•Macroinvertebrates sampling effort reduction was tested in a Mediterranean lagoon.•Combinations of three sieve mesh sizes and four sample unit sizes were compared.•Sampling was carried out at a ...perturbed and an unperturbed site.•We tested the combinations on well known assessment tools for lagoons.•A mathematical model for sampling effort estimation was developed.
The effectiveness and accuracy of biomonitoring programs, based on benthic macroinvertebrates, is strictly related to the sampling design and effort, whereas the feasibility depends on the economic sustainability of sample collection and processing methodologies. In the last decade, how to improve the Rapid Bioassessment Protocols (RBPs) maintaining the accuracy of the results has been a topic recurrently debated among researchers. It is well known that the sample unit size (i.e., surface of the sampled area, SUS) and the sieve mesh size (SMS), selected to collect and to retain benthic macroinvertebrates from soft-bottom samples, may affect the evaluation of the aquatic ecosystem ecological status; however, studies analyzing the combined influence of SUS and SMS on assessment tools are lacking, in particular for transitional water ecosystems. Even if the Water Framework Directive (WFD) suggests rapid and cost-effectiveness sampling effort and procedures, the identification of optimal SUS and SMS is a basic step to improve the RBPs and to meet WFD suggestions. Therefore, this research analyses the effects of four soft-bottom sample unit sizes (0.0225m2, 0.0450m2, 0.0675m2, 0.0900m2), and three sieve mesh sizes (4mm2, 1mm2, 0.25mm2) on the selection of benthic macroinvertebrates and, thus, on assessment tools, in a Mediterranean lagoon. A sampling survey was performed in September 2009 at a perturbed and an unperturbed study site in the Lesina lagoon (SE Italian coastline); three replicates were taken for each SUS and SMS using an Ekman–Birge grab (15cm×15cm). The samples were sieved on a column of three sieves, with decreasing mesh size. Benthic macroinvertebrates were sorted, identified, measured, weighted and included in twelve datasets (4 SUS×3 SMS). Sampling effort (SE) was calculated for each SUS and SMS combination as: SE=SUSm2×(1/SMSmm2)×100. Four simple community descriptors (numerical density, taxonomic richness, biomass density, individual body-size) and four ecological indicators (AMBI, BENTIX, BITS, M-AMBI) were compared for each combination of SUS and SMS in both study sites. Simple community descriptors and ecological indicators varied significantly between perturbed and unperturbed study site. The results showed that SMS had significant effects on simple community descriptors and ecological indicators, except for BITS index. Conversely, no significant differences were observed for different SUS analyzing simple community descriptors and ecological indicators, except for taxonomic richness and M-AMBI index. The response of the ecological indicators was only slightly affected by the SMS, whereas SUS choice did not influence the ecological status assessment. Anyway, using the larger SMS (4mm2), all ecological indicators showed either the same ecological quality status as the 1mm2 and 0.25mm2 SMS or, in some cases, one class higher, except for the AMBI index.
The present study provides energy density (
ED
) data and models for four macrobenthic invertebrate genera inhabiting freshwater lotic environments (
Baetis, Hydropsyche
,
Rhyacophila
, and
...Onychogomphus
). Samples were collected in the hydrological freshwater network of the Region Friuli Venezia Giulia within different watercourse types (creeks, streams, rivers channels, and ditches), and energy density was directly measured using an adiabatic bomb calorimeter. Measured
ED
expressed in Joule g
−1
wet weight was strongly and positively correlated with percentage of dry weight (
DW
%) for all genera investigated (
r
2
> 0.9504), allowing to obtain genus-specific predictive models based on the relationship between
ED
and
DW
%. Models were validated and showed good predictive power, as 90th percentile of observed percentage errors ranged between 4.23% and 5.18% while medians ranged between 1.32% and 2.83%. ANCOVA disclosed significant differences between the models, as those for
Rhyacophila
and
Onychogomphus
differed significantly from the others. The empirical models were used to build a dataset of estimated energy density, to assess the relationship between energy density and ecological status of the monitored riverine systems, assessed in compliance with European and Italian law by the application of four different ecological indices (ICMi, RQE_IBMR, STAR_ICMi, and LIMeco). Information regarding
ED
levels for freshwater macrobenthic invertebrates is still neglected in biomonitoring programs, but it could be useful to interpret some ecological situations in the context of ecological status assessment, especially in relation to the trophic condition of the investigated riverine systems.
