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Currents are unique drivers of oceanic phylogeography and so determine the distribution of marine coastal species, along with past glaciations and sea level changes. Here, we reconstruct the worldwide colonization history of eelgrass (Zostera marinaL.), the most widely distributed marine flowering plant or seagrass from its origin in the Northwest Pacific, based on nuclear and chloroplast genomes. We identified two divergent Pacific clades with evidence for admixture along the East Pacific coast. Multiple west to east (trans-Pacific) colonization events support the key role of the North Pacific Current. Time-calibrated nuclear and chloroplast phylogenies yielded concordant estimates of the arrival ofZ. marinain the Atlantic through the Canadian Arctic, suggesting that eelgrass-based ecosystems, hotspots of biodiversity and carbon sequestration, have only been present since ∼208 Kya (thousand years ago). Mediterranean populations were founded ∼53 Kya while extant distributions along western and eastern Atlantic shores coincide with the end of the Last Glacial Maximum (∼20 Kya). The recent colonization and 5-to 7-fold lower genomic diversity of Atlantic compared to the Pacific populations raises concern and opportunity about how Atlantic eelgrass might respond to rapidly warming coastal oceans.

Marine underwater habitats dominated by seagrass Posidonia oceanica play an essential role in fish community assembly, affecting taxonomic and functional diversity, abundance and fish behavior. The value of seagrasses as habitat depends on the spatial arrangement of the seascape elements and the availability of alternative habitats. Little is known about the effect of the seascape context of P. oceanica meadows on fish assemblages in the Mediterranean Sea. To identify P. oceanica meadows' relative importance as a habitat for fishes, fish communities in the Croatian Adriatic Sea were investigated, using SCUBA lure-assisted visual census. The results show a significant effect of different arrangements of P. oceanica meadows' seascape elements and surrounding habitats on fish community structure. Fragmented mosaic meadows with P. oceanica growing directly on and between rocky-algal reefs/boulders had significantly higher fish abundances compared to both types of continuous meadows (bordering rock and bordering sand). Continuous meadows bordering sand harbored the highest number of unique species. Evidence that alternative structured habitats within proximity to seagrass beds may affect the community structure of associated fish assemblages is provided, highlighting the need to consider P. oceanica meadows' seascape context in conservation management and experimental design for fish community structure., Naselja morske cvjetnice Posidonia oceanica igraju važnu ulogu u strukturiranju zajednica riba te utječu na taksonomsku i funkcionalnu raznolikost, brojnost i ponašanje riba. Relativna vrijednost naselja morskih cvjetnica ovisi o prostornoj organizaciji elementa podmorskog okoliša te dostupnosti alternativnih staništa. Međutim, nedovoljno je poznato koji sve čimbenici utječu na strukturu zajednice riba povezanih s ovom morskom cvjetnicom. S ciljem utvrđivanja utjecaja različite prostorne organizacije elementa podmorskog okoliša na zajednice riba, proveden je vizualni cenzus uz pomoć mamca u naseljima cvjetnice P. oceanica u hrvatskom dijelu Jadranskog mora. Utvrđen je značajan utjecaj različite prostorne organizacije elementa podmorskog okoliša na strukturu zajednice riba – u rascjepkanim mozaičnim naseljima u kojima se P. oceanica isprepliće s kamenom podlogom obraslom makro-algama zabilježena je značajno veća brojnost riba u odnosu na kontinuirana cjelovita naselja (uz sediment ili uz kamenitu obalu). U radu su predstavljeni dokazi da dostupnost alternativnih strukturiranih staništa u neposrednoj blizini naselja morske cvjetnice P. oceanica utječe na strukturu zajednice riba koje u njoj žive. Neophodno je uzeti u obzir kontekst prostornog rasporeda elemenata podmorskog okoliša kojima dominira morska cvjetnica P. oceanica prilikom planiranja znanstvenih istraživanja, ali i kod upravljanja priobalnim područjima.

