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1.
Oecologia ; 204(3): 575-588, 2024 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-38376632

RESUMO

The role of facilitation in shaping natural communities has primarily been studied in the context of plant assemblages, while its relevance for mobile animals remains less understood. Our study investigates whether reciprocal interspecific facilitation may exist between fire ants (Solenopsis richteri) and cavies (Cavia aperea), two mobile animals, in the SW Atlantic coast brackish marshes. Field samples showed a spatial association between ant mounds and cavies, and that ants prefer to use cavy runways for movement within the marsh. Through experiments involving transplanting the dominant plant, cordgrass (Spartina densiflora), and manipulating cavy presence in areas with and without ant mounds, we observed that cavies forage extensively (and defecate more) near ant mounds. The ants actively remove cavy droppings in their mound vicinity. These ant activities and interactions with cavy droppings led to reduced moisture and organic content while increasing nitrate and phosphate levels in marsh sediment. Consequently, this enhanced plant growth, indirectly facilitating the cavies, which preferred consuming vegetation near ant mounds. These cascading indirect effects persisted over time; even four months after cavies left the marshes, transplanted plants near ant mounds remained larger and exhibited more leaf senescence when exposed to cavy herbivory. Therefore, the networks of positive interactions appear to generate simultaneous selection among species (populations), promoting coexistence within the community. Although complex, these reciprocal facilitative effects among mobile animals may be more common than currently believed and should be further studied to gain a better understanding of the underlying mechanisms driving species coexistence in natural communities.


Assuntos
Formigas , Áreas Alagadas , Animais , Cobaias , Herbivoria , Plantas , Mamíferos
2.
Nat Commun ; 14(1): 8500, 2023 Dec 22.
Artigo em Inglês | MEDLINE | ID: mdl-38135682

RESUMO

Coastal vegetated ecosystems are acknowledged for their capacity to sequester organic carbon (OC), known as blue C. Yet, blue C global accounting is incomplete, with major gaps in southern hemisphere data. It also shows a large variability suggesting that the interaction between environmental and biological drivers is important at the local scale. In southwest Atlantic salt marshes, to account for the space occupied by crab burrows, it is key to avoid overestimates. Here we found that southern southwest Atlantic salt marshes store on average 42.43 (SE = 27.56) Mg OC·ha-1 (40.74 (SE = 2.7) in belowground) and bury in average 47.62 g OC·m-2·yr-1 (ranging from 7.38 to 204.21). Accretion rates, granulometry, plant species and burrowing crabs were identified as the main factors in determining belowground OC stocks. These data lead to an updated global estimation for stocks in salt marshes of 185.89 Mg OC·ha-1 (n = 743; SE = 4.92) and a C burial rate of 199.61 g OC·m-2·yr-1 (n = 193; SE = 16.04), which are lower than previous estimates.


Assuntos
Braquiúros , Áreas Alagadas , Animais , Ecossistema , Carbono , Sequestro de Carbono
3.
Nat Commun ; 14(1): 1809, 2023 03 31.
Artigo em Inglês | MEDLINE | ID: mdl-37002217

RESUMO

Plant productivity varies due to environmental heterogeneity, and theory suggests that plant diversity can reduce this variation. While there is strong evidence of diversity effects on temporal variability of productivity, whether this mechanism extends to variability across space remains elusive. Here we determine the relationship between plant diversity and spatial variability of productivity in 83 grasslands, and quantify the effect of experimentally increased spatial heterogeneity in environmental conditions on this relationship. We found that communities with higher plant species richness (alpha and gamma diversity) have lower spatial variability of productivity as reduced abundance of some species can be compensated for by increased abundance of other species. In contrast, high species dissimilarity among local communities (beta diversity) is positively associated with spatial variability of productivity, suggesting that changes in species composition can scale up to affect productivity. Experimentally increased spatial environmental heterogeneity weakens the effect of plant alpha and gamma diversity, and reveals that beta diversity can simultaneously decrease and increase spatial variability of productivity. Our findings unveil the generality of the diversity-stability theory across space, and suggest that reduced local diversity and biotic homogenization can affect the spatial reliability of key ecosystem functions.


