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Mia J Tegner - One of the best experts on this subject based on the ideXlab platform.
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Kelp Forest ecosystems: Biodiversity, stability, resilience and future
Environmental Conservation, 2002Co-Authors: Robert S Steneck, Bruce J. Bourque, Debbie Corbett, Jon M. Erlandson, Michael H. Graham, James A. Estes, Mia J TegnerAbstract:Kelp Forests are phyletically diverse, structurally complex and highly productive components of coldwater rocky marine coastlines. This paper reviews the conditions in which Kelp Forests develop globally and where, why and at what rate they become deForested. The ecology and long archaeological history of Kelp Forests are examined through case studies from southern California, the Aleutian Islands and the western North Atlantic, well-studied locations that represent the widest possible range in Kelp Forest biodiversity. Global distribution of Kelp Forests is physiologically constrained by light at high latitudes and by nutrients, warm temperatures and other macrophytes at low latitudes. Within mid-latitude belts (roughly 40–60° latitude in both hemispheres) well-developed Kelp Forests are most threatened by herbivory, usually from sea urchins. Overfishing and extirpation of highly valued vertebrate apex predators often triggered herbivore population increases, leading to widespread Kelp deForestation. Such deForestations have the most profound and lasting impacts on species-depauperate systems, such as those in Alaska and the western North Atlantic. Globally urchin-induced deForestation has been increasing over the past 2–3 decades. Continued fishing down of coastal food webs has resulted in shifting harvesting targets from apex predators to their invertebrate prey, including Kelp-grazing herbivores. The recent global expansion of sea urchin harvesting has led to the widespread extirpation of this herbivore, and Kelp Forests have returned in some locations but, for the first time, these Forests are devoid of vertebrate apex predators. In the western North Atlantic, large predatory crabs have recently filled this void and they have become the new apex predator in this system. Similar shifts from fish- to crab-dominance may have occurred in coastal zones of the United Kingdom and Japan, where large predatory finfish were extirpated long ago. Three North American case studies of Kelp Forests were examined to determine their long history with humans and project the status of future Kelp Forests to the year 2025. Fishing impacts on Kelp Forest systems have been both profound and much longer in duration than previously thought. Archaeological data suggest that coastal peoples exploited Kelp Forest organisms for thousands of years, occasionally resulting in localized losses of apex predators, outbreaks of sea urchin populations and probably small-scale deForestation. Over the past two centuries, commercial exploitation for export led to the extirpation of sea urchin predators, such as the sea otter in the North Pacific and predatory fishes like the cod in the North Atlantic. The large-scale removal of predators for export markets increased sea urchin abundances and promoted the decline of Kelp Forests over vast areas. Despite southern California having one of the longest known associations with coastal Kelp Forests, widespread deForestation is rare. It is possible that functional redundancies among predators and herbivores make this most diverse system most stable. Such biodiverse Kelp Forests may also resist invasion from non-native species. In the species-depauperate western North Atlantic, introduced algal competitors carpet the benthos and threaten future Kelp dominance. There, other non-native herbivores and predators have become established and dominant components of this system. Climate changes have had measurable impacts on Kelp Forest ecosystems and efforts to control the emission of greenhouse gasses should be a global priority. However, overfishing appears to be the greatest manageable threat to Kelp Forest ecosystems over the 2025 time horizon. Management should focus on minimizing fishing impacts and restoring populations of functionally important species in these systems.
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ecosystem effects of fishing in Kelp Forest communities
Journal of Materials Science, 2000Co-Authors: Mia J Tegner, Paul K. DaytonAbstract:Kelp Forests, highly diverse cold water communities organized around the primary productivity and physical structure provided by members of the Laminariales, support a variety of fisheries, and the Kelp itself is harvested for alginates. Worldwide, these communities generally share susceptibility to destructive overgrazing by sea urchins. The impact of sea-urchin grazing is governed by the ratio between food availability and grazing pressure, thus factors affecting the abundance of both urchins and Kelps are central to ecosystem integrity. Some Kelp ecosystems share a second generality, the association of exploitation of various urchin predators with destructive levels of urchin grazing, leading to cascading implications for other species dependent on the productivity and habitat provided by the Kelps. Competition between abalones and sea urchins also affects some Kelp communities. These ecosystem-structuring processes are complicated by a variety of bottom-up and top-down factors, including variability in ocean climate affecting Kelp productivity and recruitment of key species, and echinoid disease. Potential ecosystem effects of fisheries for predators, abalones, sea urchins, and Kelps are reviewed biogeographically. Given the hundreds to thousands of years that many nearshore marine ecosystems have been exploited, no-take marine reserves may be the only way to determine the true ecosystem effects of fishing.