Distribution of Earth's biomes is structured by the match between climate and plant traits, which in turn shape associated communities and ecosystem processes and services. However, that climate-trait match can be disrupted by historical events, with lasting ecosystem impacts. As Earth's environment changes faster than at any time in human history, critical questions are whether and how organismal traits and ecosystems can adjust to altered conditions. We quantified the relative importance of current environmental forcing versus evolutionary history in shaping the growth form (stature and biomass) and associated community of eelgrass (Zostera marina), a widespread foundation plant of marine ecosystems along Northern Hemisphere coastlines, which experienced major shifts in distribution and genetic composition during the Pleistocene. We found that eelgrass stature and biomass retain a legacy of the Pleistocene colonization of the Atlantic from the ancestral Pacific range and of more recent within-basin bottlenecks and genetic differentiation. This evolutionary legacy in turn influences the biomass of associated algae and invertebrates that fuel coastal food webs, with effects comparable to or stronger than effects of current environmental forcing. Such historical lags in phenotypic acclimatization may constrain ecosystem adjustments to rapid anthropogenic climate change, thus altering predictions about the future functioning of ecosystems., This work was supported by the US NSF (OCE-1031061, OCE-1336206, OCE0-1336741, OCE-1336905) and the Smithsonian Institution. F.T. was supported by José Castillejo Award CAS14/00177. A.H.E. was supported by the FCT (Foundation for Science and Technology) through Project UIDB/04326/2020 and Contract CEECINST/00114/2018. This is Contribution 106 from the Smithsonian’s MarineGEO and Tennenbaum Marine Observatories Network and Contribution 4105 of the Virginia Institute of Marine Science, College of William & Mary.

While considerable evidence exists of biogeographic patterns in the intensity of species interactions, the influence of these patterns on variation in community structure is less clear. Studying how the distributions of traits in communities vary along global gradients can inform how variation in interactions and other factors contribute to the process of community assembly. Using a model selection approach on measures of trait dispersion in crustaceans associated with eelgrass (Zostera marina) spanning 30° of latitude in two oceans, we found that dispersion strongly increased with increasing predation and decreasing latitude. Ocean and epiphyte load appeared as secondary predictors; Pacific communities were more overdispersed while Atlantic communities were more clustered, and increasing epiphytes were associated with increased clustering. By examining how species interactions and environmental filters influence community structure across biogeographic regions, we demonstrate how both latitudinal variation in species interactions and historical contingency shape these responses. Community trait distributions have implications for ecosystem stability and functioning, and integrating large-scale observations of environmental filters, species interactions and traits can help us predict how communities may respond to environmental change., This research was funded by National Science Foundation grants to J.E.D., J.J.S. and K.A.H. (NSF-OCE 1336206, OCE 1336905, and OCE 1336741). C.B. was funded by the Åbo Akademi University Foundation.

We investigated the formation of Artemia franciscana swarms of freshly hatched instar I nauplii larvae. Nauplii were released into light gradients but then interrupted by light-direction changes, small obstacles, or long barriers. All experiments were carried out horizontally. Each experiment used independent replicates. Freshly produced Artemia broods were harvested from independent incubators thus providing true replicate cohorts of Artemia subjected as replicates to the experimental treatments. We discovered that Artemia nauplii swarms can: 1. repeatedly react to non-obstructed light gradients that undergo repeated direction-changes and do so in a consistent way, 2. find their way to a light source within maze-like arrangements made from small transparent obstacles, 3. move as a swarm around extended transparent barriers, following a light gradient. This paper focuses on the recognition of whole-swarm behaviors, the description thereof and the recognition of differences in whole-swarm movements comparing non-obstructed swarming with swarms encountering obstacles. Investigations of the within-swarm behaviors of individual Artemia nauplii and their interactions with neighboring nauplii are in progress, e.g. in order to discover the underlying swarming algorithms and differences thereof comparing non-obstructed vs. obstructed pathways.

