A quantitative study of the movement behaviour of the brackish isopod Lekanesphaera hookeri was performed. Isopods were collected in late spring 2007 from an Italian lagoon and held in the laboratory ...under temperature-controlled conditions. We used a real-time video acquisition system to measure in resource-free arenas the mean step length, total path length, average movement speed and movement complexity of individuals characterised by a 10-fold difference in body mass. The fractal dimension D was used as a tortuosity index to estimate the complexity of the movement trajectory. No significant size-related patterns were observed for the mean step length, total path length and average movement speed of the sphaeromatids. Conversely, fractal D values varied negatively with the body mass of specimens according to a power law. Our findings indicate that L. hookeri is characterised by a size-related shift in movement behaviour, occurring independently from the availability of resources in the surrounding environment. The implications of size-related changes in movement complexity are discussed in the context of current metabolic theories.
Core samples were examined quarterly at two coastal sites (S1 and S2) and at an offshore station (S3) located in the Po River delta area (northwestern Adriatic Sea). Analyses focused on (i) ...occurrence of coarse detritus of allochthonous origin in the sedimentary matrix and (ii) the relative influence of macrodetritus enrichment and other environmental factors on the vagile macrofauna.
Plant debris occurred in site S1 sediments only in summer and autumn; in contrast, fragments of the phanerogams Cymodocea nodosa and Zostera spp. were found in site S2 sediment throughout the sampling period. Sediments from the offshore site S3 were characterized by negligible plant material, even though in summer and autumn samples debris of continental origin was observed. Even though leaf detritus occurrence at site S2 was ∼5-fold higher compared to the other coastal site S1, it did not influence the total organic matter and its distribution among grain-size classes. Conversely, the specific organic content of dimensional fractions provided an effective assessment of detritus enrichment processes occurring at the two coastal sites.
A group of brackish-originated crustaceans (i.e. the amphipods Gammarus insensibilis and G. aequicauda and the isopod Idotea baltica) was the main determinant of among-site multivariate differences in the vagile macrofauna; depositivorous ophiuroids accounted for the residual differences observed during the study period. The analysis of taxa abundance and individual body size indicated that in both site S1 and S3 macrodetritus advection to the benthic system corresponded with passive dispersal of brackish crustaceans, that provided a negligible contribution to the macrobenthic production. In contrast, in site S2 allochthonous inputs from marginal environments could have represented the key factor for the persistence of an authochthonous population of Gammarus insensibilis. The amphipod provided a considerable (19·4%) contribution to the total macrobenthic production of the site, dominated by filter-feeding bivalves and tubicolous deposit feeders. The potential effects of detritivorous crustaceans on soft-bottom macrobenthic assemblages of the northern Adriatic Sea are discussed.
An exclosure experiment was carried out in the reed-dominated littoral zone of a volcanic lake (Lake Vico, central Italy) to test whether the impact of predatory fish on benthic invertebrates ...cascades on fungal colonisation and breakdown of leaf detritus. The abundance, biomass, and Shannon diversity index of the invertebrate assemblage colonising Phragmites australis leaf packs placed inside: (1) full-exclosure cages, (2) cages allowing access only to small-sized fish predators, and (3) cageless controls, were monitored over a 45-day period together with the mass loss and associated fungal biomass of leaf packs. The species composition of the fungal assemblage was further assessed at the end of the manipulation. In general, invertebrate predators did not show any significant response to fish exclusion, either on a trophic guild or on a single taxon level. In contrast, the exclusion of large predatory fish induced a diverse spectrum of changes in the abundance and population size-structure of dominant detritivore taxa, ultimately increasing the biomass and Shannon diversity index of the whole detritivorous guild. These changes corresponded with significant variations in leaf detritus decay rates as well as in the biomass and assemblage structure of associated fungal colonisers. Our experimental findings provide evidence that in Lake Vico effects of fish predators on invertebrate detritivores influence the fungal conditioning and breakdown of the detrital substrate. We conclude that in lacustrine littoral zones predator-driven constraints may structure lower trophic levels of detritus-based food webs and affect the decomposition of leaf detritus originated from the riparian vegetation.
In the Lesina Lagoon (southern Italy), three species of crustacean mesograzers - the isopods Idotea baltica Pallas and Sphaeroma serratum Fabricius, and the amphipod Gammarus insensibilis Stock - ...dominate the epifaunal assemblage associated with the Rhodophyta Gracilaria verrucosa (Hudson) Papenfuss. We examined in laboratory feeding assays the palatability of the red macroalga to each of the three mesograzer species. Furthermore, we used a cage experiment to investigate the actual impact of the mesograzer assemblage on the growth of Gracilaria under field conditions. Cages with different mesh sizes were used to test the hypothesis that mesograzer effect on the macroalga is size dependent. Laboratory assays indicated for all the mesograzer species a negative effect on Gracilaria; in particular, I. baltica and G. insensibilis actively consumed the macroalga, whereas S. serratum grazing activity was weaker but nonetheless statistically significant. In contrast, Gracilaria was not significantly grazed under field conditions. When mesograzers were totally excluded, algal growth showed a strong negative variation compared to controls where access was not precluded (ca. 43% reduction in wet mass). Simultaneously, the abundance of the encrusting bryozoan Conopeum seurati increased significantly (from 1.5 to 24.7 mg g super(-1), corresponding to 1.7% and 28.9% cover of algal surface); an analogous increase was detected in the abundance of other sessile macrofauna (i.e. the bivalve Mytilaster marioni). When only juvenile, small-sized epifauna were given access to Gracilaria, algal mass change was reduced by around 36%. The abundance of both encrusting bryozoans and sessile bivalves showed significant positive variations, close to those observed in the total exclusion treatment. Our results suggest that, even though Gracilaria represents a potentially palatable resource for mesograzers in the Lesina Lagoon, the actual impact of epifauna on the macroalga might be beneficial, through an indirect control on the development of fouling epibionts. In addition, such a positive effect may be size specific, since the juvenile, small-sized component of the mesograzer assemblage exerted a significantly weaker control on fouling development, even at unnaturally high densities. We suggest that the occurrence of different functional roles among mesograzer size classes might represent a significant controlling factor for the establishment of mesograzer-epibiont-host plant interactions, and for their effects on macrophytal productivity.
