Mark Bertness | Brown University (original) (raw)

Papers by Mark Bertness

Journal of Ecology, Mar 1, 2006

Ecological Applications, Oct 1, 2003

Ecology, Sep 1, 2012

Belowground herbivory is commonly overlooked as a mechanism of top-down control in vegetated habi... more Belowground herbivory is commonly overlooked as a mechanism of top-down control in vegetated habitats, particularly in aquatic ecosystems. Recent research has revealed that increased densities of the herbivorous crab Sesarma reticulatum have led to runaway herbivory and widespread salt marsh die-off on Cape Cod, Massachusetts, USA. Aboveground herbivory is a major driver of this cordgrass habitat loss, but the role of belowground grazing is poorly understood. Sesarma live in communal burrows typically consisting of 1-2 openings and containing 2-3 crabs. However, at die-off sites, burrow complexes can cover .90% of the low marsh zone, with crab densities as high as 50 crabs/m 2 and burrow opening densities of 170 openings/m 2. The magnitude of belowground Sesarma activity in association with salt marsh die-off provides an excellent opportunity to extend our knowledge of belowground herbivory impacts in coastal wetlands. Since Sesarma burrows allow access to cordgrass roots and rhizomes, and Sesarma are frequently restricted to burrows by thermal stress and predation, we hypothesized that belowground herbivory would be widespread in die-off areas. We experimentally demonstrate that Sesarma readily eat belowground roots and rhizomes in addition to aboveground cordgrass leaves. We then partitioned above-and belowground herbivory with field manipulations and found that belowground grazing is not only common, but can cause total plant mortality. Additional experiments revealed that plants remain vulnerable to belowground herbivory even after reaching a size refuge from aboveground grazing. This suggests that belowground herbivory contributes to salt marsh die-offs and adds to growing evidence that belowground herbivory is a widespread structuring force in plant communities that can limit habitat persistence.

PLOS ONE, Aug 29, 2013

Predator depletion on Cape Cod (USA) has released the herbivorous crab Sesarma reticulatum from p... more Predator depletion on Cape Cod (USA) has released the herbivorous crab Sesarma reticulatum from predator control leading to the loss of cordgrass from salt marsh creek banks. After more than three decades of die-off, cordgrass is recovering at heavily damaged sites coincident with the invasion of green crabs (Carcinus maenas) into intertidal Sesarma burrows. We hypothesized that Carcinus is dependent on Sesarma burrows for refuge from physical and biotic stress in the salt marsh intertidal and reduces Sesarma functional density and herbivory through consumptive and non-consumptive effects, mediated by both visual and olfactory cues. Our results reveal that in the intertidal zone of New England salt marshes, Carcinus are burrow dependent, Carcinus reduce Sesarma functional density and herbivory in die-off areas and Sesarma exhibit a generic avoidance response to large, predatory crustaceans. These results support recent suggestions that invasive Carcinus are playing a role in the recovery of New England salt marshes and assertions that invasive species can play positive roles outside of their native ranges.

Ecology, Sep 1, 2013

With global increases in human impacts, invasive species have become a major threat to ecosystems... more With global increases in human impacts, invasive species have become a major threat to ecosystems worldwide. While they have been traditionally viewed as harmful, invasive species may facilitate the restoration of degraded ecosystems outside their native ranges. In New England (USA) overfishing has depleted salt marsh predators, allowing the herbivorous crab Sesarma reticulatum to denude hundreds of hectares of low marsh. Here, using multiple site surveys and field caging experiments, we show that the subsequent invasion of green crabs, Carcinus maenas, into heavily burrowed marshes partially reverses decades of cordgrass die-off. By consuming Sesarma, eliciting a nonlethal escape response, and evicting Sesarma from burrows, Carcinus reduces Sesarma herbivory and promotes cordgrass recovery. These results suggest that invasive species can contribute to restoring degraded ecosystems and underscores the potential for invasive species to return ecological functions lost to human impacts.

