Salvatore Aronica

Habitat Selection Response of Small Pelagic Fish in Different Environments. Two Examples from the Oligotrophic Mediterranean Sea

A number of scientific papers in the last few years singled out the influence of environmental conditions on the spatial distribution of fish species, highlighting the need for the fisheries scientific community to investigate, besides biomass estimates, also the habitat selection of commercially important fish species. The Mediterranean Sea, although generally oligotrophic, is characterized by high habitat variability and represents an ideal study area to investigate the adaptive behavior of small pelagics under different environmental conditions. In this study the habitat selection of European anchovy Engraulis encrasicolus and European sardine Sardina pilchardus is analyzed in two areas of the Mediterranean Sea that largely differentiate in terms of environmental regimes: the Strait of Sicily and the North Aegean Sea. A number of environmental parameters were used to investigate factors influencing anchovy and sardine habitat selection. Acoustic surveys data, collected during the summer period 2002–2010, were used for this purpose. The quotient analysis was used to identify the association between high density values and environmental variables; it was applied to the entire dataset in each area in order to identify similarities or differences in the “mean” spatial behavioral pattern for each species. Principal component analysis was applied to selected environmental variables in order to identify those environmental regimes which drive each of the two ecosystems. The analysis revealed the effect of food availability along with bottom depth selection on the spatial distribution of both species. Furthermore PCA results highlighted that observed selectivity for shallower waters is mainly associated to specific environmental processes that locally increase productivity. The common trends in habitat selection of the two species, as observed in the two regions although they present marked differences in hydrodynamics, seem to be driven by the oligotrophic character of the study areas, highlighting the role of areas where the local environmental regimes meet ‘the ocean triad hypothesis’.

Dynamics of Two Picophytoplankton Groups in Mediterranean Sea: Analysis of the Deep Chlorophyll Maximum by a Stochastic Advection-Reaction-Diffusion Model

A stochastic advection-reaction-diffusion model with terms of multiplicative white Gaussian noise, valid for weakly mixed waters, is studied to obtain the vertical stationary spatial distributions of two groups of picophytoplankton, i.e., picoeukaryotes and Prochlorococcus, which account about for 60% of total chlorophyll on average in Mediterranean Sea. By numerically solving the equations of the model, we analyze the one-dimensional spatio-temporal dynamics of the total picophytoplankton biomass and nutrient concentration along the water column at different depths. In particular, we integrate the equations over a time interval long enough, obtaining the steady spatial distributions for the cell concentrations of the two picophytoplankton groups. The results are converted into chlorophyll a and divinil chlorophyll a concentrations and compared with experimental data collected in two different sites of the Sicily Channel (southern Mediterranean Sea). The comparison shows that real distributions are well reproduced by theoretical profiles. Specifically, position, shape and magnitude of the theoretical deep chlorophyll maximum exhibit a good agreement with the experimental values.

Estimation of biogas produced by the landfill of Palermo, applying a Gaussian model

In this work, a procedure is suggested to assess the rate of biogas emitted by the Bellolampo landfill (Palermo, Italy), starting from the data acquired by two of the stations for monitoring meteorological parameters and polluting gases. The data used refer to the period November 2005-July 2006. The methane concentration, measured in the CEP suburb of Palermo, has been analysed together with the meteorological data collected by the station situated inside the landfill area. In the present study, the methane has been chosen as a tracer of the atmospheric pollutants produced by the dump. The data used for assessing the biogas emission refer to night time periods characterized by weak wind blowing from the hill toward the city. The methane rate emitted by the Bellolampo dump has been evaluated using a Gaussian model and considering the landfill both as a single point source and as a multiple point one. The comparison of the results shows that for a first approximation it is sufficient to consider the landfill of Palermo as a single point source. Starting from the monthly percentage composition of the biogas, estimated for the study period, the rate of biogas produced by the dump was evaluated. The total biogas produced by the landfill, obtained as the sum of the emitted component and the recovered one, ranged from 7519.97 to 10,153.7m3/h. For the study period the average monthly estimations of biogas emissions into the atmosphere amount to about 60% of the total biogas produced by the landfill, a little higher than the one estimated by the company responsible for the biogas recovery plant at the landfill.

