The macrozoobenthic community of the Santa Gilla lagoon (southern Sardinia, Italy)

1 - Macrozoobenthos is one of the most significant communities of hydrobionts for assessing the ecological state of a water body. In spite of its importance, only few data concerning the macrobenthic community of Santa Gilla lagoon are available; 2 - Santa Gilla is one of the most important wetlands in Sardinia. The aim of this study is to give data on species composition of its macrozoobenthic community; 3 - Sampling has been carried out in 2010-2011 in July, October, January and April, in three stations located along a salinity gradient and the main environmental parameters were measured; 4 - A total of 13031 specimens belonging to 92 taxonomic groups and 5 main phyla (Anellida, Mollusca, Arthropoda, Cnidaria and Nemertea) were found. Among them, 52 different taxa were collected and pointed out for the first time in Santa Gilla lagoon in this work. 5 - Finally, seasonal and space differences were observed in the abundance values of the main taxonomic groups and in the diversity indices values

Enviromental influences on the spatio-temporal distribution of Aristeus Antennatus (Risso, 1816) and Aristaeomorpha Foliacea (Risso, 1827) in the Central-Western Mediterranean

According to the Food and Agriculture of United Nations, almost 80% of the world fish populations are overexploited, depleted or in a state of collapse. In general the Mediterranean Sea is characterized by the 33% of assessed stocks fully exploited, 50% overexploited and the remaining 17% non-fully exploited. Bottom trawling fleets predominate in many Mediterranean fisheries, being responsible for a high share of total catches and, in many cases, yielding the highest earnings among all the fishing sub-sectors. The deep-sea fishing began only in the first decades of the last century, as a result of the development of new technologies that made fisheries in deeper waters possible. The main target species of the Mediterranean deep-sea bottom fishery are the red shrimps Aristeus antennatus (Risso, 1816) and Aristaeomorpha foliacea (Risso, 1827), that represent one of the most important commercial species. In general both species coexist in large part of their distribution range, but in the Mediterranean Sea, where the large part of studies have been undertaken, their distribution is patchy and seems to shows an antagonistic longitudinal gradient. In this context different hypotheses have been formulated by several authors to explain the different distribution observed. Some of them correlated various environmental variables with the presence/absence of these species to explain the spatial distribution and the temporal fluctuations in landings of these two species. All the identified factors seems not to act in synergy in determining the spatio-temporal variation of the species and which is the parameter that has a significant predictive effect is still unclear. Considering the high degree of interaction between marine organisms and the environment, a more holistic approach incorporating interspecific interactions and physical environmental influences would contribute to greater sustainability by reducing the uncertainty in predictions and promoting an ecosystem based management. In the light of the above, this thesis applies a multi-disciplinary approach to study the dynamic of the Mediterranean deep-water red shrimps. The main purpose of this thesis is to better understand how the abiotic factors could impact on the spatio-temporal distributions of the decapod crustaceans A. antennatus and A. foliacea. The first part provides information on the abundance and geographical distribution of deep-water red shrimps using 19 years of trawl survey data. Both red shrimps species occur almost exclusively on the “meso-bathyal” stratum (500-800 m). The distribution pattern appears quite different for the two species, and the abundance indexes as well the spatial maps, evidenced local higher abundances (hotspots) where the blue and red shrimp and the giant red shrimp are mainly concentrated. In general, a very high interannual variability was detected in all areas probably linked with some environmental factors that occurs in Sardinian waters. In particular the investigation of the hydrographic conditions of the shelf-slope areas, developed in the second part of the thesis, highlight presences of the typical water masses already detected in literature. In our study area the