1,721,145 research outputs found
Uncertainty in developing fish based multi-metric indices
No full textThe process of development of a multi-metric index (MMI) implies a series of decisions to complete the procedure and obtain the formulation of an indicator. We performed an uncertainty and sensitivity analysis to explore the effects of alternative decisions in this process, using the case of fish fauna-based assessment of the ecological status in transitional waters and the Venice lagoon as an example. We formulated the alternative strategies in MMI implementation as levels of three factors affecting this procedure: 1) metrics pre-selection; 2) metrics numerical pre-treatment; 3) and metrics combination rules. The outcome of the uncertainty analysis highlighted that all the decisions impacted the process, potentially leading to indicators with different characteristics, confirming that the process of developing MMIs – even following an empirical data-driven approach – is not a completely objective procedure. However, not all the choices have the same weight in influencing the final index, nor do they affect the same characteristics of the index. The initial choice of candidate metrics influences the number of metrics included in the final index, the correlation of the MMI with anthropogenic pressures and the ecological status classification (i.e. the output of the index itself). However, the most influential decision is the one related to the criterion adopted to select the metrics (i.e. to reduce the number of metrics from the original candidate set) included in the final index. This choice is the one that most likely affects the structure of the index and the ecological status classification, even if the family of indices developed in this work exhibited a certain level of robustness regarding this characteristic
Local habitat and seascape structure influence seagrass fish assemblages in the Venice lagoon: the value of conservation at multiple spatial scales.
No full textSeagrass meadows are a critical component of estuarine and coastal seascapes, and their structure influences fish assemblages at multiple spatial scales. The patch mosaic mode l, which defines the seascape as a collection of interacting habitat types, is increasingly dopted to prioritise protected areas and design ecological restoration schemes, hence helping to preserve seagrass meadows and the associated fish assemblages. Despite that, the re are few studies investigating the relative contribution of environmental characteristics measured at different spatial scales in determining the distribution of seagrass fish. This study collects fish and environmental observations taken at both site and seascape scales in seagrass meadows in the Venice lagoon (Adriatic Sea, Italy). By means of generalised linear models, it aims to disentangle the relative influence of local water qua
lity and habitat characteristics from that of habitat mosaic properties, investigating the response of whole fish assemblage descriptors, feeding guilds and dominant species. While confirming the primary importance of local habitat quality
, the study highlights that also seagrass habitat structure at the seascape scale is relevant for seagrass fish assemblages, influencing total biomass, biomass of macrobenthivorous and hyperbenthivorous/piscivorous species and seagrass specialists
such as syngnathids. Conservation of seagrass fish assemblages can therefore be promoted in Mediterranean coastal lagoons by preserving or restoring some features of the habitat mosaic, namely the extension of seagrass patches and their shape complexity, in addition to local water quality and seagrass cover
Predicting the response of fish and invertebrate assemblages to seagrass transplantations: assessment of the progress of habitat restorationin the Venice lagoon.
No full textOne of the major challenges to ensure effective restoration of estuarine habitats is to establish success criteria, allowingto determine whether the goalsof restoration are met. In the northern basin of Venice lagoon (northern Adriatic Sea, Italy), the LIFE project “SeResto” started in 2014 aiming at restoring seagrass meadows by means of small-scale manual transplantation of sods and rhizomes. The interventions are expected to increase the cover of Zostera marina and Z. noltei in the area, and to subsequently restore the typical features of faunal assemblages associated with seagrass meadows. The aim of this work is to propose a method to identify reference conditions and assess the progress of nekton (fish, decapods and cephalopods) assemblages at seagrass restoration sites.Nekton sampling took place from 2014 to 2017 during spring at eight transplantation sites. In spring 2016, five natural seagrass sites in the same area were additionally sampled, and physico-chemical water parameters and habitat structure (seagrass floristic composition, percent cover, canopy height, shoot density, leaf area index and epiphytal load) were also recorded. A multivariate approach based on GLMswas adopted, in order to disentangle the relative effect of water quality and seagrass habitat structure on nekton assemblages of natural habitats.Models were then employed to predict species composition of nekton fauna at each transplantation site under target abiotic and habitat conditions, allowing to identify the reference assemblages to evaluate the progress of fauna towards restoration goals. The analysis highlighted that desired restoration outcomes, i.e. presence of Z. marina and greater seagrass cover are positively linked to presence and density of some pipefishes (Syngnathidae), large gobies (Gobiidae) and some shrimps (Palaemonidae and Hippolytidae) in the nekton assemblage. Sites exhibiting better recovery of habitat structure also supported nekton assemblages more similar to reference conditions. However, none of the sites showed clear trajectories of progress, suggesting that more than three years are needed for nekton fauna to successfully colonise restored seagrass meadows in coastal lagoons
Microcalcareous seaweeds to assess trophic changes in transitional waters.
