Organochlorine contaminants in a coastal lagoon in Argentina: Analysis of sediment, crabs, and cordgrass from two different habitats

Burrowing crabs (Chasmagnathus granulata), sediment collected from inside and outside crab burrows as well as outside the crab bed, and cordgrass (Spartina densiflora) were collected from intertidal mudflat and cordgrass marsh habitats and analyzed for concentrations of polychlorinated biphenyl (PCB) congeners and organochlorine (OC) compounds to test the hypothesis that there are differences in the distribution and bioaccumulation of OC contaminants in coastal lagoon habitats in Argentina. PCB concentrations were relatively low, although the penta- and hexachlorobiphenyl detected in sediments and biota indicated that there had been direct inputs of PCBs into the ecosystem. Heptachlor epoxide, dieldrin, endosulfan sulphate, chlordane compounds, DDT and metabolites, and hexachlorocyclohexanes (HCHs) were the major pesticides detected in sediment and biota samples. When lipid-normalized concentration data for all OC pesticides in crabs were summed together (ΣOCC), there were higher concentrations in crabs from the cordgrass habitat in comparison to crabs from the mudflat. In sediment samples, there were no significant differences in percent organic matter of marsh and mudflat sediments, but the concentrations of ΣOCC normalized to organic carbon were higher in the sediments collected in the cordgrass marsh. Samples of rhizomes and roots from the cordgrass contained high concentrations of OC compounds and it was estimated that 2.4 kg of heptachlor epoxide, the most abundant OC pesticide, may be present in the total cordgrass root biomass in Mar Chiquita lagoon. These data indicated that the cordgrass in coastal lagoon environments is an important factor in determining the distribution of persistent contaminants, and that a significant portion of the total burden of these hydrophobic compounds may be deposited in cordgrass biomass.     

Sediment dynamics modulated by burrowing crab activities in contrasting SW Atlantic intertidal habitats

Biogenic bottom features, animal burrows and biological activities interact with the hydrodynamics of the sediment–water interface to produce altered patterns of sediment erosion, transport and deposition which have consequences for large-scale geomorphologic features. It has been suggested that depending on the hydrodynamic status of the habitat, the biological activity on the bottom may have a variety of effects. In some cases, different bioturbation activities by the same organism can result in different consequences. The burrowing crab Neohelice granulata is the most important bioturbator at SW Atlantic saltmarshes and tidal plains. Because of the great variety of habitats that this species may inhabit, it is possible to compare its bioturbation effects between zones dominated by different hydrodynamic conditions. Internal marsh microhabitats, tidal creeks bottoms and basins, and open mudflats were selected as contrasting zones for the comparison on a large saltmarsh at Bahía Blanca Estuary (Argentina). Crab burrows act as passive traps of sediment in all zones, because their entrances remain open during inundation periods at high tide. Mounds are generated when crabs remove sediments from the burrows to the surface and become distinctive features in all the zones. Two different mechanisms of sediment transport utilizing mounds as sediment sources were registered. In the first one, parts of fresh mound sediments were transported when exposed to water flow during flooding and ebbing tide, with higher mound erosion where currents were higher as compared to internal marsh habitats and open mudflats. In the second mechanism, mounds exposed to atmospheric influence during low tide became desiccated and cracked forming ellipsoidal blocks, which were then transported by currents in zones of intense water flow in the saltmarsh edge. Sedimentary dynamics varied between zones; crabs were promoting trapping of sediments in the internal saltmarsh (380 g m⁻² day⁻¹) and open mudflats (1.2 kg m⁻² day⁻¹), but were enhancing sediment removal in the saltmarsh edge (between 10 and 500 g m⁻² day⁻¹ in summer). The implication is that biologically mediated sedimentological changes could be different among microhabitats, potentially leading to contrasting geomorphologic effects within a particular ecosystem.     

