Journal of the Marine Biological Association of the United Kingdom, 2011, 91(1), 127–138. # Marine Biological Association of the United Kingdom, 2010 doi:10.1017/S0025315410001074 Crustacean assemblages along the Guadiana River estuary (south-western Iberian Peninsula) j. emilio sa’ nchez-moyano and isabel garci’a-asencio Departamento Fisiologı´a y Zoologı´a, Facultad de Biologı´a, Universidad Sevilla, Avenida Reina Mercedes 6, 41012 Sevilla, Spain The spatial distribution of the subtidal crustacean assemblages of the Guadiana River estuary was studied previous to the building of the Alqueva Dam (the biggest dam in Europe). The differences between an estuarine and marine environment seem to be the main reason responsible for the composition and distribution of the crustaceans along the study zone. The Guadiana estuary has shown high number of species in comparison with other nearby estuaries and this richness seems jus- tified by the scarce influence of pollutants (most of them have shown low or moderate values) and their hydrodynamic and granulometric characteristics (76 species were found, 39 in the estuarine area). A gradient of enrichment and structuring of the assemblages was shown from the upstream to the marine zones and a spatial segregation of species was found along this estuarine environmental gradient, e.g. the amphipod Corophium multisetosum and the isopod Cyathura carinata in the upper estuary; the amphipod Bathyporeia cf. pilosa and the isopods Lekanesphera levii and Saduriella losadoi in the middle estuary; the amphipod Melita hergensis in the mouth; and a high number of species in the marine area. Since the Alqueva Dam will reduce the river discharges and may cause changes in the abiotic characteristics such as granulometry of sediments or salinity, this study establishes a baseline against which a monitoring programme or follow-up studies could measure any significant effects of the dam or related impacts. Keywords: crustacean assemblages, environmental factors, baseline study, estuary, Iberian Peninsula Submitted 4 November 2009; accepted 4 May 2010; first published online 1 November 2010 INTRODUCTION and interannual scales and crosses a wide rural area along the Iberian Pyrite Belt, with intense mining extraction since Estuaries show both high biological activity and high pro- Phoenician and Roman times, although this activity has duction (Wolff, 1983; Valiela, 1995). In estuarine zones, the ceased in the last decade (Caetano et al., 2006). animal assemblages are established along a continuum from The Guadiana River basin is regulated by approximately internal areas to the mouth with more or less overlapping dis- 100 reservoirs, and since 2001 the Alqueva Dam, the biggest tributions of the species according to the ecocline model pro- dam in Europe, with a water storage capacity of 4150 hm3, posed by Attrill & Rundle (2002). Like a transition zone has regulated more than 80% of the freshwater flow (the between the marine and the freshwater domains, they are pre- damned area within the Guadiana River basin has increased ferential sites for the development of several human activities by 12% to a total of 89%) (Gonzalez et al., 2007). The altera- such as industry, transport, fisheries and tourism. These tion of flow regimes is recognized as one of the most serious systems are also areas with considerable pollution problems processes affecting community structure and function in (Dauvin et al., 2006). However, interpretation of the effects lagoons, estuaries and deltas of the world (Sklar & Browder, of pollution on the estuaries is often difficult since the geologi- 1998; Bunn & Arthingthon, 2002). The Alqueva Dam will cal, physical and chemical characteristics can be confounded reduce the abrupt river discharges to the estuary and may with the impacts of anthropogenic origin (Warwick, 1988; cause an important impact on the quantity and types of sedi- Weisberg et al., 1997; Gaston et al., 1998; Morrisey et al., ments and on the biogeochemical cycles of nutrients that 2003). might lead to a significant change in the food web structure The Guadiana River, located along the southern border of both the estuary and the coastal zone (Caetano et al., between Spain and Portugal, is recognized as one of the less 2006; Cravo et al., 2006; Gonzalez et al., 2007). The possible polluted European estuaries (Vasconcelos et al., 2007) and impact of this dam in the Guadiana estuary and the nearby as one of the rivers with greater contributions of sediments coastal area has been analysed for fish assemblages to the Spanish coasts (Consejerı´a de Medio Ambiente, (Chı´charo et al., 2006a; Morais et al., 2009) and planktonic 1997). This river shows an irregular flow on both seasonal assemblages (Chı´charo et al., 2006b). Besides, Wolanski et al. (2006) proposed an ecohydrology model integrating physical, chemical and biological processes (the last item Corresponding author: was determined by planktonic, bivalve and fish assemblages). J.E. Sa´nchez-Moyano The soft-bottom macrofauna is one of the more important