucus-enriched water from corals was not determined. Previous efforts obtained mucus-enriched water via coral fragmentation and agitation in seawater. This methodology detected anti-Vibrio activity from several species, but required destructive sampling of the corals. This prevents collecting data over multiple time points without confounding time with previous damage. This study evaluates the effectiveness of less destructive methodologies for sampling mucus-enriched coral water. This study evaluated the effectiveness of the less destructive method of slowly sucking coral mucus from colonies in the field using a syringe. Tests using this method on mucus enriched water from 9 species of coral detected no anti-pathogen activity. In contrast, tests using the fragmentation and shaking method found significant anti-pathogen activity in 3 of the 4 species tested. the less destructive method assayed here, is ineffective at assessing the anti-pathogen potential of corals.

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Acclimating across healthy and degraded reefs

2016-05-31 , Dell, Claire Louise Alice

As a result of human activities, many environments are becoming fragmented into areas with different community compositions and selective regimes. The coral reefs of Fiji for example, are divided into ‘fished areas’ (fragments subjected to fishing and trampling) and ‘protected areas’ (fragments with little human pressure) that occur in close proximity and now have differing community compositions and selective regimes. Theory predicts that the species able to survive in such conditions should have highly plastic genotypes allowing them to acclimatise to diverse habitats without the time lag required for local adaptation. Here we use two species -Epinephelus merra (a small grouper) and Sargassum polycystum C. Agardh (a brown macroalga)- which are found in both fished and protected reefs, to investigate this plastic response and understand how these species cope in healthy versus degraded environments. We found that the fish E. merra exhibits plasticity in diet and feeds lower in the food chain in fished reefs than similarly sized conspecifics in protected reefs. The seaweed S. polycystum exhibits plasticity in defensive traits and is able to induce increased defenses in response to being partially consumed. In addition, we found that dense stands of S. polycystum increased the survival and growth of both recruit-sized and mature-sized S. polycystum ramets, suggesting that Sargassum beds protect conspecifics from grazing by herbivorous fishes and construct conditions that facilitate their growth. Implications for management are discussed.

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Chemically mediated competition, herbivory, and the structure of coral reefs

2012-07-03 , Rasher, Douglas B.

Corals, the foundation species of tropical reefs, are in rapid global decline as a result of anthropogenic disturbance. On many reefs, losses of coral have coincided with the over-harvesting of reef herbivores, resulting in ecosystem phase-shifts from coral to macroalgal dominance. It is hypothesized that abundant macroalgae inhibit coral recovery and recruitment, thereby generating ecological feedback processes that reinforce phase-shifts to macroalgae and further diminish reef function. Notwithstanding, the extent to which macroalgae directly outcompete coral, the mechanisms involved, and the species-specificity of algal-coral competition remains debated. Moreover the capacity for herbivores to prevent vs. reverse ecosystem phase-shifts to macroalgae and the roles of herbivore diversity in such phenomena remain poorly understood. Here I demonstrate with a series of field experiments in the tropical Pacific and Caribbean Sea that multiple macroalgae common to degraded reefs directly outcompete coral using chemical warfare, that these interactions are mediated by hydrophobic secondary metabolites transferred from algal to coral surfaces by direct contact, and that the outcomes of these allelopathic interactions are highly species-specific. Using field observations and experiments in the tropical Pacific, I also demonstrate that the process of herbivory attenuates the competitive effects of allelopathic algae on corals by controlling succession of algal communities, and that the herbivore species responsible for macroalgal removal possess complementary tolerances to the diversity of chemical defenses deployed among algae, creating an essential role for herbivore diversity in reversing ecosystem phase-shifts to macroalgae. Lastly, I demonstrate with field experiments in the tropical Pacific that algal-coral competition simultaneously induces allelochemicals and suppresses anti-herbivore deterrents in some algae, likely due to trade-offs in the productions of defense metabolites with differing ecological functions. Together, these studies provide strong evidence that chemically mediated competitive and consumer-prey interactions play principal roles in coral reef degradation and recovery, and should provide resource managers with vital information needed for effective management of these ecologically and economically important but threatened ecosystems.

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Aquatic plant-herbivore interactions across multiple spatial scales.

