The use of nematodes in assessing ecological conditions in shallow waters surrounding a Mediterranean harbour facility
Introduction
Shallow coastal habitats are subject to intense environmental pressure with extensive feedback effects between natural and human systems (Turner, 2000). As well as natural fluctuations in abiotic parameters, the input of nutrients, organic matter and pollutants related to anthropogenic activities can further modify coastal environmental conditions, sometimes to a greater extent, and produce changes in the biota different to those derived from natural variability alone (Turner et al., 1995; Venturini et al., 2004). The multiple uses of coastal areas can mobilize terragenic materials to the marine environment in amounts similar to, or even exceeding, those introduced through natural weathering processes (Bruland et al., 1974). In the Mediterranean Sea, the effects of urbanization, port and harbour development, industrial activities, agriculture and aquaculture, have resulted in extensive coastal pollution (Haas, 1989). Liguria, an administrative region of NW Italy (NW Mediterranean Sea), has been subject to significant urban and industrial coastal development since the 1960s, which, together with high tourism, has concentrated both civil and industrial activities in a narrow, highly populated territory (Bertolotto et al., 2005; Montefalcone et al., 2009). In particular, the area of Vado Ligure (Savona, Ligurian Sea, NW Mediterranean) has a long history of industrial and harbour activities, with long tracts of the coastline dedicated to tourism. Anthropogenically stressed coastal areas such as these typically receive inputs which may contain hydrocarbons, heavy metals and other pollutants derived from human activities, that cause perturbations in the ecosystem, changing the abiotic conditions and influencing the biota in terms of density, diversity, structure and functioning (Venturini et al., 2004; Martínez-Lladó et al., 2007).
The use of indicators to detect and monitor environmental conditions is of primary importance and represents a worldwide incentive, detailed in the Water Framework Directive (WFD, 2000/60/EC) and Marine Strategy Framework Directive (MSFD, 2008/56/EC). Living organisms are fundamental in assessing the ecological status of an ecosystem, integrating both biotic and abiotic components through their adaptive responses (Casazza et al., 2002). Whilst contaminant concentrations in the water column can change significantly, both temporally and spatially, sediments integrate contaminants over time, accumulating natural and anthropogenic products from the overlying water. As a consequence, benthic species, living in close contact with sediment particles and interstitial water, are intimately exposed to contaminants and therefore have been used historically as indicators of environmental quality. Benthic macrofauna is more usually employed as bioindicators than the meiofauna, despite the fact that in soft sediments, where contaminants accumulate, meiobenthic invertebrates frequently represent the most abundant metazoan organisms (Gerlach, 1971; Höss et al., 2011). Moreover, in severely polluted sediments, some meiofaunal taxa represent the only significant metazoan component, whereas macrofauna may be scarce and difficult to sample representatively, or dominated by high abundance of very few taxa, in both cases providing little information that can be used effectively (Kennedy and Jacoby, 1999). The use of meiofauna in biomonitoring studies gives many advantages over macro-invertebrates owing to their high abundance and diversity, small size, short life cycles, rapid development, limited mobility, absence of pelagic life stages and the presence of both tolerant and sensitive species. These advantages lead to more robust data sets, which can show higher sensitivity, effects over smaller spatial scales, and a quicker response to disturbance (Kennedy and Jacoby, 1999; Frontalini et al., 2011).
Of the meiofaunal taxa, nematodes in particular offer a variety of possibilities for assessing changes in assemblage structure, due to their high structural and functional diversity, as the most diverse and numerically dominant metazoans in aquatic habitats, with a wide distribution varying from pristine to extremely polluted habitats. Although nematodes have already been employed in environmental quality assessment studies and have proved to be suitable indicators for pollution-induced disturbances of benthic ecosystems (Coull and Chandler, 1992; Bongers and Ferris, 1999; Höss et al., 2011), they are not currently considered as a requirement for the assessment of the ecological status of the benthic environment according to the WFD and MSFD. However, the WFD has recently proposed nematodes as indicators for evaluation of the ecological quality status of marine ecosystems (Moreno et al., 2011). The use of nematode indices, especially in soft sediments, can bridge the gap in current monitoring programs, mainly based on macro-benthic invertebrates (Höss et al., 2011) revealing different and complementary aspects of the factors structuring benthic ecosystem, fundamental in ecological status assessment (Vanaverbeke et al., 2011).
In this study we evaluated the use of nematodes as indicators of environmental quality in an area strongly influenced by human activities. The main aims were to analyze patterns of nematode assemblages in the study area and to test whether: (1) there was a relationship between the observed patterns and the main environmental variables and human influences; (2) anthropogenic impacts had influenced the nematode assemblage structure; and (3) there were nematode genera which could be reliably used as indicators of pollution or environmental quality.
In order to achieve these objectives, inorganic (heavy metal) and organic (C12–C40, polycyclic aromatic hydrocarbons) pollutants as well as organic enrichment were investigated at twenty-two stations situated along an “anthropogenic gradient” from sites located near the city of Vado Ligure and its harbour to more pristine, distant sites. To account for the effects of natural environmental variability on the structure of nematode assemblages, relationships with depth, particle size and organic matter composition were also investigated.
Section snippets
Study area and field activities
The study was carried out along the coast of Vado Ligure (Savona) in the Western Ligurian Riviera (Ligurian Sea, NW Mediterranean). The area is densely populated and influenced by the presence of a commercial port, which is an important container and oil terminal, an oil-burning power plant and by various other economic activities, such as industrial plants and tourist resources. Samples were collected in January 2010 at twenty-two stations located at increasing distance to the south of the
Grain size
The stations studied showed a large gradient of substrate type, with sediments varying from medium silt to very coarse sand and from very poorly to moderately sorted (Table 1 and Fig. 1).
Mean grain size values ranged between 0.03 mm (Station B2) and 5.82 mm (Station E1). A general pattern of decreasing grain size with depth was recorded (p < 0.05) due to the increase of clay (p < 0.001) and silt (p < 0.05) fractions with depth (Appendix A).
Sedimentary organic matter concentration and biochemical composition
The results for organic matter concentration and
Discussion
The coastal area surveyed proved to be heterogeneous in terms of bathymetry, sedimentary parameters, organic loading and anthropogenic inputs. The comparison of contaminant levels with reference values (Long et al., 1995) indicated relatively high concentrations, especially for heavy metals, with sediments at a high number of stations having the potential to cause adverse effects in sensitive species. Concentrations of both heavy metals and PAHs were similar to ones reported in previous studies
Conclusions
The pattern of nematode assemblages found in the study area was strongly related to environmental variables; contamination level, bathymetry, quantity and composition of organic matter and sediment proprieties. Anthropogenic effects were found on nematode abundance, number of genera and maturity index. The multivariate structure of the nematode assemblages was clearly related to the level of contamination of their sediments. In particular, the group of stations in the proximity of Vado Ligure
Acknowledgments
This work was partially done within the frame of the research agreement between DISTAV and CIMA Research Foundation. The authors are grateful to CIMA Research Foundation for scientific cooperation. We also thank the staff of the Laboratory of Ecology (University of Genoa) for precious help with laboratory analyses, and Mariachiara Chiantore and Luigi Vezzulli for valuable suggestions. Special thanks go to the two anonymous referees for their constructive and critical reviews of the manuscript.
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