Assuntos
Ecossistema , Pradaria , Biomassa , Biodiversidade , Reprodutibilidade dos Testes , Plantas
4.
Sci Rep ; 12(1): 10876, 2022 06 27.
Artigo em Inglês | MEDLINE | ID: mdl-35760984

RESUMO

Demersal fisheries are one of the top anthropic stressors in marine environments. In the long term, some species are more vulnerable to fishery impacts than others, which can lead to permanent changes on the food web. The trophic relationships between predator and prey constitute the food web and it represents a network of the energy channels in an ecosystem. In turn, the network structure influences ecosystem diversity and stability. The first aim of this study was to describe for the first time the food web of the San Jorge Gulf (Patagonia Argentina) with high resolution, i.e. to the species level when information is available. The San Jorge Gulf was subject to intense fisheries thus our second aim is to analyse the food web structure with and without fishery to evaluate if the bottom-trawl industrial fishery altered the network structure and stability. We used several network metrics like: mean trophic level, omnivory, modularity and quasi-sign stability. We included these metrics because they are related to stability and can be evaluated using predator diets that can weight the links between predators and prey. The network presented 165 species organized in almost five trophic levels. The inclusion of a fishery node adds 69 new trophic links. All weighted and unweighted metrics showed differences between the two networks, reflecting a decrease in stability when fishery was included in the system. Thus, our results suggested a probable change of state of the system. The observed changes in species abundances since the fishery was established, could represent the state change predicted by network analysis. Our results suggests that changes in the stability of food webs can be used to evaluate the impacts of human activity on ecosystems.


Assuntos
Pesqueiros , Cadeia Alimentar , Dieta , Ecossistema , Atividades Humanas , Humanos
5.
Ambio ; 49(2): 541-556, 2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-31301003

RESUMO

Primary production hotspots in the marine environment occur where the combination of light, turbulence, temperature and nutrients makes the proliferation of phytoplankton possible. Satellite-derived surface chlorophyll-a distributions indicate that these conditions are frequently associated with sharp water mass transitions named "marine fronts". Given the link between primary production, consumers and ecosystem functions, marine fronts could play a key role in the production of ecosystem services (ES). Using the shelf break front in the Argentine Sea as a study case, we show that the high primary production found in the front is the main ecological feature that supports the production of tangible (fisheries) and intangible (recreation, regulation of atmospheric gases) marine ES and the reason why the provision of ES in the Argentine Sea concentrates there. This information provides support to satellite chlorophyll as a good indicator of multiple marine ES. We suggest that marine fronts could be considered as marine ES hot spots.


Assuntos
Ecossistema , Pesqueiros , Fitoplâncton , Temperatura
6.
Mar Environ Res ; 146: 71-79, 2019 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-30922605

RESUMO

Using C and N isotopic signatures of food web components, we evaluated the land-marine coupling through nutrient flows and the likely changes in the food web structure in tidal channels with contrasting anthropogenic nutrient inputs at a semi desert-macrotidal coastal system (northern Argentine Patagonia). The results showed an increase in the δ13C signatures of primary producers and in the δ15N signatures in all levels of the benthic food web, from primary producers to predators, with possible changes in the relative contribution of primary food sources for consumer in the tidal channel with high anthropogenic N input. This is an example on the extent of the distribution of anthropogenic N into natural systems, flowing through the food web from terrestrial origin to coastal marine components.


Assuntos
Isótopos de Carbono/análise , Eutrofização , Isótopos de Nitrogênio/análise , Animais , Argentina , Ecossistema , Monitoramento Ambiental/métodos , Cadeia Alimentar , Oceanos e Mares
7.
Ecology ; 99(6): 1411-1418, 2018 06.
Artigo em Inglês | MEDLINE | ID: mdl-29645089