Infection by gymnophallid metacercariae enhances predation mortality of SW Atlantic stout razor clam Tagelus plebeius

Parasite life cycles are frequently completed in different hosts, thus the parasites have its life cycle overlapped to natural trophic webs. The family Gymnophallidae (Class: Trematoda; Subclass: Digenea) includes digenetic parasites whose larval stages occur on bivalves and may affect bivalve predation by the final host of these parasites. In this work we evaluated: (a) if individuals of the razor clam Tagelus plebeius with higher parasite intensity suffer higher predation by the oystercatcher Haematopus palliatus and, (b) if there is any effect of parasite intensity on burrowing and escape behaviours of these razor clams which may enhance exposure to predators. Field experiments (oystercatcher exclusion vs. open access) showed that clams with higher parasite intensity support higher predation by oystercatchers, which suggests a higher consumption of more parasitized clams and thus, a more successful reproduction of parasites linked to the intensity of infection. However, clam burrowing and escape behaviours did not show differences related to different parasite intensity, suggesting that the commonly believed mechanisms are not responsible in this case.     

Marine ecosystem-based management in the Southern Cone of South America: Stakeholder perceptions and lessons for implementation

Ecosystem-based management (EBM) has recently received considerable attention. However, examples of empirical approaches to marine EBM are scarce. Therefore, empirical information on the presence of EBM elements within existing policies and the way they may provide settings and lessons for EBM implementation is timely. This study analyses stakeholders’ perceptions on the existence of EBM principles in current marine management practices and policies, and how they determine perceptions for success and satisfaction regarding coastal management within selected case studies drawn from four developing countries in the Southern Cone of South America. Patterns of response across study sites show that although EBM principles as such are not explicitly included in management/conservation plans, there are policies (mainly local), which generate conditions for more explicit inclusion of them. These are based on participatory bottom-up planning, place-based management and consensus reaching: all elements included within the theoretical literature on EBM implementation.     

Shifts in an epibenthic trophic web across a marine frontal area in the Southwestern Atlantic (Argentina)

Marine benthic trophic relationships and food web structures may be influenced by benthic–pelagic coupling processes, which could also be intensified by the physical dynamics of marine fronts. In this work, we employed stable isotope (δ¹³C and δ¹⁵N) analysis to investigate the influence of the Southwest (SW) Atlantic shelf-break front (SBF; 38–39°S, 55–56°W; Argentina) on an epibenthic trophic web. Epibenthic organisms were sampled, at depths of ~ 100 m, with a non-selective dredge from a sandy bottom community located in frontal (F) and marginal (M) areas. The SBF position and the chlorophyll-a (chl-a) concentrations were inferred using satellite data of the sea surface temperature (SST) and satellite chl-a concentration, respectively. The most noticeable shifts in stable isotopes between the sampled areas were those of the Patagonian scallop, Zygochlamys patagonica (δ¹³C), and those of the sea urchin, Sterechinus agassizi (δ¹⁵N). Diet analyses inferred from stable isotopes and mixing models demonstrated that the dominant component of this community, Z. patagonica, had variable contributions to higher trophic levels between areas. More importantly, the epibenthic assemblage in F areas showed δ¹³C-enriched and δ¹⁵N-depleted isotopic signatures with respect to the M areas. Collectively, this evidence suggests that frontal dynamics promotes the accumulation of δ¹³C-enriched phytoplankton in the seabed in F areas, while in M areas the more degraded organic matter becomes more important in the trophic web, decreasing the δ¹⁵N isotopic signature of the assemblage. Therefore, the trophic web was sustained by fresher food in F areas than in M areas, demonstrating the role of frontal dynamics in the shaping of these communities.     

Macro benthic community assemblage before and after the 2007 tsunami and earthquake at Paracas Bay,Peru

Macrobenthic soft bottom community assemblages were studied from December 2006 to December 2007 at Paracas Bay (Atenas Beach, 13°45' S, 76°17' W, Peru), including the period of the tsunami of 15 August 2007, providing a unique opportunity to assess the effects of this type of natural disturbance in soft bottom marine ecosystems. The results show that the tsunami affected the soft bottom community assemblage by changing the sediment granulometry, the biomass and abundance of epifaunal species, and by increasing the silt proportion. The event affected all functional groups, resulting in an increased numbers and biomass of filter feeder and grazers that were followed soon after by predators during the post-tsunami period. A similar pattern was observed for biomass and the abundance of infaunal species without changing the functional groups. The slow recovery observed after four months was likely related to the loss of sediment stability. In summary, there were differences in the structure and composition of soft bottom macrofaunal assemblages before and after the earthquake and posterior tsunami disturbance, forcing benthic communities to initiate re-colonisation processes.     

