Effect of Urban Isolation on the Dynamics of River Crabs

FLORE Repository istituzionale dell'Università degli Studi di Firenze Effect of urban isolation on the dynamics of river crabs. Questa è la Versione finale referata (Post print/Accepted manuscript) della seguente pubblicazione: Original Citation: Effect of urban isolation on the dynamics of river crabs / M. SCALICI; D. MACALE; F. SCHIAVONE; F. GHERARDI; G. GIBERTINI. - In: FUNDAMENTAL AND APPLIED LIMNOLOGY. - ISSN 1863-9135. - STAMPA. - 172(2008), pp. 167- 174. [10.1127/1863-9135/2008/0172-0167] Availability: This version is available at: 2158/329866 since: Published version: DOI: 10.1127/1863-9135/2008/0172-0167 Terms of use: Open Access La pubblicazione è resa disponibile sotto le norme e i termini della licenza di deposito, secondo quanto stabilito dalla Policy per l'accesso aperto dell'Università degli Studi di Firenze (https://www.sba.unifi.it/upload/policy-oa-2016-1.pdf) Publisher copyright claim: (Article begins on next page) 25 September 2021 Urban isolation of river crabs 167 Fundamental and Applied Limnology Archiv für Hydrobiologie Vol. 172/2: 167–174, July 2008 © E. Schweizerbart’sche Verlagsbuchhandlung 2008 Effect of urban isolation on the dynamics of river crabs Massimiliano Scalici1*, Daniele Macale1, Francesca Schiavone1, Francesca Gherardi2 and Giancarlo Gibertini1 With 3 fi gures and 2 tables Abstract: European river crabs usually disappear from areas affected by human activities. However, a Potamon fl uviatile population was recently recorded within an archaeological excavation in the historical centre of Rome. Since adaptation of river-dwelling brachyurans to urban habitat is rare, we focused on some aspects of population dynamics which are considered to be strictly related to important biological processes and to the adaptation degree of a population to its habitat. To do so, length-frequency distributions of four Italian populations were obtained using the carapace length and the subsequent data was analyzed by the FiSAT program. The Roman population exhibited a lower growth rate (as demonstrated by ANCOVA) and higher asymptotic length and longevity than the other populations, suggesting that Roman crabs are affected by gigantism. Isolation was confi rmed by the absence of crabs in adjacent water systems and in the urban tract of the River Tiber, and could be a result of the progressive expansion of the city of Rome. On the other hand, an alternative explanation could be represented by a historical transfaunation from western Greece. Excluding recent intentional introduction by man, the presence of P. fl uviatile in the city of Rome is thus probably the result of this species’ ecological preferences and physiological constraints coupled with its evolutionary history, human interference, and colonisation events. It is, therefore, necessary to eschweizerbartxxx devise a conservation plan to protect this relict population as its preservation should be considered as important as the preservation of the historical monuments. Key words: Potamon fl uviatile, river crab, growth pattern, dynamics, urban isolation. Introduction 2003). These are the main reasons why today only a few aquatic sinanthropic species fi nd space in urban Inland waters are among the systems most affected by areas (e.g. Wootton et al. 1996). Pollution, homogeni- human activities (Dynesius & Nilsson 1994, Naiman & zation, habitat fragmentation, and geographic isolation Turner 2000). Among anthropogenic factors, land-use further increase the risks of species extinction (Polis and urban development have, in fact, been responsi- et al. 1997, Hanski 1998), these risks being amplifi ed ble for altering species composition (e.g. Richter et al. by a progressive fragmentation (e.g. Wolf 1987, Soulé 1997, Jansson et al. 2000), food web structure (Woot- 1991, Simberloff 1992, Kruess & Tscharntke 1994, ton et al. 1996), nutrient cycling (Johnes 1996, Meyer Turner & Corlett 1996, Bascompte & Solé 1998, Did- et al. 1999), and ecosystem functioning (Vörösmarty ham et al. 1998). et al. 2000). The timing, amount, and type of inputs of Among the few aquatic sinanthropic species, the water, light, organic matter, etc. associated with urban river crab Potamon fl uviatile (Herbst, 1785) is consid- expansion may modify and lead to degradation of river ered a new urban species (Schiavone et al. 2007). It functionality for large extensions, with serious conse- usually inhabits relatively undisturbed lentic and lotic quences for the whole aquatic system (Strayer et al. habitats (Pretzmann 1987, Barbaresi & Gherardi 1997, 1 Authors’ addresses: Università degli Studi «Roma Tre», Dipartimento di Biologia, viale G. Marconi, 446, 00146 Rome, Italy. 