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ARTICLE IN PRESS Available online at www.sciencedirect.com Marine Pollution Bulletin xxx (2008) xxx–xxx www.elsevier.com/locate/marpolbul Distribution and ecological relevance of fine sediments in organic-enriched lagoons: The case study of the Cabras lagoon (Sardinia, Italy) P. Magni a,b,*, G. De Falco a,b, S. Como b, D. Casu c, A. Floris d, A.N. Petrov e, A. Castelli f, A. Perilli a,b a CNR-IAMC, National Research Council – Institute for Coastal Marine Environment Località Sa Mardini, Torregrande, 09072 Oristano, Italy b International Marine Centre, Località Sa Mardini, Torregrande, 09072 Oristano, Italy c Dip. di Botanica ed Ecologia vegetale, Università di Sassari, 07100 Sassari, Italy d Dip. di Zoologia e Genetica evoluzionistica, Università di Sassari, 07100 Sassari, Italy e Institute of Biology of the Southern Seas NASU, 99011 Sevastopol, Ukraine f Dip. di Biologia, Università di Pisa, 56126 Pisa, Italy Abstract In organic-enriched sedimentary systems, like many Mediterranean coastal lagoons, a detailed analysis of sediment grain size composition and partitioning within the muds is crucial to investigate sedimentological trends related to both hydrodynamic energy and basin morphology. In these systems, sediment dynamics are particularly important because the partitioning and transport of fine sediments can strongly influence the redistribution and accumulation of large amounts of organic matter, and consequently the distribution of benthic assemblages and the trophic status and functioning of a lagoon. Nevertheless, studies on benthic–sediment relationships have been based mainly on a rather coarse analysis of sediment grain size features. In muddy systems, however, this approach may impede a proper evaluation of the relationships and effects of the distribution of fine sediment and organic matter on the biotic benthic components. Here we show that the distribution of sedimentary organic matter (OM) and total organic carbon (TOC) in the Cabras lagoon (Sardinia, Italy) can be explained (i.e., predicted) as a function of a nonlinear increase in the amount of the cohesive fraction of sediments (68 lm grain size particles) and that this fraction strongly influences the structure, composition and distribution of macrobenthic assemblages. Even in such a homogeneously muddy system, characterized by ‘‘naturally” occurring impoverished communities, impaired benthic assemblages were found at 68 lm, OM, TOC contents of about 77%, 11% and 3.5%, respectively. A review of studies conducted in Mediterranean coastal lagoons highlighted a lack of direct integrated analysis of sediment features and the biotic components. We suggest that, especially in organic-enriched coastal lagoons, monitoring programs should primarily investigate and consider the cohesive fraction of sediments in order to allow a better assessment of benthic–sediment relationships and ecological quality of the system. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Fine sediments; Mud; Organic matter (OM); Macrofauna; Ecological quality; Coastal lagoons 1. Introduction * Corresponding author. Address: CNR-IAMC, National Research Council – Institute for Coastal Marine Environment Località Sa Mardini, Torregrande, 09072 Oristano, Italy. Tel.: +39 0783 22027; fax: +39 0783 E-mail address: [email protected] (P. Magni). Transitional waters such as estuaries and coastal lagoons are classified by the European Water Framework Directive (WFD; 2000/60/EC) as one of the five categories of ‘‘surface water”, which also include coastal waters, rivers, lakes, and artificial and heavily modified bodies of water. Due to their partly saline character ‘‘substantially 0025-326X/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.marpolbul.2007.12.004 Please cite this article in press as: Magni, P. et al., Distribution and ecological relevance of fine sediments ..., Mar. Pollut. Bull. (2008), doi:10.1016/j.marpolbul.2007.12.004 ARTICLE IN PRESS 2 P. Magni et al. / Marine Pollution Bulletin xxx (2008) xxx–xxx influenced by freshwater flows” and their usually high sediment-surface-area to water-volume ratio, transitional waters can be considered a very sensitive aquatic system where benthic components and processes play an important regulatory function for the whole ecosystem (Viaroli et al., 2004). Accordingly, there has been a major development of biotic benthic indices in Europe in recent years, with special attention paid to the use of macroinvertebrate communities, in assessing the ecological quality status of coastal and estuarine waters (Borja et al., 2000; Simboura and Zenetos, 2002; Rosenberg et al., 2004; Dauvin and Ruellet, 2007; Muxika et al., 2007), as well as coastal lagoons (Reizopoulou et al., 1996; Fano et al., 2003; Basset et al., 2004; Ponti and Abbiati, 2004; Reizopoulou and Nicolaidou, 2007; Mistri and Marchini, in press). Comparisons of different biotic indices and assessments of their applicability in different geographical areas of the world are now also on the rise (Dı́az et al., 2004; Arvanitidis et al., 2005; Magni et al., 2005a; Quintino et al., 2006; Fleischer et al., 2007; Pranovi et al., 2007; Zettler et al., 2007; Blanchet et al., in press; Borja et al., in press). In contrast, the physical and chemical characteristics of sediments appear to be less explored and more controversial in terms both of their integration in the biological elements and their relevance in assessments of environmental quality (Crane, 2003; Borja et al., 2004; Borja and Heinrich, 2005; Marı́n-Guirao et al., 2005). This is particularly true in non-tidal (sensu McLusky and Elliott, 2007) transitional systems, such as Mediterranean coastal lagoons. Here, only recently quality/vulnerability biogeochemical tools and integrated measurements of status variables and system metabolism are being proposed (Viaroli and Christian, 2003; Viaroli et al., 2004; Giordani et al., in press). It is a classical, general assumption that sedimentary organic matter (OM) influences the composition and distribution of macrobenthos (Rhoads, 1974; Pearson and Rosenberg, 1978; Gray, 1979). It is also well known that the level of OM is related to the grain size composition of sediments. In particular, a higher content of OM tends to occur at an increasing mud (clay) content due to a greater surface area and higher number of complexing sites of the sediments (Buchanan and Longbottom, 1970; Mayer, 1994a,b; Tyson, 1995). A high mud content together with excessive OM may then result in a lower permeation of oxygen, an increased microbial oxygen uptake/demand and a subsequent buildup of toxic byproducts (e.g., ammonia, dissolved sulphide) (Florek and Rowe, 1983; Santschi et al., 1990; Fenchel et al., 1998). This can lead to impoverished benthic communities, dominated by few resistant r-selected opportunistic species (Dı́az and Rosenberg, 1995; Como et al., 2007). Notwithstanding combined and confounding effects of other major environmental factors such as bathymetry and salinity (e.g., Jones et al., 1986; Schlacher and Wooldridge, 1996; Teske