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sliding baselines ghosts and reduced expectations in Kelp Forest communities
Ecological Applications, 1998Co-Authors: Paul K. Dayton, Peter B Edwards, Mia J Tegner, Kristin L RiserAbstract:The detection of trends in ecosystems depends upon (1) a good description of the foundation or benchmark against which changes are measured and (2) a distinction between natural and anthropogenic changes. Patterns and mechanisms observed over 25 years in a large Kelp Forest suggest that definition of a meaningful benchmark is impossible, because many of the large animals have been gone for years to decades, and Kelps are sensitive to large-scale, low-frequency El Nifio-Southern Oscillation events and longer term regime shifts. A shift in the oceanographic climate has significantly reduced the average size and carrying capacity of the dominant plant. The animals that have been functionally removed from the community include sea otters, black sea bass, yellowtail, white sea bass, and abalones. Other species are still present, but fisheries have had huge effects on the abundances, size-frequencies, and/or spatial distributions of sheephead, Kelp bass, rays, flatfish, rock fish, spiny lobsters, and red sea urchins. Now even sea cucumbers, crabs, and small snails are subject to unregulated fishing. The plants continue to exist without a hint of the effects of the loss of so much animal biomass. Furthermore, most of the megafauna have been removed with very little documentation or historical understanding of what the natural community was like. Thus, our ability to separate anthropogenic impacts from the "natural" dynamics of the system is severely compromised. We discuss the importance of both an ecosystem focus on productivity and careful monitoring of as many populations as possible. In addition, we show that this community is not tightly integrated with mutual dependencies; hence, many species can be removed without much affecting the rest of the ecosystem.
Jeffrey R Koseff - One of the best experts on this subject based on the ideXlab platform.
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interaction of waves and currents with Kelp Forests macrocystis pyrifera insights from a dynamically scaled laboratory model
Limnology and Oceanography, 2013Co-Authors: Johanna H Rosman, Mark W Denny, Stephen G Monismith, Robert Zeller, Jeffrey R KoseffAbstract:The interaction of surface waves and currents with Kelp Forests was examined under controlled conditions using a dynamically matched 1/25-scale physical model in a laboratory flume. In experiments with Kelp mimics, waves increased the time-averaged drag by a factor of 2 and altered the shape of current profiles. Relative motion between model Kelp and water under waves increased wake generation of turbulence, resulting in turbulent kinetic energies 2–5 times larger, and eddy viscosities 20–50% larger, than for experiments without waves. Because mixing lengths were reduced to wake-scales in the model Kelp Forest, eddy viscosities were 25–50% smaller than when Kelp was absent. In the model Kelp-Forest surface canopy where solid obstacles were most densely spaced, wave orbital velocities were reduced by , 10% from linear wave theory predictions. This decrease in wave orbital velocities is thought to result primarily from inertial forces exerted on water by model Kelp. Stokes drift was reduced by , 20% as a result of the change in wave orbital velocities. Although hydrodynamics within Kelp Forests are more complex than in the laboratory experiments and a wide range of flow conditions can occur, laboratory results suggest that (1) Kelp Forest drag is increased by waves; (2) wave properties can be altered by drag and inertial forces; and (3) wake production of turbulence caused by waves may be the main source of turbulence in dense Kelp stands. Interactions between Kelp and waves must therefore be taken into account when developing models for drag and mixing in these systems.