RESUMO

Microbial community assembly is affected by a combination of forces that act simultaneously, but the mechanisms underpinning their relative influences remain elusive. This gap strongly limits our ability to predict human impacts on microbial communities and the processes they regulate. Here, we experimentally demonstrate that increased salinity stress, food web alteration and nutrient loading interact to drive outcomes in salt marsh fungal leaf communities. Both salinity stress and food web alterations drove communities to deterministically diverge, resulting in distinct fungal communities. Increased nutrient loads, nevertheless, partially suppressed the influence of other factors as determinants of fungal assembly. Using a null model approach, we found that increased nutrient loads enhanced the relative importance of stochastic over deterministic divergent processes; without increased nutrient loads, samples from different treatments showed a relatively (deterministic) divergent community assembly whereas increased nutrient loads drove the system to more stochastic assemblies, suppressing the effect of other treatments. These results demonstrate that common anthropogenic modifications can interact to control fungal community assembly. Furthermore, our results suggest that when the environmental conditions are spatially heterogeneous (as in our case, caused by specific combinations of experimental treatments), increased stochasticity caused by greater nutrient inputs can reduce the importance of deterministic filters that otherwise caused divergence, thus driving to microbial community homogenization.


Assuntos
Microbiota , Áreas Alagadas , Fungos , Humanos , Nitrogênio , Salinidade
8.
Ecology ; 96(8): 2147-56, 2015 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-26405740

RESUMO

Bottom-up and top-down effects act together to exert strong control over plant growth and reproduction, but how physical stress modifies those interactive forces remains unclear. Even though empirical evidence is scarce, theory predicts that the importance of both top-down- and bottom-up forces may decrease as physical stress increases. Here, we experimentally evaluate in the field the separate and interactive effect of salinity, nutrient availability, and crab herbivory on plant above- and belowground biomass, as well as on sexual and clonal reproduction in the salt marsh plant Spartina densiflora. Results show that the outcome of the interaction between nutrient availability and herbivory is highly context dependent, not only varying with the abiotic context (i.e., with or without increased salinity stress), but also with the dependent variable considered. Contrary to theoretical predictions, our results show that, consistently across different measured variables, salinity stress did not cancel bottom-up (i.e., nutrients) or top-down (i.e., consumers) control, but has additive effects. Our results support emerging theory by highlighting that, under many conditions, physical stress can act additively with, or even stimulate, consumer control, especially in cases where the physical stress is only experienced by basal levels of the trophic chain. Abiotic stress, as well as bottom-up and top-down factors, can affect salt marsh structure and function not only by affecting biomass production but also by having other indirect effects, such as changing patterns in plant biomass allocation and reproduction.


Assuntos
Ecossistema , Desenvolvimento Vegetal/fisiologia , Estresse Fisiológico/fisiologia , Animais , Argentina , Biomassa , Braquiúros/fisiologia , Herbivoria , Caules de Planta , Reprodução , Salinidade , Água do Mar
9.
Oecologia ; 175(1): 335-43, 2014 May.
Artigo em Inglês | MEDLINE | ID: mdl-24549938

RESUMO

Disturbance can generate heterogeneous environments and profoundly influence plant diversity by creating patches at different successional stages. Herbivores, in turn, can govern plant succession dynamics by determining the rate of species replacement, ultimately affecting plant community structure. In a south-western Atlantic salt marsh, we experimentally evaluated the role of herbivory in the recovery following disturbance of the plant community and assessed whether herbivory affects the relative importance of sexual and clonal reproduction on these dynamics. Our results show that herbivory strongly affects salt marsh secondary succession by suppressing seedlings and limiting clonal colonization of the dominant marsh grass, allowing subordinate species to dominate disturbed patches. These results demonstrate that herbivores can have an important role in salt marsh community structure and function, and can be a key force during succession dynamics.


Assuntos
Herbivoria , Poaceae/crescimento & desenvolvimento , Áreas Alagadas , Amaranthaceae/crescimento & desenvolvimento , Animais , Argentina , Biodiversidade , Biomassa , Brassicaceae/crescimento & desenvolvimento , Plântula/crescimento & desenvolvimento
10.
Environ Manage ; 50(6): 1058-67, 2012 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-22990683