No full textThe analysis of a wide dataset of macrophytes and the most common water parameters shows that the presence/absence and the density of microcalcareous seaweeds can be an useful tool to monitor the trophic status of the environment. These seaweeds are affected by pH changes that in turn are related to nutrient concentrations and macroalgal growth and decomposition that regulate the trophic status of the environment
Struttura e funzione della tasca incubatrice e del corion nelle strategie riproduttive dei Singnatidi
No full textFish response to multiple anthropogenic stressors in mediterranean coastal lagoons: A comparative study of the role of different management strategies
Full text linkTransitional waters are among the most productive ecosystems of the world and their biotic communities show high diversity and complex mechanisms of self-regulation that provide valuable ecosystem services and societal goods and benefits. In this work a comparison of the fish assemblages of three non-tidal Mediterranean coastal lagoons is carried out in order to evaluate the impacts of alternative management strategies. The anthropogenic pressures acting on the lagoons were quantified by means of categorical indicators, while the characteristics of the fish assemblages were summarized in multi-metric indices (MMIs). Two MMIs were developed using data collected with a beach seine net and with fyke nets, following an empirical approach that selects, from a pool of 73 metrics, the combination that maximizes the MMI/pressure relationship. The two MMIs include four metrics each, most of which are based on feeding mode functional guilds and habitat use functional guilds, and they are sensitive to anthropogenic pressures. The human activities directly or indirectly affecting water quality are the ones that most influence the fish assemblage, while the presence of artisanal fisheries, a typical and relevant resource use in these lagoons, seems to play a beneficial role. Lagoon fisheries management relies on the maintenance of infrastructures that guarantee the hydraulic functioning of the lagoon, thus ensuring exchanges with the adjacent coastal sea, and therefore indirectly contributing to the habitat quality
Functional significance of the male brood pouch in the reproductive strategies of pipefishes and seahorses: a morphological and ultrastructural comparative study on three anatomically different pouches
No full textThe morphological organization of the male brood pouch skin of three different species of syngnathids (Nerophis ophidion, Syngnathus abaster and Hippocampus hippocampus), investigated using light and electron microscopy, showed that each pouch had a skin with a different ultrastructure. This reflected different relationships between the paternal body and the developing embryos. In N. ophidion, the bilayered epidermis of the pouch consisted mainly of pavement cells (filament-containing cells) typical of fish skin. In S. abaster, pavement cells were interspersed with many mitochondria-rich cells. These cells varied in number during the different functional stages of the pouch and died by apoptosis after the breeding period. Modified secretory 'flame cone cells' rich in vesicles and granules characterized the epidermis of H. hippocampus. Although there were specific differences, the vascularized dermis was the only feature common to all three types of pouch. These findings suggest that the brood pouch in Syngnathidae has different functions, which may be related to the different reproductive strategies and ecology of each species. (C) 2002 The Fisheries Society of the British Isles. Published by Elsevier Science Ltd. All rights reserved
TESTIS STRUCTURE AND SYMPLASTIC SPERMATOGENESIS IN THE PIPEFISH SYNGNATHUS ACUS (TELEOSTEI, SYNGNATHIDAE)
No full textImplicazioni della morfologia dell’apparato riproduttore maschile nella modalità d’inseminazione in Syngnathus abaster (Teleostei, Syngnathidae)
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