and Wooldridge, 2003), clear patterns of macrobenthos change have been demonstrated for some time along marked gradients of mud and/or organic mat- ter enrichment (e.g., Ishikawa, 1989; Quintino and Rodrigues, 1989). In fact, it appears that works on benthos– sediment relationships in marine and estuarine waters have been mainly based on a rather coarse analysis of sediment grain size features, e.g., on the sand vs. mud fractions, generally restricted to the few uppermost integrated centimeters (e.g., see Table 1 in Snelgrove and Butman, 1994). Several benthic studies on animal–sediment associations have also been conducted in lagoon systems. Especially in muddy systems, however, like many of the coastal lagoons in the Mediterranean Sea, this approach may be of little use. In contrast, a detailed analysis of sediment grain size composition within the muds may reveal sedimentological trends related to both hydrodynamic energy and lagoon morphology which are not detectable otherwise (De Falco et al., 2004). In these often eutrophic and organic-enriched systems, such analysis is important also because the partitioning and transport of fine sediment particles may strongly influence the redistribution and accumulation of large amounts of organic matter, and consequently the distribution of macrozoobenthos and the overall trophic status and functioning of a lagoon. However, there is a lack of studies linking the distribution and dynamics of fine sediments to the distribution of benthic macroinvertebrate communities in coastal lagoons. In the present study, we aimed at assessing the relationships between the distribution of fine sediments, the levels of organic matter in the sediments and the structure and composition of macrobenthic assemblages in a Mediterranean lagoon system, as well as evaluating the overall ecological relevance of such relationships. For these purposes, we used the Cabras lagoon (Sardinia, Italy) as a case study, where we had previously conducted extended surveys on both sediment characteristics (De Falco et al., 2004) and macrozoobenthic assemblages (Magni et al., 2004b, 2005b). For the present study, we made a detailed analysis of sediment particle distribution within the muds, with specific analytical size intervals of 0.5 lm, and focused on the 68 lm grain size fraction of sediments (hereafter ‘‘fine sediments”). This was based on the fact that the 8 lm boundary is known to separate non-cohesive from cohesive sediments (McCave et al., 1995) and because this fraction was found to be most correlated with the total organic carbon (TOC) content of sediments in the Cabras lagoon (De Falco et al., 2004). As for the macrozoobenthos, the biomass of individual taxa as well as species’ richness and diversity, not used in our previous study (Magni et al., 2004b), were analyzed together with the total abundances. A review of studies reporting OM and/or TOC content of sediments, as well as grain size and biological benthic features, in Mediterranean coastal lagoons was also made. This was to provide a general assessment of benthic–sediment studies and monitoring schemes in these systems on a regional scale, as well as an operational framework for both lagoon ecology and management issues. Please cite this article in press as: Magni, P. et al., Distribution and ecological relevance of fine sediments ..., Mar. Pollut. Bull. (2008), doi:10.1016/j.marpolbul.2007.12.004 ARTICLE IN PRESS P. Magni et al. / Marine Pollution Bulletin xxx (2008) xxx–xxx 2. Materials and methods 2.1. Study area The Cabras lagoon is a shallow transitional system located in the Gulf of Oristano, on the west coast of the island of Sardinia (Italy), western Mediterranean Sea (Fig. 1). With an area of about 22 km2, it is the largest lagoon in Sardinia and one of the major brackish systems of the western Mediterranean Sea. The drainage system of the Cabras lagoon has a total extension of 432 km2 (Casula et al., 1999) and is characterized by two main tributaries called ‘‘Riu Mare Foghe” and ‘‘Riu Tanui”, located in the northern and southern sectors of the lagoon, respectively. The ‘‘Riu Tanui” subtends a watershed which is much smaller than the ‘‘Riu Mare Foghe”, but its contribution to the loading formation is very important because of the presence of intensive agricultural activities in this area. In addition, the ‘‘Riu Tanui” has been subjected to the disposal of untreated urban waste waters which were discharged into the Cabras lagoon till the year 2000. Nutrient loading from the drainage basin has been calculated at 16 tons of total phosphorous and 240 tons of total 3 nitrogen per year (Casula et al., 1999). Despite the current trend in increasing salinity caused by a progressive reduction of freshwater input and an increasing demand for water for land use (e.g., agriculture), salinity may drop to <10 psu following rainfall, while it rises to >30 psu during dry periods (Magni et al., 2005b). In the southern sector of the lagoon, the water exchange between the lagoon and the adjacent Gulf of Oristano has been severely affected by a channel constructed in the late 1970s, closed by a dam which raises the high-tide water level (Fig. 1). Connection to the adjacent coastal sea of the Gulf of Oristano is through narrow, convoluted creeks which flow into the main channel (Como et al., 2007). Additional man-made barriers were built in this area in the late 1990s for capturing fish. The Cabras lagoon is thus characterized by limited water exchange with the adjacent gulf (tidal amplitude <25 cm). In contrast, tide- and wind-induced currents seem to be effective in circulating the internal water mass enough to influence the resuspension and distribution of fine sediment particles within the basin (De Falco et al., 2004). The Cabras lagoon historically has a high economic rating due to fishery activities (e.g., Liza ramado, Mugil Lagoon inlet Sampling stations 39°59'N Mare e Foghe River Down-core samples C2 C1 C4 C3 C7 C6 C5 C10 C9 C8 C14 C13 C12 C11 C18 C17 C16 C15 C24 C23 C22 C28 C27 Cabras Lagoon 0 0 2 km -5 m -10 m 1km western Mediterranean -20 m -10 m -10 m C29 -5 m ITALY Gulf of Oristano Cabras Lagoon C21 C20 C19 C26 C25 C31 C30 Dam Cabras Tanui River Creeks 39°55'N Gulf of Oristano (western Mediterranean) 008°32'E -10 m Channel -5 m Sardinia Lagoon mouth 008°27'E Fig. 1. Study area and location of sampling stations in the Cabras lagoon (Sardinia, western Mediterranean sea). indicates the nine stations where grain size composition and organic matter (OM) content were determined in the 0–24 cm sediment horizon. The W-shaped dam in the southern sector of the lagoon which limits the lagoon-gulf water exchange though the channel, and the two main tributaries ‘‘Riu Mare e Foghe” and ‘‘Riu Tanui” (northern and southern sectors, respectively) are also indicated. Please cite this article in press as: Magni, P. et al., Distribution and ecological relevance of fine sediments ..., Mar. Pollut. Bull. (2008), doi:10.1016/j.marpolbul.2007.12.004 ARTICLE IN PRESS 4 P. Magni et al. / Marine Pollution Bulletin xxx (2008) xxx–xxx cephalus, Anguilla anguilla) which involve about 250 fishermen, with a yearly fish catch up to about 850 tons (400 kg ha1 year1), as in 1998 (Murenu et al., 2004). However, especially during the warm season, there is a tendency for hypoxic and anoxic conditions to occur in nearbottom waters. This may lead to dystrophic events such as the severe one which occurred in June 1999, causing a major loss of the biological resources of the lagoon and a drastic reduction of total catches in the subsequent years, falling below 80 tons in 2002 (Murenu et al., 2004). In 2006, the total fish catch was reported to be still as low as 120 tons. The major causes of these events are thought to be eutrophication and excessive organic enrichment of sediments, which cause the enhancement of sulphate reduction rates during the warm season and the subsequent release of toxic dissolved sulphide from the sediment pore water into the water column (Magni et al., 2005b, in press). 