The paper presents a database of information on wrecks, natural and artificial reefs located in the Adriatic Sea, collected within the framework of the Interreg Italy-Croatia project ADRIREEF – Innovative exploitation of Adriatic Reefs in order to strengthen Blue Economy. The data collection lasted more than one year and comprehended three surveys and a wide literature review. After being collected, data were harmonized and, where possible, made machine-readable. Moreover, data were widely metadated, published in a webGIS (https://adrireef.github.io/sandbox3/) and shared as Open Data in EMODnet (European Marine Observation Data network) through the SEANOE repository (Ferrà et al., 2020; http://doi.org/10.17882/74880). The database is composed of 285 three-dimensional records, each one described by 51 attributes. Parameters are clustered in four main groups: identification, reef and site description, management/exploitation information. Available literature (scientific and/or grey) was also included in the database and linked to the corresponding site.

Human activities degrade and fragment coastal marine habitats, reducing their structural complexity and making habitat edges a prevalent seascape feature. Though habitat edges frequently are implicated in reduced faunal survival and biodiversity, results of experiments on edge effects have been inconsistent, calling for a mechanistic approach to the study of edges that explicitly includes indirect and interactive effects of habitat alteration at multiple scales across biogeographic gradients. We used an experimental network spanning 17 eelgrass (Zostera marina) sites across the Atlantic and Pacific oceans and the Mediterranean Sea to determine (1) if eelgrass edges consistently increase faunal predation risk, (2) whether edge effects on predation risk are altered by habitat degradation (shoot thinning), and (3) whether variation in the strength of edge effects among sites can be explained by biogeographical variability in covarying eelgrass habitat features. Contrary to expectations, at most sites, predation risk for tethered crustaceans (crabs or shrimps) was lower along patch edges than in patch interiors, regardless of the extent of habitat degradation. However, the extent to which edges reduced predation risk, compared to the patch interior, was correlated with the extent to which edges supported higher eelgrass structural complexity and prey biomass compared to patch interiors. This suggests an indirect component to edge effects in which the impact of edge proximity on predation risk is mediated by the effect of edges on other key biotic factors. Our results suggest that studies on edge effects should consider structural characteristics of patch edges, which may vary geographically, and multiple ways that humans degrade habitats., This research was funded by National Science Foundation grants to JED, JJS, and KAH (NSF-OCE 1336206, OCE 1336905, and OCE 1336741). CB was funded by the Åbo Akademi University Foundation.

20 pages, 9 figures, 5 tables, supplementary data https://doi.org/10.12681/mms.25306, The Mediterranean Sea has a long-lasting history of fishery exploitation that, together with other anthropogenic impacts, has led to declines in several marine organisms. In particular, elasmobranch populations have been severely impacted, with drastic decreases in abundance and species diversity. Based on their experience, fishers can provide information on marine species occurrence, abundance and behavioural traits on a long-term scale, therefore contributing to research on the poorly studied biological aspects of elusive or rare elasmobranch species. In this study, for the first time, the use of the Local Ecological Knowledge (LEK) of fishers was applied to study the behavioural traits of sharks, rays and skates in 12 FAO-GFCM geographical sub-areas (GSAs) of the Mediterranean Sea. This study found both new insight and proved the reliability of LEK-based catch seasonality, reflecting seasonal movements, by comparing LEK-based findings and available literature on five elasmobranch taxa (Mustelus spp., Squalus acanthias, Raja spp., Myliobatis aquila and Scyliorhinus stellaris) in the Adriatic Sea and 7 taxa (Mustelus spp., Raja spp., Prionace glauca, Scyliorhinus canicula, Torpedo spp., Pteroplatytrygon violacea and Isurus oxyrinchus) in the remaining Mediterranean GSAs. In addition, LEK provided new insights into a novel comprehensive representation of species aggregations (Mustelus spp., S. acanthias, M. aquila and S. canicula) in the sampled GSAs and supplied the first descriptions of the size, number of individuals and sex composition of the aggregations. When the limits and shortcomings of LEK-based research are considered, this methodology can be a complementary and cost-effective tool used to study elasmobranchs in either a data-poor scenario or a scenario in which a baseline is missing. LEK can also be useful for the evaluation and inclusion of fishers’ perceptions on bottom-up management and to provide important evidence for conservation plans, This work was supported by funding of Ministero dell’Istruzione, dell’Università e della Ricerca (MIUR) to CM, With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S)