2010-05-21 , Morrison, Wendy Elizabeth

For decades scientists believed that herbivory had minimal impact on freshwater ecosystems. We now know that herbivory in freshwater systems equals or exceeds herbivory in terrestrial and marine systems. In extreme cases, herbivores can change clear, macrophyte dominated ecosystems into turbid plankton dominated ecosystems. Even though research on plant-herbivore interactions in freshwater systems has increased, there is still much that is unknown. This thesis is comprised of four studies investigating freshwater plant-herbivore interactions across multiple spatial scales. The first study investigated how induced chemical defenses in Cabomba caroliniana suppress herbivore consumption and growth as well as how this herbivore-generated change in plant chemistry affects the growth of plant associated microbes. At the spatial scale of individual ponds or lakes, consumers that induce their host plants may also be indirectly affecting other consumers and microbial pathogens via changes in this shared resource. The second study moves to an ecosystem scale and investigates how exotic versus native apple snails may impact Everglades' habitats. We investigated plant preference, consumption, growth and conversion efficiencies in the singly native apple snail to occur in the U.S. (Pomacea paludosa) versus four introduced species (P. canaliculata, P. insularum, P. haustrum and P. diffusa). We found that even though plant preferences are similar, invasive snails tend to eat more, grow more rapidly, and sometimes more efficiently than natives. This suggests that invasive species could have a large impact on the environment, especially the abundance of submerged plants. The third study investigated how palatability of freshwater plants varies with latitude (i.e. geographic scale). Increased herbivory at lower latitudes is hypothesized to select for increased plant defenses, which has been shown to be true for tropical forests, salt marshes, and seaweeds. When we contrasted eight confamilial plants collected in Indiana versus Southern Florida, three of four herbivores significantly preferred northern plants. When we evaluated a second set of plants collected from Indiana versus Central Florida, only one of three herbivores preferred the northern plants. Overall, our results suggest a preference for northern plants, but the strength of this relationship was variable. We hypothesize that this variability may be driven by 1) local variance in herbivore pressure that creates variance in plant defenses, and/or 2) the effect of winter length on the survival and feeding rate of herbivores. The final study expanded to a world scale, and investigated herbivore preference for native vs exotic plants. We found that both N. American crayfish and S. American snails preferred exotic plants over confamilial natives, despite responding to different plant characteristics. The single species of apple snail that occurs in N. American showed no preference for native or exotic plants from a N. American perspective, but instead exhibited preferences that correlated with its history of evolution in S. America. As the N. American species is a sister species of the S. American snails, feeding by the N. American snail appears more affected by its S. American lineage than its recent history in N. America. This suggests that phylogenetic legacy will affect choices of the herbivore as well as resistance or susceptibility of plants.

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Effects of macroalgal versus coral reef dominance on coral survival, chemical defense, and microbiomes

2018-10-24 , Beatty, Deanna S.

Coral reefs are among the earth’s most biodiverse and productive ecosystems, but are undergoing precipitous decline due to coral bleaching and disease following thermal stress events, which are increasing in frequency and spatial scale. These effects are exacerbated by local stressors such as overfishing and pollution, collectively causing an increasing number of reefs to shift from coral to macroalgal dominance. These stressors can harm or kill corals through diverse mechanisms, including alterations in how corals interact with microorganisms. By employing a variety of field sampling and field experimental approaches, I investigated consequences of local protection from fishing and coral versus macroalgal dominance of the benthos on coral survival, chemical defense, and microbiomes within paired algal dominated fished areas and coral dominated marine protected areas (MPAs) in Fiji. I demonstrate that i) coral larvae from a macroalgal dominated area exhibited higher pre-settlement mortality and reduced settlement compared to those from a coral dominated area, ii) juveniles planted into a coral dominated MPA survived better than those planted into a macroalgal dominated fished area and differential survival depended on whether macroalgae were immediately adjacent to juvenile coral, iii) corals possess chemical defenses toward the thermally-regulated coral bleaching pathogen Vibrio coralliilyticus, but this defense is compromised by elevated temperature, iv) for a bleaching susceptible but ecologically important acroporid coral, anti-pathogen chemical defense is compromised when coral resides within macroalgal dominated reefs and this effect can be influenced by both the current and historic state of the reef. Effects on coral survival and chemical defense for individuals residing within coral versus macroalgal dominated areas largely coincided with nuanced differences in coral microbiomes (e.g., in microbiome variability and specific indicator bacterial taxa) but not with major shifts in microbiome composition. These findings have implications for reef conservation and for understanding how coral-microbe interactions will respond to the pressures of global change.