2.2. Field surveys and laboratory analysis Four sampling campaigns were conducted between the end of April and the beginning of May 2001. Thirty-one sampling stations spaced 750 m one another were selected on a regular grid covering the whole lagoon (Fig. 1). Previous published work (De Falco et al., 2004) reported the analysis of sediment grain size composition, and organic matter (OM) and total organic carbon (TOC) contents of surface sediments (0–2 cm). For this work, we analyzed the sediment vertical profiles from cores collected at nine stations on the grid (see Fig. 1) using a manual corer (40 cm long, 5.5 cm £). Sediment samples were sliced at 2 cm intervals (4 cm in the last layer) down to the 24 cm layer. Sub-samples from each layer were analyzed for grain size composition and OM content (see De Falco et al., 2004 for the description of the analytical procedure). At each of the 31 stations (except Stns. 15 and 19), duplicate samples were collected for macrozoobenthos using a 216 cm2 Ekman-Birge grab. In the laboratory, the macrozoobenthos were sorted, identified to the species level, when possible, counted under a stereo-microscope and preserved in 75% ethanol. Following a description of the spatial distribution of the abundances of the most dominant taxa (Magni et al., 2004b), the wet weight (WW) biomass of each taxa was obtained for this work after excess fluid was carefully blotted off. 2.3. Data analysis 2.3.1. Sediment vertical profiles The variability of sediment grain size and OM in the vertical profile (0–24 cm sediment horizon) of the nine sediment cores was evaluated using the Hierarchical Cluster Analysis. Individual layers (n = 99) were used as the sample data. The entire grain size spectrum, expressed at one phi intervals, and the OM contents were used as data input, after the ranking of data value. The significance of the differences among groups of samples identified by the cluster analysis was then tested by Discriminant Analysis. Grain size (one phi interval) and OM data were used as data input after ranking. Discriminant Analysis allowed us to investigate the significance of group separation, the weight of the variables which provide the clustering, and the closeness of the single cases (samples) to the centroids of the groups, in order to individuate the outliers. 2.3.2. Relationships between sediment variables The relationship between fine sediments (i.e., 68 lm grain size particles) and OM was evaluated by means of a nonlinear least-squares regression model (Bates and Watts, 1988), using the nine sediment cores samples as the input data (n = 99). The function was of the form: y ¼ a ebe cx ; where y is the fine sediments (%), x is the OM (%), and a, b, and c are the parameters of the equation, where a is the ‘plateau’ value (% fine sediments), b is the ln(a/i), and i is the y value for x = 0, and c is the constant of the model. According to this function, OM increases nonlinearly with the increase of fine sediments up to a certain ‘plateau’ value, beyond which the OM increase is independent from the percentage of fine sediments. The estimate of the a, b, and c parameters is the result of the best fitting between observed data and the predicting function by minimizing the square root of the sum of the square errors between observed and predicted values. A Non-Linear-Estimation based on the Quasi–Newton algorithm for nonlinear optimization was used. 2.3.3. Macrozoobenthos and relationships with sediment variables Differences in macrozoobenthic assemblages were analyzed using a non-metric multidimensional-scaling (nmMDS) ordination model based on the Bray-Curtis dissimilarity matrix (Clarke and Warwick, 2001) calculated on the mean values among replicates within each station. A one-way ANOSIM randomization/permutation test was used to check for the significance of differences among groups of stations identified by the nmMDS ordination model (Clarke and Warwick, 2001). Taxa which contributed the most to these differences were identified by the similarity percentages procedure SIMPER (Clarke and Warwick, 2001). Correlation coefficients (R) were calculated in order to evaluate the relationships between sediment variables (i.e., 68 lm grain size particles, OM and TOC) and the macrozoobenthos. The total number of species (S) and individuals (N, ind. 216 cm2), the total biomass (gWW 216 cm2), the Shannon–Weaver diversity (H0 , calculated with natural logarithm) index, and the abundances of taxa identified by SIMPER were used as the biological variables. The graphical representation of the spatial distribution of sediment variables and the total abundance and biomass of macrozoobenthos was performed using the Surfer 7.0Ò software. Smooth-line kriging was used as the gridding Please cite this article in press as: Magni, P. et al., Distribution and ecological relevance of fine sediments ..., Mar. Pollut. Bull. (2008), doi:10.1016/j.marpolbul.2007.12.004 ARTICLE IN PRESS P. Magni et al. / Marine Pollution Bulletin xxx (2008) xxx–xxx method, where the x and y data columns are the latitude and the longitude of the sampling stations, respectively, and the z data column is the selected variable. All statistical analyses were done using the Statistica program of the StatSoft Inc. (release 6.1) and the PRIMER v5.2 package (Clarke and Warwick, 2001). 3. Results 3.1. Sediment vertical profiles Fig. 2 shows the vertical profiles of fine sediments and OM in the 0–24 cm depth horizon at nine stations randomly chosen in the Cabras lagoon. At most stations, both variables showed a sharp increase in the uppermost layers. From the whole set of data, irrespective of individual stations and different layers, two major groups of samples were identified by cluster analysis (plots not shown) as being characterized by fine sediment contents of 74.3% ± 6.3 and 54.7% ± 14.3, and OM contents of 9.3% ± 1.9 and 6.6% ± 1.6, respectively. By applying the Discriminant Analysis, the two groups of samples (clusters 1 and 2) were found to be signif- Sediment depth (cm) Sediment depth (cm) Sediment depth (cm) icantly different from each other (93% allocation success, d2 = 0.73, P = 0.0001). This allowed us to distinguish finer organic-enriched samples from coarser less organicenriched samples consistently across different core levels, as graphically represented in Fig. 3. Based on this analysis, the thickness of the fine-grained, organic-enriched layer was found to increase from north to south, most noticeably at Stns. C22, C26 and C31. In contrast, near-shore stations had fewer (Stn. C1) or no (Stn. C30) samples belonging to the organic-enriched group. 