Stefano Malavasi

Fish assemblages in different shallow water habitats of the Venice Lagoon

The small-sized fish assemblages of the Venice Lagoon were investigated and compared among five shallow subtidal habitats (seagrass beds, sparsely vegetated habitats, unvegetated sand bottoms, mudflats and saltmarsh creeks) in the Northern lagoon basin. Sampling was carried out seasonally (Spring, Summer and Autumn of 2002) in 4–7 stations for each habitat type, by means of a fine-mesh, small beach seine. Two-way analysis of variance was applied to assess the differences in species richness, fish diversity, density and standing stock amongst habitats, whereas fish assemblage composition was investigated by using multivariate analyses (MDS, ANOSIM, SIMPER). The analyses indicated that seagrass beds and saltmarsh creeks are relevant shallow habitats in structuring the small-sized fish assemblages of the Venice Lagoon, supporting specialized and recognizable fish assemblages. Those in seagrass beds, in particular, were characterized by higher species richness and standing stock with respect to all the others. The structuring role of these habitats was discussed in terms of both habitat complexity and degree of confinement. In contrast, sandy bottoms, mudflats and sparsely vegetated habitats were identified as “transition” habitats, with highly variable fish assemblages, influenced by the contribution of the adjacent habitats, and acting probably as both ‘buffer zones’ between the other habitats and migration routes for many fish species in the lagoon.

Male Courtship Sounds in a Teleost with Alternative Reproductive Tactics, the Grass Goby, Zosterisessor ophiocephalus

Male grass gobies show two alternative breeding tactics, territorial and sneaker, distinguished by body size and difference in ray elongation on the second dorsal fin. The larger males, with elongated fins, are territorial and emit sounds during courtship. Smaller males, without elongated fins, act as sneakers. Both large and small males produce sounds in the presence of a ripe female. Males produce a grunt, lasting about 300 ms, made up of pulses repeated at a low rate (22–68 pps). Pulse duration, number, and repetition rate, did not differ between the two male types, but dominant frequency and sound amplitude did. Dominant frequency had a strong, inverse relationship with body size, whereas sound amplitude showed a weak positive relation to body size. Male size, and not the particular reproductive male tactic employed, is the most important correlate of sound properties in this species.

Ethoxyresorufin O-deethylase (EROD) activity and fluctuating asymmetry (FA) in Zosterisessor ophiocephalus (Teleostei, Gobiidae) as indicators of environmental stress in the Venice lagoon

The impact of environmental stress on the grassgoby, Zosterisessor ophiocephalus, wasstudied at both biochemical and morphologicallevels, by comparing three sites in the Venicelagoon (the Northern, Central and Southernbasins) which differ in terms of the degree ofanthropogenic disturbance, in particular withregard to organic sediment contamination. At abiochemical level, the hepatic ethoxyresorufinO-deethylase (EROD) enzyme activity wasmeasured as a biomarker of the degree oforganic pollution (in particular regardingcontamination by PCBs and Dioxins). At amorphological level, the amount of fluctuatingasymmetry (FA) with regard to four bilateraltraits (postorbital length; otolith area;minimum otolith diameter; maximum and minimumotolith radii) was measured as a long termindicator of developmental stress. The ERODactivity was higher in grass gobies from theCentral basin, whereas the amount of FA washigher in the gobies collected from theNorthern basin. Both measurements indicatedthat the Southern basin was affected by lowlevels of environmental stress (low ERODinduction and a lower amount of FA). Theresults were discussed in the light of both theenvironmental differences among the threebasins and the different levels of biologicalorganisation at which the two indicators act.

Behaviour and success of sneaker males in the sand goby, Pomatoschistus minutus

Abstract. In this study we investigated in laboratory conditions the presence of alternative reproductive tactics in the sand goby and describe proximate factors affecting their expression and success. We describe the reciprocal interactions of resident males, females, and sneaking males. The pre-spawning phase proved to be important for successful nest intrusions by sneakers. The number of sneakers had no effect on the frequency of successful intrusions. When small males had exclusive access to nest sites, they built a nest and courted females, showing a full behavioural repertoire. The intensity of courtship was, however, strongly positively correlated with body size. Using microsatellite DNA markers we assessed paternity shares of territorial and sneaker males in a subset of all replicates. Following successful nest intrusion sneaker males fertilised 5–10% of the eggs. Our interpretation of the results is that sneaking in the sand goby is a conditional tactic, one that is less successful than the normal nest guarding behaviour, at least for one spawning event.

Courtship sounds and associated behaviours in the Canestrini's goby Pomatoschistus canestrinii

Courtships sounds and associated behaviours were recorded in the Canestrinis goby Pomatoschistus canestrinii using a simultaneous video-acoustic system: the male exhibited a display composed of both a visual (rapid head movements) and an acoustic component (thump sound), and its intensity was positively associated with that of a female visual display.

