A comprehensive expert consultation was conducted in order to assess the status, trends and the most important drivers of change in the abundance and geographical distribution of kelp forests in ...European waters. This consultation included an on-line questionnaire, results from a workshop and data provided by a selected group of experts working on kelp forest mapping and eco-evolutionary research. Differences in status and trends according to geographical areas, species identity and small-scale variations within the same habitat where shown by assembling and mapping kelp distribution and trend data. Significant data gaps for some geographical regions, like the Mediterranean and the southern Iberian Peninsula, were also identified. The data used for this study confirmed a general trend with decreasing abundance of some native kelp species at their southern distributional range limits and increasing abundance in other parts of their distribution (Saccharina latissima and Saccorhiza polyschides). The expansion of the introduced species Undaria pinnatifida was also registered. Drivers of observed changes in kelp forests distribution and abundance were assessed using expertsâ opinions. Multiple possible drivers were identified, including global warming, sea urchin grazing, harvesting, pollution and fishing pressure, and their impact varied between geographical areas. Overall, the results highlight major threats for these ecosystems but also opportunities for conservation. Major requirements to ensure adequate protection of coastal kelp ecosystems along European coastlines are discussed, based on the local to regional gaps detected in the study.
The use of sequence polymorphism from individual mitochondrial genes to infer past demography has recently proved controversial because of the recurrence of selective sweeps acting over genes and the ...need for unlinked multilocus data sets. However, comparative analyses using several species for one gene and/or multiple genes for one species can serve as a test for potential selective effects and clarify our understanding of historical demographic effects. This study compares nucleotide polymorphisms in mitochondrial cytochrome oxidase I across seven deep‐sea hydrothermal vent species that live along the volcanically active East Pacific Rise. Approximate Bayesian Computation (ABC) method, developed to trace shared vicariant events across species pairs, indicates the occurrence of two across species divergence times, and suggests that the present geographical patterns of genetic differentiation may be explained by two periods of significant population isolation. The oldest period dates back 11.6 Ma and is associated with the vent limpet Lepetodrilus elevatus, while the most recent period of isolation is 1.3 Ma, which apparently affected all species examined and coincides with a transition zone across the equator. Moreover, significant negative Tajima’s D and star‐like networks were observed for all southern lineages, suggesting that these lineages experienced a concomitant demographic and geographical expansion about 100 000–300 000 generations ago. This expansion may have initiated from a wave of range expansions during the secondary colonization of new sites along the Southern East Pacific Rise (founder effects below the equator) or recurrent bottleneck events because of the increase of eruptive phases associated with the higher spreading rates of the ridge in this region.
A strongly divergent lineage, putatively a new cryptic species, of colonial ascidian was first detected as an anomalous sample in a population genomics study of the well-known worldwide invasive ...species
Didemnum vexillum
Kott,
2002
. This putative new taxon, found in a marina in Roscoff, France, is indistinguishable from
Didemnum vexillum
in the external aspect and coexists with it in syntopy. However, morphological characters such as spicules and larvae allow a clear-cut distinction. In accordance with the preliminary results based on genome-wide analyses, morphological traits and mitochondrial sequences of the cytochrome oxidase I gene both support the establishment of a new species
Didemnum pseudovexillum
sp. nov. Previous unidentified sequences in public databases showed that the new species is also present in NW Mediterranean marinas.
Didemnum pseudovexillum
sp. nov. is assigned for the time being a cryptogenic species status, although its presently known disjoint distribution across two biogeographic regions and its presence in ports are suggestive of an introduced species. Further studies should be performed to ascertain its current distribution and putative natural range and settle its native vs. non-native status. This finding casts doubts on previous reports of
Didemnum vexillum
and also calls for caution when performing fast field surveys of non-indigenous species such as rapid assessment surveys (RAS) or BioBlitz surveys, based solely on external characters.
In a global context of promotion and expansion of blue growth initiatives, the development of activities such as aquaculture calls for the assessment of the potential impacts on biodiversity at ...different levels and associated services. This paper presents an assessment of the potential impact of the installation of seaweed farms on ecosystem services and the induced compensation costs. Biophysical and socioeconomic indicators have been developed for helping decision makers to select the most suitable locations. The approach considers a multi-criteria approach based on Geographical Information Systems (GIS) and Habitat Equivalency Analysis (HEA). The former is used to obtain biophysical ecosystem services and socioeconomic indicators and the latter to evaluate the costs required to compensate the loss of cultural and provisioning ecosystem services. A case-study in the Normand-Breton (Saint Malo) Gulf, France, illustrates this method through the analysis of hypothetical locations of seaweed farms. Results highlight the differences between alternative locations regarding biophysical constraints (in terms of distance and depth), potential risks of conflicts with existing uses, impacts on habitats and the ecosystem services delivered, and compensation costs. This case-study illustrates the flexibility of this approach which can be further adapted to include other indicators in order to deliver integrated information to coastal planners.
