Aim  A central question in evolutionary ecology is the nature of environmental barriers that can limit gene flow and induce population genetic divergence, a first step towards speciation. Here we study the geographical barrier constituted by the transition zone between the Atlantic Ocean and the Mediterranean Sea, using as our model Cymodocea nodosa, a seagrass distributed throughout the Mediterranean and in the Atlantic, from central Portugal to Mauritania. We also test predictions about the genetic footprints of Pleistocene glaciations.Location  The Atlantic–Mediterranean transition region and adjacent areas in the Atlantic (Mauritania to south‐west Portugal) and the Mediterranean.Methods  We used eight microsatellite markers to compare 20 seagrass meadows in the Atlantic and 27 meadows in the Mediterranean, focusing on the transition between these basins.Results  Populations from these two regions form coherent groups containing several unique, high‐frequency alleles for the Atlantic and for the Mediterranean, with some admixture west of the Almeria–Oran Front (Portugal, south‐west Spain and Morocco). These are populations where only one or a few genotypes were found, for all but Cadiz, but remarkably still show the footprint of a contact zone. This extremely low genotypic richness at the Atlantic northern edge contrasts with the high values (low clonality) at the Atlantic southern edge and in most of the Mediterranean. The most divergent populations are those at the higher temperature range limits: the southernmost Atlantic populations and the easternmost Mediterranean, both potential footprints of vicariance.Main conclusions  A biogeographical transition region occurs close to the Almeria–Oran front. A secondary contact zone in Atlantic Iberia and Morocco results from two distinct dispersal sources: the Mediterranean and southernmost Atlantic populations, possibly during warmer interglacial or post‐glacial periods. The presence of high‐frequency diagnostic alleles in present‐day disjunct populations from the southernmost Atlantic region indicates that their separation from all remaining populations is ancient, and suggests an old, stable rear edge.

Sharing experiences and results among scientists and managers working on seagrass restoration was the main objective of the first European Seagrass Restoration Workshop that gathered researchers from around Europe. The meeting was the first forum in Europe that allowed for scientists, NGOs, and managers to interact and share their experiences relating to seagrass restoration and management. The results show that none of the seagrass restoration programs developed in Europe by the participants during the last 10 years was successful. Furthermore, an informal review of data published in seagrass restoration success, showed that the results reported were biased because they were mostly based on a very short monitoring period (i.e. <1 year). Numerous decision trees, guidelines, and restoration models have been developed to aid seagrass restoration management, but the results of this workshop point toward a new paradigm in seagrass restoration were efforts should shift to give priority to natural restoration potential, with an emphasis on the fact that restoration should never be considered the first alternative when planning for the mitigation of coastal development projects or to justify mitigation as a compensation measure for economic activities.

1. Seagrasses constitute a key coastal habitat world-wide, but are exposed to multiple perturbations. Understanding elements affecting seagrass resistance to disturbances is critical for conservation. Distinct biogeographical scenarios are intrinsically linked with varying ecological and evolution backgrounds shaped across millennia.2. We addressed whether the resistance (change in shoot abundances) and performance (change in leaf morphology and growth) of the seagrass Cymodocea nodosa to a local stressor, light reduction, varied across three regions (Southeast Iberia, the Balearic Sea, and the Canaries) within the temperate northern Atlantic realm.We hypothesized that distinct biogeographical scenarios, in terms of distinct ecological/environmental conditions and genetic diversity of meadows, would affect seagrass resistance and performance, with flow-on effects on associated epifauna. The same experiments, in terms of shading intensities, timing and duration, were replicated at three seagrass meadows within each region.3. Results demonstrated inter-regional variation in the resistance and performance of C. nodosa. Under moderate and high shading, shoot abundance was abruptly decreased, relative to controls, in the Canaries with concurrent, but less accentuated, changes in leaf morphology and no changes in growth. In the other two regions, however, moderate and high shading had a negligible effect on shoot abundance, leaf morphology, and growth. Shading had no overall effect over the total abundance and assemblage structure of epifauna; these faunal attributes, however, varied between regions. Low seagrass resistance at the Canaries is linked with the peripheral distribution of the species there, favouring isolation and decreased genetic diversity.

Growth and reproductive cycle of the prawn, Palaemon adspersus were studied in Fornells Bay from April 2002 to March 2003. Samples caught using a lift net showed that abundance is markedly seasonal, with peaks in autumn and winter. P. adspersus showed distinct sexual dimorphism, the females being larger than the males. The K coefficient of the VBGF (Von Bertalanffy Growth Formula) was higher in the females (2.065 year −1 for females and 1.076 year −1 for males) and the same applies to L ∞ coefficient of the VBGF (47.8 mm in females and 34.14 mm in males). Ovigerous females were found from March to August. However, the low percentage of ovigerous females found in the study area suggests that reproduction and incubation do not occur at the study site. Also, as the ovary shows activity during the whole year cycle, it is not possible to distinguish a discrete reproductive period. RESUMENEl crecimiento y el ciclo reproductor de Palaemon adspersus fueron estudiados en la bahía de Fornells entre Abril de 2002 y Marzo de 2003. Las muestras obtenidas con una red por elevación indican una marcada variación estacional, con mayores abundancias en otoño e invierno. P. adspersus presenta dimorfismo sexual, siendo de mayor talla las hembras. Los parámetros de crecimiento calculados fueron superiores en hembras. El valor del coeficiente K de la VBGF (Fórmula de crecimiento de Von Bertalanffy fue 2.065 año −1 para las hembras y 1.076 año −1 para los machos. En el caso de L ∞ , fueron 47.8 mm en hembras y 34.14 mm en machos. Se han encontrado hembras ovígeras entre Marzo y Agosto. En cualquier caso, el bajo porcentaje de hembras ovígeras encontradas sugiere que la reproducción e incubación no se desarrollan en el área de estudio. Esto unido a que la actividad del ovario se mantiene durante todo el año no permite discernir un periodo reproductor claro.

Genetic diversity in clonal organisms includes two distinct components, (i) the diversity of genotypes or clones (i.e. genotypic richness) in a population and (ii) that of the alleles (i.e. allelic and gene diversity within populations, and differentiation between populations). We investigated how population differentiation and genotypic components are associated across a gradient of eutrophication in a clonal marine plant. To that end, we combined direct measurements of sexual allocation (i.e. flower and seed counts) and genotypic analyses, which are used as an estimator of effective sexual reproduction across multiple generations. Genetic differentiation across sites was also modelled according to a hypothesis here defined as isolation-by-demography, in which we use population-specific factors, genotypic richness and eutrophication that are hypothesized to affect the source-sink dynamics and thus influence the genetic differentiation between a pair of populations. Eutrophic populations exhibited lower genotypic richness, in agreement with lower direct measurements of sexual allocation and contemporaneous gene flow. Genetic differentiation, while not explained by distance, was best predicted by genotypic richness and habitat quality. A multiple regression model using these two predictors was considered the best model (R(2) = 0.43). In this study, the relationship between environment and effective sexual-asexual balance is not simply (linearly) predicted by direct measurements of sexual allocation. Our results indicate that population-specific factors and the isolation-by-demography model should be used more often to understand genetic differentiation.