Tiziano Bo

Field experiments on colonization and movements of stream invertebrates in an Apennine river (Visone, NW Italy)

Macroinvertebrates continuously redistribute themselves in the riverbed. A knowledge of the colonization mechanisms and movement patterns is very important for an understanding of processes of restoration of lotic environments, particularly of inland waters with severe pollution. We tested the colonization patterns of stream macroinvertebrates in the Visone River, a tributary of the highly contaminated Bormida River (NW Italy). We placed six groups of traps in the riverbed, each group consisting of three traps: the C trap allowed colonization from all directions, while the D and U traps allowed access only from downstream and upstream respectively. The C traps were the most colonized substrates, both in number of individuals and taxa. The U traps were more colonized than the D traps, demonstrating the great importance of movements directed downstream. We report data on taxonomic and seasonal differences in the colonization process.

Response of benthic invertebrate assemblages to varying drought conditions in the Po river (NW Italy)

In the rivers of northern Italy, the presence of water is typically continuous all year long, although in the last five decades there has been a conspicuous increase in drought periods, mainly caused by human impacts and climate change. The aim of this study was to assess the impact of the length of the drought periods on macroinvertebrate assemblages. We collected invertebrates in four reaches of the Po river, characterised by different periods of absence of surface water. We found significant differences among the stations in invertebrate abundance and taxa richness, with a decrease in the more drought‐affected stream reaches. Collector‐gatherers significantly increased as the drought period lengthened, while the opposite occurred for scrapers and shredders. The areas with a discontinuous presence of water were mainly colonised by small, fast‐growing, plurivoltine organisms. A main result of our study is that only a few taxa appear to be able to survive in reaches with intermittent flow, underlining the great ecological difference between perennial and naturally intermittent streams. Our results suggest that the recent increase of droughts will likely cause an impoverishment of benthic communities in prealpine rivers.

Deep Interstitial Habitat as a Refuge for Agabus paludosus (Fabricius) (Coleoptera: Dytiscidae) During Summer Droughts

Abstract We report information about the presence of Agabus (Gaurodytes) paludosus (Fabricius, 1801) within the interstitial zone of the streambed of the Po River (NW Italy) during droughts. During August and November 2004, we found adult and larval stages at depths of 70–90 cm below the surface when no water was present in the channel. These findings are discussed in the context of the origin of stygobiont diving beetles.

Life strategies of 3 Perlodidae species (Plecoptera) in a Mediterranean seasonal stream in southern Europe

Abstract We studied aspects of the nymphal biology and ecology of 3 Perlodidae species (Guadalgenus franzi, Hemimelaena flaviventris, and Isoperla curtata) in a Mediterranean seasonal stream in the southern Iberian Peninsula. Their life-history strategies were greatly influenced by the characteristics of their environment, i.e., a summer dry period with relatively warm temperatures, but strategies differed among species. Guadalgenus franzi was semivoltine and probably underwent nymphal quiescence when the stream was dry. Hemimelaena flaviventris and I. curtata had relatively short univoltine life cycles that overlapped, but I. curtata was slightly ahead of H. flaviventris. Both species passed the dry period in the egg stage, probably with a diapause phase. Growth rates of H. flaviventris and I. curtata peaked before emergence, whereas growth rate of G. franzi peaked immediately before and after the dry period. The 3 species had relatively short flight periods compared with other species from seasonal streams. Guadalgenus franzi and I. curtata were mainly scrapers that fed on diatoms, whereas H. flaviventris was mainly predatory. Diet changed somewhat in relation to size, and prey electivity patterns differed among species. All 3 species preferred Chironomidae, but G. franzi preferred Chironomidae principally when smaller. All 3 species had high secondary production relative to other stonefly species from both temporary and permanent waters.

Effects of global climate change on freshwater biota: A review with special emphasis on the Italian situation

Abstract There is much evidence that climate is rapidly changing at a global scale, especially regarding mean annual temperatures, precipitations and evaporation. The consequences of this rapid environmental change on freshwater biota are still not clear, but undoubtedly they could be severe. Among the main effects of climate change, we can individuate the enhancement of water temperatures, particularly important for poikilothermic organisms, with the consequent diminution of dissolved oxygen, and the reduction of available habitats for most stenothermal organisms. Another consequence of climate change is the alteration of hydrologic cycles, with increasing intensity and frequency of extreme events such as droughts, especially in Southern Europe. This scenario could severely affect freshwater biota, especially in mid-latitude regions, such as the Italian peninsula: shifts in phenology, life cycles and distribution ranges are likely to be expected for many organisms, with the extinction of many sensitive species. In particular, species adapted to perennial and cold waters are likely to suffer reductions in their distribution range and also local extinctions, while more tolerant organisms may enlarge their distribution ranges. Global climate change may also promote and enhance invasions of alien species. In this work, concepts and hypotheses about the presumable impacts of climate change upon freshwater biota are reported, with examples and predictions related to the Italian situation.

