Influence of sample size on ecological status assessment using marine benthic invertebrate‐based indices

Routine monitoring of the quality status of water bodies demands the best cost‐benefit relation and sample‐size reduction is therefore welcomed. However, great caution is needed because such reduction affects the accuracy and variation of the results. In the present study we tested the influence of sample size (number of replicate samples) on reference condition values and within‐sample ecological quality ratio (EQR) variability of six commonly used ecological indices (taxa richness, Shannon–Wiener diversity, AMBI, Medocc index, Bentix and M‐AMBI). Analysis of soft‐bottom benthic invertebrate data from Slovenian coastal waters showed that sample size influenced the reference condition values of richness/diversity indices (taxa richness and Shannon–Wiener diversity) but not of the sensitivity/tolerance indices (AMBI, Medocc index, Bentix). Increased sample size decreased the within‐sample EQR variability and, concomitantly, increased the accuracy of site ecological status classification for all indices. The size of EQR variability differed depending on the index used. EQR variability of M‐AMBI, an index composed of metrics with different within‐sample EQR variability, was statistically the same as that of the metric with the lowest within‐sample EQR variability. Whether this is a common principle for multimetric indices remains to be confirmed. Based on these results, the use of at least three replicates is suggested to obtain reliable measures of reference condition and EQR for the assessment of ecological status. This level of replication is particularly necessary in areas with high diversity and environmental patchiness, and when richness/diversity measures and indices that include these measures are used.     

Development of a River Macrophyte Index (RMI) for assessing river ecological status

We present the process of developing a macrophyte based index (River Macrophyte Index – RMI) for assessing river ecological status, that would be applicable for rivers with moderate to high water alkalinity, flowing over low slope terrain. A reference value and boundary values were determined for five ecological classes. The relation between the developed index and two existing indices, the Reference Index (RI) and the Trophic Index of Macrophytes (TIM), and selected environmental variables was established. The RMI is based on species composition and abundance from 208 sampling sites being in reference or good hydromorphological conditions and differing in the catchment land use. The percentage of natural areas in the sub-catchment was used for classifying macrophyte taxa into 5 ecological groups. 65 plant taxa, of which 47 were identified as indicator taxa, were included in the analysis. To assess the ecological status of a river site, the presence of at least 3 indicator taxa is necessary, otherwise the assessment is considered inconclusive. RMI is expected to indicate multiple pressures on the river, including trophic level. The developed index and RI and TIM indices differed in relation to slope, distance to source and catchment size.     

Biological and hydromorphological integrity of the small urban stream

Biological and hydromorphological integrity of five reaches of the small urban stream were assessed. Because macroinvertebrate communities respond to both organic pollution and habitat change, impacts of both measures can be hardly separated. In our study on the urbanized small stream, an impact of organic pollution was excluded as all five sampling sites were assessed as moderately polluted. On the other hand differences in morphological degradation of banks and channel of selected sites enabled us to relate hydromorphological stress and biotic metrics and taxa. Physical habitat quality was assessed using River habitat survey (RHS) methodology. A downstream-upstream gradient of physical habitat degradation was observed and related to the macroinvertebrate community characteristics. Similarity analyses and biotic metrics were calculated and correlated with results of the RHS analyses. Composition of the macroinvertebrate assemblages did not follow the longitudinal pattern of habitat modification observed by the RHS analysis. However, some metrics corresponded well. Percentage of detritivores, percentage of Caenis luctuosa, number of individuals, percentage of EPT individuals were best predictors of changes in the physical habitat quality. However, the metric percentage of EPT individuals was negatively correlated to the habitat degradation, what is in contradiction with results from studies of other authors.     

Tectono-metamorphic history of the Tacagua ophiolitic unit (Cordillera de la Costa, northern Venezuela): Insights in the evolution of the southern margin of the Caribbean Plate

Abstract   The southern margin of the Caribbean Plate is well exposed in the Cordillera de la Costa of northern Venezuela, where amalgamated terranes consisting of continental and oceanic units occur. In the Cordillera de la Costa, metamorphosed oceanic units crop out along the coast near Caracas. Among them, the Tacagua unit is characterized by metaserpentinites and metabasites showing mid-oceanic ridge basalt geochemical affinity. These lithologies, representative of a disrupted ophiolite sequence, are associated with metasediments consisting of calcschists alternating with pelitic and psammitic schists, whose protoliths were probably represented by deep-sea hemipelagic and turbiditic deposits. In the Tacagua unit, a polyphase deformation history has been reconstructed, consisting of four folding phases from D1 to D4 . Geological setting suggests an involvement of the Tacagua unit in the processes connected with a subduction zone. The following deformations (from D2 to D4 ) observed in the field might be related to the exhumation history of the Tacagua unit. The late deformation history consists of an alternation of deformation phases characterized by displacement parallel ( D2 and D4 phases) and normal ( D3 phase) to plate boundary between the Caribbean and South America Plates. All lines of geological evidence suggest that the whole evolution of the Tacagua unit was acquired in a setting dominated by oblique convergence, in which alternation of strike-slip and pure compressional or pure extensional tectonics occurred through time.     

Benthic mucilaginous aggregates in the Mediterranean Sea: Origin, chemical composition and polysaccharide characterization

Benthic mucilaginous aggregates are frequently formed in various parts of the Mediterranean basin, as in the Tyrrhenian and Adriatic Seas. Notwithstanding their wide spatial distribution, the role played by these aggregates in the biogeochemical cycling of organic matter is still largely unknown.The characteristics of the benthic aggregates examined in the present study showed that they are different from other mucilaginous aggregates, such as the “pelagic” ones that can form in the same areas in the water column and subsequently sediment to the seafloor. The aggregates are usually formed of structures of the filamentous macroalgae Acinetospora crinita, Chrysonephos lewisii and Nematochrysopsis marina. The elemental composition of the aggregates showed a marine macrophyte origin on the basis of the bulk organic matter content of the aggregates. Carbohydrates and proteins account for 26.6 to 55.9% of the organic carbon in the mucilage, respectively. Monosaccharide composition of exopolysaccharides in the mucilage aggregates revealed a characteristic pattern, with galactose, xylose or mannose and fucose as the major components. The relatively high content of deoxysugars is another distinctive feature. The abundant sulphate and uronic groups present in the polysaccharides in addition to their macromolecular dimensions and elongation contribute to inter-chain aggregation. Electron microscopic observations suggest that the polysaccharide fraction is the main macromolecular component in the formation of the persistent gel network in the aggregates.