Ecology Letters, Jan 30, 2013

The study of positive species interactions is a rapidly evolving field in ecology. Despite decade... more The study of positive species interactions is a rapidly evolving field in ecology. Despite decades of research, controversy has emerged as to whether positive and negative interactions predictably shift with increasing environmental stress as hypothesised by the stress-gradient hypothesis (SGH). Here, we provide a synthesis of 727 tests of the SGH in plant communities across the globe to examine its generality across a variety of ecological factors. Our results show that plant interactions change with stress through an outright shift to facilitation (survival) or a reduction in competition (growth and reproduction). In a limited number of cases, plant interactions do not respond to stress, but they never shift towards competition with stress. These findings are consistent across stress types, plant growth forms, life histories, origins (invasive vs. native), climates, ecosystems and methodologies, though the magnitude of the shifts towards facilitation with stress is dependent on these factors. We suggest that future studies should employ standardised definitions and protocols to test the SGH, take a multi-factorial approach that considers variables such as plant traits in addition to stress, and apply the SGH to better understand how species and communities will respond to environmental change.

Oecologia, Nov 29, 2014

Creek bank salt marsh die-off is a conservation problem in New England, driven by predator 21 dep... more Creek bank salt marsh die-off is a conservation problem in New England, driven by predator 21 depletion, which releases herbivores from consumer control. Many marshes, however, have 22 begun to recover from die-off. We examined the hypothesis that the loss of the foundation 23 species Spartina alterniflora, has decreased facilitator populations, weakening reciprocal 24 positive plant/animal feedbacks, decreasing resilience, and slowing recovery. Field surveys and 25 experiments revealed that loss of Spartina leads to decreases biodiversity, and increased 26 mortality and decreased growth of the ribbed mussel Geukensia demissa, a key facilitator of 27 Spartina. Experimental addition of Geukensia to recovering creek banks accelerated Spartina 28 recovery, showing that their loss limits recovery and the reciprocal feedbacks that drive 29 community resilience. Reciprocal positive feedbacks involving foundation species, often lost to 30 human impacts, may be a common, but generally overlooked mechanism of ecosystem 31 resilience, making their reestablishment a valuable restoration tool.

Carolina Digital Repository (University of North Carolina at Chapel Hill), 2015

Forward by JBC Jackson and Robert Treat Paine 1. A Historical Perspective of Marine Community Eco... more Forward by JBC Jackson and Robert Treat Paine 1. A Historical Perspective of Marine Community Ecology John F. Bruno, Brian R. Silliman, John J. Stachowicz and Mark D. Bertness PART 1: PROCESSES THAT GENERATE PATTERN IN MARINE COMMUNITIES 2. The Physical Context of Marine Communities Marc Weissburg, Brian Helmuth and Jon Witman 3. Foundation Species in Marine Ecosystems Andrew H. Altieri and Johan van de Koppel 4. Marine Dispersal, Ecology, and Conservation Stephen R. Palumbi and Malin L. Pinsky 5. The Role of Infectious Disease in Marine Communities Kevin D. Lafferty and C. Drew Harvell 6. Biodiversity and Ecosystem Function: Does Pattern Influence Process? Mary I. O'Connor and Jarrett E. Byrnes 7. The Biogeography of Marine Communities Eric Sanford 8. Historical Ecology: Informing the Future by Learning from the Past Heike K. Lotze and Loren McClenachan PART 2: COMMUNITY TYPES 9. Intertidal Rocky Shores Lisandro Benedetti-Cecchi and Geoffrey C. Trussell 10. Soft Sediment Communities James E. Byers and John H. Grabowski 11. Salt Marshes Mark D. Bertness and Brian R. Silliman 12. Ecology of Seagrass Communities Emmett Duffy, Randall Hughes and Per Moksnes 13. Coral Reef Ecosystems: A Decade of Discoveries Isabelle M. Cote and Nancy Knowlton 14. Kelp Beds Robert Steneck and Craig Johnson 15. Pelagic Communities Jon Fisher and Ken Frank 16. Phytoplankton Communities Kyle F. Edwards and Elena Litchman 17. Deep Sea Hydrothermal Vent Communities Lauren S. Mullineaux PART 3: CONSERVATION 18. Services of Marine Ecosystems: A Quantitative Perspective Edward B. Barbier, Heather M. Leslie and Fiorenza Micheli 19. Threats to Marine Ecosystems: Climate Change and Bottom-up Forcing John Bruno and C. Harley 20. Threats to Marine Ecosystems: Overfishing and Habitat Degradation Boris Worm and Hunter S. Lenihan 21. Ecosystem Based Approaches to Marine Conservation and Management Benjamin S. Halpern and Tundi Agardy 22. Marine Restoration Ecology Sean P. Powers and Katharyn E. Boyer 23. The Future of Marine Conservation and Management Mary Ruckelshaus, Peter Kareiva and Larry Crowder

Philosophical Transactions of the Royal Society B, Nov 2, 2020

One contribution of 17 to a theme issue 'Integrative research perspectives on marine conservation'.

