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Environmental correlates of two macro-decapods distributionin Central Italy: Multi-dimensional ecological knowledgeas a tool for conservation of endangered species

Silvia Barbaresi, Stefano Cannicci, Marco Vannini, Sara Fratini*

Dipartimento di Biologia Animale e Genetica, Universita di Firenze, Via Romana 17, 50125 Firenze, Italy

A R T I C L E I N F O

Article history:

Received 31 July 2006

Received in revised form

8 December 2006

Accepted 15 December 2006

Available online 23 February 2007

Keywords:

Spatial segregation

Ecological factors

Multi-variate statistics

Freshwater crayfish

River crab

0006-3207/$ - see front matter � 2007 Elsevidoi:10.1016/j.biocon.2006.12.013

* Corresponding author: Tel.: +39 55 2288204;E-mail addresses: silvia.barbaresi@unifi.it

sara.fratini@unifi.it (S. Fratini).

A B S T R A C T

Using a multi-dimensional ecological design, this study aimed first to analyse whether

local environmental conditions can account for the spatial segregation of two Italian native

decapods, the crayfish Austropotamobius italicus and the river crab Potamon fluviatile, in Cen-

tral Italy freshwater ecosystems. Second, we aimed to analyse which environmental vari-

ables were more closely associated with the presence/absence of the two decapods in

specific sites within their distribution area. Following a factorial design, a total of 32 sites

were selected in two neighbouring geographic areas, one occupied by crayfish and one

by crabs. Within each distribution area, eight streams where the decapod was present

and eight where it was not present were selected. At each site, macro-invertebrate commu-

nity composition and 16 abiotic variables were recorded and analysed with multi-variate

methods. Variations in physical (minimum and maximum temperatures), chemical (cal-

cium, oxygen, nitrate and nitrite) and geomorphological (substrate composition) parame-

ters explained spatial segregation of P. fluviatile and A. italicus in the study area. The

occurrence of crayfish reflected variations of chemistry (such as pH, calcium, nitrate and

nitrite concentrations), temperature, water depth and substrate composition. On the con-

trary, the presence of the river crab, within its occurrence zone, was not associated to any

biotic and abiotic parameters and was probably affected by anthropogenic pressure and

uncontrolled harvesting. These findings provide fundamental ecological data for the main-

tenance of the two decapod natural populations as well as for the selection of areas and

streams adequate for their reintroduction.

� 2007 Elsevier Ltd. All rights reserved.

1. Introduction

The presence and abundance of organisms at a specific site

are the result of the action of several multi-scale filters,

including both historical and ecological constraints ranging

from landscape to micro-habitat scales (Poff, 1997). The rela-

er Ltd. All rights reserved

fax: +39 55 222565.(S. Barbaresi), stefano.ca

tive effects of historical and ecological factors may vary

according to the considered spatial scale. At a very large scale

the role of history on biodiversity distribution is likely to be

prevailing, whereas at a local scale, the distribution of species

and the composition of communities will be explained by

environmental variables alone (Townsend et al., 2003); species

.

nnicci@unifi.it (S. Cannicci), vannini_m@dbag.unifi.it (M. Vannini),

432 B I O L O G I C A L C O N S E R V A T I O N 1 3 6 ( 2 0 0 7 ) 4 3 1 – 4 4 1

occupy locations where physiochemical conditions are appro-

priate, resources are available and competitors or predators

do not preclude them.

Many studies investigated the ecological, environmental

and habitat factors affecting the distribution of freshwater

animals at different spatial scales. Most of these studies

were performed on amphibians (see for example Meyer

et al., 1998; Wilkins and Peterson, 2000; Stallard, 2001; Hamer

et al., 2002; Lecis and Norris, 2003), fishes (Rathert et al., 1999;

Inoue and Nunokawa, 2002; Legalle et al., 2005) and macro-

invertebrates (Quinn and Hickey, 1990; Hastie et al., 2000;

Kay et al., 1999; Townsend et al., 2003; Bonada et al., 2005),

and a few on crustaceans (among these the most relevant:

Smith et al., 1996; Naura and Robinson, 1998; Gil-Sanchez

and Alba-Tercedor, 2002). Investigating the links between

distribution of freshwater species and ecological factors is

potentially very important for two main reasons. First, this

approach increases the basic knowledge of freshwater eco-

systems and of their communities. Second, these studies

can furnish important information for guiding management

and conservation decisions. Freshwater habitats are being

subject to unprecedented levels of human disturbance

around the world and the future rate of species extinction

is predicted to be almost five times greater than that for ter-

restrial animals and three times that of coastal marine mam-

mals (Ricciardi and Rasmussen, 1999).

Similarly to other European native freshwater decapods, the

crayfish Austropotamobius italicus (Faxon) and the river crab Pot-

amon fluviatile (Herbst) have declined dramatically in recent

years throughout their ranges, including Italy. This phenome-

non has been often explained as the result of a number of fac-

tors, including pollution and damage to their habitats

(Matthews and Reynolds, 1995; Gherardi and Holdich, 1999).

More recently, the introduction of non-indigenous crayfish spe-

cies in many European water systems posed a further threat to

their conservation (Gherardi and Holdich, 1999). Current na-

tional and international conservation efforts aim at preserving

freshwater decapods from decline. However, the protection of

A. italicus and P. fluviatile is nowadays inadequate. In fact, since

A. italicus was considered a subspecies of A. pallipes until re-

cently (Fratini et al., 2005), it is not included in national and

international laws with its current name. However, as A. palli-

pes this crayfish is mentioned as a vulnerable and rare species

in the IUCN Red List (Baillie and Groombridge, 1996) and in An-

nex II and Vof the 92/43/EEC Habitat Directive where actions for

its protection are stated as being firmly required. In the case of

the freshwater crab P. fluviatile, due to its narrower geographical

distribution and to the lack of socio-economic interests around

the species, little or no attention has been paid to its protection

that is still limited to local regulations often not sufficient to

preserve the species from decline.

In Italy, the crayfish A. italicus and the river crab exhibit an

area of sympatry (Central to South Italy, Pretzmann, 1987) but

within this area they are spatially segregated. The actual pat-

tern of distribution could be attributed to both ecological (i.e.,

current interaction of various abiotic and biotic factors) and

historical forces (including competitive exclusion and cli-

matic changes, Pretzmann, 1987). As we cannot retrospec-

tively determine the past processes and check whether

species competed in the past or not (Begon et al., 1996), the

pattern of the two decapod distribution can only be tested

and interpreted in terms of current ecological forces.

Using a multi-dimensional ecological design, this study

aimed first to analyse whether local environmental condi-

tions can account for the spatial segregation of the two native

decapods, the crayfish A. italicus and the river crab P. fluviatile,

in Central Italy freshwater ecosystems.

