III.2.1.a. – Faciès à Lentidium mediterraneum

International audienc

III.2.1.a. – Faciès à Lentidium mediterraneum

International audienc

Taxonomic resolution needed to describe invertebrate assemblages and to detect harvesting effects on coral reef ecosystems

Due to the cost and time required for species identification, the taxonomic sufficiency approach has been developed in order to detect community response to a disturbance, using high taxonomic level without great loss of information. This concept has been widely applied to pollution monitoring studies but rarely to other forms of perturbations such as anthropogenic exploitation of marine resources. We applied this method both to soft-bottom (seagrasses) and hard-bottom (coralline) tropical invertebrate communities in New Caledonia, South Pacific. The objective was to test whether intermediate or high taxonomic levels (genus, family, class or phylum instead of species) are good descriptors of community patterns and changes in assemblages related to harvesting, by comparing harvested to non-harvested areas for the 2 habitats. We pooled species data into coarser taxonomic categories (from genus to phylum) and showed that matrices at different taxonomic resolutions were highly correlated, particularly for genus and family level for both habitats. Differences between harvested and non-harvested locations appeared to be clearly habitat-dependent; for soft habitats, genus and family resolution allowed the detection of changes between exploited and protected assemblages, while for hard habitats, the separation between harvested and non-harvested areas was less clear at high taxonomic level and required species-level identifications. These results suggest that the taxonomic sufficiency approach could be carefully applied to poorly known environments. Family level is a good descriptor of community composition for tropical reef invertebrates. Detecting changes due to anthropogenic exploitation requires different taxonomic resolutions depending on the considered habitat

Impact of natural (storm) and anthropogenic (trawling) sediment resuspension on particulate organic matter in coastal environments

In order to assess the impact of natural and anthropogenic sediment resuspension on quantity, biochemical composition and bioavailability of particulate organic matter (POM), two field investigations were carried out in two shallow coastal areas of the Mediterranean Sea. In the Gulf of Lions, we investigated the impact of a storm resuspension of sediment, whereas in the Thermaikos Gulf we investigated the impact of bottom trawling. Resuspension in the Gulf of Lions determined the increase of sedimentation rates, modified the composition of the organic fraction of settling particles and decreased the labile fraction of POM, as indicated by a drop in the enzymatically hydrolysable amino acid fraction. The increase in the refractory fraction, following short-term storm-induced resuspension, increased also the contribution of glycine and decreased the contribution of aspartic acid contents to the total amino acid pools. Trawling activities in Thermaikos Gulf determined a significant increase in suspended POM concentrations and important changes in its biochemical composition. After trawling, the protein to carbohydrate ratio decreased (as a result of a major input of sedimentary carbohydrates at the water-sediment interface) and the fraction of enzymatically hydrolysable biopolymeric C decreased by ≈30%, thus reducing the bioavailability of resuspended organic particles. Results of the present study indicate that changes in suspended POM, induced by storms and trawling activities, can have similar consequences on benthic systems and on food webs. In fact, the potential benefit of increased organic particle concentration for suspension feeders, is depressed by the shift of suspended food particles towards a more refractory composition

Comparison of the performance of two biotic indices based on the MacroBen database

The pan-European MacroBen database was used to compare the AZTI Marine Biotic Index (AMBI) and the Benthic Quality Index (BQIES), 2 biotic indices which rely on 2 distinct assessments of species sensitivity/tolerance (i.e. AMBI EG and BQI E[S]0.05) and which up to now have only been compared on restricted data sets. A total of 12 409 stations were selected from the database. This subset (indicator database) was later divided into 4 marine and 1 estuarine subareas. We computed E(S50)0.0 in 643 taxa, which accounted for 91.8% of the total abundances in the whole marine indicator database. AMBI EG and E(S50)0.05 correlated poorly. Marked heterogeneities in E(S50)0.0 between the marine and estuarine North Sea and between the 4 marine subareas suggest that sensitivity/tolerance levels vary among geographical areas. High values of AMBI were always associated with low values of BQIES, which underlines the coherence of these 2 indices in identifying stations with a bad ecological status (ES). Conversely, low values of AMBI were sometimes associated with low values of BQIES resulting in the attribution of a good ES by AMBI and a bad ES by BQIES. This was caused by the dominance of species classified as sensitive by AMBI and tolerant by BQIES. Some of these species are known to be sensitive to natural disturbance, which highlights the tendency of BQIES to automatically classify dominant species as tolerant. Both indices thus present weaknesses in their way of assessing sensitivity/tolerance levels (i.e. existence of a single sensitivity/tolerance list for AMBI and the tight relationship between dominance and tolerance for BQIES). Future studies should focus on the (1) clarification of the sensitivity/tolerance levels of the species identified as problematic, and (2) assessment of the relationships between AMBI EG and E(S50)0.05 within and between combinations of geographical areas and habitats

L'énergie et la Chine

Ouvrage coordonné par Jean-Frnaçois Huchet et Françoise Lemoin

Distribution patterns of macrofaunal species diversity in subtidal soft sediments: biodiversity-productivity relationships from the MacroBen database

We analyzed patterns of species diversity in a compiled data set covering the European coast (from Norway to Crete) that was made available in the framework of the MarBEF European Network of Excellence. The focus was on the distribution patterns of species diversity over large areas across Europe. The objectives of our analysis were two-fold. First, we attempted to separate the effects of species-area relationships from that of species accumulation. Second, we explored the relationship between species diversity and productivity, and compared this to the proposed explaining factors (depth, survey area and latitude). The following conclusions are drawn. (1) Within a given habitat (subtidal soft sediment), the distribution of marine macrofaunal species richness in different areas between 3 and 200 m in average depth throughout Europe is shown to follow general rules derived from observations and experiments mostly based on terrestrial communities; (2) soft-bottom macrofauna accumulate in the subtidal environment (up to 200 m) following the Arrhenius plot model at a rate (˜0.5) corresponding to about a 3-fold increase in the number of species when the sampling area increases by 1 order of magnitude; (3) the distribution of the intrinsic species richness (point species richness) between the selected data sets (subtidal soft sediment) is significantly correlated with the levels of organic flux reaching the sea bottom; and (4) the close relationship between depth and the fraction of surface primary production that reaches the sea bottom is proposed as an explanation for the previously described increase of species richness with depth