Abstract In this study, we analysed the diet of two populations of Perlodes intricatus (Pictet, 1841) inhabiting river sections characterised by different environmental quality. Macrobenthic communities and nymphal gut content data were acquired in a nearby pristine environment and in a station compromised by sewage discharges. No differences in size were detected between these populations. Both populations select positively Chironomidae as prey, but marked differences are evident between their diet. Nymphs from pristine station feed on a wide range of prey, but also include algae and organic detritus. By contrast, nymphs from polluted station show a different and restricted trophic spectrum, likely because of the reduced prey availability. Interestingly, the occurrence of fine organic detritus in these latter nymphs is much higher, evidencing a shift to a more collector-gatherer feeding. This study shows that some Perlodidae can survive and develop in contaminated environments, also due to their trophic plasticity.

Most of the energy input of low-order lotic food webs derives from non-living sources of terrestrial organic matter. For this reason, many studies have examined patterns of leaf breakdown; most recently, interest has focused on the importance of water quality or the nature (native versus exotic) of plant material. In this study, we combined both aspects by analyzing the breakdown process and macroinvertebrate colonization of leaf bags containing leaves of different plant types in two nearby sites with different levels of water quality. We exposed a total of 600 leaf bags made of five leaf types (three native: Alnus incana, Populus alba and Quercus robur; and two exotic: Reynoutria japonica and Robinia pseudoacacia) at two sites of the Pellice River (northwestern Italy). Leaf bags were retrieved after 10, 20, 30, 40, 50 and 60days, leaf mass loss determined and the associated macroinvertebrates quantified. Significant differences were found in the mass loss and in the colonization of leaf bags between sites but not between native and exotic species. Dry mass loss was different among species but without any evident relation with exotic or native origin of plants. In our study sites, geographical origin of plant detritus is not per se central in shaping macroinvertebrate colonization and mass loss because the impact of wastewater treatment plant effluent seems to be much more important than plant origin in the breakdown process.

Despite the enormous importance of alpine streams, information about many aspects of their ecology is still insufficient. Alpine lotic systems differ in many environmental characteristics from those lower down, for example because above tree line streams drain catchments where terrestrial vegetation is scarce and allochthonous organic input is expected to be small. The main objectives of this study were to examine seasonal variation of autochthonous and allochthonous energetic inputs and their relationship with macroinvertebrate communities in the Po river, an alpine non-glacial stream (NW Italy). For one year, samplings were monthly performed in a homogeneous 100 m stream reach for discharge, autochthonous energy input (benthic chlorophyll a), allochthonous energy input (coarse particulate organic matter), abundance and structure of benthic macroinvertebrate community. Chlorophyll a concentrations were in the range of what reported for other alpine streams, but presented a time-lag with respect to what has been reported for glacial-fed mountain rivers. CPOM amounts were lower than those in lowland, forested streams of the same area but exhibited an intriguing, different seasonal variability, probably reported for the first time, with a maximum in spring and a minimum in winter. We collected 29,950 macroinvertebrates belonging to 13 families and 10 orders. Benthic communities were essentially dominated by Ephemeroptera, Plecoptera and Diptera. Scrapers was the most important FFG, but also Shredders were well represented. Relationships between chlorophyll a concentrations, CPOM availability and macroinvertebrate community characteristics were analysed and discussed considering the existence of different top-down or bottom-up regulation mechanisms. This study confirms that benthic algae constitute an essential resource for macroinvertebrates in alpine streams above the tree line but also underlines the importance of terrestrial organic input, a previously neglected input in environments above the tree line. The major forces shaping energetic inputs and invertebrate communities seemed to be related to the Alpine climate, and especially to snow accumulation and melting, with the consequent substantial discharge variations.

Recent studies suggested a general warming trend in the Alps, resulting in a significant migration of forests to altitudes higher than the usual, regional tree line. As a consequence, some headwater streams will likely receive more allochthonous organic matter. For this reason, the dynamics of decomposition of terrestrial leaf detritus in stream reaches that naturally lacked this resource represents a subject of considerable interest, on which no information is currently available. The aim of this study was to analyse breakdown and macroinvertebrate colonisation of leaf bags in an Alpine headwater stream above the tree line. Results of this study indicate that decomposition of terrestrial leaves in a lotic alpine environment above the tree line takes place through a process similar to what happens at lower altitudes, but with some differences. The reduced rate of decomposition observed may be due to lower temperatures. At lower altitudes, tree cover provides a supply of organic material sufficient to support a rich guild of shredders. This study demonstrates that also above tree line, where communities are dominated by scrapers, an important part of the benthic community take part in the decomposition process of leaves. We can conclude that streams above the tree line, while hosting invertebrate communities dominated by rhithrophilous organisms that feed mostly on biofilm, also harbour a rich population of opportunist invertebrates. It seems that, in the case of expected temperature increase at higher altitudes, terrestrial organic detritus may be actively degraded by lotic benthic communities.

Life cycle, feeding habits and nymphal density of a population of E phoron virgo from the B ormida river ( N orthwestern I taly) were studied. Nymphs were present in the river from the beginning of M ay until A ugust, with the highest density of nymphs recorded at the end of M ay–beginning of J une. The life cycle was univoltine and the nymphal growth was fast. During the life cycle, an obligatory egg diapause occurs and individuals remain in this stage for up to nine months. Nymphs fed mainly on detritus, although mineral matter constituted a considerable percentage of the gut contents, predominantly in smaller nymphs.

The introduction of alien species is currently one of the greatest threats to biodiversity conservation. This is particularly true in river systems, where in recent years the growth of allochtonous or non-native species has increased dramatically. Numerous studies have investigated the presence and the distribution of invasive species, but few focused on the trophic habits of fish species introduced into new lotic environments. This paper provides information on the diet of three alien species in the Bormida River, a lotic system previously altered by chemical pollution. Barbus barbus shows a wide trophic spectrum, feeding mostly on benthic invertebrates but also consuming terrestrial arthropods, coarse particulate organic matter, filamentous algae and, more rarely, fish. Feeding activity of Pseudorasbora parva was mostly based on aquatic invertebrates but also algae and fine particulate organic matter was frequently ingested. Regarding diet analysis of Rhodeus amarus, fine detritus and algae were the most important components in the examined guts. There are significant potential overlaps with the trophic spectrum of native species.

Padogobius bonelli in Curone Creek (Italy) fed mainly on aquatic insects, positively selecting Chironomidae, Simuliidae, and Hydroptilidae and negatively Bactidae, possibly related to the high mobility of the latter. When studying the variation of the diet with size, a positive correlation with some big prey items was detected. Nevertheless, no differences were detected when prey diversity was considered Finally, the huge difference in the gut content among the individuals could be related to the marked territoriality of this species in the breeding season when this study was carried out.

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.

Feeding habits of Perla grandis nymphs have been investigated in the Borbera stream, an Apenninic water course of Northwestern Italy. In this study, we analyzed gut contents of 80 nymphs of this species, with the aim of detecting feeding pref- erences. Nymphs were collected from a single riffle, whose benthic coenosis was also determined. We detected the existence of an evident trophic selection: diet was almost entirely dominated by Chironomidae, independently from their availability on the substrate. This finding is discussed and compared with data previously obtained for this species from other populations.