Second, we aimed to analyse which environmental vari-

ables were more closely associated with the presence/absence

of the two decapods at specific sites within their distribution

area. Most investigations on native freshwater decapods are

performed on crayfish and describe their distribution or the

effects of one or few environmental factors on it. In contrast,

the ecology of river crabs has been almost completely ne-

glected and only few multi-dimensional analyses of the effect

of a number of abiotic and biotic factors have been recently

conducted on crayfish (Naura and Robinson, 1998; Smith

et al., 1996; Gil-Sanchez and Alba-Tercedor, 2002; Trouilhe

et al., 2003; Renai et al., 2006).

In the light of the conservation needs of these native

endangered freshwater decapods, our investigation on the

environmental correlates of their occurrence and distribution

can be considered a basis for designing more focused applied

ecological research. In addition, it will have the potential to

assist in developing conservation protocols appropriate for

each decapod species.

2. Methods

2.1. Study area and selection of sites

The study area consists of medium to lowland streams

(ranging from 596 to 155 m a.s.l.) situated in the Northern

Apennine, Tuscany, Central Italy. In the area there are both

calcareous and siliceous sites and vegetation is dominated

by wooded areas. Watercourses belong to Arno and Reno river

basins. According to a recent systematic and phylogeographic

study (Fratini et al., 2005), the fresh water cray fish present in

this area is A. italicus.

In a previous study on the spatial distribution of P. fluviatile

and A. italicus in the area (Nocita et al., 2006) we have ascer-

tained that the two decapods occupy distinct geographic

zones. Crabs are present in the Central and Southern part of

the territory, while crayfish are found in the Northern part

of it. Both decapods occupy watercourses belonging to Arno

and Reno river basins. On the basis of this spatial distribution,

we selected 16 streams within each of the two zones, eight

streams where the corresponding species was recorded to

be present and eight where it was not present, for a total of

32 sites. In the study area any invasive decapod species,

which could affect the occurrence of A. pallipes and P. fluviatile,

was present (Nocita et al., 2006).

2.2. Data sampling

In order to assess the presence of a minimum number of both

juvenile and adult individuals, each stream was inspected by

conducting nocturnal surveys (i.e., during the temporal win-

dow of maximum activity of both the species) between March

and May 2003.

B I O L O G I C A L C O N S E R V A T I O N 1 3 6 ( 2 0 0 7 ) 4 3 1 – 4 4 1 433

2.2.1. Water parametersFor each site, a 50 m long stretch was selected and within this,

two 10 m long sub-stretches were chosen with a breadth of at

least 10 m. Inside each sub-stretch, abiotic variables were

measured in four occasions, two in May–October, when both

species show a peak in activity, and two in November–Febru-

ary, when both species are in hibernation and rest under nat-

ural refuges and/or, in the case of crabs, inside burrows

(Gherardi et al., 1988; Gherardi et al., 1998). Water sampling

was conducted between 9 and 11 a.m.

Water conductivity (lS cm�1), pH and dissolved oxygen

(mg l�1) were recorded by a multi-meter (model Multi 350i,

WTW, Germany). Water temperatures (�C) were recorded by

a maximum–minimum thermometer placed in the water for

24 h. Concentration of the following chemical substances

was determined with AQUAMERCK� test kit (Merck, Darms-

tadt, Switzerland): calcium bicarbonate (CaCO3), nitrate

(NO�3 ), nitrite (NO�2 ), ammonium (NHþ4 ), phosphate (P2O5),

and silicate (SiO2). With the exception of ammonium that

was determined in the field, water samples were collected

and analysed within 24 h. For each parameter (with the

exception of temperature) three replicates were taken in each

sub-stretch at each sampling occasion.

2.2.2. Geomorphological parameters of the streamsEach site was also characterized in terms of maximum water

depth and substrate type. At each sampling occasion, maxi-

mum water depth was measured at three separate points of

each sub-stretch (at the beginning, middle and end). The per-

centage cover of the substrate types was assessed once during

May–September, using a 80 · 80 cm grid divided into 16

squares of 20 · 20 cm. The grid was launched randomly five

times in each sub-stretch and the percentage of surface area

covered by different substrate types was visually estimated.

Substrate types were classified according to Wentworth Scale

(Wentworth, 1922): silt (<0.063 mm), sand (<2 mm), pebbles

(2–64 mm), cobbles (65–256 mm), boulders (>256 mm), and

bedrock (fixed rock formations).

The number of burrows and/or natural crevices along

banks and the length of banks (in percentage) covered by

roots, boulders and cobbles that decapods could use as shel-

ters were quantified in one occasion during May–September

(five 1 m long segments along the banks of each sub-stretch).

The extent of canopy cover was assessed in one occasion

during May–September using a digital camera (Nikon Coolpix

4500, 7.85–35 mm lens). Three pictures were taken within

each sub-stretch placing the camera in the middle of the

stream and pointing it at the sky. The percentage of cover

was estimated for each picture using the image processing

software ImageJ (<http://rsb.info.nih.gov/ij>).

2.2.3. Macro-invertebrate association assessmentAt each site, macro-invertebrate samples were collected fol-

lowing the EBI protocol (Woodiwiss, 1981), modified by Ghetti

(1997) for streams in Italy. This procedure is considered to be

a valid method for assessing water quality (Ghetti, 1986). Sam-

ples were taken once in spring, when the density of species is

maximal. Macro-invertebrates were collected from all the dif-

ferent microhabitats using a hand net (0.5 mm mesh size). All

collected material was preserved in 70% alcohol and identified

in laboratory under a stereoscopic dissection microscope fol-

lowing identification keys (Campaioli et al., 1994). Identifica-

tion was made at the taxonomic level required for each group.

For each site, three different indices were calculated: the

EBI value (Extended Biotic Index, Ghetti, 1997) and the two

most commonly used diversity indices, the Shannon–Wiener

index, H 0, and the Simpson index, 1 � k (Clarke and Warwick,

2001). The EBI value increases from 0 (complete absence of

bioindicators) to 14 (presence of the most sensitive groups

and the larger number of taxa). Higher values of the EBI index

indicate a less tolerant and better preserved community of

macro-invertebrates and a less polluted aquatic ecosystem.

Generally, the highest values (Ghetti, 1986) are not observed

in Italy and 10–12 are indicative of good water quality or min-

imally impacted condition.

2.3. Statistical analyses

Multi-variate methods were employed to analyse the relation-

ship between environmental variables and presence and spa-

tial distribution of the two freshwater macro-decapods.