water masses occurring on the continental shelf-slope zones, where the deep water red shrimps are catched, are mainly These water masses overlap and even partially mix each other during their displacement across the Sardinian shelf-slope area according to the general topography of the lands and the bottoms. Results showed that the distribution of the main water masses is comparable to the literature, moreover, the results confirmed that the great variability between basins and year of sampling is clearly associated with waters of very different origin that follow converging routes and mix together in the study area. The analysis carried out in third part underlined the influence of peculiar areas, such as seamounts, on the structure of the middle-slope assemblages as well as the behavioural rhythms of the deep water red shrimps. Their daily and nocturnal movements from the base of the seamount to the edge of the continental shelf increase the range of their distribution. This results highlights the fact that shrimps and other species in the Baronie seamount, move during a day-night cycle, probably influenced by some parameter indirectly related to their activity. These nektobenthic displacements are known to occur also in the continental shelf and slope, but in the canyon and seamounts they are broadened and can be studied more easily. These displacements could produce a bias in trawl survey data according to the time of day with effects on population assessment and demographic evaluation. The fourth part of the thesis provided also the identification of the spawning and nursery grounds, and their relationship to major, oceanographic processes The location of the area appears to be correlated with the spatial pattern of the main persistent oceanographic processes, identified in the Sardinia Sea, such as enrichment due the upwelling present in the south west shelf-slope area. Other important areas of aggregation for both juveniles and mature females were found over the bathyal zones in canyon and seamounts environments, where productivity is reported higher than elsewhere. These privileged areas for recruitment, rich in nutrients thanks to the effect of different currents, would seem to guarantee the regeneration of the resource. Finally, the analysis also suggested the existence of a seasonal bathymetric distribution of the nursery areas. The juveniles of A. foliacea are located in the upper part of the continental slope in spring-summer and reach greater depths in autumn. For A. antennatus, for which nursery areas appear only in autumn, an opposite ontogenic migration from deep sea to upper slope, has been noted during the summer. In the last part of the thesis, the influences of in situ hydrographic variables on the distribution of the Aristeid stocks on the fishing grounds of Sardinia were analysed. The comparison between hydrographic and biological data evidenced that both species seem to be connected to the peculiar features and fate of the LIW (Levantine Intermediate Water) between 400 and 600 m. In fact, in the south-eastern part, the LIW properties predominate and A. foliacea is the main species, while in the western and northern areas of Sardinia the LIW loses intensity in favor of A. antennatus, which prefers colder temperatures. Besides the oceanographic features influencing the distribution pattern of these species, the variation left unexplained by the model may be attributed to different sources of variation such as the presence of geomorphological structures or reproduction and recruitment phenomena. In conclusion, following a multidisciplinary approach, this thesis tries to give a substantial contribution to the knowledge of the spatio-temporal dynamics of the two Mediterranean deep-water red shrimps. The results highlight how these patterns of distribution strongly correlated not only with the main oceanographic process (LIW properties) but also with local hydrographic conditions. Among these conditions, upwelling events and the particular geomorphology that characterized the Sardinian shelf-slope region seem to be the most important factors. In addition life history traits of these two species linked to a heavy prolonged fisheries exploitation, could determine a masking effect that makes difficult to interpret the whole picture of the distribution of the two species. For this reason, these results should take in to account for the assessment and management of these important resources