RESUMO

Wetland loss is a frequent concern for the environmental management of rural landscapes, but poor disentanglement between climatic and land management causes frequently constrains both proper diagnoses and planning. The aim of this study is to address areal changes induced by non-climatic factors on lentic water bodies (LWB) within an agricultural basin of the Argentinean Pampas, and the human activities that might be involved. The LWB of the Mar Chiquita basin (Buenos Aires province, Argentina) were mapped using Landsat images from 1998-2008 and then corrected for precipitation variability by considering the regional hydrological status on each date. LWB areal changes were statistically and spatially analyzed in relation to land use changes, channelization of streams, and drainage of small SWB in the catchment areas. We found that 12 % of the total LWB in the basin had changed (P < 0.05) due to non-climatic causes. During the evaluated decade, 30 % of the LWB that changed size had decreased while 70 % showed steady increases in area. The number of altered LWB within watersheds lineally increased or decreased according to the proportion of grasslands replaced by sown pastures, or the proportion of sown pastures replaced by crop fields, respectively. Drainage and channelization do not appear to be related to the alteration of LWB; however some of these hydrologic modifications may predate 1998, and thus earlier effects cannot be discarded. This study shows that large-scale changes in land cover (e.g., grasslands reduction) can cause a noticeable loss of hydrologic regulation at the catchment scale within a decade.


Assuntos
Agricultura , Abastecimento de Água , Áreas Alagadas , Argentina , Drenagem , Monitoramento Ambiental
11.
Artigo em Inglês | MEDLINE | ID: mdl-21215323

RESUMO

The digestive and metabolic characteristics at the biochemical level underlying between-habitat dietary shift of the SW Atlantic euryhaline burrowing crab Neohelice granulata under natural conditions are unknown. We made studies on adult males of N. granulata from the open mudflat and the vegetated saltmarsh in a SW Atlantic costal lagoon (Mar Chiquita, 37°32'-37°45'S; 57°19'-57°26'W, Argentina). We determined and compared amylase, maltase, sucrase, proteolytic, lipase and alkaline phosphatases activities in the hepatopancreas; glycemia, and glycogen, free glucose, triglycerides and protein concentrations in hepatopancreas, chela muscle, and anterior and posterior gills. The results show that N. granulata exhibits characteristics and between-habitat differences at the biochemical level (i.e. high amylase and disaccharidase activities, differences in total proteolytic, lipase and levamisole-insensitive AP activities in the hepatopancreas, and in the concentrations of glycogen in the gills, triglycerides in the hepatopancreas and of protein in the chela muscle) which could represent adaptive digestive and metabolic strategies to face the differences in environmental conditions (i.e. food availability). The possible relationship between digestive and metabolic characteristics and feeding patterns, type of food available and environmental conditions in each habitat is discussed.


Assuntos
Braquiúros/metabolismo , Fosfatase Alcalina/metabolismo , Amilases/metabolismo , Animais , Braquiúros/enzimologia , Ecossistema , Brânquias/enzimologia , Brânquias/metabolismo , Glucose/metabolismo , Glicogênio/metabolismo , Hepatopâncreas/enzimologia , Hepatopâncreas/metabolismo , Lipase/metabolismo , Masculino , Músculos/enzimologia , Músculos/metabolismo , Peptídeo Hidrolases/metabolismo , Proteínas/metabolismo , Sacarase/metabolismo , Triglicerídeos/metabolismo , alfa-Glucosidases/metabolismo
12.
Oecologia ; 164(4): 931-41, 2010 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-20931233

RESUMO

Fiddler crabs show two different mating modes: either females search and crabs mate underground in male burrows, or males search and crabs mate on the surface near female burrows. We explored the relationship between crab density, body size, the searching behavior of both sexes, and the occurrence of both mating modes in the fiddler crab Uca uruguayensis. We found that crabs change their mating mode depending on their size and crab density. Crabs mated mostly on the surface at low densities, and underground at high densities. The proportion of wandering receptive females but not courting males accounted for the variation in mating modes. This suggests that whether crabs mate underground (or on the surface) is determined by the presence (or absence) of searching females. We found that the change in the mating mode affected the level of assortative mating; males mating underground were bigger than those mating on the surface, suggesting active female choice. Given that fiddler crabs experience multiple reproductive cycles, they are prone to showing behavioral plasticity in their mating strategy whenever the payoffs of using different mating modes differ between reproductive events. Our results suggest that the incorporation of different levels of environmental variability may be important in theoretical models aimed at improving our understanding of the evolution of alternative mating tactics and strategies.