Este artículo contiene 7 páginas, 3 figuras, 1 tabla., The global distribution of primary production and consumption by humans (fisheries) is well-documented, but we have no map linking the central ecological process of consumption within food webs to temperature and other ecological drivers. Using standardized assays that span 105° of latitude on four continents, we show that rates of bait consumption by generalist predators in shallow marine ecosystems are tightly linked to both temperature and the composition of consumer assemblages. Unexpectedly, rates of consumption peaked at midlatitudes (25 to 35°) in both Northern and Southern Hemispheres across both seagrass and unvegetated sediment habitats. This pattern contrasts with terrestrial systems, where biotic interactions reportedly weaken away from the equator, but it parallels an emerging pattern of a subtropical peak in marine biodiversity. The higher consumption at midlatitudes was closely related to the type of consumers present, which explained rates of consumption better than consumer density, biomass, species diversity, or habitat. Indeed, the apparent effect of temperature on consumption was mostly driven by temperature-associated turnover in consumer community composition. Our findings reinforce the key influence of climate warming on altered species composition and highlight its implications for the functioning of Earth’s ecosystems., We acknowledge funding from the Smithsonian Institution and the Tula Foundation.

Underwater imaging enables marine researchers to collect large datasets of seagrass images. These images can be used to monitor the health state of underwater meadows by estimating the area that is covered by seagrass and how this area changes over time. Since the manual analysis of such images is slow and error-prone, we follow the path of deep learning for automatic image analysis.Our contribution is the investigation of deep semantic segmentation for the specific task of seagrass coverage estimation. We evaluated multiple Deep Neural Network Architectures including the DeepLabv3Plus Network which performs best, with a mean intersection over union of 87.78%. The qualitative results in our experiments indicate that the Deep Learning approach is not only more accurate than a human but also multiple times faster in annotating underwater meadows. Our code is available on GitHub: https://enviewfulda.github.io/LookingForSeagrassSemanticSegmentation/.

Posidonia oceanica meadows are thought to provide refuge for prey species, which suggests that fish communities are organized according to the abundance and behavior of predators. We collected published research on fish assemblages associated with P. oceanica meadows in the Mediterranean Sea and performed a meta- analysis to test hypotheses regarding the drivers of community structure. In 14 studies documenting the relative abundance of fish species, 112 taxa within a depth range of 1-40 m were reported at local P. oceanica meadows. Sampling method had the most significant effect on community abundance. Total predator abundance and abundance of resident predators each had a significant effect on the prey fish community. A higher abundance of resident predator species such as Scorpaena notata and Zosterisessor ophiocephalus was associated with a lower abundance of small Symphodus spp., Chromis chromis, and Gobiidae, and overall lower prey species richness. Fish communities in P. oceanica meadows are, therefore, in part organized in response to the presence and abundance of piscivorous species, which reduces the value of seagrass as a refuge habitat for potential prey species. For more robust estimates of the habitat value of P. oceanica, a concerted international, collaborative research effort that applies uniform, non- destructive sampling methods, such as visual census or stereo-videography within and outside meadows, is needed.