Principal Component Analysis, on normalized data, was uti-

lized as an unconstrained method of ordination to visualise

multi-variate patterns (Clarke and Warwick, 2001). Distance-

based permutational multi-variate analysis of variance (PER-

MANOVA, Anderson, 2001) was employed in a two way full

factorial design to test null hypotheses of (1) no differences

between the crab and crayfish zone, and (2) no differences

among the streams where the decapods were present and

those where they were absent. All analyses were based on

4999 unrestricted permutations of the raw data (Anderson

and ter Braak, 2003). In addition, the canonical analysis of

principal coordinates (CAP, Anderson and Willis, 2003; Ander-

son and Robinson, 2003) was used as a constrained ordination

procedure to visualise patterns by reference to differences in

environmental parameters between zones. Both PERMANOVA

and CAP were computed using similarity matrixes based on

Euclidean distance on normalized data.

Due to their difference in variance and statistical proper-

ties, data regarding macro-invertebrate communities were

analysed in a different way. Similarity matrixes were com-

puted using Bray–Curtis distance on log10(x + 1) transformed

data and were analysed with PERMANOVA, non-metric mul-

ti-dimensional scaling (nMDS, Field et al., 1982; Clarke,

1993), utilized as an unconstrained method of ordination,

and CAP analyses. Multi-variate analyses were performed

using PRIMER v. 5.1 (Clarke and Gorley, 2001) and the FOR-

TRAN programs PERMANOVA (Anderson, 2005) and CAP

(Anderson, 2004).

A two-way Analyses of Variance (ANOVA) was employed to

test for differences between zones and between streams

where decapods were present or absent in the extent of can-

opy cover, and in the scores of each of the three indices, EBI,

Shannon–Wiener and Simpson, calculated on macro-inverte-

brate community composition. Prior to analyses, the homoge-

neity of variances was assessed using Cochran’s test and data

were transformed to x 0 = arcsin(x), only in the case of canopy

cover percentages, to remove heteroscedasticity (Underwood,

1997). ANOVAs were performed using GMAV 5 program (Uni-

versity of Sydney, Australia).

Fig. 1 – Relationship between spatial distribution of

decapods and water parameters. Two dimensional scatter

plot of the first Canonical axis for zone and the first

Canonical axis for presence calculated on water parameters

sampled during the decapod inactivity period in the two

zones and in streams where the decapods were present or

absent.

Table 2 – Relationship between spatial distribution offreshwater decapods and water parameters during theinactivity period

Positive correlation(presence)

Negative correlation(absence)

Minimum temperature 0.74 O2 �0.53

Conductivity 0.50

Maximum temperature 0.49

Ca2+ 0.47

NO�2 0.43

SiO2 0.41

NO�3 0.35

Correlation coefficients for individual parameters (jrj > 0.20) with

the first canonical axis for effects of zone. The analysis was per-

formed using the first m = 1 principal coordinate axis (explaining

49% of the variation in the original dissimilarity matrix) on nor-

malized data. A positive correlation indicates association with

decapod presence, while a negative correlation indicates an asso-

ciation with decapod absence (see Fig. 1). The analysis refers to

period when crabs and crayfish were not active.

434 B I O L O G I C A L C O N S E R V A T I O N 1 3 6 ( 2 0 0 7 ) 4 3 1 – 4 4 1

3. Results

3.1. Water parameters

The values of the water chemical parameters measured in

the inactivity period at the 16 streams of the crayfish zone

significantly differed from the ones recorded into the crab

zone (Table 1). Moreover, the PERMANOVA revealed signifi-

cant differences between the streams where decapods were

present and the ones without their presence (Table 1). The

first two Principal Components (PCs) were not able to ex-

plain most of the variance among the data and the PCA

was not explicative. On the other hand, the constrained

ordination, performed using CAP, showed a significant ef-

fect of zone factor (d2 = 0.496; P = 0.004) but not of presence

factor (d2 = 0.025; P = 0.88). The canonical axes correspond-

ing to the two main effects (Fig. 1) showed tendency of

streams where decapods were present to cluster together

on the positive quadrant of the canonical axis for zone.

These results strongly indicated that both crabs and cray-

fish preferred higher temperature and higher concentra-

tions of most of the dissolved ions, which are the

variables positively correlated with the canonical axis for

zone (Table 2).

Regarding the values of the water chemical parameters

measured within the decapod activity period, PERMANOVA

revealed significant differences only between the streams

of the two different zones (Table 3). As for the previous

analysis, the first two PCs explained only about half of the

variance among data and were not used to discuss the

results. CAP constrained ordination was more explicative

and showed a significant effect of zone factor (d2 = 0.806;

P < 0.001). In particular, the streams of the crab zone had

positive values on the canonical axis and, thus, showed

higher values of temperature and ion concentration

(Table 4).

Summarizing, the set of multi-variate analyses showed

that the lower temperature and ion concentration were asso-

ciated with the absence of both crabs and crayfish, although

these streams were the richer in oxygen. Intermediate

temperatures, recorded in the warmer months, were associ-

ated with crayfish and the warmer ones with crabs, while

both species were present in streams with high ion

concentrations.

Table 1 – Relationship between spatial distribution offreshwater decapods and water parameters during theinactivity period

Source df SS MS F P

Zone 1 32.87 32.87 3.81 0.002

Presence 1 25.48 25.48 2.95 0.013

Zone · presence 1 9.83 9.83 1.14 0.335

Residual 28 241.82 8.64

Total 31 310

Permutational MANOVA on the basis of Euclidean distance on

normalized data from 10 water parameters, measured at 32

streams. The analysis refers to period when crabs and crayfish

were not active.

Table 3 – Relationship between spatial distribution offreshwater decapods and water parameters during theactivity period

Source df SS MS F P

Zone 1 53.75 53.75 6.16 0.001

Presence 1 4.89 4.89 0.56 0.736

Zone · presence 1 6.99 6.99 0.80 0.553

Residual 28 244.36 8.73

Total 31 310

Permutational MANOVA on the basis of Euclidean distance on

normalized data from 10 water parameters, measured at 32

streams. The analysis refers to period when crabs and crayfish

were active.

Table 4 – Relationship between spatial distribution offreshwater decapods and water parameters during theactivity period

Positive correlation(crab zone)

Negative correlation(crayfish zone)

Maximum temperature 0.78 O2 �0.25

Minimum temperature 0.73

NO�3 0.53

NO�2 0.47

Conductivity 0.41

SiO2 0.39

Ca2+ 0.29

Correlation coefficients for individual parameters (jrj > 0.20) with

the first canonical axis for effects of zone. The analysis was done

using the first m = 1 principal coordinate axis (explaining 81% of

the variation in the original dissimilarity matrix) on normalized

data. A positive correlation indicates association with the crab

zone, while a negative correlation indicates an association with the

crayfish zone. The analysis refers to period when crabs and cray-

fish were active.