Assuntos
Braquiúros/fisiologia , Animais , Tamanho Corporal , Feminino , Masculino , Preferência de Acasalamento Animal/fisiologia , Modelos Biológicos , Densidade Demográfica , Reprodução , Comportamento Espacial/fisiologia
13.
Oecologia ; 163(1): 181-91, 2010 May.
Artigo em Inglês | MEDLINE | ID: mdl-19921270

RESUMO

Increasing evidence has shown that nutrients and consumers interact to control primary productivity in natural systems, but how abiotic stress affects this interaction is unclear. Moreover, while herbivores can strongly impact zonation patterns in a variety of systems, there are few examples of this in salt marshes. We evaluated the effect of nutrients and herbivores on the productivity and distribution of the cordgrass Spartina densiflora along an intertidal stress gradient, in a Southwestern Atlantic salt marsh. We characterized abiotic stresses (salinity, ammonium concentration, and anoxia) and manipulated nutrients and the presence of the herbivorous crab Neohelice (Chasmagnathus) granulata, at different tidal heights with a factorial experiment. Abiotic stress increased at both ends of the tidal gradient. Salinity and anoxia were highest at the upper and lower edge of the intertidal, respectively. Nutrients and herbivory interacted to control cordgrass biomass, but their relative importance varied with environmental context. Herbivory increased at lower tidal heights to the point that cordgrass transplants onto bare mud substrate were entirely consumed unless crabs were excluded, while nutrients were most important where abiotic stress was reduced. Our results show how the impact of herbivores and nutrients on plant productivity can be dependent on environmental conditions and that the lower intertidal limits of marsh plants can be controlled by herbivory.


Assuntos
Ecossistema , Estresse Fisiológico , Animais , Crustáceos , Oxigênio/análise , Poaceae/fisiologia , Água do Mar , Cloreto de Sódio/análise , Movimentos da Água
14.
Ecology ; 90(9): 2368-74, 2009 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-19769115

RESUMO

The stress-gradient hypothesis predicts that interactions among plants are context dependent, shifting from facilitation to competition as environmental stress decreases. Although restricted to facilitation/competition, the mechanistic model behind the hypothesis is easily modified to include other negative interactions that are as important as competition in structuring natural communities, e.g., herbivory. To evaluate this hypothesis we experimentally tested if the balance between the facilitative and trophic effect of an intertidal, burrowing, herbivorous crab in marsh plants is context dependent and shifts from positive to negative as stress decreases. By sampling salt marshes differing in sediment size characteristics, we show that sites with larger sediment particle size had less stressful oxygen levels than sites with fine sediment particles, and that the level of stress was reduced by the presence of crab burrows. We then conducted a factorial experiment manipulating sediment size and crab presence. Results show that, by decreasing soil anoxic stress, crabs increase plant growth in stressful zones, but their ecological importance as herbivores increases in more benign zones. Our findings suggest that the balance between positive and negative interactions along stress gradients is more important than previously perceived and also applies to facilitation and herbivory between animals and plants.


Assuntos
Braquiúros/fisiologia , Poaceae/fisiologia , Estresse Fisiológico , Áreas Alagadas , Animais , Argentina , Sedimentos Geológicos
15.
Ecology ; 89(1): 155-64, 2008 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-18376557

RESUMO

Interactions among plants have been hypothesized to be context dependent, shifting between facilitative and competitive in response to variation in physical and biological stresses. This hypothesis has been supported by studies of the importance of positive and negative interactions along abiotic stress gradients (e.g., salinity, desiccation), but few studies have tested how variation in biotic stresses can mediate the nature and strength of plant interactions. We examined the hypothesis that herbivory regulates the strength of competitive and facilitative interactions during succession in Argentinean marshes dominated by Spartina densiflora and Sarcocornia perennis. Spartina densiflora is preferred by the dominant herbivore in the system, the crab Chasmagnathus granulatus. We experimentally manipulated crab herbivory, plant structure, and shade, and we found that, when herbivory was low in the spring and summer, competitive interactions between plants were dominant, but in the fall, when herbivory was highest, facilitative interactions dominated, and Spartina densiflora survival was completely dependent upon association with Sarcocornia perennis. Moreover, experimental removal of Sarcocornia perennis across recently disturbed tidal flats revealed that, while Sarcocornia perennis positively affected small Spartina densiflora patches by decreasing herbivory, as patch size increases and they can withstand the impact of herbivory, competitive interactions predominated and Spartina densiflora ultimately outcompeted Sarcocornia perennis. These results show that herbivory can mediate the balance between facilitative and competitive processes in vascular plant communities and that the strength of consumer regulation of interactions can vary seasonally and with patch size.