We evaluated (1) the suitability of two alternative methods for fish monitoring: trammel net sampling and BRUV (Baited Remote Underwater Video), and (2) the potential to cross-calibrate the methods based on a set of shared species with high catch probabilities. A statistical power analysis concluded that BRUV can be conducted with sufficient sample size to perceive small changes in fish populations with high power, and therefore can be used as a sentinel monitoring method. We found that fish species detected by both methods amounted to almost a third of the number of species in each method’s catch, and that 90% of these species are candidates for cross-calibration. 74% of the species at BRUV and 50% at trammel had occurrence probabilities above 10%, a reasonable threshold allowing stock assessment of these species. The sampled and predicted total species richness, extrapolated from the species accumulation curves, were almost identical across methods. We conclude that cross-calibrating the two methods and eventual replacement of the trammel method with non-destructive BRUV is feasible. The most effective areas of improvement are increased BRUV night-sampling effort and increased total sampling size to increase the statistical power of BRUV as a monitoring tool. This work has been supported under the Croatian Science Foundation under the project COREBIO (3107).

[Context]: Spatially heterogeneous oceanographic properties such as currents, waves, and biogeochemical gradients control the movement of gametes and larvae of marine species. However, it is poorly understood how such spatial dynamics may shape the genetic connectivity, diversity, and structure of marine populations., [Objectives]: We applied a seascape genetics framework to evaluate the relationships between marine environmental factors and gene flow among populations of the endangered Mediterranean pillow coral (Cladocora caespitosa). Methods: We modelled gene flow among locations in the Adriatic and northern Ionian Seas as a function of sea surface temperature, salinity, currents and geographic distance. Isolation by distance and isolation by resistance hypotheses were then compared using model optimization in a generalized linear mixed effects modelling framework., [Results]: Overall genetic differentiation among locations was relatively low (F = 0.028). We identified two genetic groups, with the northernmost location segregating from the rest of the locations, although some admixture was evident. Almost 25% of the individuals analysed were identified as putative migrants and a potential barrier to gene flow was identified between the northern and central-southern basins. The best gene flow models predicted that genetic connectivity in this species is primarily driven by the movement along the coastlines and sea surface currents. Conclusions: A high percentage of self-recruitment and relatively low migration rates has been detected in the studied populations of C. caespitosa. Its fragmented distribution along the coast can be predicted by stepping-stone oceanographic transport by coastal currents among suitable habitat patches., This research was funded by the European project CoCoNET ‘‘Towards COast to COastNETworks of marine protected areas (from the shore to the high and deep sea), coupled with sea-based wind energy potential’’ from the VII FP of the European Commission (Grant Agreement No. 287844) and the Spanish Ministry of Economy and Competitiveness (Grant reference: CTM2014-57949-R).

Este artículo contiene 9 páginas, 6 figuras, 1 tabla., Marine protected areas (MPAs) are key tools to mitigate human impacts in coastal environments, promoting sustainable activities to conserve biodiversity. The designation of MPAs alone may not result in the lessening of some human threats, which is highly dependent on management goals and the related specific regulations that are adopted. Here, we develop and operationalize a local threat assessment framework. We develop indices to quantify the effectiveness of MPAs (or individual zones within MPAs in the case of multiple-use MPAs) in reducing anthropogenic extractive and non-extractive threats operating at local scale, focusing specifically on threats that can be managed through MPAs. We apply this framework in 15 Mediterranean MPAs to assess their threat reduction capacity. We show that fully protected areas effectively eliminate extractive activities, whereas the intensity of artisanal and recreational fishing within partially protected areas, paradoxically, is higher than that found outside MPAs, questioning their ability at reaching conservation targets. In addition, both fully and partially protected areas attract non-extractive activities that are potential threats. Overall, only three of the 15 MPAs had lower intensities for the entire set of eight threats considered, in respect to adjacent control unprotected areas. Understanding the intensity and occurrence of human threats operating at the local scale inside and around MPAs is important for assessing MPAs effectiveness in achieving the goals they have been designed for, informing management strategies, and prioritizing specific actions., This work was financially supported by the ERA-Net BiodivERsA (BUFFER project, 092337) and the EU-FP7 (COCONET project, 287844) and contributes to DG MARE SafeNet project, Ares(2017)2510058.