Differential feeding rates of native and alien predators on the invasive Asian date mussel Arcuatula senhousia (Benson in cantor, 1842) in a Mediterranean coastal lagoon

The alien Asian date mussel Arcuatula senhousia inhabits several coastal environments worldwide. This species can form dense mats where individuals attach through byssus threads, thus altering the structure, functioning and biodiversity of the native communities. We investigated the feeding preference of different predators on this alien species in a Mediterranean coastal lagoon. To do this, a mesocosm experiment was conducted using two crab species (the Mediterranean green crab Carcinus aestuarii) and the Say mud crab Dyspanopeus sayi, and one gastropod, the banded dye-murex Hexaplex trunculus as predators of A. senhousia with or without byssus mats. Our data suggest that C. aestuarii is a more effective predator against A. senhousia than D. sayi, and that H. trunculus is almost ineffective. A possible implication of this result is the potential use of the native crab C. aestuarii for limit the formation of the byssus mats, thus mitigating their potential negative effects on the native communities

Exploring Less Invasive Visual Surveys to Assess the Spatial Distribution of Endangered Mediterranean Trout Population in a Small Intermittent Stream

Simple Summary This study explores the use of alternative and non-harmful methods for monitoring endangered Mediterranean trout in small intermittent streams. Specifically, two visual survey techniques were compared: a visual survey from streambanks and an underwater visual survey using underwater cameras. The main objective was to assess the effectiveness of detecting patterns in fish occupancy in relation to a set of environmental factors. The comparison revealed that underwater camera surveys performed similarity to visual surveys from streambanks during low-flow regimes. However, visual surveys from streambanks were less effective during the highest flow regimes. The volume of pools and the percentage cover of submerged macrophytes were found to be significant environmental variables affecting fish detection probability using underwater cameras. On the other hand, the analysis of data from visual observations from streambanks indicated a clear impact of high turbulence rates on pool occupancy. In conclusion, these findings demonstrate the utility of visual methods in describing the occupancy patterns of Mediterranean trout in small streams. Monitoring the conservation status of endangered freshwater fish using less invasive methods poses challenges for ecologists and conservationists. Visual surveys have been proposed as an alternative to electrofishing, which is a standard methodology that can cause injuries, physiological stress and post-release mortality in organisms. To test the efficacy of visual methods, a study was conducted in an intermittent stream of Sardinia (Italy). Two visual methods were employed: a visual survey from streambanks (VSS) and an underwater visual survey (UVS) using cameras. The aims of this study were (1) to compare the effectiveness of these methods in detecting patch occupancy patterns and (2) to investigate the effect of environmental variables on the detection probability of Mediterranean native trout. Environmental variables characterizing pool habitats were recorded, and generalized linear models (GLMs) were employed to assess the correlation between these variables and trout presence/absence. GLM analysis revealed that UVS had higher detection probability with larger pool volume, whereas submerged macrophytes negatively affected detection probability. Detection from streambanks (VVS) was negatively affected by a high turbulence rate. In conclusion, our study suggests the utility of visual methods to describe patterns of patch occupancy of Mediterranean trout. However, methods can be differently affected by environmental variables. Therefore, monitoring programs using these methods should consider these factors to ensure a reliable description of within-stream trout distribution in intermittent streams

Hard times for catadromous fish: the case of the European eel (Anguilla anguilla, L. 1758)

Catadromous fish species can be defined important organisms for their ecological, economical, and cultural value. Because of a complex life cycle, catadromous fish species are exhibited to the cumulative effect of multiple anthropogenic threats that resulted in worldwide decline since the beginning of the 20th century. Among the most iconic catadromous species, the European eel Anguilla anguilla has aroused considerable interest, and to date, many aspects of its life cycle remain relatively unknown. Although conspicuous efforts by the research to ensure the perpetuation of the species were conducted, the identification of the best tools to reduce the threats that affect eels remains challenging. In this narrative review, the state of the knowledge and main threats about the life cycle, the habitat occupancy, the recruitment, and migration patterns of the European eel have been reported

Differences in the diet of breeding Cormorants Phalacrocorax carbo sinensis in an inland colony: the effect of years, breeding stages and locations within the colony

AbstractA study of the diet of the Great Cormorant Phalacrocorax carbo sinensis (fish species and size) in (1) different seasons (years), (2) breeding stages (incubation and chick rearing), and (3) breeding areas (center and edge) in the colony in the Dzierżno-Duże Reservoir (southern Poland) was carried out. Overall, 147 pellets of the Great Cormorant were analysed. The low values of the indexes of Levin (Bi) and Shannon (H') showed a limited trophic spectrum in the diet of the Great Cormorant. Roach (Rutilus rutilus) with a percentage index of relative importance (%IRI) of 62.89, perch (Perca fluviatilis) (%IRI = 22.63) and carp (Cyprinus carpio) (%IRI = 10.43), were the most common prey. Evident changes in the diet between 2003 and 2014, with less roach and more perch and ruffe in 2014 were found. They could be probably related to changes in the fish community. Differences in the food of cormorants between breeding stages reflected dietary requirements of the chicks. During the breeding season younger chicks require feeding with smaller fish than older chicks. The proportion of fish species found in the cormorant diet differed between the edge and the centre of the colony. We concluded that the impact of Great Cormorants on native fish assemblages may be dependent on the location within the colony, development state of the chicks and season, not just fish availability

A method for selective stimulation of leg chemoreceptors in whole crustaceans

The integration of sensory information with adequate motor outputs is critical for animal survival. Here, we present an innovative technique based on a non-invasive closed-circuit device consisting of a perfusion/stimulation chamber chronically applied on a single leg of the crayfish Procambarus clarkii. Using this technique, we focally stimulated the leg inside the chamber and studied the leg-dependent sensory-motor integration involving other sensory appendages, such as antennules and maxillipeds, which remain unstimulated outside the chamber. Results show that the stimulation of a single leg with chemicals, such as disaccharides, is sufficient to trigger a complex search behaviour involving locomotion coupled with the reflex activation of antennules and maxillipeds. This technique can be easily adapted to other decapods and/or other sensory appendages. Thus, it has opened possibilities for studying sensory-motor integration evoked by leg stimulation in whole aquatic animals under natural conditions to supplement, with a direct approach, current ablation/silencing techniques