American Scientist, 2004

An attentive observer sees the rich-ness of life during a single walk along a salt marsh. Gulls c... more An attentive observer sees the rich-ness of life during a single walk along a salt marsh. Gulls circle in the air, and mute swans swoop in to land along the marsh's edge. Dense stands of grasses and other plants—waving gently in the ocean breeze—cover seemingly every spot of ...

Journal of Biogeography, 2017

Aim: The aim of this study was to investigate the biogeography of plant zonation in salt marshes ... more Aim: The aim of this study was to investigate the biogeography of plant zonation in salt marshes on the Pacific coast of South America; to examine whether salt marsh plant zonation varies with latitude; and to explore the relative importance of climatic, tidal, edaphic and disturbance factors in explaining large-scale variation in salt marsh plant community structure. Location: A 2,000-km latitudinal gradient on the Pacific coast in Chile, with a climate shift from hyper-arid at low to hyper-humid at high latitudes. Methods: Plant zonation was quantified in field surveys of ten marshes. Climate, tidal regimes, edaphic factors and disturbances (tsunami and rainfall floods) were determined. We used multivariate analyses to explore their relative importance in explaining large-scale variation in salt marsh plant community structure. Results: Across latitude, marshes were dominated by distinct plant communities in different climate regions, especially at the extreme dry and wet latitudes. Intertidal plant species zonation was present in hyper-arid and semi-arid climates, but not in arid, humid and hyper-humid climates. Latitudinal variation in low-marsh plant communities (regularly flooded at high tide) was largely a function of precipitation, while at high marshes (never flooded at high tide) latitudinal variation was explained with precipitation, temperature, tidal cycles, soil salinity and disturbances. Main conclusions: Salt marshes on the Pacific coast of South America belong to Dry Coast and Temperate biogeographic types. Salt marsh plant zonation varies across latitude, and is explained by climatic, tidal, edaphic and disturbance factors. These patterns appear to be mechanistically explained by extrapolating experimentally generated community assembly models and have implications for predicting responses to climate change.

Estuarine, Coastal and Shelf Science, 2016

Salt marshes buffer coastlines and provide critical ecosystem services from storm protection to f... more Salt marshes buffer coastlines and provide critical ecosystem services from storm protection to food provision. Worldwide, these ecosystems are in danger of disappearing if they cannot increase elevation at rates that match sea-level rise. However, the magnitude of loss to be expected is not known. A synthesis of existing records of salt marsh elevation change was conducted in order to consider the likelihood of their future persistence. This analysis indicates that many salt marshes did not keep pace with sealevel rise in the past century and kept pace even less well over the past two decades. Salt marshes experiencing higher local sea-level rise rates were less likely to be keeping pace. These results suggest that sea-level rise will overwhelm most salt marshes' capacity to maintain elevation. Under the most optimistic IPCC emissions pathway, 60% of the salt marshes studied will be gaining elevation at a rate insufficient to keep pace with sea-level rise by 2100. Without mitigation of greenhouse gas emissions this potential loss could exceed 90%, which will have substantial ecological, economic, and human health consequences.

Ecology, Jun 1, 1998

Understanding the factors that determine community structure remains one of the most important is... more Understanding the factors that determine community structure remains one of the most important issues in ecology. In this paper, we examine the role of flow velocities in governing community structure in marine intertidal communities. We broaden the traditional definition of ''bottom-up'' forces to include the delivery of nutrients, food, and larval resources to habitats and then test the hypothesis that, by controlling these fluxes as well as mediating predator effects, flow velocities leave strong bottom-up signatures on shoreline communities. We examined this hypothesis by quantifying community structure and dynamics at high and low flow sites in a tidal estuary in Maine. High flow sites were characterized by dense barnacle and mussel cover, while low flow sites had considerable bare space. High flow sites also had greater grazer and predator densities than low flow sites. Recruitment of all common shoreline organisms with planktonic larvae was greater at high flow sites, in direct proportion to the increased fluid flux there. Flow effects on the growth of the herbivorous and carnivorous components of the food web were less predictable. High flows increased the growth of barnacles, but not mussels, and increased the growth of the carnivorous gastropods that preyed on them. In contrast, high flows decreased the accumulation of benthic diatoms, but this was unrelated to the growth rates of herbivorous gastropods. High flow sites were universally characterized by low predation intensity and per capita predation rates on all three prey species. Our results show that the strength of top-down and bottom-up forces varies with flow rate in this estuary. Consumer stress (top-down) models accurately explain patterns we saw at low flow sites, but bottom-up processes predicted from nutrient/productivity models dominate at high flow sites. High consumer pressure is the dominant structuring force at low flow sites, whereas at high flow sites predators are inhibited, and individual recruitment and growth rates become the dominant structuring forces. We suggest that hydrodynamics may commonly decouple predation and resource processes in many aquatic systems when the physical process responsible for variation in top-down forces also acts as a strong bottom-up force.