2 Università degli Studi di Firenze, Dipartimento di Biologia Animale e Genetica, via Romana 17, 50125, Florence, Italy. * Corresponding author; e-mail: [email protected] DOI: 10.1127/1863-9135/2008/0172-0167 1863-9135/08/0172-0167 $ 2.00 © 2008 E. Schweizerbart’sche Verlagsbuchhandlung, D-70176 Stuttgart 168 M. Scalici et al. Barbaresi et al. 2007) in Italy, Malta, southern Dalma- and fecundity (i.e. Sparre & Venema 1996). To this tia, Albania, Macedonia, western and southern Greece, aim, we used the sequential length-frequency data ap- and the western Ionian and Aegean Islands (Brandis et proach (Gayanilo & Pauly 1997), which provides in- al. 2000, Maurakis et al. 2004, Noel & Guinot 2007). formation concerning the adaptation of a population to In recent years, following the same trend revealed for its habitat. This analytical approach can also serve as a other European indigenous freshwater decapods such useful tool to better understand the conservation status as crayfi sh (see Souty-Grosset et al. 2006), popula- of a population of concern. Population dynamics have, tions of P. fl uviatile have drastically declined in abun- in fact, become part of monitoring activities of aquatic dance across their entire distribution range (Barbaresi ecosystems as stipulated by the Water Framework Di- et al. 2007). rective (2000/60 ECC). Ten years ago, a river crab population was recorded in the archaeological excavation of the Imperial Fo- Material and methods rum in the historical centre of Rome. This was the fi rst The Imperial Forum of Rome (instituted today as an archaeo- record of a freshwater decapod in a metropolis, with logical area, Fig. 1) was built between the 1st century B.C. and the exception of two exotic species: the Asian crab the 2nd century A.D. in a small marshy valley, which today is Eriocheir sinenis in the River Thames, London (Her- completely altered through urbanisation. In order to canalise borg et al. 2005), and the Turkey crayfi sh Astacus lep- the drainage-water, the Romans built a drainpipe system called ‘Cloaca Maxima’ (the largest still-functioning basin) from the todactylus in central London (Wiltshire & Reynolds Roman Forum to the River Tiber. In spite of the uncontrolled 2006). development, a great part of the artifi cial water system (con- Given the peculiarity of this population, our goal stantly fed by underground sources) has always remained above here was to evaluate the adaptation of river crabs to ground for at least 100 square meters. The superfi cial channels this urban habitat by studying some aspects of its are 50 cm wide; water level ranges between few centimetres and 1.5 m, depending on precipitation. population dynamics, including growth and mortality The study was conducted in this area from May to Septem- rate, under the rationale that these are related to main ber 2004–2006. During each sampling, crabs were caught by biological processes, such as alimentation, predation, hand, sexed, and measured using the image analysis program eschweizerbartxxx Fig. 1. A current panoramic view of the Trajan Forum (a) and a hypothetical condition of the study area before the Roman settle- ment (b). The rectangle in (b) delimits the sampling site, while the dotted line indicates the ancient perimeter of Rome (today the historical town centre). Urban isolation of river crabs 169 Image Tool (available on http://ddsdx.uthscsa.edu/dig/down- in the summers 2003–2004 in the L.I.P.U. (Italian League for load.html). To obtain the carapace length (CL), a picture (cali- the Preservation of Birds) preserved area of Castel di Guido brated against a graph paper) was taken using a digital camera (CG, about 10 km from Rome), (2) by Scalici et al. (2007) in placed at 20–25 cm from the carapace in order to limit spherical the Monterano Regional Reserve of Canale Monterano (CM, distortion and parallax problems. Before release, crabs were in- 25 km from Rome), and (3) by Gherardi (1988) in Borro San dividually heat-marked on the coxa of the right or left limbs by Giorgio, Antella, 5 km from Florence (FL, about 250 km north a little soldering gun and on the carapace by waterproof paint of Rome). in order to avoid duplication of measurements on the same crab Comparisons among populations were made for the curva- and then pseudo-replications during the statistical elaboration. ture parameter values, by testing the relationship between the Before their release crabs were disinfected using mercuro- curvature parameter and the asymptotic length using the Spear- chrome. man regression test (rs) for randomized data subsets (including Body size data were used to generate polymodal frequency about 30 individuals per set) of each population. We performed distribution histograms and then analyzed by the Electronic a total of 52 “k vs. L∞” regressions, 16 for RM, 10 for CG, LEngth Frequency ANalysis (ELEFAN) method. ELEFAN, 12 for CM, and 14 for FL. Since the two parameters showed part of the FiSAT computer program (FAO 2004), was used for a close relationship (mean values of rs = 0.72, 0.63, 0.71, and the computation of the growth parameters by applying the Von 0.75, respectively for RM, CG, CM, and FL, with P always < Bertalanffy (1938) formula: 0.05), only the curvature parameters were used in order to test signifi cant differences among growth curves of the analysed ] L(t) = L∞{1–exp[–k(t–t0) } populations by the application of pairwise ANCOVA tests.

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