Fig. 2 – Relationship between spatial distribution of

freshwater decapods and geomorphological characteristics

of stream beds and banks. Principal component analysis

(PCA) plot of geomorphological characteristics in the two

zones and in streams where the decapods were present or

absent.

B I O L O G I C A L C O N S E R V A T I O N 1 3 6 ( 2 0 0 7 ) 4 3 1 – 4 4 1 435

3.2. Geomorphological parameters

The geomorphological parameters (substrate composition

and water depth) sampled in each transect of each stream

were then analysed using a 3-way mixed PERMANOVA design

(Table 5). The analysis revealed a high variability at small and

large spatial scale, showing that the morphological parame-

ters of stream beds and banks consistently varied among

streams and among zones. PCA analysis confirmed this vari-

ability with streams belonging to different zones not segre-

gating from other groups (Fig. 2).

The extent of canopy cover did not differ significantly be-

tween the two zones (F = 2.81; df = 1; P = 0.10; PERMANOVA)

and was not related to the presence of the decapods

(F = 1.89; df = 1; P = 0.18; PERMANOVA).

3.3. Abiotic (water and geomorphological) parameters

A last analysis on the whole set of abiotic (water and geomor-

phological) parameters was conducted creating a data matrix

Table 5 – Relationship between spatial distribution offreshwater decapods and geomorphological parametersat the different streams

Source df SS MS F P

Presence 1 31.4862 31.4862 2.5903 0.015

Zone 1 25.7139 25.7139 1.7885 0.092

Stream (zone) 14 201.288 14.3777 2.6946 0.001

Presence · zone 1 30.5854 30.5854 2.5162 0.015

Presence · stream (zone) 14 170.179 12.1556 2.2781 0.001

Residual 32 170.747 5.3359

Total 63 630

Results of the 3-way PERMANOVA, mixed design, with ‘‘presence’’

and ‘‘zone’’ as fixed and orthogonal factors and ‘‘stream’’ as a

random factor nested in ‘‘zone’’. The analysis is based on Euclidean

distance of normalized data from 15 variables (geomorphological

parameters).

in which geomorphological characteristics of the river beds

were merged with the water chemical parameters. Table 6

summarize mean values (±SE) of these set of parameters.

The new data matrix, containing now 16 variables, was

analysed with a PERMANOVA Two-Way design which showed

significant differences both at zone and presence levels (Table

7). Although PCA was poorly informative, since the first two

PCs were not able to explain most of the variance among

the data, CAP showed significant effects of both zone

(d2 = 0.447; P < 0.012) and presence factors (d2 = 0.456;

P < 0.048; Fig. 3). The plot produced by visualizing the values

obtained on the new canonical axes corresponding to the

two main effects (Fig. 3) graphically separated the streams

where crayfish were present from the streams with no cray-

fish. In particular, almost all the streams of the crayfish area

had negative values of the canonical axis for zone, strongly

indicating that in these streams a bedrock substratum pre-

vailed and that they were richer in oxygen (Table 8). Moreover,

in Fig. 3, the streams where the crayfish were present are

clustered on the positive quadrant of the canonical axis for

presence, which is correlated with higher temperatures, high-

er densities of cobbles, pebbles and sand and Calcium con-

centration (Table 8). On the other hand, the streams

colonised by crabs were more disperse on the canonical axis

for presence, but all the streams of the crab zone were asso-

ciated with positive values of the canonical axis for zone. In

particular, the streams of the crab zone had higher ion con-

centrations and higher temperatures with respect to the ones

inhabited by crayfish, regardless of the presence of crabs

(Table 8).

3.4. Macro-invertebrate associations

The analysis on the abundance of macro-invertebrates

belonging to different taxa showed a difference between the

two zones (F = 2.60; df = 1; P = 0.03; PERMANOVA), confirmed

both by nMDS unconstrained ordination (Fig. 4a) and con-

strained CAP ordination (d2 = 0.345; P < 0.005; Fig. 4b). The re-

sults of CAP showed that the streams of the crab zone are

Table 6 – Abiotic (mean values ± SE) and biotic parameters measured during the decapod activity period in streams of the crab and of the crayfish zone

Site

no.

Zone Presence/

absence

Bedrock Boulders Cobbles Pebbles Sand Silt Depth

(cm)

T max

(� C)

T min

(� C)

O2

(mg l�1)

pH EC

(lS cm�1)

Ca2+ NO�2 NO�3 SiO2 H 0 1 � k EBI

1 A Absent 29.1 ± 6.5 14.0 ± 3.7 28.8 ± 3.8 27.9 ± 6.1 0.2 ± 0.2 0.0 ± 0.0 19.1 ± 4.2 18.8 ± 2.9 13.0 ± 1.1 5.3 ± 0.8 7.7 ± 0.0 329.5 ± 4.1 66.5 ± 4.0 0.0 ± 0.0 0.0 ± 0.0 5.3 ± 0.0 1.92 0.88 10

2 A Absent 15.7 ± 3.5 12.2 ± 4.7 14.0 ± 3.3 52.4 ± 7.1 5.7 ± 1.4 0.0 ± 0.0 31.2 ± 3.6 17.0 ± 1.9 12.0 ± 0.8 8.9 ± 0.1 7.9 ± 0.0 390.3 ± 19.1 71.0 ± 4.5 0.0 ± 0.0 0.0 ± 0.8 6.0 ± 0.2 1.55 0.84 9

3 A Absent 0.4 ± 0.4 0.0 ± 0.0 6.5 ± 2.0 55.1 ± 8.8 5.4 ± 3.1 32.6 ± 8.8 17.7 ± 3.4 14.8 ± 2.1 8.0 ± 0.7 8.4 ± 0.0 8.2 ± 0.0 354.5 ± 19.2 60.3 ± 3.6 0.0 ± 0.0 0.0 ± 0.8 6.0 ± 0.2 1.84 0.88 10

4 A Absent 24.1 ± 6.3 11.9 ± 3.4 14.5 ± 3.2 37.9 ± 5.3 5.9 ± 3.2 5.7 ± 3.9 20.2 ± 4.9 13.3 ± 1.3 10.3 ± 1.2 8.7 ± 0.8 8.2 ± 0.1 485.5 ± 9.6 72.5 ± 0.4 0.0 ± 0.0 0.0 ± 0.0 6.0 ± 0.2 2.07 0.91 10