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currents and turbulence within a Kelp Forest macrocystis pyrifera insights from a dynamically scaled laboratory model
Limnology and Oceanography, 2010Co-Authors: Johanna H Rosman, Mark W Denny, Stephen G Monismith, Jeffrey R KoseffAbstract:The effects of a Macrocystis pyrifera Forest on currents and turbulence were investigated in a controlled laboratory setting using a dynamically matched 1/25-scale model. Two Kelp configurations with surface canopies and one without a surface canopy were considered. Profiles of mean velocities and turbulence statistics were measured using acoustic Doppler velocimeters. Since flow within the model Kelp Forest was very heterogeneous, spatially averaged forms of the governing equations were used for the analysis. Stress gradients were small compared with pressure gradient, drag, and acceleration terms of the momentum budget. A good model for Kelp drag is therefore required for simulating flow through a Kelp Forest, while the model for Reynolds and dispersive stresses is less critical. The bulk drag coefficient is highest at the up-current end of a Kelp Forest and decays with down-current distance as the velocity profile adjusts to the drag profile. Modeling a Kelp Forest as an array of vertical cylinders underestimates the net drag by a factor of 1.5 to 3 if a substantial surface canopy is present. Turbulence is generated predominantly by small-scale shear in Kelp wakes. Vertical mixing of scalars is expected to be significantly smaller than in the surrounding coastal ocean because of the combination of smaller turbulent eddies and reduced currents. The decrease in horizontal transport and vertical mixing within Kelp Forests may have important implications for nutrient availability to Kelp Forest organisms and may affect the dispersal or retention of their larvae and spores. Macrocystis pyrifera (Linneaus) Agardh (commonly Giant Kelp) Forests are important components of temperate coastal ecosystems, providing food and shelter for a diverse array of organisms. Many Kelp Forest organisms, including M. pyrifera itself, extract nutrients, plankton, or particulates from the water column. The availability of these quantities is determined by mean water motion primarily due to currents and by vertical and lateral mixing due to turbulence and spatial variations in the flow. Most Kelp Forest organisms release larvae or spores into the water column, and the paths and eventual destinations of these particles are also
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a field investigation into the effects of a Kelp Forest macrocystis pyrifera on coastal hydrodynamics and transport
Journal of Geophysical Research, 2007Co-Authors: Johanna H Rosman, Stephen G Monismith, Jeffrey R Koseff, Jamie GroverAbstract:[1] Macrocystis pyrifera (Giant Kelp) Forests form important habitats in temperate coastal regions. Hydrodynamics control the transport of nutrients, food particles, larvae and spores at scales ranging from boundary layers around individual blades to entire Kelp Forests. Our measurements include vertical profiles of current and temperature, and concurrent wave measurements, at a number of different locations in and around a Kelp Forest at Santa Cruz, California. We find that flow at the site is dominated by variations at diurnal and semidiurnal frequencies. A vertically sheared across-shore flow, consistent with flow driven by an across-shore density gradient, is thought to be important for exchange between the Kelp Forest and the surrounding coastal ocean. Within the Kelp Forest, currents are reduced by a factor that correlates with surface canopy coverage, higher frequency internal waves are damped, and onshore transport due to waves (Stokes drift) is estimated to be similar in magnitude to that due to currents. Richardson numbers within the Kelp Forest are higher than those outside the Kelp Forest and indicate that the water column within the Kelp Forest is usually stable to turbulence generation by mean velocity shear.
Hartvig Christie - One of the best experts on this subject based on the ideXlab platform.
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predators of the destructive sea urchin strongylocentrotus droebachiensis on the norwegian coast
Marine Ecology Progress Series, 2014Co-Authors: Kjell Magnus Norderhaug, Hartvig Christie, Morten Foldager Pedersen, Stein FredriksenAbstract:In central Norway, populations of the green sea urchin Strongylocentrotus droe- bachiensis are collapsing, but the factors controlling its population density have not yet been elucidated. Through field sampling, we identified several sea urchin predators and investigated their predation rates on recently settled S. droebachiensis in laboratory experiments. Tethering experiments in Kelp Forest and on barren ground study sites in the area where sea urchin popula- tions are collapsing confirmed predation by some of the predators tested in laboratory experi- ments. The edible crab Cancer pagurus was the most efficient sea urchin predator, and it was more abundant at Kelp Forest sites than on barren grounds. Stocks of C. pagurus have increased dramatically in central Norway since the 1990s, and predation by C. pagurus may contribute to the decline in sea urchin densities, allowing Kelp recovery and conferring resilience of the new Kelp Forest state.