Ecology, 1999

In the Gulf of Maine, estuarine shorelines with low water flow are characterized by high crab pre... more In the Gulf of Maine, estuarine shorelines with low water flow are characterized by high crab predation on the common blue mussel, Mytilus edulis, compared to nearby shorelines with high water flow. Mussels at these high predation sites had thicker shells, relatively more shell ...

Science Advances, 2021

Large protected areas, once successful in rescuing iconic wetlands from human activities, are und... more Large protected areas, once successful in rescuing iconic wetlands from human activities, are undermined by plant invasions.

Oecologia, Mar 23, 1999

We examined the relative contribution of recruitment, intraspecific species interactions, and pre... more We examined the relative contribution of recruitment, intraspecific species interactions, and predation in controlling the upper intertidal border of the northern acorn barnacle, Semibalanusbalanoides, in a tidal estuary in Maine. We hypothesized that the contracted border at sites that experienced low tidal currents was due to flow-mediated recruitment that resulted in reduced survival due to the absence of neighbor buffering of thermal stress (i.e., positive intraspecific interactions). We tested this hypothesis by manipulating the density of recently settled barnacles and their thermal environment in a field experiment. Counter to our original hypothesis, barnacles with neighbors suffered severe mortality at low-flow sites. When density-dependent predation by the green crab (Carcinusmaenus) was experimentally eliminated, however, we did detect evidence for positive interactions at the low-flow sites but not at the high-flow sites. In spite of the close proximity of the sites, maximum daily rock temperatures at the low-flow sites were slightly, but consistently, greater than those at high-flow sites. Our findings suggest that the upper intertidal border of S. balanoides in the Damariscotta River is limited at low-flow sites by a combination of reduced recruitment, elevated mortality from thermal stress and enhanced predation by green crabs. More generally, our findings highlight how physical stress and predation interact to alter the nature of density-dependent species interactions in natural assemblages.

Ecology, Nov 1, 2006

Despite growing interest in species&a... more Despite growing interest in species' range shifts, little is known about the ecological and evolutionary factors that control geographic range boundaries. We investigated the processes that maintain the northern range limit of the mud fiddler crab (Uca pugnax) at North Scituate, Massachusetts, USA (42 degrees 14' N), located approximately 60 km north of Cape Cod. Larvae from five populations in Massachusetts were reared under controlled temperatures to test whether cooler water near the edge of this species' range inhibits planktonic development. Few larvae completed development at temperatures < 18 degrees C, a threshold that larvae would regularly encounter north of Cape Cod. Extensive salt marshes are present north of the current range boundary, and a transplant experiment using field enclosures confirmed that benthic fiddler crabs can survive severe winter conditions in this northern habitat. Taken with oceanographic data, these results suggest that the range boundary of fiddler crabs is likely maintained by the influence of cooler water temperatures on the larval phase. Analyses of mitochondrial DNA sequences from a neutral marker (COI) indicate high gene flow among U. pugnax populations in Massachusetts with little differentiation across Cape Cod. Consistent with predictions regarding the homogenizing influence of gene flow, larvae from source populations north and south of Cape Cod shared a common lower threshold for development. However, larvae produced near the range edge had faster growth rates than those from the south side of Cape Cod (typically reaching the final megalopal stage 1.0-5.5 d faster at 18 degrees C). Additional studies are needed to determine the mechanism underlying this counter-gradient variation in development time. We hypothesize that dispersal into cooler water on the north side of Cape Cod may act as a selection filter that sieves out slow developers from the larval pool by increasing planktonic duration and exposure to associated sources of mortality. Thus while high gene flow may prevent the evolution of greater cold tolerance in northern populations, recurrent selection on existing variation may lead to an unexpected concentration of favorable adaptations at the edge of the range. Such a pattern could permit edge populations to play a dominant and unrecognized role in future range extensions.

