Supplement. 1. Transect surveys of herbivorous fish abundance and size by family on the reef flat... more Supplement. 1. Transect surveys of herbivorous fish abundance and size by family on the reef flat and slope.
The loss of coral cover, frequently driven by anthropogenic disturbances, can result in a phase s... more The loss of coral cover, frequently driven by anthropogenic disturbances, can result in a phase shift to dominance by fleshy macroalgae, many of which contain anti-herbivore defenses. Using field surveys, a mesocosm experiment, and field experiments, we evaluated whether 2 human impacts-nutrient enrichment and reduction in herbivory-affected production and maintenance of thallus toughness, a physical defense of the brown macroalga Turbinaria ornata that has recently expanded across the South Pacific. In contrast to our expectations, there was a weak negative relationship between herbivorous fish abundance and thallus toughness. This relationship was driven by greater toughness in algae collected at the more eutrophic sites, which also had lower herbivore abundances. A mesocosm experiment confirmed a positive relationship between nutrients and thallus toughness with no measurable cost to growth. Mechanical damage simulating herbivory maintained thallus toughness in cages, with a significant trade-off in growth. In addition, reduction of herbivory through caging in a transplant experiment resulted in a reduction in thallus toughness; however there was no measurable benefit to growth, possibly due to a concurrent change in environmental context from the transplant. While reduction in herbivory via overfishing allows this alga to trade energy normally spent on defense for increase growth, nutrient enrichment provides T. ornata with additional resources to increase defenses. As anthropogenic impacts become increasingly prominent in coral reef systems, it is critical that we understand the processes that may facilitate the expansion and dominance of coral reef algae, especially those with inducible anti-herbivore defenses.
Sargassum horneri, a brown macroalga, recently invaded the California coast, including into criti... more Sargassum horneri, a brown macroalga, recently invaded the California coast, including into critical foundational communities such as kelp (Macrocystis pyrifera) forests. Despite its rapid spread, empirical tests that evaluate mechanisms underlying S. horneri's invasion success are lacking. To fill this knowledge gap, we conducted three field experiments on temperate rocky reefs in southern California using growth as a proxy for invasion success. We first tested whether S. horneri success differed with herbivory strength and native diversity by conducting a 2-factor experiment varying site (with different baseline levels of urchin densities and native algal diversity) and urchin access. We found S. horneri growth only differed among urchin treatments and not sites. We then evaluated whether S. horneri could successfully invade established algal canopies as a driver or whether it required open space as a passenger via a 2-factor experiment varying S. horneri size (small, medium, large) and canopy type (S. horneri, kelp, -canopy). We found that all S. horneri sizes grew fastest when canopy was lacking and light was high and slower in both canopy habitats with lower light; overall, small S. horneri grew slowest. Finally, we evaluated whether herbivore consumption for native species could facilitate S. horneri's invasion by conducting a 2-factor experiment varying species (M. pyrifera, S. horneri) and herbivore access. We found uncaged algae were consumed and caged algae grew, but there was no difference between species. Taken together, our results suggest that S. horneri is a "passenger" invader that will take advantage of points in time and space where light is plentiful, such as when M. pyrifera is removed via disturbance. Further, our results suggest that herbivory and native algal diversity are likely not key determining factors of the invasion success of S. horneri.