Standard metabolic rate is a major functional trait with large inter-individual variability in many groups of aquatic species. Here we present results of an experimental study to address variation in ...standard metabolic rates, over different scales of organisation and environments, within a specific group of aquatic macro-invertebrates (i.e. gammarid amphipods) that represent the primary consumers in detritus food webs. The study was carried out using flow-through microrespirometric techniques on male specimens of three gammarid species from freshwater, transitional water and marine ecosystems. We examined individual metabolic rate variations at three scales: (1) at the individual level, during an 8 h period of daylight; (2) at the within-population level, along body-size and body-condition gradients; (3) at the interspecific level, across species occurring in the field in the three different categories of aquatic ecosystems, from freshwater to marine. We show that standard metabolic rates vary significantly at all three scales examined, with the highest variation observed at the within-population level. Variation in individual standard metabolic rates during the daylight hours was generally low (coefficient of variation, CV<10 %) and unrelated to time. The average within-population CV ranged between 30.0 % and 35.0 %, with body size representing a significant source of overall inter-individual variation in the three species and individual body condition exerting only a marginal influence. In all species, the allometric equations were not as steep as would be expected from the 3∕4 power law, with significant variation in mass-specific metabolic rates among populations. The population from the transitional water ecosystem had the highest mass-specific metabolic rates and the lowest within-population variation. In the gammarid species studied here, body-size-independent variations in standard individual metabolic rates were higher than those explained by allometric body size scaling, and the costs of adaptation to short-term periodic variations in water salinity in the studied ecosystems also seemed to represent a major source of variation.
•This is the first synoptic study on plankton dynamics in LTER-Italy aquatic sites.•We adopted a trans-domain approach, considering lakes, lagoons and coastal sea.•We based our review on published ...studies, complemented with unpublished information.•The plankton seasonal cycles presented site-specific patterns and commonalities.•The long-term changes were mainly driven by climatic and anthropogenic drivers.
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A first synoptic and trans-domain overview of plankton dynamics was conducted across the aquatic sites belonging to the Italian Long-Term Ecological Research Network (LTER-Italy). Based on published studies, checked and complemented with unpublished information, we investigated phytoplankton and zooplankton annual dynamics and long-term changes across domains: from the large subalpine lakes to mountain lakes and artificial lakes, from lagoons to marine coastal ecosystems.
This study permitted identifying common and unique environmental drivers and ecological functional processes controlling seasonal and long-term temporal course. The most relevant patterns of plankton seasonal succession were revealed, showing that the driving factors were nutrient availability, stratification regime, and freshwater inflow. Phytoplankton and mesozooplankton displayed a wide interannual variability at most sites. Unidirectional or linear long-term trends were rarely detected but all sites were impacted across the years by at least one, but in many case several major stressor(s): nutrient inputs, meteo-climatic variability at the local and regional scale, and direct human activities at specific sites. Different climatic and anthropic forcings frequently co-occurred, whereby the responses of plankton communities were the result of this environmental complexity.
Overall, the LTER investigations are providing an unparalleled framework of knowledge to evaluate changes in the aquatic pelagic systems and management options.
► Investigation of 13 single metrics and eight methods in assessing benthic status. ► In five distinct systems across Europe, including lagoons, estuaries, coasts and fjords. ► Most of the metrics ...and methods are able to detect pressure gradients. ► Inconsistencies were mostly in transitional waters. ► Some methods i.e. diversity, richness, BAT, M-AMBI, NQI detect gradients in transitional and coastal waters.
In recent times many benthic indices have been proposed to assess the ecological quality of marine waters worldwide. In this study we compared single metrics and multi-metric methods to assess coastal and transitional benthic status along human pressure gradients in five distinct environments across Europe: Varna bay and lake (Bulgaria), Lesina lagoon (Italy), Mondego estuary (Portugal), Basque coast (Spain) and Oslofjord (Norway). Hence, 13 single metrics (abundance, number of taxa, and several diversity and sensitivity indices) and eight of the most common indices used within the European Water Framework Directive (WFD) for benthic assessment were selected: index of size spectra (ISS), Benthic assessment tool (BAT), Norwegian quality index (NQI), Multivariate AMBI (M-AMBI), Benthic quality index (BQI), (Benthic ecosystem quality index (BEQI), Benthic index based on taxonomic sufficiency (BITS), and infaunal quality index (IQI). Within each system, sampling sites were ordered in an increasing pressure gradient according to a preliminary classification based on professional judgement. The different indices are largely consistent in their response to pressure gradient, except in some particular cases (i.e. BITS, in all cases, or ISS when a low number of individuals is present). Inconsistencies between indicator responses were most pronounced in transitional waters (i.e. IQI, BEQI), highlighting the difficulties of the generic application of indicators to all marine, estuarine and lagoonal environments. However, some of the single (i.e. ecological groups approach, diversity, richness) and multi-metric methods (i.e. BAT, M-AMBI, NQI) were able to detect such gradients both in transitional and coastal environments, being these multi-metric methods more consistent in the detection than single indices. This study highlights the importance of survey design and good reference conditions for some indicators. The agreement observed between different methodologies and their ability to detect quality trends across distinct environments constitutes a promising result for the implementation of the WFD’s monitoring plans. Moreover, these results have management implications, regarding the dangers of misclassification, uncertainty in the assessment, use of conflicting indices, and testing and validation of indices.
