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Ladd E Johnson - One of the best experts on this subject based on the ideXlab platform.
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dynamics of recruitment and establishment of the invasive seaweed codium fragile within an eelgrass habitat
Marine Biology, 2016Co-Authors: Christopher W Mckindsey, Annick Drouin, Ladd E JohnsonAbstract:Knowledge of the potential distribution (i.e. abundance and spatial extent) of an invasive species is important to estimating its potential impacts on recipient communities. Most previous studies have focused on the potential spatial extent of invasive species populations at regional scales, but little is known on how species successfully recruit and establish at more local scales. In this study, we examined how recruitment of the green alga Codium fragile ssp. fragile (hereafter Codium) can vary spatially and the environmental factors associated with Codium establishment in eelgrass (Zostera marina) beds. Standardized recruitment blocks (65 blocks in a 720 × 240 m2 grid) were used to monitor the number of Codium recruits, juveniles and adults over 2 years. Environmental factors (depth, relative water flow, light and temperature) and attributes of the surrounding macrophyte assemblage (eelgrass density, eelgrass length, Codium biomass) were also measured. Recruitment occurred on all blocks or nearby artificial structures (i.e. buoys) and mainly originated from button stages (i.e. female gametes or utricles). Contrary to other studies, the abundance of Codium (recruits, juveniles and adults) was best predicted by the density of the native canopy-forming species, Z. marina, which highlights a positive interaction between native and non-native canopy-forming species. Seasonal variation in recruitment was observed; it was lower during the summer. Recruitment did not show any distinct spatial pattern (e.g. gradient or patch), but the same spatial pattern of recruitment was observed every sampling date, suggesting that there are “hotspots” for recruitment. In general, the total number of Codium fronds observed on a block at the end of the experiment was positively correlated with the cumulative number of recruits. However, recruitment occurred on some blocks but recruits never grew, suggesting that some environmental factors limit Codium distribution and abundance in eelgrass beds. Overall, the assessment of Codium recruitment over 2 years showed that the colonization of suitable locations by Codium within seagrass beds may take several years and that some factors may not only limit, but also inhibit Codium expansion within eelgrass beds.
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roles of dispersal mode recipient environment and disturbance in the secondary spread of the invasive seaweed codium fragile
Biological Invasions, 2015Co-Authors: Karine Gagnon, Christopher W Mckindsey, Ladd E JohnsonAbstract:Secondary spread largely determines the distribution and success of invasive species and depends ultimately on the capacity of the invader to disperse and colonise over multiple scales. Spread of the invasive seaweed Codium fragile ssp. fragile (Codium) can occur through the dispersal of vegetative fragments, which can be buoyant or non-buoyant depending on environmental conditions. This study examined the factors influencing the dispersal, settlement, and establishment of these two types of propagules in eelgrass (Zosteramarina) meadows of iles de la Madeleine, Canada, where Codium lives epiphytically on eelgrass rhizomes. To measure dispersal, ~1,400 Codium fragments were marked, released, and tracked under different hydrodynamic conditions in areas of high and low eelgrass density. Under all conditions, buoyant fragments dispersed one to two orders of magnitude further than non-buoyant fragments. Dispersal distance was positively correlated with wind speed (a proxy for surface currents in this system) for buoyant fragments and with current speed for non-buoyant fragments. For the latter, dispersal distance was also negatively correlated with eelgrass height and density. Natural deposition of drifting fragments in experimentally-manipulated eelgrass meadows was variable in space and time, but was not affected by eelgrass shoot density. Experimental disturbance of eelgrass meadows enhanced the density, biomass, and percent cover of Codium, suggesting that the exposure of eelgrass rhizomes by natural or anthropogenic disturbance promotes invasion by Codium. Our results highlight the importance of small-scale field experiments in determining the local factors affecting the spread of invasive species.