Assuntos
Braquiúros/fisiologia , Ecossistema , Comportamento Alimentar/fisiologia , Poaceae/crescimento & desenvolvimento , Áreas Alagadas , Animais , Argentina , Biomassa , Cadeia Alimentar , Dinâmica Populacional , Estações do Ano
16.
Ecol Lett ; 10(10): 902-8, 2007 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-17845290

RESUMO

Theory predicts that ecosystem engineers should have their most dramatic effects when they enable species, through habitat amelioration, to live in zones where physical and biological conditions would otherwise suppress or limit them. Mutualisms between mycorrhizal fungi and plants are key determinants of productivity and biodiversity in most terrestrial systems, but are thought to be unimportant in wetlands because anoxic sediments exclude fungal symbionts. Our field surveys revealed arbuscular mycorrhizal associations on salt marsh plant roots, but only in the presence of crabs that oxygenate soils as a by-product of burrowing. Field experiments demonstrate that fungal colonization is dependent on crab burrowing and responsible for nearly 35% of plant growth. These results highlight ecosystem engineers as ecological linchpins that can activate and maintain key mutualisms between species. Our findings align salt marshes with other important biogenic habitats whose productivity is reliant on mutualisms between the primary foundation species and micro-organisms.


Assuntos
Braquiúros/fisiologia , Micorrizas/fisiologia , Poaceae/crescimento & desenvolvimento , Poaceae/microbiologia , Simbiose , Animais , Argentina , Biomassa , Ecossistema , Sedimentos Geológicos/análise , Oxirredução , Oxigênio/análise , Raízes de Plantas/crescimento & desenvolvimento , Raízes de Plantas/microbiologia , Microbiologia do Solo , Áreas Alagadas
17.
Mar Pollut Bull ; 52(12): 1717-24, 2006 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-16979673

RESUMO

The influence of intertidal crab beds on the concentrations of organochlorine (OC) pesticides in sediment was studied in two different coastal environments in Argentina. Samples of male burrowing crabs (Chasmagnathus granulatus) were collected for this study. Our field data showed lower bioaccumulation of OC pesticides in crabs from sediments with a higher total organic carbon (TOC) and higher clay content. Thus, concentrations in crabs depend on the physico-chemical characteristics of the sediment where they live more than on the OC pesticide concentrations in the environment. The distribution patterns in sediment from inside and outside crab burrows were similar for both coastal areas being HCHs > or = gamma-chlordane > p,p'-DDE for San Antonio Bay (SAO), and HCHs > p,p'-DDE > or = gamma-chlordane for Mar Chiquita (MCh) coastal lagoon. OC pesticide concentrations in sediment were significantly lower inside than outside crab burrows, irrespective of the sediment physico-chemical characteristics due to the bioturbation activity of C. granulatus.


Assuntos
Braquiúros/química , Braquiúros/metabolismo , Monitoramento Ambiental , Sedimentos Geológicos , Hidrocarbonetos Clorados/farmacocinética , Praguicidas/farmacocinética , Animais , Meio Ambiente , Sedimentos Geológicos/química , Hidrocarbonetos Clorados/análise , Praguicidas/análise , Poluentes Químicos da Água/análise , Poluentes Químicos da Água/farmacocinética
18.
Oecologia ; 139(4): 572-82, 2004 May.
Artigo em Inglês | MEDLINE | ID: mdl-15042458

