The role of symbiont variation in the photobiology of reef corals was addressed by investigating the links among symbiont genetic diversity, function and ecological distribution in a single host species, Madracis pharensis. Symbiont distribution was studied for two depths (10 and 25 m), two diVerent light habitats (exposed and shaded) and three host colour morphs (brown, purple and green). Two Symbiodinium genotypes were present, as deWned by nuclear internal transcribed spacer 2 ribosomal DNA (ITS2-rDNA) variation. Symbiont distribution was depthand colour morph-dependent. Type B15 occurred predominantly on the deeper reef and in green and purple colonies, while type B7 was present in shallow environments and brown colonies. DiVerent light microhabitats at Wxed depths had no eVect on symbiont presence. This ecological distribution suggests that symbiont presence is potentially driven by light spectral niches. A reciprocal depth transplantation experiment indicated steady symbiont populations under environment change. Functional parameters such as pigment composition, chlorophyll a Xuorescence and cell densities were measured for 25 m and included in multivariate analyses. Most functional variation was explained by two photobiological assemblages that relate to either symbiont identity or light microhabitat, suggesting adaptation and acclimation, respectively. Type B15 occurs with lower cell densities and larger sizes, higher cellular pigment concentrations and higher peridinin to chlorophyll a ratio than type B7. Type B7 relates to a larger xanthophyll-pool size. These unambiguous diVerences between symbionts can explain their distributional patterns, with type B15 being potentially more adapted to darker or deeper environments than B7. Symbiont cell size may play a central role in the adaptation of coral holobionts to the deeper reef. The existence of functional diVerences between B-types shows that the clade classiWcation does not necessarily correspond to functional identity. This study supports the use of ITS2 as an ecological and functionally meaningful marker in Symbiodinium.

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The concept of a stock of fish as a management unit has been around for well over a hundred years, and this has formed the basis for the fisheries science. Methods for delimiting stocks have advanced considerably over recent years, using including genetic, tagging and phenotypic information. In parallel with these developments, concepts in population ecology such as meta-population dynamics and connectivity have advanced. The pragmatic view of stocks has always accepted some mixing during spawning, feeding and or larval drift. Here we consider the mismatch between ecological connectivity of a matrix of populations typically focussed on demographic measurements, and genetic connectivity of populations that focus on genetic exchange detected using modern molecular approaches. We suggest that from an ecological-connectivity perspective populations can delimited as management units if there limited exchange during recruitment or via migration in most years. However from a genetic-connectivity perspective such limited exchange can maintain panmixia. We use case-studies of species endangered by overexploitation and/or habitat degradation to show how current methods of stock delimitation can help in managing populations and in conservation.

a b s t r a c tThe Potomida genus (Bivalvia, Unionida) has a Circum-Mediterranean distribution and like other freshwater mussel species, its populations have suffered dramatic declines. Although this genus is currently considered as monotypic, it has a long history of taxonomic revisions and presently many aspects of its systematics and evolutionary history are unclear. We sampled a total of 323 individuals from 39 different sites across the Potomida genus distribution, and sequenced two mitochondrial (16S rDNA and Cytochrome c Oxidase Subunit I) and one nuclear (28S rDNA) genes to clarify its phylogeny and phylogeographic history. Our results show that the genus includes two well-supported clades, one comprising solely the western Mediterranean species Potomida littoralis, and the other including two eastern Mediterranean species, the Greek endemic P. acarnanica and the Anatolian and Middle Eastern P. semirugata. We suggest that Potomida started radiating during the upper Miocene, and that both vicariance and dispersal events shaped the diversification and distribution of the genus along the Mediterranean region. P. littoralis is further divided in two mitochondrial lineages, one restricted to Europe and the other occurring mostly in North Africa. Moreover, some European basins present both lineages in sympatry. The conservation status of the three recognized species should be reevaluated, particularly P. acarnanica, since it is restricted to two Greek river basins presenting a high risk of extinction. Overall, our results clarify some important gaps in knowledge concerning the phylogeny, phylogeography and evolution of the Potomida genus in the Mediterranean region with important taxonomical, ecological and conservational implications.

The uptake of natural living resources for human consumption has triggered serious changes in the balance of ecosystems. In the archipelagos of Macaronesia (NE Atlantic), limpets have been extensively exploited probably since islands were first colonized. This has led to profound consequences in the dynamics of rocky shore communities. The Patella candei complex includes various subspecies of limpets that are ascribed to a particular archipelago and has been the focus of several taxonomic surveys without much agreement. Under a conservational perspective, we apply morphometric and genetic analyses to test subspecies boundaries in P. candei and to evaluate its current population connectivity throughout Macaronesia (Azores, Madeira, and Canaries). A highly significant genetic break between archipelagos following isolation by distance was detected (F ST = 0.369, p < .001). Contrastingly, significant genetic differentiation among islands (i.e., Azores) was absent possibly indicating ongoing gene flow via larval exchange between populations. Significant shell‐shape differences among archipelagos were also detected using both distance‐based and geometric morphometric analyses. Adaptive processes associated with niche differentiation and strong barriers to gene flow among archipelagos may be the mechanisms underlying P. candei diversification in Macaronesia. Under the very probable assumption that populations of P. candei from each archipelago are geographically and/or ecologically isolated populations, the various subspecies within the P. candei complex may be best thought of as true species using the denomination: P. candei in Selvagens, Patella gomesii in Azores, Patella ordinaria in Madeira, and Patella crenata for Canaries. This would be in agreement with stock delimitation and units of conservation of P. candei sensu latu along Macaronesia.

1. Remote sensing is a powerful monitoring tool for seaweeds, providing large-scale insights into their ecosystem benefits and invasive impacts. Satellites and manned aircraft have been widely used for this purpose, but their spatial resolution is generally insufficient to map heterogeneous seaweed habitats. 2. In this study, the potential of low-cost and high-resolution drone imagery to map heterogeneous seaweed habitats was assessed on Azorean coasts, where an invasive and commercial species, Asparagopsis armata, is present. A Phantom Pro 3 drone equipped with a visible light sensor was used to create photomosaics in three sites on São Miguel island, and ground-truth data for various seaweed groups were collected with exploratory kayak sampling. The support-vector machine, random forest and artificial neural network algorithms were used to construct predictive models of seaweed coverage. 3. Wind, clouds and sun glint were the most significant factors affecting drone surveys and images. Exploratory sampling helped locate relatively homogeneous seaweed patches, however, the data were limited and spatially autocorrelated contributing to over-optimistic model evaluation metrics. Moreover, the models struggled to distinguish seaweeds deeper than three to four metres. 4. In conclusion, using drones to monitor heterogeneous seaweed habitats is challenging, especially in oceanic islands where waters are deep and weather is unpredictable. However, this study highlights the potential use of photo-interpretation to collect modelling data from drone imagery, instead of time-consuming exploratory ground-truth sampling. Future studies could assess drones to map seaweeds in less challenging conditions and use photointerpretation to improve collection of modelling data.

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The present study reports the recent occurrence and expansion of Rugulopteryx okamurae in the Azores archipelago (NE Atlantic). Morphological and molecular characters confirmed the species identification. Quick surveys around the island of São Miguel showed that it has successfully colonized the island and is quickly expanding. In some locations, R. okamurae is currently the dominant organism smothering all other benthic biota and posing a serious threat to the benthic ecosystems across the region. The species first record dates from 2019 near the main harbour of the island, suggesting that its introduction was driven by human-assisted transport, via boat ballast waters or adhered to ship hulls and likely originating from the Mediterranean populations that have been proliferating in recent years across the Strait of Gibraltar.