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colonisation of Kelp imitations by epiphyte and holdfast fauna a study of mobility patterns
Marine Biology, 2002Co-Authors: Kjell Magnus Norderhaug, Hartvig Christie, Eli RindeAbstract:The Kelp Laminaria hyperborea provides a habitat for a diverse invertebrate community. Invertebrate abundance is particularly high in the Kelp holdfasts and associated with epiphytes on the stipes. We investigated colonisation patterns of this fauna on artificial substrata (holdfast and epiphyte mimics) exposed for short time periods in the Kelp Forest in two seasons, summer and late autumn. Within 7 days, 99 taxa common on natural Kelp substratum colonised the artificial substrata in large numbers, demonstrating high mobility and indicating that there may be a rapid exchange of individuals and species among algae. Gastropods and amphipods were the most abundant colonisers. In summer, a specific “epiphyte fauna” could be distinguished from a “holdfast fauna”, and species associated with epiphytes were significantly more abundant on the artificial substrata. Colonisation was more rapid in summer than in late autumn, which may be related to animal population density. The high dispersal rate can facilitate the interaction with other communities and with higher trophic levels in the Kelp-Forest food web.
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effects of removing sea urchins strongylocentrotus droebachiensis stability of the barren state and succession of Kelp Forest recovery in the east atlantic
Oecologia, 1996Co-Authors: Hans Petter Leinaas, Hartvig ChristieAbstract:Stability properties of the barren state of a Kelp Forest-sea urchin system were studied in northern Norway. The ability of the sea urchin Strongylocentrotus droebachiensis to maintain high population densities and recover from perturbations, and the succession of Kelp Forest revegetation, were studied experimentally by reducing the sea urchin density on a barren skerry. Additional information was obtained from community changes following a natural, but patchy, sea urchin mortality that varied between sites. On the barren grounds, high sea urchin densities (30 50 per m2) is maintained by annual recruitment. Severe reductions of sea urchin densities initiated luxuriant Kelp growth, while more moderate reductions allowed establishment of opportunistic algae (during spring and early summer), but no Kelps. Succession of algal growth, after the severe decline in sea urchin densities, followed a predictable pattern. At first the substrate was colonized by filamentous algae, but within few weeks they were outcompeted by the fast growing Kelp Laminaria saccharina. After 3–4 years of the removal experiment, the slower-growing, long-lived Kelp L. hyperborea became increasingly dominant. Increased food availability after reduction in sea urchin density led to increased individual growth of the remaining sea urchins. However, the population density did not increase, neither from recruitment nor immigration from adjacent areas with high sea urchin densities. Possibly, early establishment of a dense Kelp stand, may represent a breakpoint in the ability of sea urchins to reestablish a barren state. The ability of L. saccharina quickly to invade and monopolize an area may have both positive and negative effects on the succession towards the climax L. hyperborea Kelp Forest. Competitive interactions may slow the process, but development of a dense stand of L. saccharina will also reduce grazing risk on scattered recruits of the more slowly growing L. hyperborea.
Stein Fredriksen - One of the best experts on this subject based on the ideXlab platform.
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green gravel a novel restoration tool to combat Kelp Forest decline
Scientific Reports, 2020Co-Authors: Stein Fredriksen, Karen Filbeedexter, Kjell Magnus Norderhaug, Henning Steen, Torjan Bodvin, Melinda A Coleman, Frithjof Moy, Thomas WernbergAbstract:Kelp Forests are in decline globally and large-scale intervention could be required to halt the loss of these valuable ecosystems. To date Kelp Forest restoration has had limited success and been expensive and unable to address the increasing scale of ecosystem deterioration. Here we developed and tested a new approach: “green gravel”. Small rocks were seeded with Kelp and reared in the laboratory until 2–3 cm, before out-planting to the field. The out-planted Kelp had high survival and growth over 9 months, even when dropped from the surface. This technique is cheap, simple, and does not require scuba diving or highly trained field workers. It can be up-scaled to treat large areas or even used to introduce genes from more resilient Kelp populations onto vulnerable reefs. Green gravel thus overcomes some of the current major limitations of Kelp restoration and provides a promising new defense against Kelp Forest decline.
