Lagoon Resident Fish Species of Conservation Interest According to the Habitat Directive (92/43/CEE): A Review on Their Potential Use as Ecological Indicator Species

Transitional waters are fragile ecosystems with high ecological, social and economic values, that undergo numerous threats. According to the information provided by European Member States in the framework of the European Directive 92/43/EEC (Habitat Directive), the main threat to these ecosystems is represented by morphological and hydrological changes. The present work focuses on six lagoon fish species included in the Habitat Directive annex II (species requiring conservation measures: Aphanius fasciatus, A. iberus, Knipowitschia panizzae, Ninnigobius canestrinii, Valencia hispanica and V. letourneuxi) that spend their entire life cycle in the Mediterranean priority habitat 1150* “Coastal lagoons”. The overview of the current scientific literature allowed us to highlight how the presence and abundance of these species may provide important indications on the conservation status of coastal lagoon habitats. In fact, their occurrence, distribution and biology depend on the presence of peculiar structures, such as salt marshes, small channels, isolated pools and oligohaline areas. Coastal lagoon fragmentation and habitat loss have led to a significant reduction in genetic diversity or local population extinction. Although Aphanius and gobies have been shown to survive in eutrophic environments, it is clear that they cannot complete their life cycle without salt marshes (mainly Aphanius) and wetland areas (mainly gobies)

FISH FAUNA IN THE VENICE LAGOON: UPDATING THE SPECIES LIST AND REVIEWING THE FUNCTIONAL CLASSIFICATION

This work aims at reviewing the existing ecological classification of fish fauna in the Venice lagoon, and updating the list of species found during 15+ years of research in this ecosystem. The checklist encompass all fish life stages including ichthyoplankton, and contains 94 taxa, with 14 recorded only after 2010. The new functional classification, made of eight guilds including two guilds of lagoon residents and two of marine migrants, highlights the differences in species’ use of lagoon habitats in different seasons

DISTRIBUTION OF THE ALIEN SPECIES PALAEMON MACRODACTYLUS RATHBUN, 1902 IN THE VENICE LAGOON

Palaemon macrodactylus Rathbun (1902) is an estuarine shrimp native to north-western Pacific which, due to its wide environmental tolerance to chemical-physical conditions and its long breeding period, from 1957, probably carried by ship ballast water, massively colonized estuarine ecosystems worldwide. After its first record, in 2012, P. macrodactylus appears to have rapidly colonized the entire Venice lagoon, showing higher abundance in the confined saltmarsh stations of the northern sub-basin, probably due to the relatively low salinities values of this area. Records collected from 2014 to 2020 confirm the long reproductive period, comprised between Spring (mid-April) and Autumn (October), and the potential large invasion capacity of this species, which in the future could provoke competition with autochthonous species of the genus Palaemon and Crangon crangon

Genetic structure of the South European toothcarp Aphanius fasciatus (Actinopterygii: Cyprinodontidae) populations in the Mediterranean basin with a focus on the Venice lagoon

The genetic structure of Aphanius fasciatus populations has been analysed using two mitochondrial DNA (mtDNA) markers (16S rRNA and D-loop) obtained from specimens collected in nine sites from the Venice lagoon, Comacchio saltworks and Corsica. Available GenBank sequences were also included, in order to extend the results on a Mediterranean scale. Genetic polymorphism within the Venice lagoon was very low, with most of the specimens analysed (66% for 16S rRNA and 83% for D-loop) sharing the same haplotype for either of the two markers. The genetic homogeneity found within the Venice lagoon may be the consequence of the northward migration of southern Adriatic populations after the Last Glacial Maximum: mismatch analysis showed indeed clear signs of a rapid demographic and spatial expansion. To explain this genetic homogeneity other hypotheses were also suggested, such as adaptation to the high variability of brackish water habitats, and artificial introductions. On a Mediterranean scale, phylogenetic analyses showed the presence of five distinct geographical lineages: Aegean Sea, Greek coast of the Ionian Sea, Adriatic Sea, Tyrrhenian Sea and Southern Sicily. Analysis of molecular variance revealed a genetic partitioning mainly due to differences between groups presumably due to late Miocene geological events, while less polymorphism was present within groups and populations

Small creeks in a big lagoon: The importance of marginal habitats forfish populations

Temperate transitional water systems, as in the case of the Venice Lagoon, are characterised by many different shallow-water habitats. The availability of trophic resources and the low predator pressure make salt marshes one of the most important habitats for many fish species, both resident and marine migrant, but several anthropogenic pressures, erosion and relative sea level rise in particular, are causing a significant loss of this habitat. A part from natural habitats, in many small islands of the Venice lagoon, artificial creeks of different size and morphology are present, once used in traditional aquaculture activities or built up as defence lines. Aims of this study is to analyse and compare the structure and composition of fish communities inhabiting small-sized creeks, considering both the natural and artificial ones, in order to evaluate the ecological importance of these marginal habitats for fish populations. A particular attention was given to artificial sites, assessing their ecological value as alternative refuge habitats to natural salt marsh creeks. One year samplings conducted in four sites (two natural salt marshes and two artificial creeks) allowed to describe the local fish communities, which comprised 20 species overall. The analysis of how water parameters and habitat structure influenced the fish communities showed the importance of the connection between small creeks and the open lagoon, but also the refuge function offered by confined systems. High abundances of resident fish species listed in the Annex II of the Habitat Directive were observed and juveniles of eight species of marine migrant fish were found, some of which are of economic importance. This study underlined the presence of significant densities of juvenile marine migrant and lagoon resident fish species in the two artificial habitats. Actually, species richness and density resulted to be, in some cases, higher than in natural salt marsh systems. Results of this study emphasize the ecological importance of these marginal habitats for many fish species, of both conservation and economic importance Thus a proper management and restoration strategy of these sites is needed to maintain their functionality and to buffer the disappearance of natural salt marshes