3.2. Relationships between sediment variables OM and TOC contents in the Cabras lagoon showed a highly significant (P < 0.001) linear relationship, accounting TOC for 30% of OM (Fig. 4a). In contrast, the bestfit relationship between fine sediments and OM was described by a nonlinear least-squares regression model (Fig. 4b, see Section 2). According to this model, OM increases progressively as fine sediments increase in the range of about 3–7% and much faster in the range of about 8–12%. At 82% of fine sediment content, OM increase ≤8 µm (%) ≤8 µm (%) 30 60 90 0 50 0 75 ≤8 µm (%) 100 50 0 5 5 5 10 10 10 15 15 15 20 25 ≤8 µm OM C1 5 50 10 OM (%) 15 ≤8 µm (%) 75 100 0 20 25 5 50 0 10 OM (%) 15 ≤8 µm (%) 75 100 25 5 5 10 10 15 15 15 0 20 C18 5 50 10 OM (%) 15 ≤8 µm (%) 75 100 25 0 5 0 10 OM (%) 15 ≤8 µm (%) 30 60 25 5 5 10 10 15 15 15 20 C28 5 10 OM (%) 15 25 15 ≤8 µm (%) 75 100 4 OM (%) 10 OM (%) 15 ≤8 µm (%) 75 100 20 C30 0 C26 5 50 0 5 25 10 OM (%) 20 C22 10 20 100 C12 5 50 0 5 25 75 20 C6 10 20 5 8 25 C31 5 10 15 OM (%) Fig. 2. Vertical profiles of fine sediments (i.e., 68 lm grain size particles) and organic matter (OM) at the nine stations (circled in Fig. 1) randomly chosen in the Cabras lagoon. Note the different scales at some stations. Fine sediments (i.e., 68 lm grain size fraction): all stations 50–100% range, except Stns. C1 (30–90%) and C30 (0–60%); OM: all stations 5–15% range, except Stn. C30 (0–8%). Please cite this article in press as: Magni, P. et al., Distribution and ecological relevance of fine sediments ..., Mar. Pollut. Bull. (2008), doi:10.1016/j.marpolbul.2007.12.004 ARTICLE IN PRESS 6 P. Magni et al. / Marine Pollution Bulletin xxx (2008) xxx–xxx a 5 y = 0.30x R 2 = 0.75 (n=62) TOC (%) 4 3 2 1 0 0 3 6 9 12 15 9 12 15 OM (%) b 100 -3.2e 80 ≤8 µm (%) -0.36x y = 82.1e R 2 = 0.67 (n=99) 60 40 20 0 0 3 6 OM (%) Fig. 4. (a and b) Relationships between (a) organic matter (OM) and total organic carbon (TOC), and (b) OM and fine sediments (i.e., 68 lm grain size particles). In (a), the grey circles refer to the surface sediment (0–2 cm) samples (n = 31, see Fig. 7b and c); the black circles refer to the vertical profiles of Stns. C1, C12, and C26 (OM: Fig. 2; TOC: De Falco et al. (2004)). The linear regression line includes all samples (n = 62). In (b), the best-fit nonlinear least-squares regression equation is represented (n = 99, see Fig. 2). Fig. 3. Graphical representation of individual-layer samples in nine core sections (x-axis indicates the sediment depth in cm) belonging to either Cluster 1 or Cluster 2 (see below legend) characterized by significantly marked differences in fine sediment (i.e., 68 lm grain size particles) and OM contents (tested by the Discriminant Analysis, see Section 2). Legend: j Black samples: Cluster 1 (fine sediments [68 lm grain size particles]: 74.3% ± 6.3; OM: 9.3% ± 1.9). h White samples: Cluster 2 (fine sediments [68 lm grain size particles]: 54.7% ± 14.3; OM: 6.6% ± 1.6). reaches a plateau, indicating that any further increase is independent of fine sediment content (Fig. 4b). 3.3. Macrozoobenthos and relationships with sediment variables As detailed in Magni et al. (2004b), macrozoobenthic assemblages were mainly represented by polychaetes (79.5%), oligochaetes (9.9%), crustaceans (5.7%) and bivalves (3.2%). Among the most dominant taxa, the serpulid Ficopomatus enigmaticus and the spionid Polydora ciliata accounted for 40.9% and 30.1% of the total abundance, respectively. Polychaetes also dominated in biomass (88.8%), with a major contribution of Neanthes succinea (62.2%) and F. enigmaticus (21.3%). At individual stations, the total abundance and biomass varied from 13.5 to 1552.5 ind. 216 cm2, and from 0.05 to 9.35 gWW 216 cm2, respectively. Multivariate analysis revealed major differences in the structure and species composition of macrozoobenthic assemblages among three groups of stations (Fig. 5 and Table 1). As indicated by the nmMDS ordination model (Fig. 5), one group (hereafter ‘‘Central”) included stations located in the relatively deeper, central sector of the lagoon (mean water depth 1.9 m). The other two groups included shallower stations (mean water depth 1.6 m) which were named ‘‘Shore” and ‘‘Reef-shore” based on the exclusive presence of F. enigmaticus in the latter group. The ANOSIM test confirmed the differences among these three groups of stations (ANOSIM test, global R: 0.673, P < 0.001). As indicated by the pairwise test, the highest R values were found when comparing the Central with Shore and Reef-shore stations (Table 1). Four taxa were mainly responsible for the differences among the three groups of stations (SIMPER, cut-off 60%; Table 2). F. enigmaticus was present exclusively in the Reef-shore stations. Please cite this article in press as: Magni, P. et al., Distribution and ecological relevance of fine sediments ..., Mar. Pollut. Bull. (2008), doi:10.1016/j.marpolbul.2007.12.004 ARTICLE IN PRESS P. Magni et al. / Marine Pollution Bulletin xxx (2008) xxx–xxx 23 16 17 24 27 22 26 13 11 12 28 6 5 4 9 21 7 14 25 29 8 2 30 3 31 10 20 18 1 Fig. 5. Non-metric multidimensional-scaling (nmMDS) ordination model. Stress = 0.15. Symbols: black circles [Central], grey triangles [Shore], white squares [Reef-shore]. Stations number (see Fig. 1) is indicated. Table 1 Results of pairwise test from one-way ANOSIM for differences among groups of stations (Central, Shore, Reef-shore) Also, at the Reef-shore stations the abundances of N. succinea and the oligochaetes Tubificidae were higher than at the Central and Shore stations. In contrast, P. ciliata was most abundant in the Central stations (Table 2). A graphical representation of the distribution of macrozoobenthos clearly showed a marked spatial trend, with several central stations being the most impoverished both in terms of total abundances and total biomass (Figs. 6a and b). In contrast, the spatial distribution of fine sediments, OM and TOC in the surface sediments showed an opposite trend with values increasing from the near-shore to the central stations (Figs. 7a–c, respectively). Consistently, we found several significant (P < 0.05) correlations between macrozoobenthos and the sediment variables, all of them negative (Table 3). Most noticeably, the fine sediments correlated negatively with most biotic univariate measures, including S, N, and the total biomass, as well as the abundances of F. enigmaticus, Tubificidae and N. succinea. Among the dominant taxa, N. succinea correlated negatively with all three sediment variables considered in this study. In contrast, P. ciliata did not show any significant correlation. Group R P (%) Possible permutations Actual permutations 4. Discussion Central vs. Shore Central vs. Reef-shore Shore vs. Reef-shore 0.782 0.688 0.383 0.1 0.1 1.3 38,760 817,190 5005 999 999 999 4.1. Fine sediment distribution and organic matter enrichment Table 2 Differences (< and >) in average abundance of taxa which contribute to dissimilarity (cut-off 60%) between groups of stations (Central, Shore, Reef-shore) identified by SIMPER Ficopomatus enigmaticus Tubificidae Neanthes succinea Polydora ciliata Central Shore 0 13.93 5.43 116.29 0 5.5 30.83 7.17 > < > Reef-shore < < < < 373.89 65.56 34.67 89.11 7 Despite the fact that the relationship between sediment grain size and organic matter is well known (e.g., Mayer, 1994b; Tyson, 1995), an evaluation of the distribution of organic matter in relation to the sediment dynamics in coastal lagoons has received less attention. Such an analysis is particularly important because the partitioning and transport of fine sediments may strongly influence the redistribution and accumulation of large amounts of sedimentary organic matter which often characterize these systems. In our companion paper (De Falco et al., 2004), we Fig. 6. (a and b) Spatial distribution of (a) the total abundance (ind. 216 cm2) and (b) total biomass (gWW 216 cm2) of the macrozoobenthos. Please cite this article in press as: Magni, P. et al., Distribution and ecological relevance of fine sediments ..., Mar. Pollut. Bull. (2008), doi:10.1016/j.marpolbul.2007.12.004 ARTICLE IN PRESS 8 P. Magni et al. / Marine Pollution Bulletin xxx (2008) xxx–xxx Fig. 7. (a, b, and c) Spatial distribution of (a) fine sediments (i.e., 68 lm grain size particles), (b) organic matter (OM), and (c) total organic carbon (TOC) in surface sediments (0–2 cm) in the Cabras lagoon. Table 3 Correlation coefficient R between sediment variables (fine sediments [68 lm grain size], organic matter [OM] and total organic carbon [TOC]) and the total number of species [S] and individuals [N], total biomass, Shannon–Weaver diversity [H0 ] index, and the most dominant taxa identified by SIMPER (ns non-significant, *P < 0.05, **P < 0.01) 68 lm * OM TOC S N Biomass H0 0.38 0.47* 0.50** ns ns ns ns ns 0.43* ns ns ns Abundances Ficopomatus enigmaticus Tubificidae Neanthes succinea Polydora ciliata 0.41* 0.49** 0.44* ns ns ns 0.38* ns ns ns 0.39* ns Note: all significant correlations are negative. showed that the surface sediments of the Cabras lagoon are quite homogeneously muddy and that the spatial variability of TOC can be explained in terms of grain size fractionation within the muds. In particular, the 68 lm grain size particles of sediments are found to be most strongly correlated with TOC, while the 8–64 lm fractions do not show clear trends. The fractionation of muddy sediments has been attributed to the resuspension of sediment in highenergy areas, resulting in a transport of fine sediments and organic matter to the relatively deeper, low-energy sectors of the lagoon (De Falco et al., 2004). The primary sources of organic matter in the sediments of the Cabras lagoon can be related to both a high primary production in the water column, with up to about 40 lg l1 of chlorophyll a measured in winter (Magni et al., unpublished), and to an external input from the two main tributaries. As for the latter input, the ‘‘Riu Mare Foghe” and the ‘‘Riu Tanui”, in the northern and southern sectors of the lagoon, respectively (Fig. 1), subtend watersheds with intensive diary and agricultural activities, respectively. In addition, the southern sector of the lagoon was subjected to the loading of high amounts of untreated urban waste waters discharged into the lagoon through the ‘‘Riu Tanui” until 2000. This helps explain a major accumulation of organic-enriched fine sediments in several southern stations of the lagoon (e.g., Stns. C22, C26, C31), as revealed by the analysis of down-core profiles (Figs. 2 and 3). The findings of this study also support our earlier hypothesis that the construction of an artificial channel and a dam at the lagoon’s inlet at the end of the 1970s has reduced the internal hydrodynamic energy of the lagoon (De Falco et al., 2004). This may have favoured the trapping, deposition and accumulation of organic C-bounding fine sediment particles inside the lagoon over the past few decades. In the present study, we also show that the distribution of organic matter (OM) can be explained (i.e., predicted) as a function of a nonlinear increase in the amount of fine sediments (i.e., 68 lm grain size particles). According to this relationship (Fig. 4b), the OM content of sediments shows two different trends. In its lower range (about 3–7%), OM increases progressively as fine sediment increases, while in the upper range of about 8–12% (or about 2.4–3.6% of TOC) OM increases at a much faster rate than the relative increase of fine sediments. Such a rapid increase is then followed by a plateau, indicating that at values of above 80% of fine sediments, OM starts varying independently from grain size, thus having a less predictable behaviour. The above two OM ranges (3–7% and 8–12% OM) roughly correspond to the two groups of samples identified by Discriminant Analysis (Fig. 3), i.e., coarser less organicenriched samples (mean values: 54.7% 68 lm, 6.6% OM) and finer organic-enriched samples (mean values: 74.3% 68 lm, 9.3% OM), respectively (Fig. 3). The latter samples were mostly found in the upper layers of the sediment cores suggesting that they can be used as a proxy for evaluating the amount of organic matter accumulated in the sediments over the last few decades. The relationship between OM Please cite this article in press as: Magni, P. et al., Distribution and ecological relevance of fine sediments ..., Mar. Pollut. Bull. (2008), doi:10.1016/j.marpolbul.2007.12.004 ARTICLE IN PRESS P. Magni et al. / Marine Pollution Bulletin xxx (2008) xxx–xxx and grain size thus clearly demonstrates the importance of quantifying the amount of fine sediments present in each lagoon system in order to evaluate the extent of organic matter enrichment. In fact, the term ‘‘organic enrichment” cannot be given an absolute value because it depends on the system considered. This study provides one such an example by defining threshold values and ranges of fine sediments within the muds. This knowledge is also important because, in anthropogenic-polluted lagoons, the presence of high amounts of organic-C bounding fine sediments can lead to the mobilization and transport of contaminants (e.g., heavy metals), with a potential enhancement of the toxic effects to biota. 