172 research outputs found
Importancia de los fenómenos físicos y la disponibilidad de nutrientes en el control de la concentración de clorofila estimada por satélite en el área costera de afloramiento del Canal de Sicilia
The northern sector of the Sicilian Channel is an area of favourable upwelling winds, which ought to support primary production. However, the values for primary production are low when compared with other Mediterranean areas and very low compared with the most biologically productive regions of the world’s oceans: California, the Canary Islands, Humboldt and Benguela. The aim of this study was to identify the main factors that limit phytoplankton biomass in the Sicilian Channel and modulate its monthly changes. We compared satellite-based estimates of chlorophyll a concentration in the Strait of Sicily with those observed in the four Eastern Boundary Upwelling Systems mentioned above and in other Mediterranean wind-induced coastal upwelling systems (the Alboran Sea, the Gulf of Lions and the Aegean Sea). Our results show that this low level of chlorophyll is mainly due to the low nutrient level in surface and sub-surface waters, independently of wind-induced upwelling intensity. Further, monthly changes in chlorophyll are mainly driven by the mixing of water column and wind-induced and/or circulation-related upwelling processes. Finally, primary production limitation due to the enhanced stratification processes resulting from the general warming trend of Mediterranean waters is not active over most of the coastal upwelling area off the southern Sicilian coast.El sector norte del Canal de Sicilia es un área de vientos favorables para el afloramiento, lo cual debe favorecer la producción primaria. Sin embargo, los valores de producción primaria son bajos comparados con otras áreas del Mediterráneo y muy bajos comparados con las regiones biológicamente más productivas de los océanos a nivel mundial: California, Canarias, Humboldt y Benguela. El objetivo de este estudio fue identificar los principales factores que limitan la biomasa del fitoplancton y modulan sus cambios mensuales. Comparamos estimas de la concentración de clorofila a basadas en satélite en el estrecho de Sicilia, con las observadas en los cuatro sistemas orientales de afloramiento mencionados anteriormente y en otros sistemas costeros del Mediterráneo en los que el viento favorece los afloramientos (Mar del Alborán, Golfo de León y Mar Egeo). Nuestros resultados muestran que la baja producción primaria es debida principalmente a la baja entrada de nutrientes en aguas superficiales, independientemente de la intensidad del afloramiento causado por el viento. Por otro lado, los cambios mensuales en la producción primaria se deben a la mezcla de la columna de agua y afloramientos asociados al viento y/o procesos de circulación en la zona. Finalmente, la limitación de la producción primaria debida al aumento del proceso de estratificación resultante de la tendencia general de calentamiento de las aguas del Mediterráneo, no es activa a lo largo de la mayor parte del área de afloramiento en la costa sur de Sicilia
Fluid escape structures revealing volcanic and tectonic activity in the Graham Bank (Sicily Channel)
The Graham Bank (NW Sicily Channel, Central Mediterranean) is characterised by a complex seafloor morphology,
where morphostructural highs, submarine plain, escarpments, and negative and positive relieves indicate a complex
structural setting and the occurrence of seepage fluids.
New high-resolution acoustic data (multibeam, Chirp profiles) and multi-channel profiles, allowed us to differentiate
two main morphological sectors, and to identify several pockmarks and mounds linked to fluid escape phenomena.
The eastern sector, corresponding to the volcanic edifices of the Graham Bank, is characterised by volcanic context
with rough morphology, several mounds, focused seepage plumes and magmatic acoustic substrate, all related to the
activity forming both the Graham Bank and the new volcanic cones here identified.
The western sector displays a generally flat morphology dominated by Late Pleistocene-Holocene outer shelf deposits,
where mounds and pockmarks with sub-circular and ellipsoidal shapes, V- to U-shaped in cross-section, are the prevailing
features indicating the migration of fluids to the seafloor.
These two areas are separated by a vertical deep fault forming a deeply incised channel with NW-SE direction. The
latter is bordered by steep walls forming fault escarpments, which shed the eroded materials to the adjacent lower slope
and deep-water zones.
The overall morphostructural setting suggests a tectonic control in the morphological conformation of the seabed and
in the distribution of both pockmarks and mounds. The aligned mounds have both NW-SE and NNW-SSE orientation,
sometimes extending several hundred metres and forming hummocky surfaces. The aligned pockmarks are strictly
comparable to the orientation of the faults related to the most recent tectonic activity.
The good correlation between fluid escape structures and the main fault systems involving the kilometric sedimentary
cover suggests that the degassing of fluids is rooted in depth revealing that extensional tectonics acts with very deep subvertical recent faults developing along and reactivating the Cenozoic (both Plio-Quaternary and Messinian) and Mesozoic
tectonic systems.peer-reviewe
Volcano- and neoectonic-related slope failures in the north-western Sicily Channel (Central Mediterranean Sea) : implications for understanding and assessing geohazard risk
The southern Sicily coasts represent an important contribution to Italian tourism and marine geological processes in
the Sicily Channel could pose a significant risk to neighbouring populations and goods.