Underwater videography enables marine researchers to collect enormous amounts of seagrass image data. This collection is fast and cheap but the manual analysis of such data is slow and expensive. Therefore, we propose a machine-learning approach for the automatic seagrass coverage estimation of the sea bottom. Our contribution is the investigation of CNN features to describe patches and superpixels of seagrass. CNN features are the activations of a specific layer in a deep convolutional neural network. We also provide the first public available dataset of seagrass images that can be used as a benchmark for automatic seagrass segmentation. Our best method achieves an accuracy of 94.5% for seagrass segmentation on the provided dataset. Our code and dataset is available on GitHub: https://enviewfulda.github.io/LookingForSeagrass/

Latitudinal gradients in species interactions are widely cited as potential causes or consequences of global patterns of biodiversity. However, mechanistic studies documenting changes in interactions across broad geographic ranges are limited. We surveyed predation intensity on common prey (live amphipods and gastropods) in communities of eelgrass (Zostera marina) at 48 sites across its Northern Hemisphere range, encompassing over 37 degrees of latitude and four continental coastlines. Predation on amphipods declined with latitude on all coasts but declined more strongly along western ocean margins where temperature gradients are steeper. Whereas insitu water temperature at the time of the experiments was uncorrelated with predation, mean annual temperature strongly positively predicted predation, suggesting a more complex mechanism than simply increased metabolic activity at the time of predation. This large-scale biogeographic pattern was modified by local habitat characteristics; predation declined with higher shoot density both among and within sites. Predation rates on gastropods, by contrast, were uniformly low and varied little among sites. The high replication and geographic extent of our study not only provides additional evidence to support biogeographic variation in predation intensity, but also insight into the mechanisms that relate temperature and biogeographic gradients in species interactions. NSF BIO-OCE [1336206, 1336741, 1336905] info:eu-repo/semantics/publishedVersion

Este artículo contiene 12 páginas, 5 figuras, 2 tablas., The assessment of the genetic structuring of biodiversity is crucial for management and conservation. For species with large effective population sizes a low number of markers may fail to identify population structure. A solution of this shortcoming can be high-throughput sequencing that allows genotyping thousands of markers on a genome-wide approach while facilitating the detection of genetic structuring shaped by selection. We used Genotyping-by-Sequencing (GBS) on 176 individuals of the endemic East Atlantic peacock wrasse (Symphodus tinca), from 6 locations in the Adriatic and Ionian seas. We obtained a total of 4,155 polymorphic SNPs and we observed two strong barriers to gene flow. The first one differentiated Tremiti Islands, in the northwest, from all the other locations while the second one separated east and south-west localities. Outlier SNPs potentially under positive selection and neutral SNPs both showed similar patterns of structuring, although finer scale differentiation was unveiled with outlier loci. Our results reflect the complexity of population genetic structure and demonstrate that both habitat fragmentation and positive selection are on play. This complexity should be considered in biodiversity assessments of different taxa, including non-model yet ecologically relevant organisms., Acknowledgements This work was supported by project CTM2013-48163 from Ministerio de Economía y Competitividad and by the European FP7 CoCoNet project (Ocean 2011-4, grant agreement #287844). CC, EM and MP are part of the research groups 2014SGR-1364, 2014SGR-120 and 2014SGR-336 of the Generalitat de Catalunya. CC was supported by a grant of the Beatriu de Pinós program of the Generalitat de Catalunya. LZ was supported by the University of Padua grant CPDA148387/14.

Connectivity between populations influences both their dynamics and the genetic structuring of species. In this study, we explored connectivity patterns of a marine species with long‐distance dispersal, the edible common sea urchin Paracentrotus lividus, focusing mainly on the Adriatic–Ionian basins (Central Mediterranean). We applied a multidisciplinary approach integrating population genomics, based on 1,122 single nucleotide polymorphisms (SNPs) obtained from 2b‐RAD in 275 samples, with Lagrangian simulations performed with a biophysical model of larval dispersal. We detected genetic homogeneity among eight population samples collected in the focal Adriatic–Ionian area, whereas weak but significant differentiation was found with respect to two samples from the Western Mediterranean (France and Tunisia). This result was not affected by the few putative outlier loci identified in our dataset. Lagrangian simulations found a significant potential for larval exchange among the eight Adriatic–Ionian locations, supporting the hypothesis of connectivity of P. lividus populations in this area. A peculiar pattern emerged from the comparison of our results with those obtained from published P. lividus cytochrome b (cytb) sequences, the latter revealing genetic differentiation in the same geographic area despite a smaller sample size and a lower power to detect differences. The comparison with studies conducted using nuclear markers on other species with similar pelagic larval durations in the same Adriatic–Ionian locations indicates species‐specific differences in genetic connectivity patterns and warns against generalizing single‐species results to the entire community of rocky shore habitats.