Dataset: fish species countsThis dataset present fish species counts in three 20x40 m transects. ... more Dataset: fish species countsThis dataset present fish species counts in three 20x40 m transects. The surveys were conducted at the Uva Island coral reef (7o48’46”N, 81o45’35”W), Gulf of Chiriquí, Panama from 1980 to 2010 during both the wet and dry seasons. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/516234NSF Division of Ocean Sciences (NSF OCE) OCE-8415615, NSF Division of Ocean Sciences (NSF OCE) OCE-8716726, NSF Division of Ocean Sciences (NSF OCE) OCE-9018392, NSF Division of Ocean Sciences (NSF OCE) OCE-9314798, NSF Division of Ocean Sciences (NSF OCE) OCE-9711529, NSF Division of Ocean Sciences (NSF OCE) OCE-0002317, NSF Division of Ocean Sciences (NSF OCE) OCE-052636
Worldwide, ecological subsidies enhance ecosystem productivity and therefore trophic support for ... more Worldwide, ecological subsidies enhance ecosystem productivity and therefore trophic support for greater biodiversity of taxa. While studies in terrestrial and aquatic ecosystems demonstrate that the magnitude of subsidies into ecosystems differs widely, the thresholds where subsidies may switch from exerting positive to negative effects are poorly understood. In estuaries, eutrophication promotes drift macroalgae that deposit on the benthos, cover intertidal flats for months and serve as pressed resource subsidies for benthic consumers. We hypothesized there would be a critical threshold of macroalgal biomass where ecosystem-level effects would turn from positive to negative. We used manipulative field experiments varying macroalgal mat thickness (0.5, 1.5 and 4 cm) over eight weeks and quantified effects on macrofauna on a lagoon mudflat in California. We documented that plots with mat depths of 0.5 and 1.5 cm had higher diversity by supporting both surface feeding and burrowing detritivores. Non-metric multidimensional scaling showed that the benthic community diverged with mat depth over the course of the experiment. After eight weeks, surface deposit feeders were associated mainly with 0.5 cm macroalgal subsidies, whereas subsurface deposit feeding capitellids were closely linked with 4 cm mats. Depth profiles of pore water sulfide concentration collected from 4 cm mats were 7622 ± 5294 μM, mean ± SE, (mean of means across depth profiles), whereas 0.5 cm treatments resulted in sulfide concentrations that were 0.25% of the 4 cm treatments. This suggests that the mechanism of negative effects for elevated macroalgal subsidies was development of anoxic conditions promoting sulfide accumulation. Thus, our study was the first to find a critical threshold, or ecological tipping point, beyond which the effects of anthropogenically enhanced subsidies to estuarine mudflat communities switched from positive to negative and to describe the mechanism by which elevated subsides altered the abiotic environment and likely reduced ecosystem functioning.
Coral reefs are shifting from coral to algal‐dominated ecosystems worldwide. Recently, Turbinaria... more Coral reefs are shifting from coral to algal‐dominated ecosystems worldwide. Recently, Turbinaria ornata, a marine alga native to coral reefs of the South Pacific, has spread in both range and habitat usage. Given dense stands of T. ornata can function as an alternative stable state on coral reefs, it is imperative to understand the factors that underlie its success. We tested the hypothesis that T. ornata demonstrates ontogenetic variation in allocation to anti‐herbivore defense, specifically that blade toughness varied nonlinearly with thallus size. We quantified the relationship between T. ornata blade toughness and thallus size for individual thalli within algal stands (N = 345) on seven fringing reefs along the north shore of Moorea, French Polynesia. We found that blade toughness was greatest at intermediate sizes that typically form canopies, with overall reduced toughness in both smaller individuals that refuge within the understory and older reproductive individuals that ul...
Journal of Experimental Marine Biology and Ecology, 2021
Abstract Coral-dominated reefs typically have abundant refuges and limited resources for herbivor... more Abstract Coral-dominated reefs typically have abundant refuges and limited resources for herbivores; conversely, algal-dominated reefs have abundant resources but often have limited refuges. This difference results in a trade-off between risk and reward for herbivorous fishes. However, disturbances that kill coral but retain topographic complexity can decouple this tradeoff, challenging this paradigm. Many fringing reefs in Moorea, French Polynesia are algal-dominated with heterogeneous structural complexity likely driven by disturbances associated with crown-of-thorns predation and typhoons, which occurred between 2006 and 2010. Short turfs are a good recruitment surface for coral larvae, and thus has a greater potential to recover to coral dominance than long turfs. To explore how variation in complexity impacts the behavior of herbivorous fishes, we compared abundance, residence time, and time budgets of Acanthurus nigrofuscus, a common herbivore species, in paired high versus low complexity areas. We chose areas in close proximity to maximize the likelihood fish could choose between complexity types. We also measured turf height in high versus low complexity plots. Fish were ~3× more abundant, spent roughly double the time in, and budgeted more than 4× as much time to hiding in high complexity reef areas. Although, on average, individual herbivores spent the same proportion of time foraging in both areas, their greater abundance and longer residence time suggests their local herbivory rates could be 7.5 times higher in high complexity areas. We also found turfs in high complexity plots were roughly 75% the height of turfs in low complexity plots. This provides some evidence for stronger overall herbivory pressure in high complexity areas, albeit differences in absolute turf height were modest (~0.5 mm). Combined, these results suggest reefs that retain structural complexity following disturbance may be more likely to recover due to the higher localized herbivory rates resulting from uncoupling of the tradeoff between structural complexity and resource limitation.
