Taxonomic level for assessing oil spill effects on soft-bottom sublittoral benthic communities
Introduction
Benthic communities are sensitive to oil spills, but the effects of oil pollution strongly depend on the proportion of hydrocarbon-sensitive species, especially crustaceans, in the affected community (see Dauvin, 1998, Dauvin, 2000). Some species, such as Ampelisca and other amphipods, can be considered as good indicators of oil pollution; by contrast, polychaetes appear to be resistant to high levels of hydrocarbons in sediment (Gomez Gesteira and Dauvin, 2000). These authors propose the use a polychaetes/amphipods ratio to reflect temporal changes in the soft-bottom macrobenthos, analogous to the nematodes/copepods ratio previously suggested for the meiobenthos. The polychaetes/amphipods ratio requires only family-level identification of polychaetes, since the characteristic opportunistic polychaete response to increased organic matter is generally detectable as family-level increases in the abundance of Capitellidae, Cirratulidae, Spionidae and/or Eunicidae (Gomez Gesteira and Dauvin, 2000).
After an oil spill, the objectives of monitoring studies are usually: (i) to identify the short-term effects of the hydrocarbons (categories of organism affected by the spill, and estimation of mortalities; i.e. the “resistance” of the community), and (ii) to evaluate the time required for decontamination of the sediment and organisms, and for recovery of pre-spill population levels (i.e., the “resilience” of the community). In several cases, the time required for recovery of pre-spill population levels has 10 years (see Dauvin, 1998 and Gomez Gesteira, 2001 for reviews). In contrast, some communities, such as the fine-sand Abra alba community of the Bay of Morlaix, have shown very high resiliences: 15 years after the Amoco Cadiz spill the Ampelisca populations which initially disappeared showed complete recovery. In such surveys, several authors have recommended the identification of organisms to species-level, in view of the information offered by such an approach (species richness, species appearance and disappearance, comparative investigations at the mesoscale, etc.).
The effects of the 1992 Aegean Sea spill on the infralittoral muddy-sand macrobenthic communities of the Ares and Betanzos Ria in Galicia (Spain) were monitored in detail over a four-year period (1992–1996) (Mora et al., 1996a, Mora et al., 1996b; Gomez Gesteira, 2001). These studies revealed strong similarities with the impact of the Amoco Cadiz spill on the infralittoral communities of the Bay of Morlaix (Western English Channel). The comparison of these two spills has revealed general patterns in the effects of oil on soft-bottom macrobenthic species and populations (Gomez Gesteira and Dauvin, 2000).
The aim of this paper is to investigate which taxonomic level (species, genus or family) corresponding to the ‘taxonomic sufficiency’ (TS) (Ellis, 1985) is sufficient to detect different post-spill trends in soft-bottom benthic assemblages from the Ares and Betanzos Ria in Galicia (Spain) and the Bay of Morlaix in Brittany (France).
Section snippets
Study areas and oil spills
The main characteristics of the study areas, the sampling design, and the oil spills are described in detail in Gomez Gesteira and Dauvin (2000); in what follows we provide only a summary.
Ares and Betanzos Ria
Five sites were sampled in infralittoral muddy-sand macrobenthic areas of the Ares and Betanzos Ria. Two of these sites (<10 m depth) are located in the inner part of the ria, in muddy Abra-alba communities near a freshwater input: site K (43°21.92′N; 8°13.92′W) and site T (43°25.7′N; 8°12.8′W). The three
Taxonomic structure of communities
Table 1 shows the number of taxa at different taxonomic levels from phylum to species, for each of the seven sites after pooling all samples collected over the corresponding four-year periods. Three phyla (Annelida, Arthropoda and Mollusca), contained most of the species, genera and families. A sharp discontinuity in number of taxa is apparent when the order level is considered rather than the family- or genus-level. At the five Galician sites the number of species was in all cases very similar
Discussion
Gomez Gesteira and Dauvin (2000) compared the effects of oil spills on infralittoral soft-bottom communities in the Bay of Morlaix (western English Channel, polluted by the Amoco Cadiz spill in 1978), and from the Ares and Betanzos Ria (north-western Iberian Peninsula, polluted by the Aegean Sea spill in 1992). The pre-spill communities showed similar biological characteristics in the two regions. The effects of the spills were very similar in the two regions, notably (i) the disappearance of
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2020, Ecological IndicatorsCitation Excerpt :We categorized the taxa used in the studies into the following groups: microorganisms (e.g., bacteria, ciliate, microcrustaceans and microalgae; Jiang et al., 2016; Ribas and Padial, 2015; Vilmi et al., 2016), macroscopic plants (e.g., bryophytes, vascular plants and macroalgae; Alves et al., 2016; Díez et al., 2010; Jantz et al., 2014; Ribas and Padial, 2015), invertebrates (e.g., aquatic macroinvertebrates, arthropods and insects; Pérez-Fuertes et al., 2016; Rosser, 2017; Vilmi et al., 2016) and vertebrates (e.g., fish, amphibians, reptiles, mammals and birds; Kallimanis et al., 2012; Mazaris et al., 2008; Ribas and Padial, 2015). We also categorized two studies as fungi (Balmford et al., 2000; Sebek et al., 2012), one as macrolichen (Negi and Gadgil, 2002) and two as benthos (Dethier and Schoch, 2006; Gesteira et al., 2003). Also, we recorded whether the study was conducted in aquatic or terrestrial ecosystems.