Despite its inhospitable appearance and lack of any ... - Udine Cultura

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42 adaptive features to life underground, which enable them to survive in transitional environments: they are often partially or totally depigmented and have reduced or totally absent visual organs. From the evolutionary viewpoint, since groundwater is a secondary colonisation environment, the species now found exclusively here are thought to have been stygophiles in the past. But the contrary cannot be ruled out - i.e., that all past stygophiles are now exclusive groundwater dwellers. Evolutionary destiny depends on the opportunities which single stygophilic species had of colonising groundwater, surviving and successfully reproducing. Stygophiles which regularly frequent the subterranean environment where they can reproduce, but which do not have marked adaptive characteristics, are called substygophiles. They include, for instance, some aquatic benthic insects found in watercourses, where they may spend the early phases of their development in the fluvial hyporheic environment. This is a winning adaptive strategy as regards avoiding predators, but their life-cycle is always completed in shallow waters, and adults often inhabit the subaerial habitat. This is true of many ephemeropterans, plecopterans and dipterans, mainly chironomids. Conversely, those stygophiles which show not only marked pre-adaptations but also an elective preference for the subterranean environment, where they are regular guests, are called eustygophiles. This is the case of many molluscs and crustaceans. Paracyclops imminutus (stygophyle) ● Stygobionts. Animal species closely associated with underground environments, on which they depend for completing their life-cycle, are called stygobionts. They often have marked adaptations to underground life like depigmentation, anophthalmy (absence of eyes), well-developed sensory organs, and a reduced fecundity rate (described in the chapter on the ecological aspects of groundwater). These adaptations are partially shared by terrestrial troglobionts (cave-dwelling species) and by those living in soil (endogean species). Stygobionts may be ubiquitous and live in all types of aquifers, and sometimes in marginal waters (for instance, under dead leaves in humid forests), or they may be associated with specific habitats, like phreatobionts, which live exclusively in saturated alluvial aquifers, and karstic stygobionts, which are limited to aquifers in limestone and evaporites. A clear distinction between these ecological categories is difficult to make, and there are many intermediate levels. In some taxa, of which all species appear to be pre-adapted to life in humid soil and groundwater, like nematodes and some families of oligochaetes, it is impossible to divide them according to morphology, and their preference for underground habitats is evident from the frequency with which they are found there. This chapter on groundwater fauna describes exclusive dwellers, i.e., stygobionts. We will discover a fascinating multitude of dark-loving organisms, with sometimes bizarre morphological adaptations. Niphargus steueri (stygobiont) 43
44 45 Methods for sampling and analysing groundwater fauna Fabio Stoch Groundwater habitats are difficult to reach, and researchers have had to come up with ingenious methods for sampling and analysing underground fauna which, according to the depth and accessibility of aquifers, are sometimes expensive and so complex that only specialised research institutes can carry them out. In karstic waters, traditional sampling methods include: ● continuous filtering of trickling water funnelled into containers with filters which are periodically emptied; ● collection of percolating water in gours and micro-gours, by means of rubber pumps or syringes; filtering of concretion water with plankton nets (60-100-µm mesh) which are emptied with rubber piping; ● direct filtering of water from large pools with plankton nets with handles; ● in streams and small watercourses: after coarse debris has been shaken out, water is filtered through plankton nets (with semi-circular openings 20-25 cm in diameter); ● direct collection of large organisms with aquarium nets and tweezers; ● in order to collect large predatory crustaceans (1), traps containing meat or tid-bits of food can be placed in suitable positions in open cans (to avoid the death of animals trapped inside, if the trap itself is lost); ● placing artificial substrates (twisted nylon netting compressed in tubes, or tubes filled with locally collected washed sediment) which are periodically emptied in order to analyse the colonisation of various types of substrates. Collecting specimens from wells or boreholes in alluvial soils may be carried out with: ● modified plankton nets (Cvetkov nets) with valves to prevent material from escaping when the nets are quickly lifted and replaced on the bottom of the well to agitate the sediments (2); ● various types of pumps (peristaltic, rotor, compressed-air), according to water-table depth (rotor pumps of greater power unfortunately easily destroy material). Lastly, in flooding watercourses where collection is concentrated in upwelling or outwelling stretches (see chapter on ecology), two methods are used: ● Karaman-Chappuis method: a hole is dug along the shore of a watercourse, and the water permeating from nearby sediments is collected and filtered through a plankton net; ● Bou-Rouch method: a hand-pump (3) is used to remove interstitial water from the bed of a watercourse, by means of a Filtering trickling water with a plankton net Equipment for sample collection 1 2 perforated tube inserted deeply into the sediments (for a detailed description of this method, see Teaching Suggestions). Research teams with the most recent equipment can use drills to place piezometers at varying depths, from which groundwater is extracted with pumps and filtered through plankton nets. Other, quite expensive methods, like freeze-coring, use liquid nitrogen to freeze sediment cores collected from boreholes and subsequently examined in the laboratory. More advanced research methods involve inserting transparent perspex piezometers with optical-fibre videocameras into the soil or sediment in the river bed. In this way, researchers can analyse large organisms in their natural environment without disturbing the underground community. 3
Page 1: Fauna FABIO STOCH Despite its inhos
Page 5 and 6: 48 Shells of gastropods Iglica voba
Page 7 and 8: 52 collected in phreatic waters in
Page 9 and 10: 56 ● Cyclopoid copepods. So far,
Page 11 and 12: 60 those associated with percolatin
Page 13 and 14: 64 Species of genus Niphargus; top:
Page 15 and 16: 68 ■ Decapods Italian fauna has o
Page 17 and 18: 72 Stygofaunal provinces in Italy T
Page 19 and 20: 76 aquifers in the Sabini mountains
Page 21 and 22: 80 ■ The ecology of aquifers Acco
Page 23 and 24: 84 85 The discovery of a new submer
Page 25 and 26: 88 anastomoses, often adjacent to t
Page 27 and 28: 92 93 The saline springs of Poiano:
Page 29 and 30: 96 Modified sensory setae on the an
Page 31 and 32: 100 Theoretical evolutionary sequen
Page 33 and 34: 104 Sketch showing degrading phases
Page 35 and 36: 108 109 Stygodiversity in the Presc
Page 37: 112 animal groups still living on t

Despite its inhospitable appearance and lack of any ... - Udine Cultura

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