•Seaweed farms installation requires a multi-criteria approach.•A GIS-based methodology combined with HEA is proposed.•We deliver integrated information about ES impacts and compensation costs.
Effective population size (Ne) is a measure of genetic drift and is thus a central parameter in evolution, conservation genetics and invasion biology. Interestingly, in native marine species, Ne is ...typically several orders of magnitude lower than the census size. This pattern has often been explained by high fecundity, variation in reproductive success and pronounced early mortality, resulting in genetic drift across generations. Data documenting genetic drift and/or Ne in marine invasive species are, however, still scarce. We examined the importance of genetic drift in the invasive species Crepidula fornicata by genotyping 681 juveniles sampled during each annual recruitment peak over nine consecutive years in the Bay of Morlaix (Brittany, France). Observed variations in genetic diversity were partially explained by variation in recruitment intensity. In addition, substantial temporal genetic differentiation was documented (that is, genetic drift), and was attributed to nonrandom variance in the reproductive success of different breeding groups across years in the study species. Using a set of single-sample and temporal estimators for Ne, we estimated Ne to be three or four orders of magnitude smaller than the census size (Nc). On one hand, this reduction in Ne relative to Nc appeared congruent with, although slight higher than, values commonly observed in native marine species. Particular life-history traits of this invasive species may play an important role in buffering genetic drift. On the other hand, Ne still remained far below Nc, hence, possibly reducing the efficiency of selection effects.
The historic processes which have led to the present‐day patterns of genetic structure in the marine coastal fauna of the Northeast Atlantic are still poorly understood. While tectonic uplifts and ...changes in sea level may have caused large‐scale vicariance, warmer conditions during glacial maxima may have allowed pockets of diversity to persist to a much wider extent than in the Northwestern Atlantic. The large‐scale geographic distribution of deeply divergent lineages of the coastal polychaete tubeworms Pectinaria koreni (two clades) and Owenia fusiformis (three clades) were compared using a fragment of the mitochondrial cytochrome oxidase I gene (mtCOI). All lineages were present along the biogeographic transition zone on the north coast of Brittany (France) and we found evidence pointing towards congruence in the timing of cladogenic events between Pectinaria sp. (P. auricoma/P. belgica and P. koreni) and Owenia sp., suggesting a shared history of vicariant events. More conserved 16SrRNA sequences obtained from four species of Pectinariidae together with mtCOI sequences of P. koreni seem consistent with an initial establishment of pectinariids in the north, and a southward colonization of the Northeast Atlantic. Phylogeographic patterns in O. fusiformis were also consistent with a north/south pattern of lineage splitting and congruent levels of divergence were detected between lineages of both species. We observed signatures of both persistence in small northern glacial refugia, and of northwards range expansion from regions situated closer to the Mediterranean. However, whether the recolonization of the Northeast Atlantic by both species actually reflects separate interglacial periods is unclear with regards to the lack of molecular clock calibration in coastal polychaete species.
Since the 1970s, the nassariid gastropod Cyclope neritea has been extending its range north along the French Atlantic coasts from the Iberian Peninsula. This may be due to natural spread because of ...the recent warming of the northeastern Atlantic. However, human-mediated introductions related to shellfish culture may also be a probable explanation for this sudden range expansion. To examine these two hypotheses, we carried out a comprehensive study based on mitochondrial gene sequences (cytochrome oxidase I) of the five recently colonized French bays as well as 14 populations located in the recognized native range of the species. From a total of 594 individuals, we observed 29 haplotypes to split into three divergent clades. In the native range, we observed a low molecular diversity, strong genetic structure and agreement between geography and gene genealogies. Along the French coasts, we observed the opposite: high genetic diversity and low genetic structure. Our results show that recurrent human-mediated introductions from several geographical areas in the native range may be a source for the French Atlantic populations. However, despite the low dispersal ability of C. neritea, the isolation-by-distance pattern in France suggested that this gastropod may have been present (although unnoticed) on the French Atlantic coasts before the 1970s. As C. neritea shows characteristics of a cryptogenic species, the classification of Atlantic populations as either native or introduced is not straightforward. Cryptogenic species should be studied further to determine the status of new populations close to their recognized native range.