When the Eel Meets Dams: Larger Dams’ Long-Term Impacts on Anguilla anguilla (L., 1758)

Diadromous fish, like the European eel Anguilla anguilla (L., 1758), are highly threatened by dams that disrupt river connectivity, consequently impeding fish movements to reach feeding and spawning habitats. In this study, variation in eel occurrence between a historical period (1940–1970) and recent data (2016–2020) was assessed throughout the Sardinian rivers’ network (more than 450 sites). Using Boosted Regression Trees (BRT) we investigated relationships between eel’s occurrence and a set of spatial and temporal environmental variables including a set of dams’ construction features for each period. An overall decrease by 65% of eel’s occurrence was noticed during the ca. 80-years period under scrutiny. Considering a subset (105 and 88 sites for the historical and the recent period, respectively) characterized by the presence of larger dams (height >15 m), eel’s occurrence dropped by 85%. Conversely, eel’s occurrence dropped only by ca. 44% in dam-free sites. During the historical period, eel’s occurrence was mostly affected by time since the initial habitat fragmentation, flow, distance to dams, connectivity, and dams’ height. In the most recent period, eel’s occurrence is mostly affected by dams’ building year, dam-to-sea distance, and, again, dams’ height. Results pinpoint that dams’ construction features and the time from their construction have significant negative effects on eel’s occurrence. Addition of future effective eel restoration practices, apart any other adverse environmental stressor, must consider dams’ removal, wherever socially sustainable or alternatively, the modification of construction features of dams (like excessive height) and the addition of fish ladders

Pug-Headedness Anomaly in a Wild and Isolated Population of Native Mediterranean Trout Salmo trutta L., 1758 Complex (Osteichthyes: Salmonidae)

Skeletal anomalies are commonplace among farmed fish. The pug-headedness anomaly is an osteological condition that results in the deformation of the maxilla, pre-maxilla, and infraorbital bones. Here, we report the first record of pug-headedness in an isolated population of the critically endangered native Mediterranean trout Salmo trutta L., 1758 complex from Sardinia, Italy. Fin clips were collected for the molecular analyses (D-loop, LDH-C1* locus. and 11 microsatellites). A jaw index (JI) was used to classify jaw deformities. Ratios between the values of morphometric measurements of the head and body length were calculated and plotted against values of body length to identify the ratios that best discriminated between malformed and normal trout. Haplotypes belonging to the AD lineage and the genotype LDH-C1*100/100 were observed in all samples, suggesting high genetic integrity of the population. The analysis of 11 microsatellites revealed that observed heterozygosity was similar to the expected one, suggesting the absence of inbreeding or outbreeding depression. The frequency of occurrence of pug-headedness was 12.5% (two out of 16). One specimen had a strongly blunted forehead and an abnormally short upper jaw, while another had a slightly anomaly asymmetrical jaw. Although sample size was limited, variation in environmental factors during larval development seemed to be the most likely factors to trigger the deformities

Distribution of spawning and nursery grounds for deep–water red shrimps in the central western Mediterranean Sea

The presence of spawning and nursery grounds of Aristeids in the central western Mediterranean Sea were investigated using fishery-independent data (trawl surveys, 1994–2012). Spatial distributions were generated for mature animals and recruits, for both spring/summer and autumn data, using an inverse distance-weighted deterministic interpolation. The persistence index was used to identify stable spawning and nursery grounds in the Sardinian slope region for Aristaeomorpha foliacea and Aristeus antennatus. Areas of aggregation for recruits and mature females appear to be connected with important physical habitat features. The analysis also suggests a seasonal bathymetric distribution for nursery areas. The recruits of A. foliacea are located in the upper part of the continental slope (377-450 m) in spring/summer and reach greater depths (468-628 m) in autumn. For A. antennatus, for which nursery areas only emerge in autumn, there is presumably an opposite ontogenic migration, from deep sea to upper slope, during the summer (575-681 m). The results also indicate a partial overlap between the nursery and spawning grounds of both species. In this particular area, local environmental conditions such as upwelling events or the presence of canyons and seamounts seem to play an important role in their distribution. This study also generated relevant information on the spatial and temporal distribution of seasonal or persistent aggregations of spawners and recruits, providing scientific elements to suggest the protection of these important resources