1. Humans have a long history of changing species’ ranges and habitat distributions, making studi... more 1. Humans have a long history of changing species’ ranges and habitat distributions, making studies of the ecological processes that may facilitate these changes of key importance, particularly in cases where a primary foundation species is replaced by another, less desirable species. 2. We investigated the impact of nutrients and herbivory on Turbinaria ornata, a secondary foundational macroalga that depends on and likely competes with coral, the primary foundational community. T. ornata is also rapidly expanding in range and habitat across the South Pacific. We conducted: 1) a mesocosm experiment assessing relative nutrient limitation, 2) a field experiment comparing importance of nutrients (+/-) and herbivory (+/-) to biomass accumulation, and 3) an herbivory assay and toughness test comparing enriched and ambient thalli to assess changes to anti-herbivory defences. 3. We found no evidence of growth being nutrient limited in T. ornata; rather than stimulating growth, nutrient addition deterred herbivores. However, when physical toughness was removed, enriched algae were preferred, with consumption rates 25-fold those of unenriched algae. Additionally, enriched thalli were tougher than ambient thalli, suggesting physical defences were bolstered by nutrient enrichment. 4. Synthesis. We found a unique interaction where nutrients inhibit herbivory and facilitate Turbinaria ornata biomass accumulation. While concern is often placed on degradation of foundation species via anthropogenic change, instead here we show that anthropogenic change can facilitate secondary foundation species. This facilitation may allow a secondary foundation species to better compete with primary foundation species
A description of the site, a summary of the functional group model (FGM), a statistical summary t... more A description of the site, a summary of the functional group model (FGM), a statistical summary table, a figure with percent cover of each species, and a figure of fish abundances.
Algae from two kingdoms and four major phyla form productive benthic communities that play key ec... more Algae from two kingdoms and four major phyla form productive benthic communities that play key ecological roles on coral reefs of the eastern tropical Pacific (ETP). The diversity of algae that comprise these communities is being actively explored throughout the region, with new species still being discovered. Due to its physical setting, there are several distinct algal habitats in the ETP, including reef crests dominated by crustose coralline algae and algal turfs, reef flats that support a higher abundance of foliose macroalgae, unconsolidated accumulations of dead coral rubble that may support rhodoliths and cryptic macroalgae, and deeper-water refuges from herbivory dominated by more of the palatable forms of macroalgae rarely found on reefs. Past work has identified a number of ecological processes that control algal populations and communities at play in the ETP, but research elucidating their relative roles is still limited in this region. Recent work suggests that these reefs are supported by allochthonous nutrient supplies such as upwelling and thermocline shoaling, though reduced light during these events may limit productivity to shallow reef zones. Though at least partially sheltered from major disturbances that structure other reef systems, such as hurricanes and outbreaks of crown-of-thorns sea stars, reefs of the ETP are strongly affected by sea surface temperature extremes associated with El-Nino-Southern Oscillation (ENSO) leading to major coral mortality with the opening of space for colonization by algae. Biotic processes that control algal communities include herbivory and competition with coral, both of which limit algal proliferation and may enhance recovery after disturbance. However, facilitative interactions within algal communities, such as reduced herbivory and amelioration of nutrient limitation by internal recycling that act as positive feedbacks within areas dominated by algae, may stabilize algal communities after disturbance. There is some empirical and modeling evidence that suggests these processes may drive reefs of the ETP to display alternative stable states. This evidence includes a bifurcated pattern of recovery after ENSO disturbance, the patchy nature of this recovery within certain reefs, and the existence of stabilizing feedbacks that support resilience of both coral and algal states. Further, a simulation model (cellular automaton) of ETP reefs parameterized with experimentally-derived feedback relationships suggests these reefs exist under environmental conditions that produce bistability. However, much research is still needed to fully understand the physical and ecological processes that structure algal communities, and how these controls may shift with anthropogenic impacts.
