Sandra Casellato

Animal xenodiversity in Italian inland waters: distribution, modes of arrival, and pathways

The paper provides a list of the non-indigenous animal species occurring today in Italian inland waters. Xenodiversity was found to amount to 112 species (64 invertebrates and 48 vertebrates), which contribute for about 2% to the inland-water fauna in Italy. Northern and central regions are most affected, and Asia, North America, and the rest of Europe are the main donor continents. The large majority of non-indigenous species entered Italy as a direct or indirect effect of human intervention. A difference between invertebrates and vertebrates was found for their mode of arrival (unintentional for invertebrates and intentional for vertebrates). Accidental transport, in association with both fish (for aquaculture or stock enhancement) and crops, has been the main vector of invertebrate introductions, whereas vertebrates were mostly released for stocking purposes. Overall stock enhancement (47.92%) and culture (37.5%) prevailed over the other pathways. Seventeen and 7 species of our list are included among the 100 worst invasive species of Europe (DAISIE) and of the world (IUCN), respectively. For some (but not all) non-indigenous species recorded in Italy the multilevel impact exerted on the recipient communities and ecosystems is known, even if rarely quantified, but knowledge on their chronic impact is still missing. Additional research is needed to provide criteria for prioritizing intervention against well established invaders and identify which new potential invader should be targeted as “unwanted”.

Dikerogammarus villosus (Sowinsky, 1894) (Crustacea, Amphipoda, Gammaridae) for the first time in Italy

The recent discovery in Lake Garda, and in other watercourses of northern Italy, of Dikerogammarus villosus, an amphipod crustacean from the Ponto‐Caspian region, is a worrying confirmation of how it is rapidly spreading in Europe. In Lake Garda, the species is present, with high population density, in the southern basin, where it is the only gammarid of the littoral benthos, and in the northern basin, with lower population density, where it still coexists with the native species Echinogammarus stammeri. Ovigerous females and juveniles are present most of the year in all the explored areas. Considering that the species has often replaced the native gammarids in invaded waters in most European regions, we want to raise the alarm for a possible progressive elimination of the native species E. stammeri by the invading one from the Garda littoral benthos.

Hidden secrets of the Northern Adriatic: “Tegnúe”, peculiar reefs

Research carried out over the last 40 years has underlined the scientific importance of the rocky outcrops scattered on the Northern Adriatic Sea bed sometimes referred to as “tegnúe”. The zoobenthic biocenoses developing over these peculiar geological formations are as extraordinary as they are unique. A study carried out for an entire year in two sampling stations, at different distances from the coast, revealed a very high number of zoobenthic species, including those which have now become rare and are therefore protected in Italian seas. The water turbidity of the northern Adriatic Sea greatly reduces the quantity of light reaching these outcrops, limiting the activity of autotrophic organisms only to sciaphilous genera. Thus, the most represented trophic categories of zoobenthos are suspension, especially filter feeders. Biodiversity values calculated for the communities of these particular reefs are far higher than normally found in the soft seabed in nearby areas, but even higher than in other coralligenous outcrops in other marine ecosystem in the world. The ecological role played by the tegnúe in the Northern Adriatic is extraordinary because as well as being true oases of biodiversity, they are areas naturally protected against bottom trawl-fishing. Thus, they offer shelter and reproduction sites for a number of fish and invertebrate species, including some under stress due to severe fishing pressure.

Life-cycle and karyology of Branchiura sowerbyi Beddard (Oligochaeta, Tubificidae)

Data on the life-cycle of a population of Branchiura sowerbyi Beddard in a water-lily tank at the Botanical Garden in Padua are reported. The breeding period is from April to July, after which the reproductive system is partially resorbed (August-September) and reformed later in the autumn. The karyology of the species was also studied, and revealed 38 mitotic chromosomes in the gonia, and 19 bivalents in the primary spermatocytes and in the primary oocytes.

Acute and chronic effects of an anionic surfactant on some freshwater tubificid species

We report the results of research on acute and chronic effects of linear alkylbenzensulfonate (LAS) on two tubificid species. 96 h LC50 assay values were estimated at 10° for Limnodrilus hoffmeisteri and Branchiura sowerbyi exposed to different concentrations of LAS dissolved in water, both with and without sediment. The presence of sediments modified LAS toxicity and increased values: NOEC and LOEC resulted in values 2.5 times higher for Branchiura sowerbyi and 4–4.5 times for Limnodrilus hoffmeisteri, when the sediments were present. The chronic effects induced by a long exposure to LAS were evaluated for different stages of the biological cycle of Branchiura sowerbyi. Using concentrations between the NOEC and LOEC (0.5, 2.5, and 5 ppm), with control, we could observe that: 1) at 5 ppm the cocoons were laid precociously compared to controls, 2) in all treated series the number of cocoons was lower than in controls, 3) the mean number of oocytes per cocoon was lower for the worms submitted to LAS, compared to the control, 4) the period of embryonic development was similar for all used concentrations and for control, and 5) the number of degenerated cocoons was unchanged by the LAS treatment.