In this work, we are presenting the first results of the data collection that allowed us to identify and map several
geological elements that can be used to assess submarine geohazards in the Sicily Channel. By using multibeam data and
high-resolution seismic reflection profiles acquired during the ACUSCAL 2015 Cruise, we defined the characteristics of
the morphostructural highs, and the morphology of slope failures and the stratigraphy of the mass transport deposits
(MTD).peer-reviewe
Condition of pteropod shells near a volcanic CO2 vent region
Natural gradients of pH in the ocean are useful analogues for studying the projected impacts of Ocean Acidification (OA) on marine ecosystems. Here we document the in situ impact of submarine CO2 volcanic emissions (CO2 vents) on live shelled-pteropods (planktonic gastropods) species Creseis conica in the Gulf of Naples (Tyrrhenian Sea, Mediterranean). Since the currents inside the Gulf will likely drive those pelagic calcifying organisms into and out of the CO2 vent zones, we assume that pteropods will be occasionally exposed to the vents during their life cycle. Shell degradation and biomass were investigated in the stations located within and nearby the CO2 vent emission in relation to the variability of sea water carbonate chemistry. A relative decrease in shell biomass (22%), increase in incidence of shell fractures (38%) and extent of dissolution were observed in Creseis conica collected in the Gulf of Naples compared to those from the Northern Tyrrhenian Sea (control stations). These results suggest that discontinuous but recurrent exposure to highly variable carbonate chemistry could consistently affect the characteristic of the pteropod shells
Growth variability in Atlantic horse mackerel Trachurus trachurus (Linneus, 1758) across the central Mediterranean Sea: contrasting latitudinal gradient and different ecosystems
Data on Atlantic horse mackerel Trachurus trachurus (Linneus, 1758) were collected along 8-year acoustic surveys (2011-2018). Age and growth variability of horse mackerel from the Central Mediterranean Sea were investigated within different, contrasting habitats, from the south of Sicily to the north Tyrrhenian (Ligurian Sea). Data from satellite provided the habitat features along the study period over the whole surveyed area. For comparison purposes, according to the ecosystems difference the study area has been split into four subareas: Strait of Sicily (SoS), North of Sicily (NS), south Tyrrhenian Sea (ST) and north Tyrrhenian Sea (NT). In terms of the FAO Geographical Sub-Area definition the SoS corresponding to GSA15 and 16, NS to GSA 10 south, ST to GSA10 north and NT to GSA 9. Results showed a growth homogeneity in the study area, suggesting a unique stock inhabiting these waters. The only exception was recorded for juveniles (Age 0 class) in the SoS, where a lower size at age was detected compared to other areas. A multiple linear modelling analyses suggested that variability in length at age 0 was mainly linked to the oceanographic differences between an upwelling driven system (Strait of Sicily) and the other ecosystems, where enrichment processes are mainly due to river runoff (relevant in ST and NT). Namely, Absolute Dynamic Topography (ADT) and body condition factor (Kn) were significantly related to differences in length at age 0. Results revealed that currents (and gyres) are among the principal abiotic factors controlling Atlantic horse mackerel growth in its first year of life, suggesting that circulation and food-related processes (i.e., zooplankton concentration) are of major importance for this species. Finally preliminary observations suggest the Strait of Sicily may be the main spawning area among those analyzed
Catch of pelagic hauls in Mediterranean acoustic surveys: Is it the same between day and night?