Humans have increased nitrogen inputs to estuaries, necessitating research on the patterns of the... more Humans have increased nitrogen inputs to estuaries, necessitating research on the patterns of these resource subsidies. When originating outside an estuary, nitrogen is a resource subsidy. This subsidy can be delivered with a variety of temporal patterns, ranging from presses to pulses. In other communities, press versus pulse subsidies has substantial and divergent impacts; however, this framework is not typically used in estuaries. This study documents nitrogen concentration-frequencies in 5 Southern California estuaries that demonstrate these nutrients subsidies can often be characterized as pulse-interpulse. There were extremely high pulses of nitrogen (> 500 uM NH 4 , > 2500 uM NO 3), even compared with other eutrophic estuaries, that were likely driven by strong seasonal and rare rainfall typical of Mediterranean climates. High nutrient concentrations were occasionally decoupled from rainfall, likely due to land use. Extreme eutrophy may have the potential to dampened pulses, producing uniform, elevated concentration-frequency inputs. These data suggest managers should target rainfall events in nutrient sampling protocols as well as monitor changes in biological indicators following these events to characterize the impact of these inputs. Climate change, population size, and coastal development will likely increase nutrient subsidies to estuaries, necessitating further research on the timing, frequency, and duration of these inputs as well as their ecological consequences. In particular, our work highlights the need to integrate pulse events into work on biological indicators in estuaries.
Ecological systems are subjected to multiple stressors that can interact in complex ways resultin... more Ecological systems are subjected to multiple stressors that can interact in complex ways resulting in "ecological surprises". We examine the pivotal role of 'control' assignment in the categorization of stressors into five classes: additive, +synergistic, -synergistic, +antagonistic, and -antagonistic. We demonstrate if an alternate treatment can reasonably be considered the experimental control, nonlinear interaction classifications change, both in sign (+/-) and in direction (synergistic/antagonistic). Further, switching of interaction classifications is not predictable as changing control can result in multiple possible alternate nonlinear classifications. To explore the magnitude of this problem, we evaluate publications gathered for a recent meta-analysis to 1) explore rationales for choice of controls and 2) quantify how frequently it is reasonable to reassign the control. We found controls were designated with a variety of implicit and explicit justifications, with two overall rationales: 1) controls based on 'natural' conditions (historic, current, or future); 2) controls based on direction of impact, such that stressors always have negative impacts. We reasoned that control re-assignment was justified if an alternate treatment met one of these rationales. Of the 844 interactions classified in the meta-analysis, we determined >95% could be reassigned. Based on these findings, we recommend a new approach to meta-analyses, where the 'control' is strictly and consistently defined by the authors of the meta-analysis. These controls should be based on their broader question, rather than following the common practice of defaulting to controls assigned by the authors of each study, as we found these rationales vary broadly based on the specific questions of each study. Consistent control designation within the ecological or toxicological framework of each meta-analysis may provide deeper and more consistent insight into the nature of interactive effects between multiple stressors. Gaining this insight is crucial because stressor interactions are certain to increase in the Anthropocene.
This paper analyzes the adjustment of consumption expenditures if the subjective mortality hazard... more This paper analyzes the adjustment of consumption expenditures if the subjective mortality hazard increases after a shock. The life-cycle model with mortality risk implies an upward adjustment of consumption expenditures as a response to such a shock. I use data from the Survey of Health, Ageing and Retirement in Europe (SHARE) to test this implication. In each survey wave, the mortality hazard measure is based on the response to a question on subjective survival probability. The e¤ect of the subjective hazard is identi…ed by using the death of a sibling as instrument. The estimation results indicate that the consumption expenditures are adjusted upwards after the hazard shock among those who have positive wealth holdings and are thus not liquidity constrained.
