Pasquale Carlino

δ15N variation in Ulva lactuca as a proxy for anthropogenic nitrogen inputs in coastal areas of Gulf of Gaeta (Mediterranean Sea)

We tested the capacity of Ulva lactuca to mark N sources across large marine areas by measuring variation in its δ(15)N at several sites in the Gulf of Gaeta. Comparisons were made with the macroalga Cystoseira amentacea. Variation of δ(15)N values was assessed also in the coastal waters off the Circeo Natural Park, where U. lactuca and C. amentacea were harvested, as these waters are barely influenced by human activities and were used as reference site. A small fragment from each frond was preserved before deployment in order to characterize the initial isotopic values. After 48 h of submersion, U. lactuca was more responsive than C. amentacea to environmental variation and δ(15)N enrichment in the Gulf of Gaeta was observed. The spatial distribution of δ(15)N enrichment indicated that different macro-areas in the Gulf were affected by N inputs from different origins. Comparison of the δ(15)N values of fragments taken from the same transplanted frond avoided bias arising from natural isotopic variability.

Seasonal abundance and trophic position of the Atlantic blue crab Callinectes sapidus Rathbun 1896 in a Mediterranean coastal habitat

The blue crab Callinectes sapidus, native to the western coasts of the Atlantic Ocean, has been introduced in Mediterranean waters where it is currently considered an invasive species. Here, we verified the occurrence of an established population of C. sapidus in the Torre Colimena basin, a Mediterranean habitat located in SE Italy, and provided a first assessment of its functional role in a Mediterranean coastal ecosystem. Crab traps were used to estimate the species abundance at a seasonal frequency; in addition, its trophic position was estimated in summer using nitrogen stable isotopes. Estimations were performed using both a generally adopted value of 3.4 ‰ for the nitrogen trophic level fractionation factor ∆15N, and species-specific estimations obtained from the literature. C. sapidus was sampled throughout the year, reaching peak abundances in summer. This result, taken together with the observed patterns of variation in the average body size and sex ratio of captured specimens, provided evidence of a fully established population in the Torre Colimena basin. The estimated trophic position of the crab was consistent with the literature information on western Atlantic populations, and resulted, irrespective of the fractionation factor used, significantly higher than those characterizing an autochthonous brachyuran (Pachygrapsus marmoratus) and a fish predator (Sparus aurata). The present study provided novel information on the occurrence and potential functional impact of this non-indigenous species in Mediterranean coastal habitats, highlighting current knowledge lacunae and identifying future research lines on marine alien species.

Site-scale isotopic variations along a river course help localize drainage basin influence on river food webs

In human-impacted rivers, nutrient pollution has the potential to disrupt biodiversity organisation and ecosystem functioning, prompting calls for effective monitoring and management. Pollutants, together with natural variations, can modify the isotopic signature of aquatic organisms. Accordingly, we explored the potential of isotopic variations as an indicator of drainage basin influences on river food webs. We assessed stable N and C isotopes within six food webs along a river affected by multiple pollution sources. CORINE land cover maps and Digital Elevation Models (DEMs) were also applied to understand the impact on surface waters of anthropogenic pressures affecting the catchment. N isotopic signatures of taxa fell in association with ammonium inputs from agriculture, indicating that nitrogen pollution was related to synthetic fertilizers. Isotopic variations were consistent across trophic levels, highlighting site-specific communities and identifying taxa exposed to pollutants. This allowed us to locate point sources of disturbance, suggesting that food web structure plays a key role in pollutant compartmentalisation along the river. Thematic maps and DEMs helped understand how the anthropogenic impact on river biota is mediated by hydro-geomorphology. Thus, the integration of site-scale analyses of stable isotopes and land use represents a promising research pathway for explorative nutrient pollution monitoring in human-impacted rivers.

Change in carbon stable isotope ratios of the predatory bugOrius majusculusafter dietary shifts

Orius majusculus Reuter (Hemiptera: Anthocoridae) is an important component of the pest predatory complex in arable crops in Mediterranean areas. It moves between crops searching for prey, and improving knowledge on its dispersal abilities will help to develop conservation biological control strategies. Stable isotope ratios may be used as a tool for tracking insect movements, as the isotopic composition of insect tissues changes to reflect that of their diet when they undergo dietary shifts on moving between isotopically distinct crops. We carried out laboratory diet switch experiments with a stable isotope approach to infer information on dispersal of O. majusculus individuals among C3 and C4 crops to better understand isotopic field data collections. Switching the aphid food source caused a quick change in δ13C signatures, regardless of the original and final food source. Changes in the δ13C ratio of O. majusculus after diet switching fitted with an exponential model that showed similar turnover rates, and thus half‐lives, between shifting diets up to 20 days. Subsequently, whereas individuals feeding on C4 aphids did not survive, turnover rate decreased in individuals that switched from C4 to C3 aphids. However, δ13C traces from the original source remained in the predator until 25 days after switching, and this is enough time to help determine the movement of O. majusculus between crops in the field and to plan the timing of predator sampling and crop practices that may enhance predator ecological services. Orius majusculus that switched to a maize aphid diet showed different turnover rates between sexes, although this did not influence the pattern of switchover.

The effects of nitrogen pollutants on the isotopic signal (δ15N) of Ulva lactuca: Microcosm experiments

Effects of two chemical forms of Nitrogen (NH4+ and NO3-) on δ15N in Ulva lactuca were analysed separately and in mixture at two concentrations. We assessed whether the δ15N values of U. lactuca discriminate between Nitrogen from synthetic fertilisers (inorganic) and from fresh cow manure (organic), and the isotopic ability of the macroalga to reflect Nitrogen concentrations. Isotopic signature and N content of the macroalga reflected different nitrogenous sources and their concentrations after 48h. The inorganic Nitrogen source (NH4NO3) altered the isotopic values of the macroalgae more than Nitrogen from fresh cow manure (NO3-). δ15N values observed in the mixed solution did not differ from those displayed in NH4NO3 treatment alone. We conclude that stable isotope analysis of U. lactuca collected in an unpolluted site and experimentally submerged in sites suspected of being affected by disturbance is a useful tool for rapid monitoring of anthropogenic discharges of Nitrogen pollutants.