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detecting the impacts of notorious invaders experiments versus observations in the invasion of eelgrass meadows by the green seaweed codium fragile
Oecologia, 2012Co-Authors: Christopher W Mckindsey, Annick Drouin, Ladd E JohnsonAbstract:Biological invasions can vary in the extent of their effects on indigenous communities but predicting impacts for particular systems remains difficult. In coastal marine ecosystems, the green seaweed Codium fragile ssp. fragile is a notorious invader with its reputation based on studies conducted largely on rocky shores. The green seaweed has recently invaded soft-bottom eelgrass communities by attaching epiphytically to eelgrass (Zostera marina) rhizomes, thereby creating the potential for disruption of these coastal habitats through competition or disturbance. We investigated the effect of this invader on various aspects of eelgrass performance (shoot density and length, shoot growth, above- and below-ground biomass, carbohydrate storage) using both small-scale manipulative and large-scale observational experiments. Manipulative experiments that varied Codium abundance demonstrated clear negative effects over a 4-month period on shoot density and carbohydrate reserves, but only for high, but realistic, Codium biomass levels. Light levels were much lower under canopies for high and medium density Codium treatments relative to low and control Codium cover treatments, suggesting that shading may influence eelgrass growing under the algal cover. In contrast, these effects were either not detectable or very weak when examined correlatively with field surveys conducted at larger spatial scales, even for sites that had been invaded for over 4 years. It is premature to extend generalizations of Codium’s impact derived from studies in other systems to eelgrass communities; further efforts are required to assess the long-term threats that the alga poses to this ecosystem. This study demonstrates the need to investigate impacts of invasions over multiple scales, especially those that incorporate the temporal and spatial heterogeneity of the invader’s abundance.
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higher abundance and diversity in faunal assemblages with the invasion of codium fragile ssp fragile in eelgrass meadows
Marine Ecology Progress Series, 2011Co-Authors: Annick Drouin, Christopher W Mckindsey, Ladd E JohnsonAbstract:The present study examined how species-specific attributes of the invasive alga Codium fragile ssp. fragile (hereafter Codium) and eelgrass Zostera marina influenced faunal assemblages associated with eelgrass ecosystems in iles de la Madeleine, eastern Canada. Direct association of species with Codium (<1 m) was evaluated and compared to eelgrass faunal assemblages from invaded beds. Potential neighborhood effects (ca. 10 m) were assessed by comparing invertebrates associated with eelgrass in invaded and non-invaded beds. The influence of Codium on more mobile species was evaluated by comparing fish assemblages associated with macrophytes in invaded and non-invaded beds. In addition, species-area relationships for low mobility species associated with Codium were contrasted between beds where Codium or eelgrass was the dominant structuring macrophyte. Codium had distinct invertebrate species assemblages, as there was a greater abun- dance and diversity of invertebrates associated with Codium than with eelgrass, and multivariate assemblage structure differed between macrophyte types. In contrast, no neighborhood patterns were observed as invertebrate assemblages associated with eelgrass did not differ between invaded and non-invaded beds, suggesting that the mechanisms that account for differences between the invertebrate assemblages are a function of the macrophyte's nature and operate at small spatial scales. Fish community structure differed between invaded and non-invaded beds, largely due to a greater abundance of 2 fishes, Apeltes quadracus and Tautogolabrus adspersus, in invaded beds. Epifaunal abundance and species richness were positively correlated with Codium thallus biomass, and the abundance relative to biomass correlation was greatest where Codium was the dominant macrophyte. Experimental manipulation of thallus structure to create straight or branched Codium fronds with similar surface area showed that associated invertebrate and gastropod abundance was not influenced by this factor and indicated that factors other than macrostructure complexity influ- enced the presence of epifauna on the introduced alga. Overall, the present study suggests that the invasion of eelgrass beds by Codium increases faunal density and diversity. However, longer-term effects of Codium invasion in this and other eelgrass ecosystems require further assessment, as the severity of the invasion effects on faunal communities likely depends on the interaction between Codium and eelgrass.
Annick Drouin - One of the best experts on this subject based on the ideXlab platform.