Supplement. 1. Transect surveys of herbivorous fish abundance and size by family on the reef flat... more Supplement. 1. Transect surveys of herbivorous fish abundance and size by family on the reef flat and slope.
The loss of coral cover, frequently driven by anthropogenic disturbances, can result in a phase s... more The loss of coral cover, frequently driven by anthropogenic disturbances, can result in a phase shift to dominance by fleshy macroalgae, many of which contain anti-herbivore defenses. Using field surveys, a mesocosm experiment, and field experiments, we evaluated whether 2 human impacts-nutrient enrichment and reduction in herbivory-affected production and maintenance of thallus toughness, a physical defense of the brown macroalga Turbinaria ornata that has recently expanded across the South Pacific. In contrast to our expectations, there was a weak negative relationship between herbivorous fish abundance and thallus toughness. This relationship was driven by greater toughness in algae collected at the more eutrophic sites, which also had lower herbivore abundances. A mesocosm experiment confirmed a positive relationship between nutrients and thallus toughness with no measurable cost to growth. Mechanical damage simulating herbivory maintained thallus toughness in cages, with a significant trade-off in growth. In addition, reduction of herbivory through caging in a transplant experiment resulted in a reduction in thallus toughness; however there was no measurable benefit to growth, possibly due to a concurrent change in environmental context from the transplant. While reduction in herbivory via overfishing allows this alga to trade energy normally spent on defense for increase growth, nutrient enrichment provides T. ornata with additional resources to increase defenses. As anthropogenic impacts become increasingly prominent in coral reef systems, it is critical that we understand the processes that may facilitate the expansion and dominance of coral reef algae, especially those with inducible anti-herbivore defenses.
Sargassum horneri, a brown macroalga, recently invaded the California coast, including into criti... more Sargassum horneri, a brown macroalga, recently invaded the California coast, including into critical foundational communities such as kelp (Macrocystis pyrifera) forests. Despite its rapid spread, empirical tests that evaluate mechanisms underlying S. horneri's invasion success are lacking. To fill this knowledge gap, we conducted three field experiments on temperate rocky reefs in southern California using growth as a proxy for invasion success. We first tested whether S. horneri success differed with herbivory strength and native diversity by conducting a 2-factor experiment varying site (with different baseline levels of urchin densities and native algal diversity) and urchin access. We found S. horneri growth only differed among urchin treatments and not sites. We then evaluated whether S. horneri could successfully invade established algal canopies as a driver or whether it required open space as a passenger via a 2-factor experiment varying S. horneri size (small, medium, large) and canopy type (S. horneri, kelp, -canopy). We found that all S. horneri sizes grew fastest when canopy was lacking and light was high and slower in both canopy habitats with lower light; overall, small S. horneri grew slowest. Finally, we evaluated whether herbivore consumption for native species could facilitate S. horneri's invasion by conducting a 2-factor experiment varying species (M. pyrifera, S. horneri) and herbivore access. We found uncaged algae were consumed and caged algae grew, but there was no difference between species. Taken together, our results suggest that S. horneri is a "passenger" invader that will take advantage of points in time and space where light is plentiful, such as when M. pyrifera is removed via disturbance. Further, our results suggest that herbivory and native algal diversity are likely not key determining factors of the invasion success of S. horneri.