Email: [email protected] structuring elements of the food web inside estuaries (Herman 127 128 j. emilio sa’ nchez-moyano and isabel garci’a-asencio et al., 1999) and is considered a key element of many marine and estuarine monitoring programmes (Ysebaert & Herman, 2002). The crustacean assemblages are among the most diverse and abundant groups of soft-bottom macrofauna (Cuhna et al., 1999; Lourido et al., 2008) and have been recog- nized as one of the most sensitive to changes in environmental conditions (Desrosiers et al., 1990; Sa´nchez-Moyano & Garcı´a-Go´mez, 1998; Guerra-Garcia & Garcı´a-Go´mez, 2004). To date, however, there is no information on the impact on the composition and distribution of the subtidal macrofauna in the Guadiana estuary. Thus, the aim of this work was to characterize the composition and distribution of the crustacean assemblages of subtidal soft-bottom sedi- ments along the estuarine gradient previous to the building of the Alqueva Dam. This work may contribute to assessing changes in the marine–estuarine system related to the impact of the dam since it can be used as a reference condition in a long term perspective. MATERIALS AND METHODS Study area The Guadiana River is one of the main rivers of the Iberian Peninsula with 820 km in length and a drainage basin area Fig. 1. Location of the sampling stations at the Guadiana River estuary. around 67.500 km2, which 12.000 km2 belong to Portugal. The estuary is a single-channel mesotidal estuary of about 80 km in length, 70 to 800 m wide and 5 to 15 m depth. used as a relative measure of metal pollution in the sediments There are two natural protected areas located near the for Cr, Cu and Zn according to the regional background estab- ¼ mouth: Natural Park of Isla Cristina Marshes and Natural lished by Ruiz (2001) for unpolluted sandy sediments. Igeo Reserve of Sapal de Castro Marim, in the Spanish and log2 (Cn/1.5 x Bn), where Cn is the value of the element n Portuguese margin, respectively. Both areas belonged to the and Bn is the background data of that element. According to ancient Guadiana delta and are formed by a complex web of Ruiz (2001), the index values were divided in five groups: unpol- channels. In recent years, some Spanish and Portuguese luted (Igeo , 1); very low polluted (1 , Igeo , 2); low polluted associations have proposed the creation of the International (2 , Igeo , 3); moderate polluted (3 , Igeo , 4); highly Natural Park of the Lower Guadiana. The Guadiana River polluted (4 , Igeo , 5); and very highly polluted (Igeo . 5). flows into a wide continental shelf with soft slope (20 m in For water analysis, a water sample per station was obtained depth is reached up 4–5 nautical miles out). close to the bottom by a vertical Alpha Van Dorn-style bottle. The following parameters were measured in situ: temperature, conductivity and salinity by conductivimeter WTW LF-323; Sampling and laboratory analysis pH by phmeter WTW 330i; and dissolved oxygen by oximeter Sampling was undertaken in the summer of 2000 at 14 subti- WTW OXI-196. dal stations: 8 along 38 km in Guadiana main course, 2 in Carreras River (Isla Cristina Marshes) and 4 in near coastal Data analysis area (Figure 1). At each station, six replicates samples (five for biological analysis and one for sediment analysis) were Univariate and multivariate analyses for environmental vari- taken with a 0.05 m2 van Veen grab. Each replicate was ables and crustacean assemblages were performed using the sieved in seawater through a mesh of 0.5 mm, fixed with 4% PRIMER v 5.2.8 software package. Previously, the replicate formalin and stained with Bengal rose. Crustaceans were data were pooled for the multivariate analysis. The crustacean sorted and, whenever possible, identified to species level. data were analysed to obtain the total number of taxa, abun- For sediment analysis, granulometry was assessed follow- dance, evenness and Shannon diversity index using neperian ing Buchanan & Kein (1984) methodology, and organic logarithms. Spatial differences for univariate variables were matter percentage was obtained as weight loss by ignition at analysed by a one-way analysis of variance (ANOVA), after 4508C for 24 hours (mean value of 3 replicates per station). verifying normality (Kolmogorov–Smirnov test) and hom- + The other sediment parameters were measured by laboratories ogeneity of variances (Barlett test). The data were log10 (x of the Environmental Agency of the government of Andalusia 1) transformed prior to analysis. Homogeneous groups were (South Spain): total organic carbon (TOC) was determined by separated by a Tukey test set at the 5% significance level. EPA 415.1; total nitrogen in the sediment was assessed via Affinities between stations were established using cluster Kjedahl digestion; phosphate was measured using UV visible and MDS (non-metric multidimensional scaling) analysis spectrophotometry; and the metal contents were measured with the species abundance (transformed by the fourth by SM 3111 A and B for Cd, Zn, Cu, Ni and Cr, and EPA root).