4.2. Benthic–sediment relationships This study provides novel insights on benthic–sediment relationships using the Cabras lagoon, an enclosed, muddy coastal lagoon of the Mediterranean Sea, as a case study. In fact, while large variations in grain size composition and/or organic matter content of sediments may evidence clear patterns in the distribution of the benthos (e.g., Snelgrove and Butman, 1994), the muddy sediments often found in Mediterranean coastal lagoons render such investigations more difficult. In addition, it is well known that the lagoon systems are increasingly affected by excessive inputs of nutrients and organic matter. This is often a direct consequence of human activities (e.g., sewage discharge, fish farming) or an indirect consequence (e.g., eutrophication) of the same. These factors, as well as the large environmental variability typical of these systems, determine a selection of species and communities which are able to cope with disturbed conditions and to recolonize relatively quickly (Magni et al., in press). Here, we could assess the benthic–sediment relationships upon a detailed analysis of grain size fractionation within the muds (specific analytical size intervals of 0.5 lm), with a special focus on the cohesive fraction of sediments (i.e., 68 grain size particles). The most impaired benthic assemblages, in terms of lowest species’ diversity and biomass, were found in the central-southern sector of the lagoon. In particular, one single species in the Central group stations, the spionid P. ciliata, dominated numerically without showing any negative correlation with fine sediments, OM or TOC (Table 3). This is consistent with the fact that spionids are very opportunistic and show high resilience after disturbances. In fact, larval and post-larval stages of Polydora spp. are reported to colonize patches of sediment all year round (Hansen, 1999). Furthermore, spionids are also known to switch their feeding mode from filter feeding to deposit feeding depending on the environmental conditions such as hydrodynamics (Kihslinger and Woodin, 2000). Consistently, the Central group stations were characterized by the highest mean contents of fine sediments, OM and TOC in the surface layer, i.e., 77.5% ± 1.6, 11.3% ± 0.3, and 3.5% ± 0.1, respectively. In these organic-enriched sectors of the lagoon, the periodic occurrence of severe envi- 9 ronmental conditions (e.g., extreme hypoxia or anoxia) and/or the development of toxic compounds (e.g., dissolved sulphide) strongly contribute to a major impoverishment of benthic assemblages (Magni et al., 2005b). The TOC values found in the Central group stations support the results of Hyland et al. (2005) who have shown a major shift in the benthic data obtained from seven coastal regions of the world and have highlighted the high risks of reduced species richness at TOC values >3.5%. It is our hope that synoptic data on the structure of benthic communities and TOC content of sediments from different lagoons will be merged and analyzed in order to further test such relationships as a general screening-level indicator for evaluating the likelihood of reduced sediment quality and associated bioeffects in coastal lagoons (Magni et al., 2005a). Multivariate analysis of macrozoobenthos also revealed that, in contrast, the serpulid F. enigmaticus was exclusive to the Reef-shore group. We have previously shown that F. enigmaticus, in association with the amphipod Corophium sextonae, correlates positively with the sediment sorting (r); an index of sediment selection due to hydrodynamic energy (Magni et al., 2004b). This is consistent with the inference that F. enigmaticus may take advantage of resuspended food particles along the shores with its filter-feeding activity. In the Reef-shore stations, all dominant taxa, including Tubificidae, N. succinea and P. ciliata, as well as the highest number of species, abundances and biomass were found. These results are consistent with the facilitative role played by serpulid reefs. F. enigmaticus is an invasive cosmopolitan species which is highly tolerant of environmental stress and anthropogenic disturbance (Bianchi and Morri, 2001). Extremely common in sheltered bays, coastal lagoons and harbors, serpulid reefs can strongly modify the hydrological and sedimentary features of a basin by completely refilling shallow areas (Schwindt and Iribarne, 2000; Bianchi and Morri, 2001). At the same time, serpulid reefs create secondary hard bottoms (Bianchi and Morri, 2001). They increase the habitat structures and provide refuge from predators for many, thus favouring the recruitment and the coexistence of different animals (Bianchi and Morri, 1996; Schwindt and Iribarne, 2000). Overall, stations along the shores were characterized by lower contents of fine sediments, OM and TOC than the Central group stations. Here, more oxygenated waters may help to explain the relatively richer associations in spite of the opportunistic characteristics of the dominant taxa found in the Cabras lagoon, including tubificids, nereids and spionids. The relationship of the macrozoobenthos with fine sediments and OM was largely supported by the sediment analysis of vertical profiles (i.e., 0–24 cm depth horizon). In particular, several stations characterized by a thick layer of fine-grained organic-enriched sediments, such as Stns. C22, C26, and C28 (Fig. 3), had impoverished macrozoobenthos belonging to the Central stations (Fig. 5). In contrast, stations characterized by a vertical profile with coarser, less organic-enriched sediments, such as Stns. C1 Please cite this article in press as: Magni, P. et al., Distribution and ecological relevance of fine sediments ..., Mar. Pollut. Bull. (2008), doi:10.1016/j.marpolbul.2007.12.004 ARTICLE IN PRESS 10 P. Magni et al. / Marine Pollution Bulletin xxx (2008) xxx–xxx and C31, had relatively richer macrozoobenthic assemblages belonging to the Reef-shore stations. The analyses of sediment horizons also highlighted an increase of the thickness of the fine-grained organic-enriched layer from the north to the central-south area of the lagoon, the latter considered to be critical in terms of development of dystrophic events. In a subsequent temporal study, we have shown a marked impoverishment of the benthic communities in the southern sector of the lagoon at the end of summer (Magni et al., 2005b). This was thought to be the result of severe hypoxic conditions and an increase in acid-volatile sulphide concentrations of sediments caused by excessive amounts of sedimentary organic matter. The results of the present study clearly indicate the importance of not restricting the analysis of sediment grain size features and composition to a single uppermost layer. In fact, we showed that a detailed analysis of the sectioned sediment horizons was instrumental in assessing the extent (i.e., thickness) of the organic-enriched layer of sediments in different sectors of the lagoon (see also Magni et al., in press). This allowed for a better evaluation of the ecological quality of the lagoon and the identification of areas characterized by impoverished assemblages which could be more subject than others to the risks of developing dystrophic crisis (Magni et al., 2005b, in press). 