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Interactions between ecosystems and disease in the plankton of freshwater lakes

2013-11-18 , Penczykowski, Rachel M.

I investigated effects of environmental change on disease, and effects of disease on ecosystems, using a freshwater zooplankton host and its fungal parasite. This research involved lake surveys, manipulative experiments, and mathematical models. My results indicate that ecosystem characteristics such as habitat structure, nutrient availability, and quality of a host’s resources (here, phytoplankton) can affect the spread of disease. For example, a survey of epidemics in lakes revealed direct and indirect links between habitat structure and epidemic size, where indirect connections were mediated by non-host species. Then, in a mesocosm experiment in a lake, manipulations of habitat structure and nutrient availability interactively affected the spread of disease, and nutrient enrichment increased densities of infected hosts. In a separate laboratory experiment, poor quality resources were shown to decrease parasite transmission rate by altering host foraging behavior. My experimental results also suggest that disease can affect ecosystems through effects on host densities and host traits. In the mesocosm experiment, the parasite indirectly increased abundance of algal resources by decreasing densities of the zooplankton host. Disease in the experimental zooplankton populations also impacted nutrient stoichiometry of algae, which could entail a parasite-mediated shift in food quality for grazers such as the host. Additionally, I showed that infection dramatically reduces host feeding rate, and used a dynamic epidemiological model to illustrate how this parasite-mediated trait change could affect densities of resources and hosts, as well as the spread of disease. I discuss the implications of these ecosystem–disease interactions in light of ongoing changes to habitat and nutrient regimes in freshwater ecosystems.

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A test of optimal defense theory vs. the growth-differentiation balance hypothesis as predictors of seaweed palatability and defenses

2011-08-31 , Heckman, Melanie L.

Because organisms have limited resources to allocate to multiple life history traits, the Optimal Defense Theory (ODT) and the Growth-Differentiation Balance Hypothesis (GDBH) were developed by terrestrial plant ecologists to predict intraindividual defense allocation based on the cost of defense and these life history trade-offs. However, these theories have garnered equivocal experimental support over the years and are rarely experimentally extended from predictions of plant physiology to the palatability of the tissues an herbivore experiences. We therefore examined tissue palatability, nutritional value, and defense mechanisms in multiple Dictyotalean seaweeds in two Caribbean locations, using two herbivores. Relative palatability of tissues varied greatly with algal species, grazer species, and location. Because older bases were not consistently defended, GDBH did not predict relative palatability. We could not reject ODT without intensive measures of tissue fitness value and herbivore risk, and this theory was therefore not useful in making broad predictions of tissue palatability. In testing the physiological predictions of these theories, we found the young, growing apices of these seaweeds to be generally more nutritionally valuable than the old, anchoring bases and found organic-rich apices to be more chemically deterrent, thus supporting ODT. However, the combined chemical, nutritional, and structural traits of these algae all influenced herbivore choice. As a result, these patterns of apical value and chemical defense reflected palatability of live tissues for only one of five algal species, which rendered ODT and GDBH poor predictors of relative palatability for most algae.

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Predation, competition, and facilitation on tropical reefs: implications for corals as reefs degrade 

2017-11-13 , Clements, Cody Shane

Tropical coral reefs are among the most diverse and productive ecosystems on Earth, but reefs worldwide have experienced dramatic declines in coral and often transitioned from coral- to macroalgal dominance. As local and global threats to corals increase in severity and frequency, there is an urgent need to understand how reef degradation, as well as efforts to manage and restore corals, are reshaping ecological interactions that are critical to the function of coral reef ecosystems. Here, I utilize a range of experimental approaches to investigate how interactions between corals, competing macroalgae, and coral predators (i.e. corallivores) are being altered within mosaics of coral reef habitat characterized by different levels of degradation and local protection in the tropical Pacific. I first demonstrate, via a series of field observations and experiments, the direct negative effects of competition for corals competing with macroalgae that commonly dominate degraded reefs, including the spatial and temporal constraints of these competitive interactions, as well as the indirect positive effects that can arise due to the presence of a common coral predator, the crown-of-thorns sea star (Acanthaster cf. planci). I also provide observational and experimental evidence that protected reefs can help alleviate predation by corallivorous snails (Coralliophila violacea) for some stress-tolerant corals (Porites cylindrica), but that stark habitat contrasts between coral-dominated protected reefs and macroalgal-dominated fished reefs can simultaneously attract and concentrate feeding by other corallivores (Acanthaster cf. planci) – potentially contributing to coral demise and compromising the conservation value of small Marine Protected Areas. Lastly, I use a field-based manipulative experiment to explore the implications of coral species loss for ecosystem function on degraded reefs; demonstrating that greater coral species richness can enhance coral growth and survivorship, and reduced colonization by competing macroalgae. Together, these studies highlight the need to better understand the novel and context-dependent role of ecological interactions – both for fundamental ecology and effective management – in rapidly changing ecosystems subject to increasing disturbances.