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changes in Kelp Forest biomass and depth distribution in kongsfjorden svalbard between 1996 1998 and 2012 2014 reflect arctic warming
Polar Biology, 2016Co-Authors: Inka Bartsch, Stein Fredriksen, Martin Paar, Max Schwanitz, Claudia Daniel, Haakon Hop, Christian WienckeAbstract:Arctic West Spitsbergen in Svalbard is currently experiencing gradual warming due to climate change showing decreased landfast sea-ice and increased sedimentation. In order to document possible changes in 2012–2014, we partially repeated a quantitative diving study from 1996 to 1998 in the Kelp Forest at Hansneset, Kongsfjorden, along a depth gradient between 0 and 15 m. The seaweed biomass increased between 1996/1998 and 2012/2013 with peak in Kelp biomass shifted to shallower depth, from 5 to 2.5 m. The Kelp biomass at 2.5 m was 8.2-fold higher in 2012/2013 (14 kg fresh biomass m−2) than in 1996/1998 and mostly due to an increase in the Kelp Laminaria digitata. This resulted in a very high density of 2- to 8-year-old Kelp (70 ind. m−2) and a high leaf area index of nearly 10 at 2.5 m. The entire zonation seemed to have shifted upwards to shallower depth, since also the lower depth limit of most dominant brown algae was shallower as well as the biomass maximum of several taxa. The cumulated annual photosynthetic active radiation at 15 m depth (42 mol m−2 year−1) determined the current depth limit of Kelps. Changes also resulted in an altered seaweed community pattern. The complex pattern of change was probably driven by opposing effects of co-acting environmental drivers, namely lack of ice-scouring, elongation of the open-water period and deterioration of the underwater irradiance climate. The results are interpreted as a consequence of Arctic warming probably reflecting a typical scenario for change along other Arctic shores in near future.
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predators of the destructive sea urchin strongylocentrotus droebachiensis on the norwegian coast
Marine Ecology Progress Series, 2014Co-Authors: Kjell Magnus Norderhaug, Hartvig Christie, Morten Foldager Pedersen, Stein FredriksenAbstract:In central Norway, populations of the green sea urchin Strongylocentrotus droe- bachiensis are collapsing, but the factors controlling its population density have not yet been elucidated. Through field sampling, we identified several sea urchin predators and investigated their predation rates on recently settled S. droebachiensis in laboratory experiments. Tethering experiments in Kelp Forest and on barren ground study sites in the area where sea urchin popula- tions are collapsing confirmed predation by some of the predators tested in laboratory experi- ments. The edible crab Cancer pagurus was the most efficient sea urchin predator, and it was more abundant at Kelp Forest sites than on barren grounds. Stocks of C. pagurus have increased dramatically in central Norway since the 1990s, and predation by C. pagurus may contribute to the decline in sea urchin densities, allowing Kelp recovery and conferring resilience of the new Kelp Forest state.
Michael H. Graham - One of the best experts on this subject based on the ideXlab platform.