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dynamics of recruitment and establishment of the invasive seaweed codium fragile within an eelgrass habitat
Marine Biology, 2016Co-Authors: Christopher W Mckindsey, Annick Drouin, Ladd E JohnsonAbstract:Knowledge of the potential distribution (i.e. abundance and spatial extent) of an invasive species is important to estimating its potential impacts on recipient communities. Most previous studies have focused on the potential spatial extent of invasive species populations at regional scales, but little is known on how species successfully recruit and establish at more local scales. In this study, we examined how recruitment of the green alga Codium fragile ssp. fragile (hereafter Codium) can vary spatially and the environmental factors associated with Codium establishment in eelgrass (Zostera marina) beds. Standardized recruitment blocks (65 blocks in a 720 × 240 m2 grid) were used to monitor the number of Codium recruits, juveniles and adults over 2 years. Environmental factors (depth, relative water flow, light and temperature) and attributes of the surrounding macrophyte assemblage (eelgrass density, eelgrass length, Codium biomass) were also measured. Recruitment occurred on all blocks or nearby artificial structures (i.e. buoys) and mainly originated from button stages (i.e. female gametes or utricles). Contrary to other studies, the abundance of Codium (recruits, juveniles and adults) was best predicted by the density of the native canopy-forming species, Z. marina, which highlights a positive interaction between native and non-native canopy-forming species. Seasonal variation in recruitment was observed; it was lower during the summer. Recruitment did not show any distinct spatial pattern (e.g. gradient or patch), but the same spatial pattern of recruitment was observed every sampling date, suggesting that there are “hotspots” for recruitment. In general, the total number of Codium fronds observed on a block at the end of the experiment was positively correlated with the cumulative number of recruits. However, recruitment occurred on some blocks but recruits never grew, suggesting that some environmental factors limit Codium distribution and abundance in eelgrass beds. Overall, the assessment of Codium recruitment over 2 years showed that the colonization of suitable locations by Codium within seagrass beds may take several years and that some factors may not only limit, but also inhibit Codium expansion within eelgrass beds.
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detecting the impacts of notorious invaders experiments versus observations in the invasion of eelgrass meadows by the green seaweed codium fragile
Oecologia, 2012Co-Authors: Christopher W Mckindsey, Annick Drouin, Ladd E JohnsonAbstract:Biological invasions can vary in the extent of their effects on indigenous communities but predicting impacts for particular systems remains difficult. In coastal marine ecosystems, the green seaweed Codium fragile ssp. fragile is a notorious invader with its reputation based on studies conducted largely on rocky shores. The green seaweed has recently invaded soft-bottom eelgrass communities by attaching epiphytically to eelgrass (Zostera marina) rhizomes, thereby creating the potential for disruption of these coastal habitats through competition or disturbance. We investigated the effect of this invader on various aspects of eelgrass performance (shoot density and length, shoot growth, above- and below-ground biomass, carbohydrate storage) using both small-scale manipulative and large-scale observational experiments. Manipulative experiments that varied Codium abundance demonstrated clear negative effects over a 4-month period on shoot density and carbohydrate reserves, but only for high, but realistic, Codium biomass levels. Light levels were much lower under canopies for high and medium density Codium treatments relative to low and control Codium cover treatments, suggesting that shading may influence eelgrass growing under the algal cover. In contrast, these effects were either not detectable or very weak when examined correlatively with field surveys conducted at larger spatial scales, even for sites that had been invaded for over 4 years. It is premature to extend generalizations of Codium’s impact derived from studies in other systems to eelgrass communities; further efforts are required to assess the long-term threats that the alga poses to this ecosystem. This study demonstrates the need to investigate impacts of invasions over multiple scales, especially those that incorporate the temporal and spatial heterogeneity of the invader’s abundance.