Nutrients and Abiotic Stress Interact to Control Ergot Plant Disease in a SW Atlantic Salt Marsh

Over the last decades, human activities have strongly affected ecosystems, with pervasive increases in nutrient loadings, abiotic stress, and altered herbivore pressure. The evaluation of how those environmental factors interact to influence plant–pathogen interactions under natural conditions becomes essential to fully understand the ecology of diseases and anticipate the possible effects of global change on natural and agricultural systems. In a SW Atlantic salt marsh, we performed a field factorial experiment to evaluate the effect of herbivory, salinity, and nutrient availability, three main limiting factors for salt marsh plant growth, on the infection of the fungus Claviceps purpurea (ergot) upon the cordgrass Spartina densiflora. Results show that herbivory has no effect but both nutrients and salinity increase fungal infection. The combined effect of salinity and nutrients is not additive but interactive. Salinity stress increases infection at ambient nutrient levels but in combination with fertilizer it buffers the higher infection produced by increased nutrient availability. Since both, nitrogen availability and salinity are factors predicted to globally increase due to human impact on ecosystems, this interaction between environmental factors and ergot infection can have strong effects on natural and productive agricultural systems.     

Changes in Coastal Benthic Algae Succession Trajectories and Assemblages Under Contrasting Nutrient and Grazer Loads

Eutrophication plays a crucial role in coastal systems, driving changes in the composition and abundance of flora and fauna with consequent effects for the entire ecosystem. Sensitive to nutrient levels, micro- and macroalgal blooms serve as valuable indicators of eutrophication. The San Antonio Bay (Northern Argentinean Patagonia, 40° 43′ S, 64° 56′ W) provides an appropriate system to study in situ eutrophication processes on coastal communities. In a multi-scale approach, using two different kind of settlement substrates (micro: polyethylene terephthalate, and macro: ceramic), the present study followed benthic algal dynamics over one year, distinguishing changes in natural succession and seasonality. Strong differences were found in the biofilm assemblages after three days, marked by tube dwelling diatoms and Cocconeis spp. under high nutrient-grazer conditions and needle like diatoms (e.g. Nitzschia spp., Tabularia spp.) under lower nutrient-grazer loads. The succession continued by the colonization of macroalgae, with a higher recruitment rate in the nutrient and grazer rich environment with a concomitant higher diversity. Our results show that under higher nutrient-grazer conditions natural benthic succession not only differs in trajectory but in its final taxa composition promoting higher biodiversity and biomass accumulation. In addition, taxa specific substrate preferences interfere with the observed eutrophication pattern, suggesting substrate dependant interrelations between the bloom forming taxa. These findings provide evidence that nutrient enrichment can not only affect an established assemblage but also affect the early succession stages, changing the succession trajectory and thus the final assemblage.     

Processes of tidal channel development in salt and freshwater marshes

Mechanisms for the formation of creeks in tidal ?ats are rarely discussed in literature. There are some general theories about their formation but there are no data to support the evidence. It is generally believed that marshes inherit creeks from previous tidal ?ats that their plants colonize and further modify them. The aim of this paper is to present three mutually exclusive cases from marshes in Argentina where creeks are formed by either purely physical or biological–physical interactions. Except for Loyola Bay, this is the ?rst discussion of these mechanisms. They may represent special cases, but the fact that all three of them occur along the coast of Argentina, could indicate that similar cases may be found somewhere else. Copyright © 2003 John Wiley & Sons, Ltd.     

The oxidation of S(IV) during riming by cloud droplets

Experiments have been performed to investigate whether the process of freezing during riming in clouds may induce oxidation of dissolved SO₂ to SO ₄ ^2– . The experiments were conducted in a cold room at varying temperatures between –6 and –15 °C. Solutions containing dissolved SO₂ and NH₄OH in various proportions, in the range of concentrations between 3×10^–5 and 10^–3 M, were sprayed. Rime was collected on a rotating cylinder and analyzed. Absorption of oxygen from laboratory air was prevented, except in the spray, to avoid spurious oxidation. Blank experiments were made at +3 to +6 °C. The results indicate clearly that, as the dominant cation becomes NH ₄ ⁺ rather than H⁺, substantial oxidation of S(IV) occurs during riming. This is consistent with redox reactions taking place as a result of charge separation at the ice-water interface during freezing.