Sound production in the Ponto-Caspian goby Neogobius fluviatilis and acoustic affinities within the Gobius lineage: implications for phylogeny

The aim of this study was to describe the vocal repertoire of the Ponto-Caspian goby Neogobius fluviatilis and to compare the acoustic properties of this species with those of other soniferous Mediterranean gobies belonging to the Gobius lineage. Vocalizations and associated behaviours were recorded under controlled aquarium conditions in female and male N. fluviatilis. Sound emission was elicited by means of 'intruder tests', using an individual of the same or opposite sex as an intruder, and recording sounds using a hydrophone placed 20 cm from the shelter used as a nest for the resident fish. Five acoustic properties, including spectral and temporal properties, were measured from 13 individuals. The vocal repertoire of the species consisted of sequences of short vocalizations during both agonistic and reproductive intraspecific interactions. The wave form of each sound resolved in a pure sine wave composed of rapidly repeated pulses. Sounds lasted about 200 ms, showing an average fundamental frequency of about 80 Hz. Sound properties did not differ between reproductive and the aggressive contexts, and the general structure of sounds was highly stereotyped. The individual means of three acoustic independent traits characterizing the sounds of seven species of the Gobius lineage, including N. fluviatilis, were then entered in a discriminant function analysis to assess how well species could be differentiated on the basis of acoustics, and their degree of affinities. The results suggested that the pulse repetition rate of the sounds, i.e. the relative tonal/pulsatile nature of the sounds, was the most important property in differentiating the species, and that this trait may contain a high level of phylogenetic signal, as the species producing tonal sounds clustered together, in line with the results of recent molecular phylogenic studies. The results were discussed in light of the geological and phylogeographical events believed to have driven the diversification of European gobies

Interspecific Aggression and Food Competition between the Global Invader Palaemon macrodactylus and the Native Palaemon elegans

The impact of invasive alien species on native communities can act at different levels both by affecting the ecosystem’s structure (i.e., mainly in the case of vegetation) and through direct interactions (i.e., competition for food or space). Behavioral studies under controlled conditions can provide relevant information on both the invasive potential of alien species and the potential impact of the invaders on the local native species. In the laboratory, the competition for food resources between the invasive oriental shrimp Palaemon macrodactylus, Rathbun, 1902, and the Mediterranean native shrimp Palaemon elegans, Rathke, 1836, was analyzed. These species are typical residents of coastal transitional and estuarine waters, so the experiments were carried out using two salinity conditions that characterize the coastal lagoon of Venice. Although at both salinity treatments the alien species tended to be more aggressive than the native one, significant differences between the two species were mainly observed at a salinity of 30. In particular, at a salinity of 30, P. macrodactylus spent more time attending to the food source than the native species. The results are discussed in light of the potential inter-specific competition between the two species within the conditions of the Venice lagoon

Interspecific Aggression and Food Competition between the Global Invader <i>Palaemon macrodactylus</i> and the Native <i>Palaemon elegans</i>

The impact of invasive alien species on native communities can act at different levels both by affecting the ecosystem’s structure (i.e., mainly in the case of vegetation) and through direct interactions (i.e., competition for food or space). Behavioral studies under controlled conditions can provide relevant information on both the invasive potential of alien species and the potential impact of the invaders on the local native species. In the laboratory, the competition for food resources between the invasive oriental shrimp Palaemon macrodactylus, Rathbun, 1902, and the Mediterranean native shrimp Palaemon elegans, Rathke, 1836, was analyzed. These species are typical residents of coastal transitional and estuarine waters, so the experiments were carried out using two salinity conditions that characterize the coastal lagoon of Venice. Although at both salinity treatments the alien species tended to be more aggressive than the native one, significant differences between the two species were mainly observed at a salinity of 30. In particular, at a salinity of 30, P. macrodactylus spent more time attending to the food source than the native species. The results are discussed in light of the potential inter-specific competition between the two species within the conditions of the Venice lagoon

The influence of habitat structure on energy allocation tactics in an estuarine batch spawner

Trade-off between fecundity and survival was tested in a batch spawner, the Mediterranean killifish Aphanius fasciatus, using an integrated modelling-data approach based on previously collected empirical data. Two sites of the lagoon of Venice (Northern Adriatic sea, Italy) were selected in order to compare the energy allocation between growth and reproduction in two contrasting habitats. These were characterised by high and comparable level of richness in basal resources, but showed two different mortality schedules: an open natural salt marsh, exposed to high level of predation, and a confined artificial site protected from piscivorous predation. By means of a bioenergetic Scope for Growth model, developed and calibrated for the specific goals of this work, we compared the average individual life history between the two habitats. The average individual life history is characterised by a higher number of spawning events and lower per-spawning investment in the confined site exposed to lower predation risk, compared to the site connected with the open lagoon. Thus, model predictions suggest that habitat structure with different extrinsic mortality schedules may shape the life history strategy in modulating the pattern of energy allocation. Model application highlights the central role of energy partitioning through batch spawning, in determining the life history strategy. The particular ovary structure of a batch spawner seems therefore to allow the fish to modulate timing and investment of spawning events, shaping the optimal life history in relation to the environmental conditions. © 2016 Elsevier Ltd