Journal of Ecology, Mar 1, 2006

Ecological Applications, Oct 1, 2003

Ecology, Sep 1, 2012

Belowground herbivory is commonly overlooked as a mechanism of top-down control in vegetated habi... more Belowground herbivory is commonly overlooked as a mechanism of top-down control in vegetated habitats, particularly in aquatic ecosystems. Recent research has revealed that increased densities of the herbivorous crab Sesarma reticulatum have led to runaway herbivory and widespread salt marsh die-off on Cape Cod, Massachusetts, USA. Aboveground herbivory is a major driver of this cordgrass habitat loss, but the role of belowground grazing is poorly understood. Sesarma live in communal burrows typically consisting of 1-2 openings and containing 2-3 crabs. However, at die-off sites, burrow complexes can cover .90% of the low marsh zone, with crab densities as high as 50 crabs/m 2 and burrow opening densities of 170 openings/m 2. The magnitude of belowground Sesarma activity in association with salt marsh die-off provides an excellent opportunity to extend our knowledge of belowground herbivory impacts in coastal wetlands. Since Sesarma burrows allow access to cordgrass roots and rhizomes, and Sesarma are frequently restricted to burrows by thermal stress and predation, we hypothesized that belowground herbivory would be widespread in die-off areas. We experimentally demonstrate that Sesarma readily eat belowground roots and rhizomes in addition to aboveground cordgrass leaves. We then partitioned above-and belowground herbivory with field manipulations and found that belowground grazing is not only common, but can cause total plant mortality. Additional experiments revealed that plants remain vulnerable to belowground herbivory even after reaching a size refuge from aboveground grazing. This suggests that belowground herbivory contributes to salt marsh die-offs and adds to growing evidence that belowground herbivory is a widespread structuring force in plant communities that can limit habitat persistence.

PLOS ONE, Aug 29, 2013

Predator depletion on Cape Cod (USA) has released the herbivorous crab Sesarma reticulatum from p... more Predator depletion on Cape Cod (USA) has released the herbivorous crab Sesarma reticulatum from predator control leading to the loss of cordgrass from salt marsh creek banks. After more than three decades of die-off, cordgrass is recovering at heavily damaged sites coincident with the invasion of green crabs (Carcinus maenas) into intertidal Sesarma burrows. We hypothesized that Carcinus is dependent on Sesarma burrows for refuge from physical and biotic stress in the salt marsh intertidal and reduces Sesarma functional density and herbivory through consumptive and non-consumptive effects, mediated by both visual and olfactory cues. Our results reveal that in the intertidal zone of New England salt marshes, Carcinus are burrow dependent, Carcinus reduce Sesarma functional density and herbivory in die-off areas and Sesarma exhibit a generic avoidance response to large, predatory crustaceans. These results support recent suggestions that invasive Carcinus are playing a role in the recovery of New England salt marshes and assertions that invasive species can play positive roles outside of their native ranges.

Ecology, Sep 1, 2013

With global increases in human impacts, invasive species have become a major threat to ecosystems... more With global increases in human impacts, invasive species have become a major threat to ecosystems worldwide. While they have been traditionally viewed as harmful, invasive species may facilitate the restoration of degraded ecosystems outside their native ranges. In New England (USA) overfishing has depleted salt marsh predators, allowing the herbivorous crab Sesarma reticulatum to denude hundreds of hectares of low marsh. Here, using multiple site surveys and field caging experiments, we show that the subsequent invasion of green crabs, Carcinus maenas, into heavily burrowed marshes partially reverses decades of cordgrass die-off. By consuming Sesarma, eliciting a nonlethal escape response, and evicting Sesarma from burrows, Carcinus reduces Sesarma herbivory and promotes cordgrass recovery. These results suggest that invasive species can contribute to restoring degraded ecosystems and underscores the potential for invasive species to return ecological functions lost to human impacts.