Elongation of fin rays in parental males of Zosterisessor ophiocephalus (Pisces: Gobiidae)

The first description of the elongation of rays of the second dorsal fin in the parental male of the grass goby, Zosterisessor ophiocephalus, is reported. The exhibition of fin ray elongation in the male grass goby may be a useful diagnostic character to identify individuals adopting alternative styles (i.e. parental males vs. parasitic spawners). The possible role played by this secondary sexual trait in the context of alternative reproductive styles adopted by smaller males of this species to gain fertilization is also discussed.

Vulnerability of artisanal fisheries to climate change in the Venice lagoon

Within the context of global warming, the western coast of the northern Adriatic Sea can be regarded as an extremely vulnerable area. Owing to the local geographic features, this area has been described as the Venetian lacuna, where Mediterranean Sea climatic conditions are replaced by Atlantic Ocean ones, supporting the presence of glacial relicts, such as sprat Sprattus sprattus, flounder Platichthys flesus and brown shrimp Crangon crangon. Nektonic assemblage therefore represents a good candidate in terms of an early proxy for thermal regime alterations. It represents a dynamic component of the lagoon ecosystem, changing in space and time, actively moving through the entire system, and dynamically exchanging with the open sea. Here, the first signals of the change have been already detected, such as the presence of alien thermophilic species. Within this context, since the beginning of the century, sampling of the nektonic assemblage has been carried out, integrating them with landings data from the fish market. Vulnerabilities to thermal regime changes have been tested by (1) categorizing species according to the mean distribution area in terms of latitudinal range (over 45°, 30°-45° and below 30°), and (2) analysing both spatial and temporal variations within fishing grounds. Results indicated a high potential vulnerability of the artisanal fishery to climate change, as the commercial catch is entirely composed of species from cold (>45° N) and temperate (between 45° and 30° N) latitudes. At present no alien thermophilic species have been recorded within the lagoon, which is possibly a sign of good resilience of the assemblage. Finally, abundance of species from cold latitudes has decreased during the past decade. All of this has been discussed in the context of the mean annual temperature trend.

Environmental influences on fish assemblage in the Venice Lagoon, Italy

This study aimed to investigate the small fish assemblage in the Venice Lagoon shallow waters in relation to selected environmental variables, such as water-quality parameters, sediment grain-size variables, and habitat structure factors. Fish sampling was carried out in 68 stations, seasonally, by using a small beach seine net. The results highlighted the primary importance of habitat structure variables, such as seagrass and salt marsh coverages, with regard to fish distribution in the lagoon, in association with turbidity and salinity gradients. Two distinct fish assemblages were identified, corresponding to opposite species preferences in relation to salt marsh coverage-turbidity and seagrass coverage-salinity gradients. These results confirmed the importance of the biologically mediated influence of environmental parameters over physical parameters on small fish assemblages in dynamic systems such as the Venice Lagoon.

Quantitative Ethogram of Male Reproductive Behavior in the South European Toothcarp Aphanius fasciatus

This work provides an ethogram of male reproductive behavior in the most widespread Mediterranean killifish, the South European toothcarp Aphanius fasciatus. The ethogram was obtained by video-recording the behavior of breeding groups under aquarium conditions. The behavioral analysis revealed the existence of seven behavioral states, with the expression of different forms of male-male competition: single and multiple courtship, single and multiple spawning, aggression, homosexual courtship, and post-mating cannibalism. These behaviors were organized into sequences that followed a first-order Markov chain. Single courtship was the most prevalent behavior, but more than one male, from two to five, could participate simultaneously in courtship and spawning. Results suggested that the breeding system is based on mate monopolization, with high levels of sperm competition and parasitic spawning. Results are discussed in light of the current literature on alternative mating tactics and male-male competition in teleost fishes.

Relationships between relative size of sexual traits and male mating success in the Mediterranean killifish Aphanius fasciatus (Nardo, 1827)

Some relationships between the relative size of secondary sexual traits and male mating success were investigated in the killifish Aphanius fasciatus (Nardo, 1827). The relative ability of a male to compete with another male for access to a ripe female was related to the relative size of male sexual traits by means of a behavioural experiment under controlled laboratory conditions. Furthermore, the covariation in the expression of sexual traits was analysed from a sample of field-collected males. Results of the behavioural experiment showed that male dominance and success were positively related to the relative height of the dorsal fin, but not to the pattern of vertical bars along body sides. Within the analysed male population, males with larger fins tended to have thinner bars, whereas there was no statistically significant correlation with bar number or with bar asymmetry. The results were discussed in terms of advantages conferred by larger dorsal fins in killifish breeding systems, and developmental constraints defining a multiple set of traits correlated to male quality were also hypothesised.