4.3. Implications for monitoring and ecological quality assessment of coastal lagoons A significant challenge in studying shallow transitional waters such as estuaries and coastal lagoons is that they are under the influence of multiple factors and have a great internal patchiness and heterogeneity, which can often bias the application of the most common indicators and indices of environmental quality and health status. In these systems, water-quality criteria that are suited for deep lakes and marine ecosystems cannot be used due to the shallow depth, the pelagic components being quantitatively less important than the benthic subsystem. Overall, in coastal lagoons, the sediment-surface-area to water-volume ratio is of paramount importance in determining levels of ecosystem metabolism throughout benthic communities. There is therefore a need for a common, integrated set of indicators and monitoring approaches for use in shallow transitional waters that takes the unique properties of these systems into account. Yet, because of the complexity of most stressor–response relationships in nature, it is usually impractical if not impossible to completely characterize all contributing variables (Fisher et al., 2001). Under these circumstances, one should identify a set of basic benthic/sedimentary variables indicative of operative ecosystem properties and functions, which could then be used for classification and quality-assessment purposes (Viaroli et al., 2004; Hyland et al., 2005; Magni et al., 2005a). This work aims at providing a scientific assessment of benthic studies carried out on a regional scale in Mediterranean coastal lagoons in order to evaluate some general features of these systems and the monitoring approaches adopted. Coastal lagoons are often described as organicenriched sedimentary systems. However, this information is mostly found in individual studies, while a quantitative comparison of organic matter content of sediments in different lagoons at the regional (Mediterranean) level is lacking. Within this context, Table 4 provides an overview of OM and TOC content of sediments reported for several coastal lagoons in the Mediterranean Sea, as well as the methodology used to determine them. The OM and TOC contents indicate that these systems have generally much higher values than those found in coastal marine and estuarine systems (e.g., Tyson, 1995) when we exclude sites impacted by aquaculture activities (e.g., Cancemi et al., 2003) or accumulations of seagrass leaf litter (e.g., Como et al., 2007). Table 4 also demonstrates the wide use of loss of weight on ignition method (LOI) for OM determination. Yet, it should be noted that there is a large variability among studies in the analytical conditions used, such as the temperature and the time of ignition, as well as in the sediment layer considered, in most cases as being restricted to one single uppermost layer. The Cabras lagoon was one of the very few lagoons where both OM and TOC contents were determined and the sediment horizon sectioned and analyzed in detail, with values of both surface and several deeper layers (Fig. 2) in the upper ranges of the studies considered. Whereas the determination of OM by LOI is a more direct and less expensive procedure, it is a semi-quantitative method. A parallel analysis of organic matter using a CHN analyzer is strongly suggested, at least on a subset of samples, in order to obtain a more accurate measure of the total organic carbon content of sediments (Leong and Tanner, 1999). The determination of OM by LOI could then be reasonably employed on a larger group of samples, e.g., for routine/monitoring surveys, applying site-specific OM vs. TOC conversion factors. In fact, we suggest that, due to the large variability in the pool of sedimentary organic matter in the lagoon systems (e.g., Pusceddu et al., 1999; Frangipane, 2005), such relationships should be tested and applied in each individual lagoon. On a related note, we must caution that methodological differences in the determination of OM among the various studies (Table 4) may render a comparison difficult between different lagoons and/or studies if no proper standardization is made. The analysis of case studies reported in Table 4 also highlights that sediment grain size is often not considered at all (about half of cases), with only 9 out of 40 studies reporting combined analysis of grain size, organic matter (either as OM or TOC) and benthic communities. Furthermore, among these cases, grain size data are mostly reported to describe the general characteristics of sediments of the investigated environment without any statistical correlation with the chemical and biological variables. Confounding terms are even used sometimes to describe sediment classes (e.g., the use of the term ‘silt’ is sometimes referred to the <63 lm grain size intervals). This review Please cite this article in press as: Magni, P. et al., Distribution and ecological relevance of fine sediments ..., Mar. Pollut. Bull. (2008), doi:10.1016/j.marpolbul.2007.12.004 Lagoon Subbasin Sediment layer (cm) OM (%)a TOC (%)e Grain size Benthos Authors De Falco and Guerzoni (1995) Mesnage and Picot (1995) Bartoli et al. (1996) Mean and/or range(s) (±SD) LOI temperature/ time Mean and/or range (±SD) Variable used Method 350 °C/18 h Nd Sand–Mud Sieve + Laser Nd Nd 0.67-4.84 Sand–Silt–Clay Laser Nd 550 °C/‘‘Until constant weight” 500 °C/6 h Nd Nd Nd Nd Nd Sand–Silt Sieve Nd 450 °C/24 h Nd Nd Nd Nd Nd 2.4 ± 1.6 (0.1–6.3) Sand–Silt–Clay Na Nd SWE 0–5 NWE 0–5 2.0 ± 1.2– 10.0 ± 3.0 Nd 3. Prévost (France) NWE 0–10 10.1 ± 1.4 4. Thau (France) NWE 0–5 5. Sacca di Goro (Italy) ADR 0–2 6. Nador (Morocco) ALB ‘‘Surface” 1.3 ± 0.2– 5.0 ± 2.5 5.3 ± 1.0– 13.7 ± 1.9 Nd 7. Méjean-Pérols (France) 8. Venice, Palude della Rosa (Italy) 9. Stagnone Marsala (Italy) NWE ADR 0–5 0–5 Nd 6.8–12.8 Nd 550 °C/Na 5.1 (2.6–7.1) Nd Sand–Silt–Clay Nd Laser Nd Nd Macrobenthos TYR 0–1 10.4–17.2b 450 °C/2 h 1.37–2.37f Nd Nd Nd 10. 11. 12. 13. TYR ADR TYR SWE 0–2 0–2 0–1 0–5 Nd 550 °C/3 h 450 °C/4 h 600 °C/Na Nd Nd Nd Nd Nd Nd Nd Nd Nd Nd Nd Nd Nd Nd Macrobenthos Ndi 14. Sacca di Goro (Italy) ADR 0–10 450 °C/4 h Nd Sand–Silt–Clay Sieve + Pipette Macrobenthos 15. Bardawil (Egypt) SLE 0–2 Nd 11.4 ± 3.5 4–16h 9.4 ± 8.7 (0.6– 23.6) 12.0 ± 0.1– 16.4 ± 0.1 Nd De Casabianca et al. (1997) Giordani et al. (1997) El-Alami et al. (1998) Gomez et al. (1998) Tagliapietra et al. (1998) Pusceddu et al. (1999) Added (2001) Azzoni et al. (2001) Lardicci et al. (2001) Draredja and Beldi (2001) Mistri et al. (2001) Nd Sand–Silt–Clay Sieve + Pipette Nd Taher (2001) 16. Fattibello and Spavola (Italy) 17. Lesina (Italy) 18. Valli di Comacchio (Italy) 19. Berre (France) ADR 0–2 Nd Nd Sand–Mud Frascari et al. (2002) Nd 7–20h Nd Nd 500 °C/Na Nd Meiobenthos Macrobenthos Macrobenthos 20. Cabras (Sardinia, Italy) SWE 0–1 0–0.5 ‘‘Sed–water interface” 0–2 Sieve-X-ray Sedigraph Sieve Nd Laser Nd ADR ADR NWE 1.2 ± 0.45 (0.87– 2.4) 2.34 ± 1.16– 2.85 ± 1.04 0.4–1.7f Nd 2.30–2.93 500 °C/3 h 21. Monolimni (Greece) 22. Cabras (Sardinia, Italy) 23. Stagnone Marsala (Italy) AEG SWE TYR 0–10 0–2 0–10 Na Nd 450 °C/4 h 24. Tsopeli, Tsoukalio, Rodia and Logarou (Greece) ION 0–2 10.5 ± 2.4 (3.5– 14.3) 0.15–2.2 Nd 0.6 ± 0.1– 15.6 ± 1.3 Nd Gambi et al. (2003) Munari et al. (2003) Rosenberg et al. (2003) De Falco et al. (2004) Kevrekidis (2004) Magni et al. (2004b) Mirto et al. (2004) 25. Papas (Greece) ION 