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higher abundance and diversity in faunal assemblages with the invasion of codium fragile ssp fragile in eelgrass meadows
Marine Ecology Progress Series, 2011Co-Authors: Annick Drouin, Christopher W Mckindsey, Ladd E JohnsonAbstract:The present study examined how species-specific attributes of the invasive alga Codium fragile ssp. fragile (hereafter Codium) and eelgrass Zostera marina influenced faunal assemblages associated with eelgrass ecosystems in iles de la Madeleine, eastern Canada. Direct association of species with Codium (<1 m) was evaluated and compared to eelgrass faunal assemblages from invaded beds. Potential neighborhood effects (ca. 10 m) were assessed by comparing invertebrates associated with eelgrass in invaded and non-invaded beds. The influence of Codium on more mobile species was evaluated by comparing fish assemblages associated with macrophytes in invaded and non-invaded beds. In addition, species-area relationships for low mobility species associated with Codium were contrasted between beds where Codium or eelgrass was the dominant structuring macrophyte. Codium had distinct invertebrate species assemblages, as there was a greater abun- dance and diversity of invertebrates associated with Codium than with eelgrass, and multivariate assemblage structure differed between macrophyte types. In contrast, no neighborhood patterns were observed as invertebrate assemblages associated with eelgrass did not differ between invaded and non-invaded beds, suggesting that the mechanisms that account for differences between the invertebrate assemblages are a function of the macrophyte's nature and operate at small spatial scales. Fish community structure differed between invaded and non-invaded beds, largely due to a greater abundance of 2 fishes, Apeltes quadracus and Tautogolabrus adspersus, in invaded beds. Epifaunal abundance and species richness were positively correlated with Codium thallus biomass, and the abundance relative to biomass correlation was greatest where Codium was the dominant macrophyte. Experimental manipulation of thallus structure to create straight or branched Codium fronds with similar surface area showed that associated invertebrate and gastropod abundance was not influenced by this factor and indicated that factors other than macrostructure complexity influ- enced the presence of epifauna on the introduced alga. Overall, the present study suggests that the invasion of eelgrass beds by Codium increases faunal density and diversity. However, longer-term effects of Codium invasion in this and other eelgrass ecosystems require further assessment, as the severity of the invasion effects on faunal communities likely depends on the interaction between Codium and eelgrass.
Christopher W Mckindsey - One of the best experts on this subject based on the ideXlab platform.
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dynamics of recruitment and establishment of the invasive seaweed codium fragile within an eelgrass habitat
Marine Biology, 2016Co-Authors: Christopher W Mckindsey, Annick Drouin, Ladd E JohnsonAbstract:Knowledge of the potential distribution (i.e. abundance and spatial extent) of an invasive species is important to estimating its potential impacts on recipient communities. Most previous studies have focused on the potential spatial extent of invasive species populations at regional scales, but little is known on how species successfully recruit and establish at more local scales. In this study, we examined how recruitment of the green alga Codium fragile ssp. fragile (hereafter Codium) can vary spatially and the environmental factors associated with Codium establishment in eelgrass (Zostera marina) beds. Standardized recruitment blocks (65 blocks in a 720 × 240 m2 grid) were used to monitor the number of Codium recruits, juveniles and adults over 2 years. Environmental factors (depth, relative water flow, light and temperature) and attributes of the surrounding macrophyte assemblage (eelgrass density, eelgrass length, Codium biomass) were also measured. Recruitment occurred on all blocks or nearby artificial structures (i.e. buoys) and mainly originated from button stages (i.e. female gametes or utricles). Contrary to other studies, the abundance of Codium (recruits, juveniles and adults) was best predicted by the density of the native canopy-forming species, Z. marina, which highlights a positive interaction between native and non-native canopy-forming species. Seasonal variation in recruitment was observed; it was lower during the summer. Recruitment did not show any distinct spatial pattern (e.g. gradient or patch), but the same spatial pattern of recruitment was observed every sampling date, suggesting that there are “hotspots” for recruitment. In general, the total number of Codium fronds observed on a block at the end of the experiment was positively correlated with the cumulative number of recruits. However, recruitment occurred on some blocks but recruits never grew, suggesting that some environmental factors limit Codium distribution and abundance in eelgrass beds. Overall, the assessment of Codium recruitment over 2 years showed that the colonization of suitable locations by Codium within seagrass beds may take several years and that some factors may not only limit, but also inhibit Codium expansion within eelgrass beds.