Spatio-temporal dynamics of a planktonic system and chlorophyll distribution in a 2D spatial domain: matching model and data

Field data on chlorophyll distribution are investigated in a two-dimensional spatial domain of the Mediterranean Sea by using for phytoplankton abundances an advection-diffusion-reaction model, which includes real values for physical and biological variables. The study exploits indeed hydrological and nutrients data acquired in situ, and includes intraspecific competition for limiting factors, i.e. light intensity and phosphate concentration. As a result, the model allows to analyze how both the velocity field of marine currents and the two components of turbulent diffusivity affect the spatial distributions of phytoplankton abundances in the Modified Atlantic Water, the upper layer of the water column of the Mediterranean Sea. Specifically, the spatio-temporal dynamics of four phytoplankton populations, responsible for about 80% of the total chlorophyll a, are reproduced. Results for phytoplankton abundances obtained by the model are converted in chlorophyll a concentrations and compared with field data collected in twelve marine sites along the Cape Passero (Sicily)- Misurata (Libya) transect. Statistical checks indicate a good agreement between theoretical and experimental distributions of chlorophyll concentration. The study can be extended to predict the spatio-temporal behaviour of the primary production, and to prevent the consequent decline of some fish species in the Mediterranean Sea.

The impact of landfills on the air quality of towns: a simple heuristic model for the city of Palermo

In this study, the landfill of Palermo, is investigated as a potential source of the unusual methane concentrations found in the urban context. The source for these pollution episodes is identified by means of a simple heuristic method. A cross-correlation analysis between wind data and methane concentration levels is also used to confirm the hypotheses formulated. Doppler Sound Detection And Ranging (SODAR) measurements are used to investigate the air masses dynamics at the landfill, in order to better support the adopted assumptions. This interpretative method can be adopted in the first assessment stages of the environmental site performance in order to single out the candidate pollution sources in urban areas, before any analytical computation takes place. In this sense, the method is intended as a viable tool in decision-making processes where in local administrations are currently involved in the selection of sustainable policies for the correct management of the territory.

Anchovy (Engraulis encrasicolus) early life stages in the Central Mediterranean Sea: connectivity issues emerging among adjacent sub-areas across the Strait of Sicily

The combined use of field data on anchovy (Engraulis encrasicolus, Linnaeus, 1758) egg distribution in the Central Mediterranean Sea on both sides of the Strait of Sicily (Sicilian–Maltese and Tunisian waters) and Lagrangian simulations were used to assess the pattern of connectivity between these two sub-areas as a result of spawning activity. The field data were collected during ichthyoplankton surveys carried out in summer 2008 and 2010. The simulation runs showed considerable (up to 20%) rates of particle exchange in both directions (from Tunisian to Sicilian–Maltese waters and vice versa). However, considering the typical high mortality rates of anchovy early stages, the actual larval exchange rates across the Sicily Strait are supposed to be significantly lower (<1%), supporting the hypothesis that the anchovy population sub-units in the Strait of Sicily can be considered as separate fish stocks for the evaluation of their optimum exploitation rates.

Space utilization by key species of the pelagic fish community in an upwelling ecosystem of the Mediterranean Sea

Most of the studies carried out in the past on economically important fish species rely on single species approach. Ecosystem dynamics are characterized by complex interaction among species, sharing common habitat needs and thus forming characteristic assemblages. The analysis of spatio-temporal variability of fish community, coupled to the analysis of spatial indices, provides a synthetic view of the fish community status evidencing, if any, the way a community changes. Such considerations drive also to the development of ecosystem-based fishery management paradigm. In the present study changes in pelagic fish community structure in an upwelling ecosystem of the central Mediterranean Sea during the last 10 years was analysed, by focusing the attention on the five most abundant small pelagic species: Engraulis encrasicolus, Sardina pilchardus, Sardinella aurita, Trachurus trachurus and Boops boops. Our results evidenced a quite stable community structure, characterized by spatial occupation strongly driven by ecosystem characteristics and modulated according to specie-specific behaviour. Obtained results lead us to hypothesize that the observed stability of community could be linked to the presence of different environments leading to efficient space partitioning and resources utilization among species.

Effects of habitat conditions at hatching time on growth history of offspring European anchovy, Engraulis encrasicolus , in the Central Mediterranean Sea

The knowledge of the growth history in young fishes represents an important aspect of fishery ecology. This is especially relevant in short-living species like European anchovy, since they suffer a high mortality rate in their early life stages until recruitment. Although it is well known that habitat condition significantly affects spawning dynamics of fishes, it is not yet clear if these conditions affect growth trajectories during the early life stage’s critical period. Otolith microstructure analysis has been proven a useful tool to back-calculate growth history of young fishes. Thus, we analysed the effect of habitat variability on their growth history using otolith microstructures and environmental variables obtained from satellite imagery. Growth trajectories in juvenile anchovies, collected in two recruitment surveys carried out in 2004 and 2005 in the Strait of Sicily, were characterized by means of three indices within the fast growing period: the maximum increment width, the mean value of increment width, and the time extension of the fast growing period. Obtained results evidenced a clear effect of environmental conditions, particularly of sea surface temperature and chlorophyll-a concentration, on the growth histories of juveniles of anchovy. Furthermore, delayed effects of environmental conditions at hatching time on the forthcoming growth dynamics were discussed.