Ecology Letters, Jan 30, 2013

The study of positive species interactions is a rapidly evolving field in ecology. Despite decade... more The study of positive species interactions is a rapidly evolving field in ecology. Despite decades of research, controversy has emerged as to whether positive and negative interactions predictably shift with increasing environmental stress as hypothesised by the stress-gradient hypothesis (SGH). Here, we provide a synthesis of 727 tests of the SGH in plant communities across the globe to examine its generality across a variety of ecological factors. Our results show that plant interactions change with stress through an outright shift to facilitation (survival) or a reduction in competition (growth and reproduction). In a limited number of cases, plant interactions do not respond to stress, but they never shift towards competition with stress. These findings are consistent across stress types, plant growth forms, life histories, origins (invasive vs. native), climates, ecosystems and methodologies, though the magnitude of the shifts towards facilitation with stress is dependent on these factors. We suggest that future studies should employ standardised definitions and protocols to test the SGH, take a multi-factorial approach that considers variables such as plant traits in addition to stress, and apply the SGH to better understand how species and communities will respond to environmental change.

Oecologia, Nov 29, 2014

Creek bank salt marsh die-off is a conservation problem in New England, driven by predator 21 dep... more Creek bank salt marsh die-off is a conservation problem in New England, driven by predator 21 depletion, which releases herbivores from consumer control. Many marshes, however, have 22 begun to recover from die-off. We examined the hypothesis that the loss of the foundation 23 species Spartina alterniflora, has decreased facilitator populations, weakening reciprocal 24 positive plant/animal feedbacks, decreasing resilience, and slowing recovery. Field surveys and 25 experiments revealed that loss of Spartina leads to decreases biodiversity, and increased 26 mortality and decreased growth of the ribbed mussel Geukensia demissa, a key facilitator of 27 Spartina. Experimental addition of Geukensia to recovering creek banks accelerated Spartina 28 recovery, showing that their loss limits recovery and the reciprocal feedbacks that drive 29 community resilience. Reciprocal positive feedbacks involving foundation species, often lost to 30 human impacts, may be a common, but generally overlooked mechanism of ecosystem 31 resilience, making their reestablishment a valuable restoration tool.

Carolina Digital Repository (University of North Carolina at Chapel Hill), 2015

Forward by JBC Jackson and Robert Treat Paine 1. A Historical Perspective of Marine Community Eco... more Forward by JBC Jackson and Robert Treat Paine 1. A Historical Perspective of Marine Community Ecology John F. Bruno, Brian R. Silliman, John J. Stachowicz and Mark D. Bertness PART 1: PROCESSES THAT GENERATE PATTERN IN MARINE COMMUNITIES 2. The Physical Context of Marine Communities Marc Weissburg, Brian Helmuth and Jon Witman 3. Foundation Species in Marine Ecosystems Andrew H. Altieri and Johan van de Koppel 4. Marine Dispersal, Ecology, and Conservation Stephen R. Palumbi and Malin L. Pinsky 5. The Role of Infectious Disease in Marine Communities Kevin D. Lafferty and C. Drew Harvell 6. Biodiversity and Ecosystem Function: Does Pattern Influence Process? Mary I. O'Connor and Jarrett E. Byrnes 7. The Biogeography of Marine Communities Eric Sanford 8. Historical Ecology: Informing the Future by Learning from the Past Heike K. Lotze and Loren McClenachan PART 2: COMMUNITY TYPES 9. Intertidal Rocky Shores Lisandro Benedetti-Cecchi and Geoffrey C. Trussell 10. Soft Sediment Communities James E. Byers and John H. Grabowski 11. Salt Marshes Mark D. Bertness and Brian R. Silliman 12. Ecology of Seagrass Communities Emmett Duffy, Randall Hughes and Per Moksnes 13. Coral Reef Ecosystems: A Decade of Discoveries Isabelle M. Cote and Nancy Knowlton 14. Kelp Beds Robert Steneck and Craig Johnson 15. Pelagic Communities Jon Fisher and Ken Frank 16. Phytoplankton Communities Kyle F. Edwards and Elena Litchman 17. Deep Sea Hydrothermal Vent Communities Lauren S. Mullineaux PART 3: CONSERVATION 18. Services of Marine Ecosystems: A Quantitative Perspective Edward B. Barbier, Heather M. Leslie and Fiorenza Micheli 19. Threats to Marine Ecosystems: Climate Change and Bottom-up Forcing John Bruno and C. Harley 20. Threats to Marine Ecosystems: Overfishing and Habitat Degradation Boris Worm and Hunter S. Lenihan 21. Ecosystem Based Approaches to Marine Conservation and Management Benjamin S. Halpern and Tundi Agardy 22. Marine Restoration Ecology Sean P. Powers and Katharyn E. Boyer 23. The Future of Marine Conservation and Management Mary Ruckelshaus, Peter Kareiva and Larry Crowder

Philosophical Transactions of the Royal Society B, Nov 2, 2020

One contribution of 17 to a theme issue 'Integrative research perspectives on marine conservation'.