0–2 Nd Nd 26. Molino (Italy) ADR 0–3 7.8–13.4 Na Ghar El Melh (Tunisia) Valle Smarlacca (Italy) Orbetello (Italy) Mellah (Algeria) Nd 3.28 ± 0.72 (0.96– 4.29) Nd Nd 0.2 ± 0.1– 2.1 ± 0.6f 2.82 ± 1.55– 3.11 ± 0.96 (1.1– 5.3) 4.61 ± 0.17 (2.95.6) Nd Sand–Mud Nd Sand–Mud All grain size spectra (one phi interval) Median Statistical moments Nd Sieve + Laser Ndj Sieve + Pipette Sieve + Laser Nd Macrobenthos Macrobenthos Meiobenthos Sand–Silt–Clay Sieve + Pipette Macrobenthos Sand–Silt–Clay Sieve + Pipette Macrobenthos Nd Nd Reizopoulou and Nicolaidou (2004) Reizopoulou and Nicolaidou (2004) Macrobenthos Sorokin et al. (2004) (continued on next page) ARTICLE IN PRESS 1. S’Ena Arrubia (Sardinia, Italy) 2. Thau (France) P. Magni et al. / Marine Pollution Bulletin xxx (2008) xxx–xxx 11 Please cite this article in press as: Magni, P. et al., Distribution and ecological relevance of fine sediments ..., Mar. Pollut. Bull. (2008), doi:10.1016/j.marpolbul.2007.12.004 Table 4 Comparison of organic matter (OM) and total organic carbon (TOC) content of sediments in Mediterranean coastal lagoons 12 Lagoon Subbasin Sediment layer (cm) 27. Lesina (Italy) ADR 28. Venice (Italy) OM (%)a TOC (%)e Grain size Authors Sieve Meiobenthos Sieve + Pipette Ndk Fabbrocini et al. (2005) Frangipane (2005) Nd Macrobenthos Magni et al. (2005b) Nd Nd Macrobenthos Median Sieve + Pipette Macrobenthos Sand– Mud Nd Sieve Nd Marı́n-Guirao et al. (2005) Mogias and Kevrekidis (2005) Sfriso et al. (2005) Nd Nd Nd Sieve-X-ray Sedigraph Nd Nd Nd Nd Nd Nd Nd Sand– Silt–Clay Nd Nd Macrobenthos Nd 450 °C/2 h Nd Nd Nd Nd 1.9–16.7 500 °C/3 h 0.48–4.25 Nd Nd Macrobenthos 8.1 ± 2.2 (2.6–12.9) 500 °C/3 h 3.28 ± 0.72 (0.96– 4.29)g 68 lm Sieve + Laser Macrobenthos LOI temperature/ time Mean and/or range (±SD) Variable used Method 0–5 9.8 ± 1.7–17.3 ± 1.3 550 °C/3 h Nd ADR 0–5 0.3–22.3 350 °Cc/16 h 0.21–15.0 29. Cabras (Sardinia, Italy) SWE 0–2 500 °C/3 h Nd 30. Mar Menor (Spain) SWE 0–5 14.5 ± 3.1 (8.6– 22.2) 2.2 ± 0.1–8.2 ± 0.3 Sand– Mud Sand– Silt–Clay Nd 450 °C/6 h 31. Laki (Greece) AEG 0–10 0.31–2.15 Na 0.90 ± 0.02– 1.60 ± 0.24 Nd 32. Venice, central basin (Italy) ADR 0–5 Nd Nd 0.3–2h 33. Bizerte (Tunisia) TYR ‘‘Top” Nd Nd 0.23–1.91 34. Marsala (Italy) 35. Tsopeli, Tsoukalio, Rodia and Logarou (Greece) 36. Valle Smarlacca (Italy) 37. Lesina (Italy) TYR ION 0–1 ‘‘Surface” 0.8–5.2d Nd 450 °C/4 h Nd Nd 2.92–6.55 ADR ADR Na 0–5 550 °C/8 h 450 °C/2 h 38. Sacca di Goro (Italy) ADR 0–5 3.5–17.7 12.9 ± 1.5– 22.8 ± 1.6b 1.8 ± 1.0–14.5 ± 0.6 39. Santa Giusta (Sardinia, Italy) SWE 0–20l 40. Cabras (Sardinia, Italy) SWE 0–24l Trabelsi and Driss (2005) Culotta et al. (2006) Karageorgis (2007) Ponti et al. (2007) Giordani et al. (in press) Giordani et al. (in press) Magni et al. (in press) This study Details on sediment grain size and benthic invertebrate assemblages are also given when available (SD: standard deviation; Nd: not determined; Na: not available). Lagoons were classified according to the ten marine sub-basins in which the whole Mediterranean basin is usually divided (UNEP/FAO/WHO/IAEA (1990)). ADR, Adriatic Sea; AEG, Aegean Sea; ALB, Alboran Sea; ION, Ionian Sea; NWE, Northwestern Mediterranean Sea; SLE, South-Levantine Sea; SWE, Southwestern Mediterranean Sea; TYR, Tyrrhenian Sea (not present: Central Sea and North Levantine Sea sub-basins). Studies are listed by the year of publication and, within one year, by alphabetical order of Authors. a Organic matter (OM) determined by loss of weight on ignition (LOI), except: Sorokin et al., 2004 (wet chromic oxidation, assuming 40% of TOC in OM); Kevrekidis, 2004; and Mogias and Kevrekidis, 2005 (oxidation by H2O2). b OM bulk in the highest range mainly associated with angiosperms. c OM determined by fractionation at various temperatures (i.e., 250 °C, 350 °C, 450 °C, and 550 °C). d OM determined after elimination of carbonates. e Total organic carbon (TOC) determined by CHN elemental analyzer, except: Mesnage and Picot, 1995 (reported as a pers. comm. by Gadel); El-Alami et al., 1998; Pusceddu et al., 1999; Gambi et al., 2003; Mirto et al., 2004 (colorimetric method); Added, 2001 (chemical oxidation); Reizopoulou and Nicolaidou, 2004 (Tsopeli, Tsoukalio, Rodia and Lagarou lagoons: titration); Trabelsi and Driss, 2005 (titration). In Sfriso et al. (2005), TOC calculated as the difference between total carbon and inorganic carbon (determined by CHN elemental analyzer). f Biopolymeric carbon (sum of carbohydrate, protein and lipid C-equivalents). g Based on De Falco et al. (2004). h Values estimated from figure. i Macrobenthos investigated by: Draredja (2005). j Macrobenthos investigated by: Magni et al. (2004b). k Macrobenthos investigated by: Pessa (2005). l Sectioned cores at 2 cm intervals. ARTICLE IN PRESS Benthos Mean and/or range(s) (±SD) P. Magni et al. / Marine Pollution Bulletin xxx (2008) xxx–xxx Please cite this article in press as: Magni, P. et al., Distribution and ecological relevance of fine sediments ..., Mar. Pollut. Bull. (2008), doi:10.1016/j.marpolbul.2007.12.004 Table 4 (continued) ARTICLE IN PRESS P. Magni et al. / Marine Pollution Bulletin xxx (2008) xxx–xxx highlights that (bio)geochemical approaches often do not consider benthic-community features, while biologicallyoriented approaches lack an evaluation of the (bio)geochemical properties of a specific lagoon system. A final consideration can be made of the geographical distribution of the studies analyzed here. The Adriatic sub-basin was the most studied area (ADR, 14 out of 40 studies) followed by the southwestern sub-basin (SWE, eight out of 40 studies), whereas significant data gaps existed in the south and southeastern basin. In addition, most studies (87.5%) were conducted in fewer European countries (Italy, France, Greece, and Spain). This calls for increased cooperation and coordination among scientists and institutions in the whole Mediterranean basin towards a better understanding of the lagoon and of coastal marine and estuarine systems at the regional (basin) level (Magni, 2003; Magni et al., 2004a). Overall, it appears that much still remains to be done with regard to the monitoring of Mediterranean coastal lagoons and the integration of the results from different disciplines, such as analysis of sediment grain size and compositional trends in relation to the distribution and composition of the biotic components. We have provided here a framework for evaluating the importance of investigating the distribution and dynamics of fine sediments in relation to both organic enrichment and benthic macroinvertebrate communities. We suggest that monitoring programs, especially in organic-enriched lagoons, should consider the sediment fraction most tightly correlated with organic matter (often being the overlooked cohesive fraction of sediments) to be integrated in direct correlation analysis with other major abiotic (e.g., TOC) and biotic (e.g., benthic assemblages) variables in order allow a better assessment of benthic–sediment relationships and the ecological quality of the system. 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