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Seaweed allelopathy against coral: surface distribution of seaweed secondary metabolites by imaging mass sepctrometry

2012-08-16 , Andras, Tiffany D.

Coral reefs are in global decline, with seaweeds increasing as corals decrease. Though seaweeds have been shown to inhibit coral growth, recruitment, and survivorship, the mechanism of these interactions is poorly known. Here we use field experiments to show that contact with four common seaweeds induces bleaching on natural colonies of Porites rus. Controls in contact with inert, plastic mimics of seaweeds did not bleach, suggesting treatment effects resulted from allelopathy rather than shading, abrasion, or physical contact. Bioassay-guided fractionation of the hydrophobic extract from the red alga Phacelocarpus neurymenioides revealed a previously characterized antibacterial metabolite, Neurymenolide A, as the main allelopathic agent. For allelopathy of lipid soluble metabolites to be effective, the metabolites would need to be deployed on algal surfaces where they could transfer to corals on contact. We used desorption electrospray ionization mass spectrometry (DESI-MS) to visualize and quantify Neurymenolide A on the surface of P. neurymenioides and found the metabolite on all surfaces analyzed. The highest concentrations of Neurymenolide A were on basal portions of blades where the plant is most likely to contact other benthic competitors.

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Freshwater red algae use activated chemical defenses against herbivores

2011-07-12 , Goodman, Keri M.

Chemically mediated interactions have important ecological and evolutionary effects on populations and communities. Despite recognition that herbivory can significantly affect the biomass and composition of freshwater macrophyte communities, there are few investigations of chemical defenses among freshwater vascular plants and mosses and none of freshwater red algae. This study compares the palatability of five species of freshwater red algae (Batrachospermum helminthosum, Boldia erythrosiphon, Kumanoa sp., Paralemanea annulata, and Tuomeya americana) that occur in the southeastern United States relative to two co-occurring macrophytes (the chemically defended aquatic moss Fontinalis novae-angliae and the broadly palatable green alga Cladophora glomerata). We assessed the potential role of structural, nutritional, and chemical traits in reducing macrophyte susceptibility to generalist crayfish grazers. Both native and non-native crayfish significantly preferred the green alga C. glomerata over four of the five species of red algae. B. erythrosiphon was palatable, while the cartilaginous structure of P. annulata reduced its susceptibility to grazing, and chemical defenses of B. helminthosum, Kumanoa sp., and T. americana rendered these species as unpalatable as the moss F. novae-angliae. Extracts from these latter species reduced feeding by ~30-60% relative to solvent controls if tissues were crushed (simulating herbivore damage) prior to extraction in organic solvents. However, if algae were first soaked in organic solvents that inhibit enzymatic activity and then crushed, crude extracts stimulated or had no effect on herbivory. B. helminthosum, Kumanoa sp., and T. americana all exhibited "activated" chemical defenses in which anti-herbivore compounds are produced rapidly upon herbivore attack via enzymatic processes. In an additional accept/reject behavioral assay, B. helminthosum extracts reduced the number of crayfish willing to feed by >90%. Given that three of the five red algal taxa examined in this study yielded deterrent crude extracts, selection for defensive chemistry in freshwater rhodophytes appears to be substantial. Activated chemical defenses are thought to be an adaptation to reduce the resource allocation and ecological costs of defense. As such, activated chemical defenses may be favored in freshwater red algae, whose short-lived gametophytes must grow and reproduce rapidly. Roughly 20% of the known chemical defenses produced by marine algae are activated; further examination is needed to determine whether the frequency of activated chemistry is higher in freshwater red algae compared to their marine counterparts. Continued investigation of chemical defenses in freshwater red algae will contribute to among-system comparisons, providing new insights in the generality of plant-herbivore interactions and their evolution.

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