5 A Absent 16.5 ± 5.8 17.8 ± 5.4 18.5 ± 4.0 46.6 ± 7.0 0.7 ± 0.5 0.0 ± 0.0 20.4 ± 2.9 18.0 ± 0.6 9.5 ± 0.8 8.0 ± 0.2 7.8 ± 0.0 336.8 ± 10.5 64.0 ± 1.1 0.0 ± 0.0 2.5 ± 0.0 6.0 ± 0.5 1.72 0.84 9

6 A Absent 32.2 ± 6.4 7.6 ± 2.0 26.3 ± 3.6 31.9 ± 5.8 0.3 ± 0.3 1.7 ± 0.8 35.3 ± 3.1 15.3 ± 3.4 11.0 ± 0.9 8.2 ± 0.6 7.9 ± 0.1 396.3 ± 27.0 78.3 ± 3.6 0.0 ± 0.1 0.0 ± 0.8 6.0 ± 0.0 1.63 0.85 8

7 A Absent 35.3 ± 10.5 6.8 ± 3.5 13.1 ± 3.1 42.2 ± 9.8 0.0 ± 0.0 2.8 ± 2.1 32.7 ± 9.4 18.5 ± 1.4 12.5 ± 1.1 5.7 ± 0.1 8.1 ± 0.0 452.0 ± 15.8 80.3 ± 3.4 0.0 ± 0.0 0.0 ± 0.8 6.0 ± 0.2 1.74 0.84 10

8 A Absent 25.6 ± 5.5 17.4 ± 3.4 18.1 ± 3.7 36.8 ± 6.8 0.3 ± 0.3 1.8 ± 1.7 20.0 ± 6.1 19.0 ± 1.8 10.0 ± 1.8 8.1 ± 0.2 7.8 ± 0.2 321.0 ± 3.7 63.8 ± 1.2 0.0 ± 0.0 0.0 ± 0.0 4.5 ± 0.2 1.70 0.89 8

9 A Present 24.3 ± 5.6 4.4 ± 2.3 12.7 ± 2.9 56.4 ± 7.5 0.0 ± 0.0 2.2 ± 1.6 17.5 ± 3.2 24.5 ± 1.4 13.5 ± 0.9 5.2 ± 0.8 8.2 ± 0.2 492.0 ± 17.6 83.0 ± 1.8 0.0 ± 0.0 0.0 ± 0.0 6.0 ± 0.4 1.89 0.94 6

10 A Present 15.3 ± 8.4 12.5 ± 2.7 25.3 ± 4.9 36.4 ± 5.9 1.7 ± 1.6 8.9 ± 4.3 26.6 ± 1.7 18.3 ± 0.9 11.5 ± 1.2 8.4 ± 0.2 8.3 ± 0.1 296.3 ± 6.1 51.5 ± 0.8 0.0 ± 0.0 2.5 ± 0.0 6.8 ± 0.0 1.86 0.91 9

11 A Present 30.4 ± 6.5 18.4 ± 4.5 17.8 ± 3.6 27.7 ± 4.3 1.1 ± 0.7 4.7 ± 2.4 28.4 ± 2.1 19.0 ± 0.1 11.3 ± 0.3 7.9 ± 0.1 8.1 ± 0.0 270.8 ± 8.9 43.0 ± 0.9 0.0 ± 0.0 2.5 ± 0.0 6.4 ± 0.0 1.55 0.85 9

12 A Present 31.6 ± 9.8 11.4 ± 3.7 10.8 ± 2.7 44.3 ± 9.9 0.0 ± 0.0 1.9 17.8 ± 1.2 18.8 ± 0.9 13.0 ± 0.8 5.3 ± 0.0 7.7 ± 0.0 457.3 ± 12.8 100.8 ± 0.8 0.0 ± 0.0 0.0 ± 0.7 5.6 ± 0.2 1.84 0.88 9

13 A Present 19.9 ± 8.9 7.5 ± 3.4 14.2 ± 3.4 34.9 ± 7.1 4.4 ± 2.1 19.1 ± 3.3 28.4 ± 2.9 18.5 ± 0.1 13.5 ± 0.4 8.0 ± 0.2 8.2 ± 0.0 551.5 ± 5.9 81.0 ± 0.8 0.0 ± 0.0 2.5 ± 0.0 6.8 ± 0.0 2.05 0.91 10

14 A Present 18.4 ± 5.3 8.9 ± 2.9 23.5 ± 2.8 32.3 ± 6.5 3.7 ± 2.5 13.1 ± 1.6 24.6 ± 1.4 20.0 ± 0.3 12.0 ± 0.6 8.7 ± 0.1 7.6 ± 0.0 369.0 ± 2.3 64.8 ± 1.3 0.0 ± 0.0 0.0 ± 0.0 6.8 ± 0.3 1.92 0.88 9

15 A Present 61.5 ± 12.0 3.7 ± 1.4 13.6 ± 5.1 17.9 ± 6.7 0.0 ± 0.0 3.4 ± 1.8 11.1 ± 2.6 13.5 ± 0.3 11.0 ± 0.4 8.4 ± 0.1 8.3 ± 0.0 516.0 ± 29.4 77.0 ± 4.0 0.0 ± 0.0 0.0 ± 0.0 6.8 ± 0.2 1.49 0.86 8

16 A Present 13.6 ± 5.4 12.7 ± 3.0 25.8 ± 6.7 40.8 ± 6.0 5.7 ± 4.4 1.4 ± 1.2 12.2 ± 3.3 18.3 ± 0.4 11.3 ± 0.1 7.5 ± 0.2 8.2 ± 0.1 439.0 ± 14.9 72.0 ± 2.9 0.0 ± 0.0 0.0 ± 0.8 6.8 ± 0.2 1.91 0.89 8

17 P Absent 8.6 ± 4.4 4.0 ± 1.3 15.2 ± 3.5 22.5 ± 4.1 0.3 ± 0.3 49.4 ± 9.1 13.6 ± 3.6 14.0 ± 0.2 6.5 ± 0.5 7.5 ± 0.2 8.2 ± 0.0 325.8 ± 11.2 62.3 ± 2.0 0.0 ± 0.0 0.0 ± 1.3 7.0 ± 0.5 2.11 0.90 9

18 P Absent 34.3 ± 9.6 8.9 ± 3.4 15.2 ± 2.5 29.3 ± 6.6 1.9 ± 1.1 10.4 ± 3.5 13.8 ± 13.5 14.0 ± 1.4 6.5 ± 0.8 8.1 ± 0.7 8.2 ± 0.0 280.5 ± 4.9 54.8 ± 0.3 0.0 ± 0.0 1.3 ± 0.0 6.8 ± 0.0 2.04 0.91 8