Dataset: fish species countsThis dataset present fish species counts in three 20x40 m transects. ... more Dataset: fish species countsThis dataset present fish species counts in three 20x40 m transects. The surveys were conducted at the Uva Island coral reef (7o48’46”N, 81o45’35”W), Gulf of Chiriquí, Panama from 1980 to 2010 during both the wet and dry seasons. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/516234NSF Division of Ocean Sciences (NSF OCE) OCE-8415615, NSF Division of Ocean Sciences (NSF OCE) OCE-8716726, NSF Division of Ocean Sciences (NSF OCE) OCE-9018392, NSF Division of Ocean Sciences (NSF OCE) OCE-9314798, NSF Division of Ocean Sciences (NSF OCE) OCE-9711529, NSF Division of Ocean Sciences (NSF OCE) OCE-0002317, NSF Division of Ocean Sciences (NSF OCE) OCE-052636
Worldwide, ecological subsidies enhance ecosystem productivity and therefore trophic support for ... more Worldwide, ecological subsidies enhance ecosystem productivity and therefore trophic support for greater biodiversity of taxa. While studies in terrestrial and aquatic ecosystems demonstrate that the magnitude of subsidies into ecosystems differs widely, the thresholds where subsidies may switch from exerting positive to negative effects are poorly understood. In estuaries, eutrophication promotes drift macroalgae that deposit on the benthos, cover intertidal flats for months and serve as pressed resource subsidies for benthic consumers. We hypothesized there would be a critical threshold of macroalgal biomass where ecosystem-level effects would turn from positive to negative. We used manipulative field experiments varying macroalgal mat thickness (0.5, 1.5 and 4 cm) over eight weeks and quantified effects on macrofauna on a lagoon mudflat in California. We documented that plots with mat depths of 0.5 and 1.5 cm had higher diversity by supporting both surface feeding and burrowing detritivores. Non-metric multidimensional scaling showed that the benthic community diverged with mat depth over the course of the experiment. After eight weeks, surface deposit feeders were associated mainly with 0.5 cm macroalgal subsidies, whereas subsurface deposit feeding capitellids were closely linked with 4 cm mats. Depth profiles of pore water sulfide concentration collected from 4 cm mats were 7622 ± 5294 μM, mean ± SE, (mean of means across depth profiles), whereas 0.5 cm treatments resulted in sulfide concentrations that were 0.25% of the 4 cm treatments. This suggests that the mechanism of negative effects for elevated macroalgal subsidies was development of anoxic conditions promoting sulfide accumulation. Thus, our study was the first to find a critical threshold, or ecological tipping point, beyond which the effects of anthropogenically enhanced subsidies to estuarine mudflat communities switched from positive to negative and to describe the mechanism by which elevated subsides altered the abiotic environment and likely reduced ecosystem functioning.
Coral reefs are shifting from coral to algal‐dominated ecosystems worldwide. Recently, Turbinaria... more Coral reefs are shifting from coral to algal‐dominated ecosystems worldwide. Recently, Turbinaria ornata, a marine alga native to coral reefs of the South Pacific, has spread in both range and habitat usage. Given dense stands of T. ornata can function as an alternative stable state on coral reefs, it is imperative to understand the factors that underlie its success. We tested the hypothesis that T. ornata demonstrates ontogenetic variation in allocation to anti‐herbivore defense, specifically that blade toughness varied nonlinearly with thallus size. We quantified the relationship between T. ornata blade toughness and thallus size for individual thalli within algal stands (N = 345) on seven fringing reefs along the north shore of Moorea, French Polynesia. We found that blade toughness was greatest at intermediate sizes that typically form canopies, with overall reduced toughness in both smaller individuals that refuge within the understory and older reproductive individuals that ul...
Journal of Experimental Marine Biology and Ecology, 2021
Abstract Coral-dominated reefs typically have abundant refuges and limited resources for herbivor... more Abstract Coral-dominated reefs typically have abundant refuges and limited resources for herbivores; conversely, algal-dominated reefs have abundant resources but often have limited refuges. This difference results in a trade-off between risk and reward for herbivorous fishes. However, disturbances that kill coral but retain topographic complexity can decouple this tradeoff, challenging this paradigm. Many fringing reefs in Moorea, French Polynesia are algal-dominated with heterogeneous structural complexity likely driven by disturbances associated with crown-of-thorns predation and typhoons, which occurred between 2006 and 2010. Short turfs are a good recruitment surface for coral larvae, and thus has a greater potential to recover to coral dominance than long turfs. To explore how variation in complexity impacts the behavior of herbivorous fishes, we compared abundance, residence time, and time budgets of Acanthurus nigrofuscus, a common herbivore species, in paired high versus low complexity areas. We chose areas in close proximity to maximize the likelihood fish could choose between complexity types. We also measured turf height in high versus low complexity plots. Fish were ~3× more abundant, spent roughly double the time in, and budgeted more than 4× as much time to hiding in high complexity reef areas. Although, on average, individual herbivores spent the same proportion of time foraging in both areas, their greater abundance and longer residence time suggests their local herbivory rates could be 7.5 times higher in high complexity areas. We also found turfs in high complexity plots were roughly 75% the height of turfs in low complexity plots. This provides some evidence for stronger overall herbivory pressure in high complexity areas, albeit differences in absolute turf height were modest (~0.5 mm). Combined, these results suggest reefs that retain structural complexity following disturbance may be more likely to recover due to the higher localized herbivory rates resulting from uncoupling of the tradeoff between structural complexity and resource limitation.