We report the first record of vertical rhizome growth in the temperate seagrass Zostera marina. In a population of Z. marina occurring on subtidal sand in the Novigrad Sea (Croatia), an area subject to episodic high sediment transport, collected plants of Z. marina showed vertical rhizomes with shorter and narrower inter-nodes (mean length = 3.4 ± 1.5 SD mm, mean width = 1.9 ± 0.3 SD mm) than those recorded for horizontal rhizomes (mean length = 9.0 ± 3.5 SD mm, mean width = 2.8 ± 0.4 SD mm). Out of a sample of 1130 rhizome fragments, 288 (25.5%) were vertical. Repeated moderate burial events may have stimulated the production of vertical rhizomes, and the ability of Z. marina to produce vertical rhizomes may enable it to withstand moderate burial in this highly dynamic environment.

International audience; Understanding the distribution of genetic diversity in the light of past demographic events linked with climatic shifts will help to forecast evolutionary trajectories of ecosystems within the current context of climate change. In this study, mitochondrial sequences and microsatellite loci were analysed using traditional population genetic approaches together with Bayesian dating and the more recent approximate Bayesian computation scenario testing. The genetic structure and demographic history of a commercial fish, the black scorpionfish, Scorpaena porcus, was investigated throughout the Mediterranean and Black Seas. The results suggest that the species recently underwent population expansions, in both seas, likely concomitant with the warming period following the Last Glacial Maximum, 20 000 years ago. A weak contemporaneous genetic differentiation was identified between the Black Sea and the Mediterranean Sea. However, the genetic diversity was similar for populations of the two seas, suggesting a high number of colonizers entered the Black Sea during the interglacial period and/or the presence of a refugial population in the Black Sea during the glacial period. Finally, within seas, an east/west genetic differentiation in the Adriatic seems to prevail, whereas the Black Sea does not show any structured spatial genetic pattern of its population. Overall, these results suggest that the Black Sea is not that isolated from the Mediterranean, and both seas revealed similar evolutionary patterns related to climate change and changes in sea level.

We derive statistical properties of standard methods for monitoring of habitat cover worldwide, and criticize them in the context of mandated seagrass monitoring programs, as exemplified by Posidonia oceanica in the Mediterranean Sea. We report the novel result that cartographic methods with non-trivial classification errors are generally incapable of reliably detecting habitat cover losses less than about 30 to 50%, and the field labor required to increase their precision can be orders of magnitude higher than that required to estimate habitat loss directly in a field campaign. We derive a universal utility threshold of classification error in habitat maps that represents the minimum habitat map accuracy above which direct methods are superior. Widespread government reliance on blind-sentinel methods for monitoring seafloor can obscure the gradual and currently ongoing losses of benthic resources until the time has long passed for meaningful management intervention. We find two classes of methods with very high statistical power for detecting small habitat cover losses: 1) fixed-plot direct methods, which are over 100 times as efficient as direct random-plot methods in a variable habitat mosaic ; and 2) remote methods with very low classification error such as geospatial underwater videography, which is an emerging, low-cost, non-destructive method for documenting small changes at millimeter visual resolution. General adoption of these methods and their further development will require a fundamental cultural change in conservation and management bodies towards the recognition and promotion of requirements of minimal statistical power and precision in the development of international goals for monitoring these valuable resources and the ecological services they provide.