Fish sampling is a critical aspect of acoustic surveys, because it is directly related to the “transformation” of echo into species biomass and subsequently affects the accuracy of acoustic estimates. In the present study, we investigated the differences between day and night sampling in a) the catch composition through certain diversity indices and b) the length frequency distribution of anchovy and sardine using catch data of pelagic hauls collected from four different regions of the European Mediterranean waters. In addition, the possible bias in trawl efficiency due to sampling time and the possible error introduced in acoustic estimates were investigated. No statistically significant differences were found between day and night in any of the parameters examined. The results showed that a more flexible strategy can be adopted to reduce the duration and the cost of acoustic sampling for small pelagic species. The advantages and disadvantages of the two sampling strategies are discussedPublicado
Reproductive strategy and fecundity of meagre <i>Argyrosomus regius</i> Asso, 1801 (Pisces: Sciaenidae): implications for restocking programs
Variability of water mass properties in the Strait of Sicily in summer period of 1998–2013
The Strait of Sicily plays a crucial role in determining the water-mass exchanges and related properties between the western and eastern Mediterranean. Hydrographic measurements carried out from 1998 to 2013 allowed the identification of the main water masses present in the Strait of Sicily: a surface layer composed of Atlantic water (AW) flowing eastward, intermediate and deep layers mainly composed of Levantine intermediate water (LIW), and transitional eastern Mediterranean deep water (tEMDW) flowing in the opposite direction. Furthermore, for the first time, the signature of intermittent presence of western intermediate water (WIW) is also highlighted in the northwestern part of the study area (12.235◦ E, 37.705◦ N). The excellent area coverage allowed to highlight the high horizontal and vertical inter-annual variability affecting the study area and also to recognize the permanent character of the main mesoscale phenomena present in the surface water layer. Moreover, strong temperature-salinity correlations in the intermediate layer, for specific time intervals, seem to be linked to the reversal of surface circulation in the central Ionian Sea. The analysis of CTD data in deeper water layer indicates the presence of a large volume of tEMDW in the Strait of Sicily during the summers of 2006 and 2009.peer-reviewe
Relazione tecnica sulle attività della campagna oceanografica “Ancheva 2015”
Nelle acque Italiane dello Stretto di Sicilia sin dal 1998 vengono effettuate ogni anno campagne di valutazione dell’abbondanza e distribuzione della biomassa pelagica con l’impiego di strumentazione elettroacustica. Dal 2009 lo svolgimento dei survey acustici è parte integrante del Progetto MEDIAS (MEDiterranean International Acoustic Survey), inserito dagli Stati Membri partecipanti al Progetto all'interno del Programma Nazionale 2014-2016. Il Progetto prevede lo svolgimento di survey acustici annuali con lo scopo di valutare la biomassa e la distribuzione spaziale dei piccoli pelagici in aree del Mediterraneo, appartenenti all’Unione Europea.
Le specie target sono le principali specie commerciali di piccoli pelagici in Mediterraneo, ovvero l’acciuga (Engraulis encrasicolus) e la sardina (Sardina pilchardus). Si tratta di specie a ciclo di vita breve caratterizzate da ampie oscillazioni interannuali nella biomassa. Negli anni in cui i livelli di biomassa sono particolarmente bassi l’effetto di un elevato sforzo di pesca porterebbe ad un collasso di tali risorse anche da un anno all’altro.
Il collasso di tali specie è stato ben documentato in letteratura mostrando che i tempi di recupero sono molto lunghi e hanno effetti socio-economici catastrofici anche sulle comunità marinare che vivono grazie agli introiti derivanti dalla pesca e commercializzazione di prodotti in scatola.
La presente relazione mostra le attività svolte a seguito del survey condotto a bordo della N/O Dallaporta nello Stretto di Sicilia (GSA 16) nell’estate del 2015. Oltre all’acquisizione dei dati acustici, sono state eseguite stazioni di pesca sui piccoli pelagici con rete da traino pelagica sperimentale (volante monobarca), accessoriata con sensori per il controllo dell’apertura e della posizione della rete nella colonna d’acqua. Nell’area di studio sono stati inoltre acquisiti i profili delle principali variabili oceanografiche con sonda multiparametrica CTD.
Il rapporto descrive le diverse procedure adottate per l’analisi dei dati acquisiti ed il trattamento dei campioni biologici raccolti. Per le due specie target viene quindi fornita la distribuzione spaziale e la stima della biomassa, complessiva ma anche suddivisa per classi di taglia e classi di età
Reproduction and Sexual Maturity of European Sardine (Sardina pilchardus) in the Central Mediterranean Sea
Understanding drivers of fish maturity is essential to predict the productivity, stability, and resiliency of exploited populations. Size at maturity for European sardine (Sardina pilchardus) in the Central Mediterranean Sea has never been published within rigorous peer review process. In the past, stock assessment working groups in the Mediterranean requested such information; however, the size at which 50% of the fish population reaches the sexual maturity (L50) often received weak estimates based on a single or few years of observation, which do not necessarily reflect the whole stock. To address this data gap for the Central Mediterranean Sea, the present research estimated size at maturity of European sardine in the Strait of Sicily. In the study period (2009–2017), sampled individuals exhibited significant differences in size range as well as in body condition and reproductive effort. Data also permitted a clear identification of the spawning season, starting in September–October and ending in March–April the following year. Along the analyzed period, the size at first maturity ranged from 108 to 124 mm (total length) for females and from 102 to 122 mm for males. Significant differences were recorded among genders and years. Moreover, a goodness-of-fit measure was proposed to assess the robustness and reliability of L50 estimates, and thus selecting those that minimize the fitting-associated errors. Finally, results suggested that the low proportion of immature individuals in the samples represents the main source of bias in L50 estimation and possible solution was also proposed
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