1. Humans have a long history of changing species’ ranges and habitat distributions, making studi... more 1. Humans have a long history of changing species’ ranges and habitat distributions, making studies of the ecological processes that may facilitate these changes of key importance, particularly in cases where a primary foundation species is replaced by another, less desirable species. 2. We investigated the impact of nutrients and herbivory on Turbinaria ornata, a secondary foundational macroalga that depends on and likely competes with coral, the primary foundational community. T. ornata is also rapidly expanding in range and habitat across the South Pacific. We conducted: 1) a mesocosm experiment assessing relative nutrient limitation, 2) a field experiment comparing importance of nutrients (+/-) and herbivory (+/-) to biomass accumulation, and 3) an herbivory assay and toughness test comparing enriched and ambient thalli to assess changes to anti-herbivory defences. 3. We found no evidence of growth being nutrient limited in T. ornata; rather than stimulating growth, nutrient addition deterred herbivores. However, when physical toughness was removed, enriched algae were preferred, with consumption rates 25-fold those of unenriched algae. Additionally, enriched thalli were tougher than ambient thalli, suggesting physical defences were bolstered by nutrient enrichment. 4. Synthesis. We found a unique interaction where nutrients inhibit herbivory and facilitate Turbinaria ornata biomass accumulation. While concern is often placed on degradation of foundation species via anthropogenic change, instead here we show that anthropogenic change can facilitate secondary foundation species. This facilitation may allow a secondary foundation species to better compete with primary foundation species
A description of the site, a summary of the functional group model (FGM), a statistical summary t... more A description of the site, a summary of the functional group model (FGM), a statistical summary table, a figure with percent cover of each species, and a figure of fish abundances.
Algae from two kingdoms and four major phyla form productive benthic communities that play key ec... more Algae from two kingdoms and four major phyla form productive benthic communities that play key ecological roles on coral reefs of the eastern tropical Pacific (ETP). The diversity of algae that comprise these communities is being actively explored throughout the region, with new species still being discovered. Due to its physical setting, there are several distinct algal habitats in the ETP, including reef crests dominated by crustose coralline algae and algal turfs, reef flats that support a higher abundance of foliose macroalgae, unconsolidated accumulations of dead coral rubble that may support rhodoliths and cryptic macroalgae, and deeper-water refuges from herbivory dominated by more of the palatable forms of macroalgae rarely found on reefs. Past work has identified a number of ecological processes that control algal populations and communities at play in the ETP, but research elucidating their relative roles is still limited in this region. Recent work suggests that these reefs are supported by allochthonous nutrient supplies such as upwelling and thermocline shoaling, though reduced light during these events may limit productivity to shallow reef zones. Though at least partially sheltered from major disturbances that structure other reef systems, such as hurricanes and outbreaks of crown-of-thorns sea stars, reefs of the ETP are strongly affected by sea surface temperature extremes associated with El-Nino-Southern Oscillation (ENSO) leading to major coral mortality with the opening of space for colonization by algae. Biotic processes that control algal communities include herbivory and competition with coral, both of which limit algal proliferation and may enhance recovery after disturbance. However, facilitative interactions within algal communities, such as reduced herbivory and amelioration of nutrient limitation by internal recycling that act as positive feedbacks within areas dominated by algae, may stabilize algal communities after disturbance. There is some empirical and modeling evidence that suggests these processes may drive reefs of the ETP to display alternative stable states. This evidence includes a bifurcated pattern of recovery after ENSO disturbance, the patchy nature of this recovery within certain reefs, and the existence of stabilizing feedbacks that support resilience of both coral and algal states. Further, a simulation model (cellular automaton) of ETP reefs parameterized with experimentally-derived feedback relationships suggests these reefs exist under environmental conditions that produce bistability. However, much research is still needed to fully understand the physical and ecological processes that structure algal communities, and how these controls may shift with anthropogenic impacts.