Understanding the mechanisms of phytoplankton community assembly is a fundamental issue of aquatic ecology. Here, we use field data from transitional (e.g. coastal lagoons) and coastal water ...environments to decode patterns of phytoplankton size distribution into organization and adaptive mechanisms. Transitional waters are characterized by higher resource availability and shallower well-mixed water column than coastal marine environments. Differences in physico-chemical regime between the two environments have been hypothesized to exert contrasting selective pressures on phytoplankton cell morphology (size and shape). We tested the hypothesis focusing on resource availability (nutrients and light) and mixed layer depth as ecological axes that define ecological niches of phytoplankton. We report fundamental differences in size distributions of marine and freshwater diatoms, with transitional water phytoplankton significantly smaller and with higher surface to volume ratio than marine species. Here, we hypothesize that mixing condition affecting size-dependent sinking may drive phytoplankton size and shape distributions. The interplay between shallow mixed layer depth and frequent and complete mixing of transitional waters may likely increase the competitive advantage of small phytoplankton limiting large cell fitness. The nutrient regime appears to explain the size distribution within both marine and transitional water environments, while it seem does not explain the pattern observed across the two environments. In addition, difference in light availability across the two environments appear do not explain the occurrence of asymmetric size distribution at each hierarchical level. We hypothesize that such competitive equilibria and adaptive strategies in resource exploitation may drive by organism's behavior which exploring patch resources in transitional and marine phytoplankton communities.
Biovolume is commonly used as a size descriptor in the study of phytoplankton ecology. Usually, biovolume is not measured directly but is obtained from a standardized set of geometric models based on ...linear dimensions measured by light microscopy. This commonly used method allows visualization and measurement in two dimensions (2D) yielding no information at all on the third dimension of phytoplankton cells. Inaccurate biovolume assessment resulting from geometric approximation leads to erroneous interpretation of eco-physiological processes and morpho-functional traits. Here, we use confocal microscopy coupled with an image analysis system (NIS Elements AR software, Nikon) to determine directly shape and biovolume by means a 3D reconstruction of Coscinodiscus cf. granii specimens. We evaluate the accuracy of current methods by comparing the results obtained using geometric models with direct biovolume and shape. We find that calculation of biovolume by approximation to geometric models (cylindrical and complex shapes) leads to a significant overestimation with respect to direct volume. We also propose a data-driven formula for calculating the biovolume of Coscinodiscus cf. granii specimens based on diameter or other linear measurements.
The river continuum concept represents the most general framework addressing the spatial variation of both structure and function in river ecosystems. In the Mediterranean ecoregion, summer drought ...events and dams constitute the main sources of local disturbance to the structure and functioning of river ecosystems occurring in the river basin. In this study, we analysed patterns of spatial variation of detritus processing in a 7th order river of the Mediterranean ecoregion (River Tirso, Sardinia-Italy) and in three 4th order sub-basins which were exposed to different summer drought pressures. The study was carried out on Phragmites australis and Alnus glutinosa leaf detritus at 31 field sites in seasonal field experiment. Detritus processing rates were higher for Alnus glutinosa than for Phragmites australis plant detritus. Processing rates of Alnus glutinosa leaves varied among seasons and study sites from 0.006 d(-1) to 0.189 d(-1) and those of Phragmites australis leaves ranged from 0.0008 d(-1) to 0.102 d(-1), with the lowest values occurring at sites exposed to summer drought. Seasons and sites accounted for a significant proportion of such variability. Alder detritus decay rates generally decreased with increasing stream order, while reed detritus decay rates generally increased on the same spatial gradient. Summer drought events affected these spatial patterns of variation by influencing significantly the decay rates of both plant detritus. The comparisons among and within sub-basins showed strong negative influence of summer drought on detritus processing rates. Similarly, in the entire River Tirso basin decay rates were always lower at disturbed than at undisturbed sites for each stream order; decay rates of reed detritus remained lower at those sites even after the end of the disturbance events, while alder decay rates recovered rapidly from the summer drought perturbations. The different recovery of the processing rates of the two leaves could also explain the different patterns of spatial variation observed between the two leaves.
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