Long-term experiment on Branchiura sowerbyi Beddard (Oligochaeta, Tubificidae) using sediment treated with LAS (Linear Alkylbenzene Sulphonate)

A long-term experiment was performed with Branchiura sowerbyi in order to assess possible effects of LAS sorbed to sediment on its reproductive cycle, using concentrations in sediment 2–5 times higher than those calculated for the LC50 values of LAS dissolved in water. No significant effects were observed during the whole experiment, so that we can confirm that LAS adsorbed on sediment has a much lower influence on the examined animals than LAS dissolved in water.

Karyology of Lumbricidae III° Contribution

SUMMARYWe have studied the chromosome set and the gametogenesis of three earthworm species originating from Iceland: Dendrobaena rubida, D. octaedra, Lumbricus rubellus; three species coming from the Friuli area: D. octaedra, Allolobophora caliginosa, A. rosea, and one species coming from the isle of Kerkyra: Octolasium croaticum.As regards to the D. rubida, we have studied the hexaploid parthenogenic and the octoploid amphigonic strains. In the Friuli, we have found the diploid amphigonic, the triploid parthenogenetic and the decaploid amphigonic strains of Allolobophora rosea.Concerning the A. caliginosa, the diploid strains that we have studied, present a normal spermathogenesis and a condition of amphigony; the triploid strain is parthenogenetic.With the Lumbricus rubellus, our data have confirmed the constancy of its diploid and amphigonic condition.The Octolasium croaticum of Corfu is an amphigonic diploid.As regards to the D. octaedra, we have studied the common exaploid and the subhexaploid strains.

Ultrastructural features of gametogenesis during the life cycle in Branchiura sowerbyi Beddard (Oligochaeta, Tubificidae)

An uitrastructural analysis of the gametogenetic phases in Branchiura sowerbyi,a tubificid oligochaete, has been accomplished. These phases mostly conform to the usual pattern for the family, however, some interesting peculiarities are pointed out. The regression of sexual apparatus after reproductive period and its regeneration up to a new period of sexual maturity, has been followed throughout the year.

Composition and distribution of bottom oligochaete fauna of a north Italian eutrophic lake (Lake Ledro)

The profundal macroinvertebrates, particularly the oligochaetes, of Lake Ledro (Trento, Italy), that has recently undergone eutrophication, were studied.A statistical approach of random sampling was used to study the distribution and abundance of the oligochaete species. The optimum sample number was calculated from a preliminary sample series. The oligochaete community was made up of five tubificid species, one naidid and one lumbriculid species that on average represents more than 80% of the macrobenthic community. Population density was correlated with depth and decreasing oxygen concentration. The role of Tubifex tubifex as a eutrophic, tolerant species was confirmed; and in fact it was the only species found (although at low density) in the deepest and anoxic zone. No comparable data are available for the lake prior to eutrophication, but these data will be valuable for future comparison once a remediation program for the lake has been implemented.

Influence of temperature on fluoride toxicity and bioaccumulation in the nonindigenous freshwater mollusk Dreissena polymorpha Pallas, 1769

Fluoride toxicity and bioaccumulation tests (short- and long-term) were performed on the nonindigenous freshwater mollusk Dreissena polymorpha at two different temperatures: 17 ± 0.5°C and 22 ± 0.5°C. Concentrations that did not result in toxicity in short-term experiments (96 h) induced effects over a longer period (17 weeks), especially at the warmest temperature, highlighting the role of this parameter. Fluoride bioaccumulation increased linearly with increasing concentration and temperature, reaching 4,202 µg F(-)/g dry weight in soft tissues only after 48 h of exposure at 22°C at a concentration of 640 mg F(-)/L. Comparing tolerance to fluoride and bioaccumulation values of this species with those of other freshwater invertebrates, D. polymorpha was much more resistant and revealed its capacity to accumulate a great quantity of this xenobiotic substance. The results of the present study demonstrated that fluoride accumulation in the soft tissue of this animal was much higher (up to 1,409.6 µg F(-)/g dry wt) than that in its shell (up to 706.4 µg F(-)/g dry wt). If we consider this datum and the fact that D. polymorpha is widespread in many aquatic ecosystems around the world, representing a food source for many birds and other vertebrates, we must acknowledge the possibility that it can represent a serious danger in view of fluoride biomagnification in the aquatic environment.