Humans have increased nitrogen inputs to estuaries, necessitating research on the patterns of the... more Humans have increased nitrogen inputs to estuaries, necessitating research on the patterns of these resource subsidies. When originating outside an estuary, nitrogen is a resource subsidy. This subsidy can be delivered with a variety of temporal patterns, ranging from presses to pulses. In other communities, press versus pulse subsidies has substantial and divergent impacts; however, this framework is not typically used in estuaries. This study documents nitrogen concentration-frequencies in 5 Southern California estuaries that demonstrate these nutrients subsidies can often be characterized as pulse-interpulse. There were extremely high pulses of nitrogen (> 500 uM NH 4 , > 2500 uM NO 3), even compared with other eutrophic estuaries, that were likely driven by strong seasonal and rare rainfall typical of Mediterranean climates. High nutrient concentrations were occasionally decoupled from rainfall, likely due to land use. Extreme eutrophy may have the potential to dampened pulses, producing uniform, elevated concentration-frequency inputs. These data suggest managers should target rainfall events in nutrient sampling protocols as well as monitor changes in biological indicators following these events to characterize the impact of these inputs. Climate change, population size, and coastal development will likely increase nutrient subsidies to estuaries, necessitating further research on the timing, frequency, and duration of these inputs as well as their ecological consequences. In particular, our work highlights the need to integrate pulse events into work on biological indicators in estuaries.
Ecological systems are subjected to multiple stressors that can interact in complex ways resultin... more Ecological systems are subjected to multiple stressors that can interact in complex ways resulting in "ecological surprises". We examine the pivotal role of 'control' assignment in the categorization of stressors into five classes: additive, +synergistic, -synergistic, +antagonistic, and -antagonistic. We demonstrate if an alternate treatment can reasonably be considered the experimental control, nonlinear interaction classifications change, both in sign (+/-) and in direction (synergistic/antagonistic). Further, switching of interaction classifications is not predictable as changing control can result in multiple possible alternate nonlinear classifications. To explore the magnitude of this problem, we evaluate publications gathered for a recent meta-analysis to 1) explore rationales for choice of controls and 2) quantify how frequently it is reasonable to reassign the control. We found controls were designated with a variety of implicit and explicit justifications, with two overall rationales: 1) controls based on 'natural' conditions (historic, current, or future); 2) controls based on direction of impact, such that stressors always have negative impacts. We reasoned that control re-assignment was justified if an alternate treatment met one of these rationales. Of the 844 interactions classified in the meta-analysis, we determined >95% could be reassigned. Based on these findings, we recommend a new approach to meta-analyses, where the 'control' is strictly and consistently defined by the authors of the meta-analysis. These controls should be based on their broader question, rather than following the common practice of defaulting to controls assigned by the authors of each study, as we found these rationales vary broadly based on the specific questions of each study. Consistent control designation within the ecological or toxicological framework of each meta-analysis may provide deeper and more consistent insight into the nature of interactive effects between multiple stressors. Gaining this insight is crucial because stressor interactions are certain to increase in the Anthropocene.
This paper analyzes the adjustment of consumption expenditures if the subjective mortality hazard... more This paper analyzes the adjustment of consumption expenditures if the subjective mortality hazard increases after a shock. The life-cycle model with mortality risk implies an upward adjustment of consumption expenditures as a response to such a shock. I use data from the Survey of Health, Ageing and Retirement in Europe (SHARE) to test this implication. In each survey wave, the mortality hazard measure is based on the response to a question on subjective survival probability. The e¤ect of the subjective hazard is identi…ed by using the death of a sibling as instrument. The estimation results indicate that the consumption expenditures are adjusted upwards after the hazard shock among those who have positive wealth holdings and are thus not liquidity constrained.
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Papers by Peggy Fong