Bryozoa connectivity along the Atlantic-Mediterranean region

Knowledge about the species diversity, their distribution and their genetic variation is fundamental to address species conservation and management strategies. During this project we will focus in the European Atlantic-Mediterranean coast to give answer to different questions about these topics. This region could be considered one of the most studied areas in the world but still with big gaps in the knowledge of the process that affect to the species distribution and their genetic variability, particularly to sessile invertebrates with low dispersal capacity. These invertebrates are very important in the formation of different habitats. In the particular case of the Mediterranean, besides, it is considered one of the most diverse seas on the Earth in terms of animal and plant diversity; but in turn it is severely threatened by anthropogenic activities (pollution, species extraction, habitat degradation, lost and altered native diversity, etc.). To try understand the process that affect to the distribution and the genetic variability of sessile invertebrates and the relation of this diversity and variability between them and with abiotic components of the habitats, in this project the use of the bryozoans as a model organism is proposed. Bryozoans are colonial, filter-feeding animals that live attached to hard or ephemeral substrates, or are rooted within loose sediment. They are most abundant and speciose between the subtidal and the shelf edge, occasionally forming rigid 3D-structures that provide habitats for a wide range of other organisms. Around 600 species of bryozoans are currently known from the European Atlantic- Mediterranean region that which corresponds to around 10% of the overall bryozoan fauna known to date: 6000 bryozoans species. The larva has a very short life with a very limited dispersal capacity (centimetres to few kilometres). Thus, analysing the geographic distribution and genetic variability of bryozoans at the species level will provide spatial patterns with a high resolution, which allow tracing flow regimes of currents as well as evolutionary histories. Three main objectives are proposed in the project: 1) to investigate the distribution of the genetic diversity and assess population differentiation and connectivity of several species of bryozoans; 2) to evaluate the patterns of bryozoan diversity in order to compare them with the genetic diversity and abiotic data; 3) to investigate species- genetic diversity correlation, adopting a multi-species approach to provide a broad view on community assembly processes. To collect the necessary data, sampling campaigns will be organized along the study area, using mainly diving techniques to collect specimens of bryozoans and to characterize the communities, habitat types and substrate. Data will be analyzed from a biogeographic point of view to detected patterns of distribution. And new generation methods will be used to study the genetic diversity.

A total of 31 localities were sampled along the European Mediterranean and Atlantic coasts, comprising 66 dives primarily focused on coralligenous habitats (biodiversity-rich, reef-like systems formed by marine organisms). The analysis of the collected material, together with the revision of specimens from major European museum collections (including NHM London, MNHN Paris, and NHM Denmark), has so far led to the description of 13 new bryozoan species (colonial marine invertebrates), as well as the establishment of a new genus. In addition, three non-indigenous species have been recorded for the first time in European waters. The project has also improved our understanding of species distributions and biogeographic patterns, mainly by extending known latitudinal ranges. Next-generation sequencing techniques (modern DNA analysis methods) have been applied for the first time to study the genetic structure of bryozoan populations, including the implementation of the MobiSeq protocol in this group. Samples from 13 populations, ranging from the Adriatic Sea to the Bay of Biscay, are currently being analyzed. Three species with continuous distributions across the study area were selected: Myriapora truncata, Smittina cervicornis, and Schizomavella mamillata. Despite several technical challenges-mainly related to DNA sequencing and primer development, and linked to the innovative nature of the project and the lack of prior data-relevant preliminary results have been obtained. These results reveal patterns that differ from those typically observed in other marine animals, where genetic variation is often shaped by geographic barriers. In bryozoans, these barriers seem to play a weaker role. For example, the Strait of Gibraltar does not appear to significantly limit gene flow (exchange of genetic material) in Myriapora truncata. In contrast, the Almeria-Oran Front and the Strait of Otranto seem to have a stronger influence on genetic differences between populations. In Smittina cervicornis, the genetic differences observed among populations from the Adriatic Sea, the western Mediterranean, and the Bay of Biscay suggest the possible existence of three distinct cryptic species (species that are genetically different but look very similar), although these findings are still being evaluated. Overall, this work significantly advances our understanding of bryozoan diversity, distribution, and connectivity in European seas. Because bryozoans play a key role as habitat-forming organisms in coralligenous assemblages, these results also help us better understand how these important and highly diverse marine habitats are distributed and how resilient they may be to environmental change, with direct relevance for biodiversity conservation.