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roles of dispersal mode recipient environment and disturbance in the secondary spread of the invasive seaweed codium fragile
Biological Invasions, 2015Co-Authors: Karine Gagnon, Christopher W Mckindsey, Ladd E JohnsonAbstract:Secondary spread largely determines the distribution and success of invasive species and depends ultimately on the capacity of the invader to disperse and colonise over multiple scales. Spread of the invasive seaweed Codium fragile ssp. fragile (Codium) can occur through the dispersal of vegetative fragments, which can be buoyant or non-buoyant depending on environmental conditions. This study examined the factors influencing the dispersal, settlement, and establishment of these two types of propagules in eelgrass (Zosteramarina) meadows of iles de la Madeleine, Canada, where Codium lives epiphytically on eelgrass rhizomes. To measure dispersal, ~1,400 Codium fragments were marked, released, and tracked under different hydrodynamic conditions in areas of high and low eelgrass density. Under all conditions, buoyant fragments dispersed one to two orders of magnitude further than non-buoyant fragments. Dispersal distance was positively correlated with wind speed (a proxy for surface currents in this system) for buoyant fragments and with current speed for non-buoyant fragments. For the latter, dispersal distance was also negatively correlated with eelgrass height and density. Natural deposition of drifting fragments in experimentally-manipulated eelgrass meadows was variable in space and time, but was not affected by eelgrass shoot density. Experimental disturbance of eelgrass meadows enhanced the density, biomass, and percent cover of Codium, suggesting that the exposure of eelgrass rhizomes by natural or anthropogenic disturbance promotes invasion by Codium. Our results highlight the importance of small-scale field experiments in determining the local factors affecting the spread of invasive species.
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detecting the impacts of notorious invaders experiments versus observations in the invasion of eelgrass meadows by the green seaweed codium fragile
Oecologia, 2012Co-Authors: Christopher W Mckindsey, Annick Drouin, Ladd E JohnsonAbstract:Biological invasions can vary in the extent of their effects on indigenous communities but predicting impacts for particular systems remains difficult. In coastal marine ecosystems, the green seaweed Codium fragile ssp. fragile is a notorious invader with its reputation based on studies conducted largely on rocky shores. The green seaweed has recently invaded soft-bottom eelgrass communities by attaching epiphytically to eelgrass (Zostera marina) rhizomes, thereby creating the potential for disruption of these coastal habitats through competition or disturbance. We investigated the effect of this invader on various aspects of eelgrass performance (shoot density and length, shoot growth, above- and below-ground biomass, carbohydrate storage) using both small-scale manipulative and large-scale observational experiments. Manipulative experiments that varied Codium abundance demonstrated clear negative effects over a 4-month period on shoot density and carbohydrate reserves, but only for high, but realistic, Codium biomass levels. Light levels were much lower under canopies for high and medium density Codium treatments relative to low and control Codium cover treatments, suggesting that shading may influence eelgrass growing under the algal cover. In contrast, these effects were either not detectable or very weak when examined correlatively with field surveys conducted at larger spatial scales, even for sites that had been invaded for over 4 years. It is premature to extend generalizations of Codium’s impact derived from studies in other systems to eelgrass communities; further efforts are required to assess the long-term threats that the alga poses to this ecosystem. This study demonstrates the need to investigate impacts of invasions over multiple scales, especially those that incorporate the temporal and spatial heterogeneity of the invader’s abundance.