19 P Absent 8.8 ± 5.5 8.4 ± 2.1 15.0 ± 3.0 44.5 ± 7.0 1.9 ± 1.4 21.4 ± 10.2 32.2 ± 1.7 12.5 ± 0.2 9.8 ± 0.3 8.8 ± 0.2 8.2 ± 0.0 281.8 ± 9.0 48.8 ± 1.8 0.0 ± 0.0 0.0 ± 0.0 6.8 ± 0.2 1.81 0.88 9

20 P Absent 42.6 ± 8.3 19.0 ± 3.4 14.6 ± 3.0 23.3 ± 5.0 0.4 ± 0.3 0.0 ± 0.0 17.2 ± 6.3 14.3 ± 0.5 10.3 ± 0.2 8.4 ± 0.2 8.3 ± 0.0 482.3 ± 12.3 63.0 ± 1.4 0.0 ± 0.0 0.0 ± 0.0 6.0 ± 0.2 1.93 0.90 9

21 P Absent 66.6 ± 8.8 6.1 ± 3.5 5.8 ± 2.3 21.6 ± 5.6 0.0 ± 0.0 0.0 ± 0.0 27.2 ± 4.2 13.0 ± 1.8 10.8 ± 1.1 8.6 ± 0.0 8.4 ± 0.2 429.0 ± 12.9 73.5 ± 1.5 0.0 ± 0.0 0.0 ± 1.3 4.5 ± 0.0 2.09 0.92 9

22 P Absent 26.6 ± 10.1 11.3 ± 3.6 16.7 ± 4.4 32.0 ± 4.2 0.0 ± 0.0 13.4 ± 4.9 12.3 ± 5.5 13.5 ± 0.5 8.0 ± 0.4 8.4 ± 0.2 8.4 ± 0.0 480.0 ± 6.1 76.0 ± 0.7 0.0 ± 0.0 0.0 ± 0.0 7.0 ± 0.6 2.14 0.95 8

23 P Absent 37.1 ± 8.7 7.3 ± 2.9 17.1 ± 3.2 34.5 ± 6.4 0.0 ± 0.0 4.1 ± 1.2 31.8 ± 4.6 12.8 ± 0.3 9.8 ± 0.1 8.7 ± 0.2 8.1 ± 0.0 232.0 ± 9.6 41.5 ± 1.7 0.0 ± 0.0 0.0 ± 0.0 6.0 ± 0.5 1.71 0.87 9

24 P Absent 51.7 ± 10.7 13.6 ± 5.9 12.6 ± 3.5 20.5 ± 5.6 0.3 ± 0.2 1.3 ± 0.9 16.3 ± 2.1 14.5 ± 1.4 10.5 ± 0.2 8.6 ± 1.2 8.4 ± 0.0 416.3 ± 10.6 68.0 ± 0.4 0.0 ± 0.0 6.3 ± 0.0 7.4 ± 0.2 1.79 0.87 10

25 P Present 3.1 ± 1.1 5.1 ± 2.3 10.4 ± 2.6 5.9 ± 3.3 0.0 ± 0.0 75.4 ± 7.4 43.1 ± 1.6 18.5 ± 1.4 12.5 ± 0.2 5.8 ± 1.5 8.3 ± 0.0 412.3 ± 9.7 79.0 ± 0.1 0.0 ± 0.0 0.0 ± 0.0 6.0 ± 0.0 2.02 0.94 8

26 P Present 19.4 ± 5.5 13.9 ± 3.6 17.9 ± 2.5 47.5 ± 7.0 0.8 ± 0.6 0.5 ± 0.4 17.3 ± 11.1 11.9 ± 1.1 15.3 ± 0.5 6.9 ± 0.2 8.1 ± 0.0 496.5 ± 11.2 84.8 ± 3.3 0.3 ± 0.0 2.5 ± 0.0 7.5 ± 0.6 2.02 0.94 8

27 P Present 12.9 ± 3.9 27.2 ± 5.5 11.7 ± 2.2 47.4 ± 3.6 0.7 ± 0.4 0.1 ± 0.1 17.4 ± 10.0 16.0 ± 0.7 13.0 ± 1.2 7.4 ± 0.1 8.1 ± 0.1 492.5 ± 5.0 84.0 ± 1.4 0.0 ± 0.0 0.0 ± 0.0 6.1 ± 0.0 2.02 0.94 8

28 P Present 19.3 ± 7.3 19.8 ± 5.1 11.6 ± 3.1 39.6 ± 4.9 5.2 ± 3.1 4.6 ± 2.7 18.3 ± 4.5 15.0 ± 1.4 11.3 ± 1.1 8.3 ± 0.7 8.2 ± 0.1 353.5 ± 3.6 50.3 ± 1.0 0.2 ± 0.0 0.0 ± 0.0 6.8 ± 0.0 2.02 0.87 10

29 P Present 26.3 ± 7.5 11.9 ± 5.5 20.1 ± 2.9 36.7 ± 7.3 0.1 ± 0.1 5.0 ± 1.4 12.7 ± 9.0 16.3 ± 1.3 10.3 ± 0.2 7.4 ± 0.2 8.0 ± 0.0 444.5 ± 16.7 71.5 ± 3.8 0.0 ± 0.0 7.5 ± 0.8 6.8 ± 0.0 2.03 0.90 10

30 P Present 13.8 ± 3.5 13.3 ± 2.5 19.7 ± 2.6 52.5 ± 3.6 0.1 ± 0.1 0.6 ± 0.5 10.2 ± 2.6 18.3 ± 2.1 11.3 ± 1.2 8.4 ± 0.1 8.3 ± 0.1 435.0 ± 6.9 75.3 ± 1.8 0.0 ± 0.0 0.0 ± 0.0 7.5 ± 0.5 1.98 0.92 9

31 P Present 42.1 ± 11.5 7.6 ± 2.4 16.3 ± 4.6 23.2 ± 6.2 1.1 ± 0.8 9.7 ± 5.0 36.8 ± 1.6 17.8 ± 0.2 11.8 ± 0.6 8.6 ± 0.2 8.2 ± 0.0 460.0 ± 7.3 83.8 ± 1.0 0.0 ± 0.0 0.0 ± 0.0 6.0 ± 0.5 2.04 0.97 7

32 P Present 16.4 ± 6.4 6.4 ± 2.0 17.9 ± 3.2 55.6 ± 8.0 0.1 ± 0.1 3.4 ± 1.7 27.7 ± 3.7 19.3 ± 0.4 11.5 ± 0.2 8.5 ± 0.1 8.1 ± 0.0 439.3 ± 13.3 81.5 ± 0.8 0.0 ± 0.0 2.5 ± 0.0 6.0 ± 0.0 1.84 0.86 9

For each site (1–32), the following data are reported: zone (A: A. italicus, P: P. fluviatile), decapod presence or absence, geomorphological parameters, water parameters, and biological diversity indices

(H 0: Shannon–Wiener index; 1 � k: Simpson index; EBI: Extended Biotic Index).