American Scientist, 2004

An attentive observer sees the rich-ness of life during a single walk along a salt marsh. Gulls c... more An attentive observer sees the rich-ness of life during a single walk along a salt marsh. Gulls circle in the air, and mute swans swoop in to land along the marsh's edge. Dense stands of grasses and other plants—waving gently in the ocean breeze—cover seemingly every spot of ...

Journal of Biogeography, 2017

Aim: The aim of this study was to investigate the biogeography of plant zonation in salt marshes ... more Aim: The aim of this study was to investigate the biogeography of plant zonation in salt marshes on the Pacific coast of South America; to examine whether salt marsh plant zonation varies with latitude; and to explore the relative importance of climatic, tidal, edaphic and disturbance factors in explaining large-scale variation in salt marsh plant community structure. Location: A 2,000-km latitudinal gradient on the Pacific coast in Chile, with a climate shift from hyper-arid at low to hyper-humid at high latitudes. Methods: Plant zonation was quantified in field surveys of ten marshes. Climate, tidal regimes, edaphic factors and disturbances (tsunami and rainfall floods) were determined. We used multivariate analyses to explore their relative importance in explaining large-scale variation in salt marsh plant community structure. Results: Across latitude, marshes were dominated by distinct plant communities in different climate regions, especially at the extreme dry and wet latitudes. Intertidal plant species zonation was present in hyper-arid and semi-arid climates, but not in arid, humid and hyper-humid climates. Latitudinal variation in low-marsh plant communities (regularly flooded at high tide) was largely a function of precipitation, while at high marshes (never flooded at high tide) latitudinal variation was explained with precipitation, temperature, tidal cycles, soil salinity and disturbances. Main conclusions: Salt marshes on the Pacific coast of South America belong to Dry Coast and Temperate biogeographic types. Salt marsh plant zonation varies across latitude, and is explained by climatic, tidal, edaphic and disturbance factors. These patterns appear to be mechanistically explained by extrapolating experimentally generated community assembly models and have implications for predicting responses to climate change.

Estuarine, Coastal and Shelf Science, 2016

Salt marshes buffer coastlines and provide critical ecosystem services from storm protection to f... more Salt marshes buffer coastlines and provide critical ecosystem services from storm protection to food provision. Worldwide, these ecosystems are in danger of disappearing if they cannot increase elevation at rates that match sea-level rise. However, the magnitude of loss to be expected is not known. A synthesis of existing records of salt marsh elevation change was conducted in order to consider the likelihood of their future persistence. This analysis indicates that many salt marshes did not keep pace with sealevel rise in the past century and kept pace even less well over the past two decades. Salt marshes experiencing higher local sea-level rise rates were less likely to be keeping pace. These results suggest that sea-level rise will overwhelm most salt marshes' capacity to maintain elevation. Under the most optimistic IPCC emissions pathway, 60% of the salt marshes studied will be gaining elevation at a rate insufficient to keep pace with sea-level rise by 2100. Without mitigation of greenhouse gas emissions this potential loss could exceed 90%, which will have substantial ecological, economic, and human health consequences.

Ecology, Jun 1, 1998

Understanding the factors that determine community structure remains one of the most important is... more Understanding the factors that determine community structure remains one of the most important issues in ecology. In this paper, we examine the role of flow velocities in governing community structure in marine intertidal communities. We broaden the traditional definition of ''bottom-up'' forces to include the delivery of nutrients, food, and larval resources to habitats and then test the hypothesis that, by controlling these fluxes as well as mediating predator effects, flow velocities leave strong bottom-up signatures on shoreline communities. We examined this hypothesis by quantifying community structure and dynamics at high and low flow sites in a tidal estuary in Maine. High flow sites were characterized by dense barnacle and mussel cover, while low flow sites had considerable bare space. High flow sites also had greater grazer and predator densities than low flow sites. Recruitment of all common shoreline organisms with planktonic larvae was greater at high flow sites, in direct proportion to the increased fluid flux there. Flow effects on the growth of the herbivorous and carnivorous components of the food web were less predictable. High flows increased the growth of barnacles, but not mussels, and increased the growth of the carnivorous gastropods that preyed on them. In contrast, high flows decreased the accumulation of benthic diatoms, but this was unrelated to the growth rates of herbivorous gastropods. High flow sites were universally characterized by low predation intensity and per capita predation rates on all three prey species. Our results show that the strength of top-down and bottom-up forces varies with flow rate in this estuary. Consumer stress (top-down) models accurately explain patterns we saw at low flow sites, but bottom-up processes predicted from nutrient/productivity models dominate at high flow sites. High consumer pressure is the dominant structuring force at low flow sites, whereas at high flow sites predators are inhibited, and individual recruitment and growth rates become the dominant structuring forces. We suggest that hydrodynamics may commonly decouple predation and resource processes in many aquatic systems when the physical process responsible for variation in top-down forces also acts as a strong bottom-up force.