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higher abundance and diversity in faunal assemblages with the invasion of codium fragile ssp fragile in eelgrass meadows
Marine Ecology Progress Series, 2011Co-Authors: Annick Drouin, Christopher W Mckindsey, Ladd E JohnsonAbstract:The present study examined how species-specific attributes of the invasive alga Codium fragile ssp. fragile (hereafter Codium) and eelgrass Zostera marina influenced faunal assemblages associated with eelgrass ecosystems in iles de la Madeleine, eastern Canada. Direct association of species with Codium (<1 m) was evaluated and compared to eelgrass faunal assemblages from invaded beds. Potential neighborhood effects (ca. 10 m) were assessed by comparing invertebrates associated with eelgrass in invaded and non-invaded beds. The influence of Codium on more mobile species was evaluated by comparing fish assemblages associated with macrophytes in invaded and non-invaded beds. In addition, species-area relationships for low mobility species associated with Codium were contrasted between beds where Codium or eelgrass was the dominant structuring macrophyte. Codium had distinct invertebrate species assemblages, as there was a greater abun- dance and diversity of invertebrates associated with Codium than with eelgrass, and multivariate assemblage structure differed between macrophyte types. In contrast, no neighborhood patterns were observed as invertebrate assemblages associated with eelgrass did not differ between invaded and non-invaded beds, suggesting that the mechanisms that account for differences between the invertebrate assemblages are a function of the macrophyte's nature and operate at small spatial scales. Fish community structure differed between invaded and non-invaded beds, largely due to a greater abundance of 2 fishes, Apeltes quadracus and Tautogolabrus adspersus, in invaded beds. Epifaunal abundance and species richness were positively correlated with Codium thallus biomass, and the abundance relative to biomass correlation was greatest where Codium was the dominant macrophyte. Experimental manipulation of thallus structure to create straight or branched Codium fronds with similar surface area showed that associated invertebrate and gastropod abundance was not influenced by this factor and indicated that factors other than macrostructure complexity influ- enced the presence of epifauna on the introduced alga. Overall, the present study suggests that the invasion of eelgrass beds by Codium increases faunal density and diversity. However, longer-term effects of Codium invasion in this and other eelgrass ecosystems require further assessment, as the severity of the invasion effects on faunal communities likely depends on the interaction between Codium and eelgrass.
Robert Eric Scheibling - One of the best experts on this subject based on the ideXlab platform.
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role of grazing by sea urchins strongylocentrotus droebachiensis in regulating the invasive alga codium fragile ssp tomentosoides in nova scotia
Marine Ecology Progress Series, 2005Co-Authors: Catherine B T Sumi, Robert Eric ScheiblingAbstract:To assess the potential of herbivory in regulating the invasive green alga Codium frag- ile ssp. tomentosoides, field and laboratory experiments were conducted with the green sea urchin Strongylocentrotus droebachiensis in Nova Scotia, Canada. In the field, urchins at different densities (0, 50 and 100 urchins m -2 ) were caged on boulders covered with a canopy of either the kelp Lami- naria longicruris, Codium, or a mixture of both species for 13 wk. In the treatment with Laminaria only, ∼90% of the canopy was removed within 34 and 75 d in cages with 100 and 50 urchins m -2 , respectively. In contrast, Codium cover decreased by ∼20% at both levels of urchin density in the treatment with Codium only, and did not differ significantly from the control (no urchins) at the end of the experiment. In the mixed canopy treatment, urchins showed a preference for Laminaria, con- suming 90% of kelp cover within 39 and 54 d (at 100 and 50 urchins m -2 , respectively), while Codium cover increased gradually. Urchins grazed turf-forming red algae in all treatments, although in treat- ments with Laminaria, intensive grazing of turf only occurred once kelp was completely consumed. In the laboratory, urchins fed single diets of Laminaria or Codium for 8 wk had similar grazing rates (∼0.20 dry weight g urchin -1 d -1 ), while urchins fed a mixed diet consumed 2 times more kelp (0.15 g urchin -1 d -1 ) than Codium (0.08 g urchin -1 d -1 ). These experimental results indicate that urchins prefer kelp but will consume Codium when other algal foods are not available. We predict that urchin aggregations encountering mixed stands of kelp and Codium will initially graze the kelp and turf algae, creating patches of Codium that ultimately will be consumed as well.