43

6B

IO

LO

GI

CA

LC

ON

SE

RV

AT

IO

N1

36

(2

00

7)

43

1–

44

1

Table 7 – Relationship between spatial distribution offreshwater decapods and abiotic (water plus geomor-phological) parameters

Source df SS MS F P

Zone 1 34.87 34.87 2.39 0.013

Presence 1 34.39 34.39 2.35 0.019

Zone · presence 1 17.62 17.62 1.21 0.292

Residual 28 409.13 14.61

Total 31 496

Permutational MANOVA on the basis of Euclidean distance on

normalized data from six geomorphological and ten water

parameters, assessed at 32 streams.

Fig. 3 – Relationship between spatial distribution of

freshwater decapods and abiotic parameters. Two

dimensional scatter plot of the first canonical axis for zone

and the first canonical axis for presence of abiotic

parameters.

Table 8 – Relationship between spatial distribution offreshwater decapods and abiotic parameters

Canonical axis for zone Canonical axis for presence

Positive correlation (crabs) Positive correlation (crayfish presence)

Minimum temperature 0.77 Maximum temperature 0.68

NO�2 0.56 Cobbles 0.44

Ca2+ 0.53 Pebbles 0.43

Conductivity 0.50 Minimum temperature 0.31

SiO2 0.40 Sand 0.24

Maximum temperature 0.37 Ca2+ 0.23

NO�3 0.30 Water depth 0.22

Pebbles 0.26

Negative correlation (crayfish) Negative correlation (crayfish absence)

O2 �0.52 pH �0.66

Bedrock �0.33 NO�2 �0.50

SiO2 �0.41

NO�3 �0.32

Silt �0.28

Bedrock �0.25

Correlation coefficients for individual parameters (jrj > 0.20) with

the canonical axis for effects of zone and for effects of presence.

The analysis was done using the first m = 1 principal coordinate

axis (explaining 45% and 46%, respectively, of the variation in the

original dissimilarity matrix) on normalized data. For the effects of

zone, a positive correlation indicates association with crabs, while

a negative correlation indicates an association with crayfish (see

Fig. 3). For the effects of presence, a positive correlation indicates

association with crayfish presence, while a negative correlation

indicates an association with crayfish absence (see Fig. 3).

Fig. 4 – Macro-invertebrate assemblages. Non-metric multi-

dimensional scaling (nMDS) plot of assemblages of

freshwater invertebrates in the two zones and in streams

where the decapods were present or absent (a) and one

dimensional scatter plot of the canonical axis for zone (b).

B I O L O G I C A L C O N S E R V A T I O N 1 3 6 ( 2 0 0 7 ) 4 3 1 – 4 4 1 437

more abundant in Gastropods, Odonata, Amphipods, Triclads

and Coleopterans, while Plecopterans are more abundant in

the streams of the crayfish zone (Table 9).

EBI index calculated for the sampled streams (see Table 6)

did not vary between the zones (F = 0.13; df = 1; P = 0.72; two-

way ANOVA) and between sites where decapods were present

or not (F = 2.13; df = 1; P = 0.15; two-way ANOVA). EBI values

were high for all sites, indicating that they are unpolluted

streams. On the other hand, the diversity of macro-inverte-

brates was higher in the crab zone, regardless of the presence

of crabs themselves, both when expressed with H 0 (F = 10.97;

df = 1; P = 0.003; two-way ANOVA) and 1 � k (F = 7.92; df = 1;

P = 0.009; two-way ANOVA).

4. Discussion

Actual patterns of species distribution are the complex result

of ecological preferences and physiological constraints cou-

pled with evolutionary history, human interference and colo-

nisation events. From a conservation perspective, it is thus

crucial to determine which local factors are most important

in determining actual species diversity patterns.

Despite the large number of studies describing the distri-

bution of freshwater decapods, few authors have analysed

Table 9 – Distribution of freshwater macro-invertebratesin the sampled zones

Positive correlation(crayfish zone)

Negative correlation(crab zone)

Plecopterans 0.29 Gastropods �0.66

Odonata �0.63

Amphipods �0.56

Triclads �0.51

Coleopterans �0.34

Correlation coefficients for individual parameters (jrj > 0.20) with

the first canonical axis for effects of zone. The analysis was done

using the first m = 1 principal coordinate axis (explaining 35% of

the variation in the original dissimilarity matrix) on normalized

data. A positive correlation indicates association with the crayfish

zone, while a negative correlation indicates an association with the

crab zone (see Fig. 4b).

438 B I O L O G I C A L C O N S E R V A T I O N 1 3 6 ( 2 0 0 7 ) 4 3 1 – 4 4 1

their ecological correlates using a multi-variate design (in

crayfish: Smith et al., 1996; Naura and Robinson, 1998; Renai

et al., 2006). The survey design used in this study allowed us

to demonstrate that environmental variables significantly af-

fect the distribution of both P. fluviatile and A. italicus in the

Southern Tuscan Apennine and the occurrence of crayfish

in specific sites within its distribution zone. On the contrary,

we could not demonstrate that the presence of the river crab,

within its distribution zone, is associated to any biotic or abi-

otic parameters. Although behaviour of freshwater crabs has

been widely studied (see as an example Vannini and Gherardi,

1981) their ecology has been almost completely neglected and

thus our results cannot be compared with those obtained

elsewhere.

The area occupied by the river crab differs from that occu-

pied by crayfish mainly for the higher minimum and maxi-

mum water temperatures. Moreover, streams of the crayfish

zone are characterized by higher oxygen contents, a general

lower amount of dissolved ions and bedrock substrates.

The differences found between the two zones in terms of

chemical–physical parameters may account for the differ-

ences in macro-invertebrate community composition (ex-

pressed as the Shannon–Wiener index and the Simpson

index). Overall, the crab zone is characterized by higher diver-

sity indexes. Although, the crayfish zone is associated with

Plecoptera, a taxon typical of cold and clean water. Grandjean

et al. (2001) suggested that the presence of Plecoptera seems

to be an excellent criterion for the selection of suitable sites

for crayfish restocking.