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Effects of Local DeForestation on the Diversity and Structure of Southern California Giant Kelp Forest Food Webs
Ecosystems, 2004Co-Authors: Michael H. GrahamAbstract:It has been hypothesized that the high diversity of giant Kelp Forests is due primarily to the provision of energy and habitat by the giant Kelp ( Macrocystis pyrifera ). In this article, I use a 19-year-long Kelp Forest-monitoring data set from the Channel Islands National Park (a) to identify associations between subtidal species and Forested or deForested habitats, (b) to generate an idealized food web for Southern California giant Kelp Forests in order to identify the primary conduits of energy flow through the system, and (c) to determine changes in the diversity and complexity of this food web due to localized giant Kelp deForestation. A total of 275 common species were observed in the park between 1982 and 2000, of which 36% occurred significantly more often in Kelp-Forested areas than in deForested areas (that is, sea urchin barrens); 25 species were found exclusively in Forested areas. Most of these associations were clearly identified as trophic and/or structural associations with giant Kelp itself. The producer level of the food web was diverse, although giant Kelp apparently represents the greatest single source of fixed carbon through either direct grazing or the production of phytodetritus. Primary, secondary and tertiary consumer levels were also represented by numerous species, and generalist consumers were common. With deForestation, the source of primary production shifts from primarily Kelps to ephemeral microalgae, macroalgae, and phytoplankton. These results support the reliance of giant Kelp Forest food-web structure and diversity on the presence of the Forest itself.
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Kelp Forest ecosystems: Biodiversity, stability, resilience and future
Environmental Conservation, 2002Co-Authors: Robert S Steneck, Bruce J. Bourque, Debbie Corbett, Jon M. Erlandson, Michael H. Graham, James A. Estes, Mia J TegnerAbstract:Kelp Forests are phyletically diverse, structurally complex and highly productive components of coldwater rocky marine coastlines. This paper reviews the conditions in which Kelp Forests develop globally and where, why and at what rate they become deForested. The ecology and long archaeological history of Kelp Forests are examined through case studies from southern California, the Aleutian Islands and the western North Atlantic, well-studied locations that represent the widest possible range in Kelp Forest biodiversity. Global distribution of Kelp Forests is physiologically constrained by light at high latitudes and by nutrients, warm temperatures and other macrophytes at low latitudes. Within mid-latitude belts (roughly 40–60° latitude in both hemispheres) well-developed Kelp Forests are most threatened by herbivory, usually from sea urchins. Overfishing and extirpation of highly valued vertebrate apex predators often triggered herbivore population increases, leading to widespread Kelp deForestation. Such deForestations have the most profound and lasting impacts on species-depauperate systems, such as those in Alaska and the western North Atlantic. Globally urchin-induced deForestation has been increasing over the past 2–3 decades. Continued fishing down of coastal food webs has resulted in shifting harvesting targets from apex predators to their invertebrate prey, including Kelp-grazing herbivores. The recent global expansion of sea urchin harvesting has led to the widespread extirpation of this herbivore, and Kelp Forests have returned in some locations but, for the first time, these Forests are devoid of vertebrate apex predators. In the western North Atlantic, large predatory crabs have recently filled this void and they have become the new apex predator in this system. Similar shifts from fish- to crab-dominance may have occurred in coastal zones of the United Kingdom and Japan, where large predatory finfish were extirpated long ago. Three North American case studies of Kelp Forests were examined to determine their long history with humans and project the status of future Kelp Forests to the year 2025. Fishing impacts on Kelp Forest systems have been both profound and much longer in duration than previously thought. Archaeological data suggest that coastal peoples exploited Kelp Forest organisms for thousands of years, occasionally resulting in localized losses of apex predators, outbreaks of sea urchin populations and probably small-scale deForestation. Over the past two centuries, commercial exploitation for export led to the extirpation of sea urchin predators, such as the sea otter in the North Pacific and predatory fishes like the cod in the North Atlantic. The large-scale removal of predators for export markets increased sea urchin abundances and promoted the decline of Kelp Forests over vast areas. Despite southern California having one of the longest known associations with coastal Kelp Forests, widespread deForestation is rare. It is possible that functional redundancies among predators and herbivores make this most diverse system most stable. Such biodiverse Kelp Forests may also resist invasion from non-native species. In the species-depauperate western North Atlantic, introduced algal competitors carpet the benthos and threaten future Kelp dominance. There, other non-native herbivores and predators have become established and dominant components of this system. Climate changes have had measurable impacts on Kelp Forest ecosystems and efforts to control the emission of greenhouse gasses should be a global priority. However, overfishing appears to be the greatest manageable threat to Kelp Forest ecosystems over the 2025 time horizon. Management should focus on minimizing fishing impacts and restoring populations of functionally important species in these systems.