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growth and survival of the invasive green alga codium fragile ssp tomentosoides in tide pools on a rocky shore in nova scotia
Botanica Marina, 2003Co-Authors: Chantale Begin, Robert Eric ScheiblingAbstract:We monitored growth and survival of the invasive green alga Codium fragile ssp. tomentosoides, and physical environmental factors (temperature, water flow, wave force), in eight tide pools in the low/mid intertidal zone on a rocky shore near Halifax, Nova Scotia, Canada, from May to October 1999. Growth in thallus length of individually tagged plants generally increased from May to a peak in August, and did not differ between pools. Growth in circumference also increased during this period but differed significantly between pools in each month, as did growth in fresh weight (estimated from length and circumference). An index of thallus bushiness (circumference-to-length ratio) increased gradually between May and August and then decreased in September. Fragmentation of Codium occurred throughout the summer, as evidenced by tagged plants that decreased in length, and the percentage of fragmenting plants nearly doubled between August and October as wave forces increased. Growth rate based only on plants that increased in length (i.e., did not undergo substantial fragmentation) was positively correlated with pool temperature and peaked in August--September (5.6 cm/month) when temperatures were warmest (16 °C). Survival of tagged Codium did not differ between pools each month and decreased exponentially over the study to 30 % by October. Survival of Codium in tide pools was negatively related to bushiness index, suggesting that large bushy plants are more likely to be dislodged by wave forces. Mortality of Codium was offset by recruitment between May and August, such that plant density remained relatively stable in four of five pools, and increased markedly in one other. Our study demonstrates that Codium has become successfully established in wave-exposed intertidal habitats at the northern limit of its current geographic range in the northwest Atlantic.
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feeding growth and reproduction of sea urchins strongylocentrotus droebachiensis on single and mixed diets of kelp laminaria spp and the invasive alga codium fragile ssp tomentosoides
Marine Biology, 2001Co-Authors: Robert Eric Scheibling, S X AnthonyAbstract:Since its introduction to Nova Scotia in the early 1990s, the invasive green alga Codium fragile ssp. tomentosoides has spread rapidly to become a dominant and persistent component of seaweed assemblages in the rocky subtidal zone. To examine the potential of sea urchins (Strongylocentrotus droebachiensis) to regulate Codium, and the potential of the alga to support urchin growth and reproduction, we fed urchins Codium and/or kelp (Laminaria spp., a high quality and preferred native food) in the laboratory for 11 months. Urchins showed a strong and active preference for kelp: they consumed more Laminaria than Codium (as dry weight) in single and mixed diet treatments. Urchins fed only Codium consumed 3.5 times more of the alga than those on a mixed diet, but did not increase their feeding rate in winter when kelp consumption was greatest. Laminaria was consumed at the same rate in single and mixed diets, indicating that the presence of an alternative food had no effect on kelp consumption. Survival and growth (change in test diameter) were lowest on the Codium diet, although the differences among diets were not statistically significant. Urchins on the Codium diet showed no gonadal production over the annual reproductive cycle, compared to a marked rise in gonad index on the Laminaria and mixed diets. Our results indicate that Codium is an unattractive, unpalatable and poor quality food, which is not readily consumed by urchins. Thus we predict that urchins at moderate densities will be much more likely to graze kelp than Codium in mixed stands, creating a mosaic of Codium patches and barren areas. At high densities, however, urchins are likely to destructively graze all seaweeds, although dense stands of the invasive alga may prolong the widespread formation of barrens.
George A Olah - One of the best experts on this subject based on the ideXlab platform.
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ab initio giao mp2 calculated structures and 11 b 13 c nmr chemical shift relationship in hypercoordinate onium carbonium dications and isoelectronic onium boronium cations
Proceedings of the National Academy of Sciences of the United States of America, 2002Co-Authors: Golam Rasul, G Surya K Prakash, George A OlahAbstract:The boronium–carbonium ion continuum was extended to include hypercoordinated onium-carbonium dications and the isoelectronic onium-boronium cation analogs. Structures and 13C and 11B NMR chemical shifts of the onium-carbonium dications and the corresponding isoelectronic and isostructural onium-boronium cations were calculated with the ab initio/GIAO-MP2 method. The data show a good linear correlation between 11B and 13C NMR chemical shifts, indicating that the same factors that determine the chemical shifts of the boron nuclei also govern the chemical shifts of carbon nuclei of these hypercoordinated onium ions and dications.