All the examined streams, independent of the zone and

presence/absence of decapods, have a high water quality as

revealed by the EBI values. Water quality and lack of pollu-

tants, in addition to habitat heterogeneity, have been reported

as a fundamental condition for the presence of indigenous

crayfish (Grandjean et al., 2003; Trouilhe et al., 2003). However,

a number of studies have shown that this crayfish can live in

brooks with sub-optimal water quality and that it is present

also in degraded conditions (Demers et al., 2003; Fureder

et al., 2003). Grandjean et al. (2001) and Broquet et al. (2002)

had already demonstrated this phenomenon in France, De-

mers and Reynolds (2002) in Ireland and, recently, Scalici

and Gibertini (2005) in Italy. The high water quality of all the

analysed streams do not allow us to establish whether A. ita-

licus may be considered a good bio-indicator, nor whether P.

fluviatile may be more resistant than A. italicus to water pollu-

tion, as often hypothesised on the basis of field observation

and records in urban and pre-urban areas (Present authors,

personal observation).

Our results indicate that substratum composition, in par-

ticular the presence of exposed pebbles and cobbles, is a

strong determinant for the occurrence of the two decapods.

This association reflects the importance of availability of ref-

uges of the correct size, as previously shown in crayfish (Fos-

ter, 1995; Naura and Robinson, 1998). Shelters and burrows,

available within a stream, are critical resources for adult cray-

fish survival, their availability being the ‘principle resource

bottleneck’ in crayfish populations (Hobbs, 1991). In the case

of crabs, although adults can refuge also out of the stream,

in holes and burrows under the riparian vegetation, exposed

pebble and cobbles allow juveniles to avoid predation by

fishes and adult conspecifics.

Due to its geology, the crab area is more calcareous

than the crayfish area (74.305 ± 17.99 mg l�1 versus 66.238 ±

12.61 mg l�1), but concentration of calcium is an important

factor associated to the occurrence of both crayfish and crabs.

This result is expected because calcium is an essential ele-

ment for exoskeleton calcification. In fact, in some areas

(e.g., in Britain: Jay and Holdich, 1981; Naura and Robinson,

1998), lotic distribution of crayfish is limited to calcareous

catchments, where erosion provides receiving watercourses

with a high concentration of inorganic ions (higher than

5 mg l�1, Jay and Holdich, 1981).

Differently from previous studies performed on crayfish

(Naura and Robinson, 1998; Broquet et al., 2002; Smith et al.,

1996), our data showed that the occurrence and distribution

of both decapods were not associated with the extent of can-

opy cover. Although litter represents an important compo-

nent of the diet of both species, it does not constitute the

sole source of proteins (for crayfish, Gherardi et al., 2001; for

crabs, Gherardi et al., 1987).

To conclude, our ecological data are able to explain the

spatial segregation of the studied species in Central Italy

freshwater ecosystems according to a multi-factorial and

complex picture. However, historical factors (interference

competition between the two species and climatic change)

can have also played a role in the past. Pretzmann (1987)

hypothesized that competitive interactions began during the

Pleistocene, when crabs and crayfish converged in Italy after

migrating from Eastern European regions. In the area of

sympatry, they entered into competition and the prevalence

of crabs over crayfish led to the present distribution. Even if

some ethological evidences (Barbaresi and Gherardi, 1997;

Gherardi and Cioni, 2004) give support to this hypothesis,

how interference competition could have contribute to the

present ecological separation between river crabs and fresh-

water crayfish cannot be ascertained.

4.1. Implications for conservation

Habitat protection and preservation of freshwater ecosystems

are obviously the main goal for conservation of their biodiver-

B I O L O G I C A L C O N S E R V A T I O N 1 3 6 ( 2 0 0 7 ) 4 3 1 – 4 4 1 439

sity. However, in order to optimise conservation efforts it is

fundamental to translate general indications to specific man-

agement recommendations for individual species in any gi-

ven landscape. Effective conservation of natural populations

is often limited by the lack of species-specific ecological

knowledge. Our multi-dimensional ecological approach,

underlining the synergic effects of many biotic and abiotic

factors on the occurrence and spatial distribution of two na-

tive endangered decapods, provides fundamental informa-

tion for maintenance of their natural populations as well as

for the selection of areas and streams adequate for their

reintroduction.

Underlining the existence of ecological differences among

the two decapod species in terms of their habitat require-

ments, our data enable us to make two general consider-

ations. First, conservation planners need to tailor their

efforts to each decapod species and situation. Second, since

ecological factors can account for the spatial segregation of

the two freshwater decapods in the study area, it appears

necessary to consider the area as a main factor guiding man-

agement decisions during reintroduction programs. Given the

crisis that populations of native freshwater decapods are fac-

ing (Gherardi and Holdich, 1999; Fureder et al., 2003), it is

imperative that conservation planners make the most effec-

tive use of the information currently available.

Specific considerations emerge concerning the preserva-

tion of the two decapods here studied. The lack of discrimina-

tion from an ecological point of view between the streams

where P. fluviatile is present and those where it is absent

may sound alarming since it should mean that crabs have

completely disappeared from some streams. River crab fish-

ing was extensively practised in the study area as well as in

other zones of Italy until few decades ago and today, even if

crabs are protected by local laws, poaching still occurs. Thus,

over-exploitation may be the cause of local river crab absence.

The information available from local people and our personal

observations on the past presence of crabs in some streams of

the area support this hypothesis. In addition, the alternative

hypothesis that crabs have never occupied some streams in

the area sound unlikely, considering their semiterrestrial hab-

its and their high dispersal capabilities coupled with the rela-

tively short distances among streams (in some cases in the

order of few kilometers).

In our opinion, the protection of both decapods should be

strongly regulated at all levels of legislation (from communi-

tarian to regional scale) in order to guarantee their preserva-

tion throughout their distribution range. Notwithstanding

A. italicus requires urgent conservation measures, Italian laws

(at national and regional level) do not mention this species as

protected. Regarding the freshwater crab, P. fluviatile, the spe-

cies is not included in the IUCN red list (likely due to its re-

stricted geographic distribution, the scarce knowledge on its

ecology and biology, and the lack of economic value) and its

protection is strictly delegated to regional laws, until now

only adopted by few Italian Regions (Latium, Tuscany, Liguria

and Abruzzo).

Concerning crayfish, in the light of the systematic revision

that underlined the presence of the two well distinguished

species A. pallipes and A. italicus, the latter with four subspe-

cies (ESU, Fratini et al., 2005), specific conservation efforts

should be necessary. These evolutionary significant units

should have different ecological preferences as well as local

genetic adaptations. Further ecological and population genet-

ic studies will be necessary to assess whether such differ-

ences do exist.

Acknowledgements

This work was funded by the Province of Prato, Natural Re-

sources and Protected Areas Agency. We would like to thank

Polizia Provinciale personnel in Prato, A. Bruni, L. Gori and

A. Nocita for their contribution to the field work, Rocco

Rorandelli and Francesca Zacchi for the linguistic revision of

the manuscript.

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