Ecology, 1999

In the Gulf of Maine, estuarine shorelines with low water flow are characterized by high crab pre... more In the Gulf of Maine, estuarine shorelines with low water flow are characterized by high crab predation on the common blue mussel, Mytilus edulis, compared to nearby shorelines with high water flow. Mussels at these high predation sites had thicker shells, relatively more shell ...

Science Advances, 2021

Large protected areas, once successful in rescuing iconic wetlands from human activities, are und... more Large protected areas, once successful in rescuing iconic wetlands from human activities, are undermined by plant invasions.

Oecologia, Mar 23, 1999

We examined the relative contribution of recruitment, intraspecific species interactions, and pre... more We examined the relative contribution of recruitment, intraspecific species interactions, and predation in controlling the upper intertidal border of the northern acorn barnacle, Semibalanusbalanoides, in a tidal estuary in Maine. We hypothesized that the contracted border at sites that experienced low tidal currents was due to flow-mediated recruitment that resulted in reduced survival due to the absence of neighbor buffering of thermal stress (i.e., positive intraspecific interactions). We tested this hypothesis by manipulating the density of recently settled barnacles and their thermal environment in a field experiment. Counter to our original hypothesis, barnacles with neighbors suffered severe mortality at low-flow sites. When density-dependent predation by the green crab (Carcinusmaenus) was experimentally eliminated, however, we did detect evidence for positive interactions at the low-flow sites but not at the high-flow sites. In spite of the close proximity of the sites, maximum daily rock temperatures at the low-flow sites were slightly, but consistently, greater than those at high-flow sites. Our findings suggest that the upper intertidal border of S. balanoides in the Damariscotta River is limited at low-flow sites by a combination of reduced recruitment, elevated mortality from thermal stress and enhanced predation by green crabs. More generally, our findings highlight how physical stress and predation interact to alter the nature of density-dependent species interactions in natural assemblages.

Ecology, Nov 1, 2006

Despite growing interest in species&a... more Despite growing interest in species' range shifts, little is known about the ecological and evolutionary factors that control geographic range boundaries. We investigated the processes that maintain the northern range limit of the mud fiddler crab (Uca pugnax) at North Scituate, Massachusetts, USA (42 degrees 14' N), located approximately 60 km north of Cape Cod. Larvae from five populations in Massachusetts were reared under controlled temperatures to test whether cooler water near the edge of this species' range inhibits planktonic development. Few larvae completed development at temperatures < 18 degrees C, a threshold that larvae would regularly encounter north of Cape Cod. Extensive salt marshes are present north of the current range boundary, and a transplant experiment using field enclosures confirmed that benthic fiddler crabs can survive severe winter conditions in this northern habitat. Taken with oceanographic data, these results suggest that the range boundary of fiddler crabs is likely maintained by the influence of cooler water temperatures on the larval phase. Analyses of mitochondrial DNA sequences from a neutral marker (COI) indicate high gene flow among U. pugnax populations in Massachusetts with little differentiation across Cape Cod. Consistent with predictions regarding the homogenizing influence of gene flow, larvae from source populations north and south of Cape Cod shared a common lower threshold for development. However, larvae produced near the range edge had faster growth rates than those from the south side of Cape Cod (typically reaching the final megalopal stage 1.0-5.5 d faster at 18 degrees C). Additional studies are needed to determine the mechanism underlying this counter-gradient variation in development time. We hypothesize that dispersal into cooler water on the north side of Cape Cod may act as a selection filter that sieves out slow developers from the larval pool by increasing planktonic duration and exposure to associated sources of mortality. Thus while high gene flow may prevent the evolution of greater cold tolerance in northern populations, recurrent selection on existing variation may lead to an unexpected concentration of favorable adaptations at the edge of the range. Such a pattern could permit edge populations to play a dominant and unrecognized role in future range extensions.