•Biomarkers displayed high variation across eight populations living in dissimilar sites.•Biomarkers, proteome and shell size were able to discriminate between populations.•Proteome and shell size ...were under both genes and environment influence.•Biomarkers (IBR index) were rather under environmental influence.•The use of biomarkers implies to properly understand population responsiveness.
In order to provide reliable information about responsiveness of biomarkers during environmental monitoring, there is a need to improve the understanding of inter-population differences. The present study focused on eight populations of zebra mussels and aimed to describe how variable are biomarkers in different sampling locations. Biomarkers were investigated and summarised through the Integrated Biomarker Response (IBR index). Inter-site differences in IBR index were analysed through comparisons with morphological data, proteomic profiles and genetic background of the studied populations. We found that the IBR index was a good tool to inform about the status of sites. It revealed higher stress in more polluted sites than in cleaner ones. It was neither correlated to proteomic profiles nor to genetic background, suggesting a stronger influence of environment than genes. Meanwhile, morphological traits were related to both environment and genetic background influence. Together these results attest the benefit of using biological tools to better illustrate the status of a population and highlight the need of consider inter-population difference in their baselines.
Question: Do contrasting biotic contexts in nutrient-poor grasslands affect the predictability of invasion by exploitative species following fertilization? Location: French Alps. Methods: We examined ...community responses after 2 years of nutrient addition for two nutrient-poor European calcareous grasslands, a mesoxeric community dominated by the short bunchgrass Bromus erectus and a mesic community dominated by the tall rhizomatous grass Brachypodium rupestre. We also performed reciprocal transplantations of these two dominant slow-growing species and Arrhenatherum elatius, a tall fast-growing grass that dominates nutrient-rich communities and is likely to invade nutrientpoor communities after fertilization. Transplants were grown with or without neighbors, in order to measure their individual responses (without neighbors) and competition intensity (by comparing performances with and without neighbors using the Relative Neighbor Effect index-RNE) during one growing season in all three communities. Results: In the Bromus community, fertilization induced a strong increase in fast-growing grasses (including A. elatius). Competition intensity was low for the three transplanted grasses, but strongly increased with resource addition, to reach values observed in the Arrhenatherum community. In the Brachypodium community, no change in competition intensity with fertilization was detected, because of the high mortality of the two "non-resident" species, irrespective of the presence of neighbors. Conclusions: Community responses to nutrient improvement are context-dependent and vary as a function of the biotic environment. Soil processes are proposed as the main drivers of community resistance to the invasion of fastgrowing species in the mesic, nutrient-poor grassland dominated by the large conservative competitor B. rupestre.
Hybrid zones are fascinating systems to investigate the structure of genetic barriers. Marine hybrid zones deserve more investigation because of the generally high dispersion potential of planktonic ...larvae which allows migration on scales unrivalled by terrestrial species. Here we analyse the genetic structure of the mosaic hybrid zone between the marine mussels Mytilus edulis and M. galloprovincialis, using three length‐polymorphic PCR loci as neutral and diagnostic markers on 32 samples along the Atlantic coast of Europe. Instead of a single genetic gradient from M. galloprovincialis on the Iberian Peninsula to M. edulis populations in the North Sea, three successive transitions were observed in France. From South to North, the frequency of alleles typical of M. galloprovincialis first decreases in the southern Bay of Biscay, remains low in Charente, then increases in South Brittany, remains high in most of Brittany, and finally decreases again in South Normandy. The two enclosed patches observed in the midst of the mosaic hybrid zone in Charente and Brittany, although predominantly M. edulis‐like and M. galloprovincialis‐like, respectively, are genetically original in two respects. First, considering only the various alleles typical of one species, the patches show differentiated frequencies compared to the reference external populations. Second, each patch is partly introgressed by alleles of the other species. When introgression is taken into account, linkage disequilibria appear close to their maximum possible values, indicating a strong genetic barrier within all transition zones. Some pre‐ or postzygotic isolation mechanisms (habitat specialization, spawning asynchrony, assortative fertilization and hybrid depression) have been documented in previous studies, although their relative importance remains to be evaluated. We also provided evidence for a recent migratory ‘short‐cut’ connecting M. edulis‐like populations of the Charente patch to an external M. edulis population in Normandy and thought to reflect artificial transfer of spat for aquaculture.
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