Mass loss and macroinvertebrate colonisation of fish carcasses in riffles and pools of a NW Italian stream

AbstractIn this study, we analysed the decomposition of trout carcasses in a low-order Apennine stream, with the aim to investigate the mass loss rate in a Mediterranean lotic system, and to examine the influence of microhabitats on the invertebrates colonising fish carcasses. In May 2003, we put 56 dead rainbow trout (Oncorhynchus mykiss) in the stream, placing seven sets (four trout each) in both riffle and pool habitats. At four dates, we removed one trout per set to measure its dry mass and determine the associated macroinvertebrate assemblage. Fifty-eight macroinvertebrate taxa colonised the carcasses, with significant differences between the erosive and depositional microhabitats. Riffle trouts hosted richer and denser colonist communities than pool trouts. Chironomidae, Serratella ignita, Habrophlebia sp., Dugesia sp. and Protonemura sp. were the five most abundant taxa. Decomposition was initially very rapid in both environments and then tapered off over time. The mass loss rate was higher (k= −0.057 day−1) than that found in other studies. Higher Mediterranean temperatures probably increase the process. Although we found no significant difference between riffles and pools, mass loss was more regular in erosive habitats, underlining the importance of local, small-scale conditions. In small, low-order, heterotrophic streams, fish carcasses represent an important resource and shelter for rich and diversified invertebrate assemblages.

Temporal and Spatial Patterns of Coarse Particulate Organic Matter and Macroinvertebrate Distribution in a Low-Order Apennine Stream

ABSTRACT We described the microdistribution of benthic macroinvertebrates in a 50 m riffle segment of the Rio del Giovo (Sassello, NW Italy) during a period of rapid loss of leaf mass, from March to May 2003. We analyzed the relationship between the taxonomic composition and functional organization of benthic communities and the availability of coarse particulate organic matter (CPOM), as well as the influence of micro-environmental characteristics (water velocity, depth, and substratum). Patches without CPOM hosted specialized communities. The temporal variation of CPOM influenced the distribution of functional feeding groups in the riverbed. In particular, shredder assemblages were widespread in the riverbed when CPOM was abundant, but when this resource became scarce and localized, their density was related to the availability of allochthonous organic detritus.

Feeding of Perla grandis nymphs (Plecoptera: Perlidae) in an Apennine first order stream (Rio Berga, NW Italy)

Abstract Feeding habits of Perla grandis (Rambur) nymphs have been investigated in the Rio Berga, an Apenninic stream of Northwestern Italy. In this study, we analysed gut contents of 50 nymphs of this species, with the aim to investigate feeding preferences. Nymphs were collected from a single riffle, of which benthic coenosis was also determined. We detected a change in the diet during ontogenesis, with small instars feeding mainly on detritus and large instars strictly carnivorous. We also detected the existence of an evident trophic selection: diet was almost entirely dominated by Chironomidae, independently from their availability on the substratum. This finding is discussed on the basis of ecological and ethological considerations.

Contribution of macro- and micro-consumers to the decomposition of fish carcasses in low-order streams: an experimental study

Vertebrate carrions, in particular fish, can provide a significant source of organic matter to lotic systems. Most studies related to animal matter degradation have been undertaken in Western North America, where entire lotic networks depend on large masses of anadromous salmonids, but less is known of other aquatic environments. In this study, the decomposition process of trout was analyzed in a Northern Italian stream, investigating the different importance of macro (invertebrates)—and micro (fungi)—consumers. Trout carcasses exhibited an exponential mass loss over time and attracted a rich community of microbic and invertebrate colonists. Final values for fish decay were significantly affected by the presence of macro-consumers; nevertheless, the role of macroinvertebrates seems to be not as predominant as in other ecological systems. Our study indicates that in lotic environments, which lack specialized necrophagous or sarcophagous invertebrate taxa equivalent to those found in terrestrial environments (such as maggots or carrion beetles), micro-consumers play a main role in fish carrions decomposition.

Diet of Dinocras cephalotes and Perla marginata (Plecoptera: Perlidae) in an Apennine stream (northwestern Italy)

The feeding habits of nymphs of Perla marginata (Panzer) and Dinocras cephalotes (Curtis) were investigated in the Rio Orbarina (northwestern Italy). These species are among the largest European carnivorous freshwater invertebrates and they play an important role in the trophic structure of small, fishless Apennine streams. We examined the gut contents of 60 P. marginata and 60 D. cephalotes nymphs to characterize the diets and evaluate possible feeding differences between the species. In both of these predaceous stoneflies, the diet included vegetable detritus, mainly in the smaller instars. Both species showed trophic preferences, since only a few taxa constituted most of the ingested prey items, independently of their availability in the substratum. Interestingly, there were no clear differences in prey selection between nymphs of the two species.