A wide range of environmental chemicals have been shown to alter the endocrine system of both wildlife and humans. There is increasing evidence that many of these endocrine disruptors (EDs), in ...particular estrogenic chemicals, can rapidly affect cellular homeostasis and signaling in mammalian Ca2+ systems. In this work, in vitro and in vivo data are summarised on the effects of different compounds known or suspected as EDs on homeostasis in Ca2+ marine invertebrate, the blue mussel Mytilus spp. Both synthetic estrogens and different EDs (DES, BPA, NP, PCB congeners, etc.) rapidly increased sytosolic Ca2+ in mussel hemosytes, as evaluated by FURA2 single cell fluorescence microscopy. The observed Ca2+ increase was unaffected by the antiestrogen Tamoxifen and was due to either increased influx or release from Ca2+ intracellular stores, depending on the compound. Moreover, different ED,s including the brominated flame retardant TBBPA (tetrabromo bisphenol A) induced a dose-dependent inhibition of the plasma membrane Ca2+ -ATPase (PMCA) activity from mussel gills in vitro, this supporting a direct effect on membrane pumps. The in vitro effects of EDs were observed at concentrations generally higher than those of E2. However, in vivo, mussel exposure to environmetal concentrations of Bisphenol A (BPA) and of the polybrominated diphenyl ether TBDE-47 resulted in large inhibition of PMCA activity in the digestive gland. The results indicate that, in invertebrate like in mammalian systems, interference with Ca2+ homeostasis may represent a significant mode of action of a variety of EDs.
Interculturalidad y educación desde el Sur. Contextos, experiencias y voces es un libro colectivo que corona once trabajos de investigación realizados por diecisiete autores con diferentes ...adscripciones institucionales que se articulan a través de grupos de trabajo latinoamericanos en torno al debate actual sobre la Interculturalidad y Educación. Y con ello obligan al lector a pensar simultáneamente en un conjunto de movimientos o desplazamientos teórico-conceptuales, en el despliegue de posicionamientos filosóficos, políticos y jurídicos, y en el desarrollo de metodologías de investigación novedosas, que nos posibiliten revelar y actuar sobre una diversidad de experiencias, modelos y programas que buscan potenciar los procesos interculturales en el Sur. La obra en su conjunto es un aporte a la creciente producción bibliográfica que se genera en la última década desde la perspectiva crítica de Latinoamérica.
In sediments sampled in Northern Adriatic Sea invertebrate benthic macrofauna was examined in comparison with both substratum bulk parameters (average grain size, sorting, total organic matter ...content) and attributes of grain size classes (specific organic matter content of dimensional fractions). The aims were: 1) to determine whether variations of community overall parameters (total spatial density, number of taxa) and in numerically dominant feeding types (deposit-feeders and suspension-feeders) patterns were related to changes in sediment general properties; 2) to evaluate whether the observed patterns of abundance for deposit- and filter-feeders had more valid correlates in specific properties of substratum dimensional fractions. Number of taxa and animal spatial density resulted conventionally related to substratum bulk parameters while feeding types patterns in comparison with sediment total organic matter content exibited a reciprocal negative effect; only when both feeding types and sediment structure were resolved to their specific attributes in terms of prevalence of tubicolous taxa among deposit-feeders and organic matter richness of single dimensional fractions, the analysis emphasized patterns unequally affected by specific size fractions abundance and organic matter content: deposit feeders demonstrated to be related to the presence in the substrate of intermediate grain size classes necessary for tube-building. Those intermediate fractions proved to be more adequate descriptors than average grain size or other overall sediment parameters per se of relations actually established between feeding types and the complex nature of bottom sediments. Our results emphasize that in the Northern Adriatic Sea, sediment organic matter content may represent a factor of minor importance in comparison with other substrate attributes, for which it may be necessary a detailed analysis of sediment structure. Thus, we concluded that the complexity of soft-bottom communities may defy any simple paradigm relating macrobenthic patterns to any single sediment bulk attribute, and we propose a shift in focus towards an higher resolution of both functional groups in macrobenthic associations (as already suggested in other investigations) and of substratum structural description.PUBLICATION ABSTRACT
PDF