RESUMO

Habitat structure is often assumed to be a predictor of habitat function. However, habitat structure may be insufficient to predict the functional significance of a habitat if the level of resources in the habitat is a consequence of the interaction between the habitat structure and physical or biological factors. In this study, we investigated whether depressions in tidal flat sediments generated by stout razor clams, Tagelus plebeius, affect the spatial patterns of pit digging by deposit-feeding burrowing crabs, Chasmagnathus granulata. The pits dug by crabs while feeding overlapped with clam siphon holes at a frequency higher than expected at random, and measurements of pit-digging by crabs integrated over several days indicated a higher frequency of feeding in the sediment of depressions. The daily frequency of pit-digging by crabs in depressions was positively related to the organic matter content of their sediments, but was significantly higher than the frequency of pit-digging away from clam siphon holes only after events of high bedload sediment transport, when the organic matter in the sediments of these depressions peaked. This example demonstrates the conditional nature of the relationship between habitat structure and function by illustrating how a physical process--bedload sediment transport--may introduce variation in the function that depressions play as feeding sites for burrowing crabs. Published information suggests that such conditional responses of organisms to habitat structure: (1) occur in a variety of habitats; (2) involve a variety of structures either of biotic or abiotic origin; and (3) are the consequence of either physical or biological controls that vary in importance according to the general mechanism through which habitat structure affect resources. This broad experimental evidence suggests that the accuracy of predictive models linking habitat structure and function can be improved by incorporating a mechanistic perspective that allows recognition of the potential for conditional responses of organisms to habitat structure.


Assuntos
Bivalves/fisiologia , Braquiúros/fisiologia , Ecossistema , Meio Ambiente , Comportamento Alimentar/fisiologia , Sedimentos Geológicos , Modelos Biológicos , Análise de Variância , Animais , Oceano Atlântico , Cadeia Alimentar
19.
Mar Pollut Bull ; 48(3-4): 240-7, 2004 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-14972575

RESUMO

The effect of crab beds and bioturbation activity of the SW Atlantic intertidal crab Chasmagnathus granulata on the organochlorine pesticide (OCP) concentrations in Bahía Blanca estuary, Argentina were studied. Total OCP concentration was significantly lower inside than outside the crab burrows. Nevertheless, the concentrations from outside the crab beds were lower than from outside crab burrows, which indicated that crab beds act as sinks of sediment-bound OCP due to the bioturbation activities of the crabs. The same distribution patterns were found in all sediments as well as in crabs, being cyclodienes>HCHs>DDTs, although large amounts of metabolites rather than the respective parental were found in the organism showing the capacity of C. granulata for metabolising parental compounds. These more water-soluble compounds are excreted by the faeces and finally removed by tidal flushing to the sea. Our results suggest that crabs when present play a role in the distribution of sediment-bound OCP and the crab beds are modifiers of the dynamic of organic pollutants in estuarine areas.


Assuntos
Braquiúros , Sedimentos Geológicos/química , Hidrocarbonetos Clorados , Inseticidas/análise , Inseticidas/farmacocinética , Movimento , Poluentes Químicos da Água/análise , Poluentes Químicos da Água/farmacocinética , Animais , Biotransformação , Monitoramento Ambiental , Fezes , Inseticidas/química , Distribuição Tecidual
20.
Mar Pollut Bull ; 46(2): 197-202, 2003 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-12586115

RESUMO

The Río de la Plata, one of the most important South American estuarine environments, is characterized by a bottom salinity front that generates an ecotone between the river and the estuary. Based on bottom trawls and costal sampling we describe the distribution, types, and amount of debris found in the bottom and shoreline across this front. Plastics and plastic bags were the main debris types in both areas. Concentrations of total debris upriver the front were always significantly higher than downriver the front showing that the front acts as a barrier accumulating debris. Moreover, a large part of debris end ups accumulated in the coastal area upriver the frontal position. This area is particularly sensitive because the coastline encompasses an UNESCO Man and the Biosphere Reserve and a Ramsar site, and due to the ecological significance of the front for many valuable species.


Assuntos
Resíduos de Alimentos , Plásticos , Cloreto de Sódio , Movimentos da Água , Argentina , Conservação dos Recursos Naturais , Monitoramento Ambiental , Uruguai , Poluentes da Água/análise
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