Description: The north‐east Atlantic (NEA) is an important and complex biogeographic region with a very rich marine fauna. However, little is known about the role of the Macaronesian islands in the evolutionary history and diversification of marine invertebrates in the NEA. Among the amphipods, the members of the family Hyalidae are particularly common and abundant in intertidal rocky shores of NEA. In this study, we aimed to investigate the genetic structure and diversity of seven hyalid species inhabiting the Macaronesian, European and Moroccan Atlantic coasts, with a focus on the genetic differentiation between island and Continental populations. Analysis of mitochondrial DNA sequences of the cytochrome oxidase I gene, unravelled a very high level of hidden diversity, consisting of 26–32 molecular operational taxonomic units (MOTUs), the majority of them recorded in Macaronesian populations. Except for Apohyale stebbingi, all remaining MOTUs were in general allopatrically distributed, with a trend for segregation between islands and Continental populations on one side, but also for the occurrence of private MOTUs among islands. Results indicate distinct evolutionary and diversification patterns among Hyalidae species, but a strong separation between Continental and islands’ lineages appears to be a common feature to all of them. Apparently, the complex geomorphological history of the Macaronesian archipelagos served as an important promoter of extensive diversification of marine invertebrates in NEA, a phenomenon which only now starts to be fully appreciated through the use of molecular data.

Description: Diversification and speciation of terrestrial organisms are anticipated in oceanic islands such as Macaronesia, a group of Atlantic islands that have remained unconnected to continental landmasses. Hitherto, the diversification of marine organisms in oceanic islands, especially those with low vagility, has received little direct empirical analysis using molecular markers. Here, we focus on such a case study, through applying a multilocus molecular approach to investigate the diversity and evolution of a group that lacks a planktonic larval stage, the isopod genus Dynamene, in Macaronesia and Northeast Atlantic. Sequences of two mitochondrial (cytochrome c oxidase subunit I and 16S rRNA) and two nuclear (18S rRNA and 28S rRNA) loci were obtained from specimens of Dynamene edwardsi (Lucas, 1849), Dynamene magnitorata Holdich, 1968 and Dynamene bidentata (Adams, 1800) collected along the Northeast Atlantic and Macaronesia. Although no major phylogeographic structure was detected in D. bidentata and D. magnitorata, from five to nine deeply divergent lineages were evident within D. edwardsi. The divergent lineages displayed genetic distances comparable to those found among established species of peracarids. D. edwardsi exhibits a long, rich and complex phylogeographic history in Macaronesia, where the geodynamics of the islands possibly associated with founder effects and subsequent lack of gene flow among populations confounds patterns based on geographic proximity of targeted populations. Our findings collectively suggest a much larger role of oceanic islands in the diversification of marine invertebrates than previously anticipated. The work provides insights into the origins and dynamics of ongoing geographic segregation and associated deep divergence among sister evolutionary lineages in Macaronesia.

Description: The geographic distributions of some coastal marine species have appeared as cosmopolitan ever since they were first scientifically documented. In particular, for many benthic species that are associated with anthropogenic substrata, there is much speculation as to whether or not their broad distributions can be explained by natural mechanisms of dispersal. Here, we focused on two congeneric coastal crustaceans with cosmopolitan distributions—the tube-dwelling amphipods Jassa marmorata and Jassa slatteryi. Both species are common elements of marine biofouling on nearly all kinds of artificial hard substrata in temperate to warm seas. We hypothesized that the two species’ modern occurrences across the oceans are the result of human shipping activities that started centuries ago. Mitochondrial DNA sequences of the CO1 fragment of specimens from distinct marine regions around the world were analysed, evaluating genetic structure and migration models and making inferences on putative native ranges of the two Jassa species. Populations of both species exhibited considerable genetic diversity with differing levels of geographic structure. For both species, at least two dominant haplotypes were shared among several geographic populations. Rapid demographic expansion and high migration rates between geographically distant regions support a scenario of ongoing dispersal all over the world. Our findings indicate that the likely former native range of J. marmorata is the Northwest Atlantic, whereas the likely former native range of J. slatteryi is the Northern Pacific region. As corroborated by the genetic connectivity between populations, shipping still appears to be the more successful vector of the two species’ dispersal when compared to natural mechanisms. Historical invasion events that likely started centuries ago, along with current ongoing dispersal, confirm these species’ identities as true “neocosmopolitans”.

Description: The amphipod genus Jassa Leach, 1814 now comprises 24 species that occur in temperate regions of both hemispheres on solid substrates from the lower intertidal zone to 500 m depth. The propensity for some species to form dense colonies in water intake structures and offshore platforms has brought them to attention as an unwanted pest. Based on the examination of ~25,000 specimens from ~1,100 museum and private collections, it is evident that some species of Jassa have been transported by human vectors since at least the 19th century and now occur widely. Their colonial, tube-living habit enables such transport, and collection records document them on ships, buoys and portable water systems as well as on natural movable substrates such as logs, drift algae and larger crustaceans. Because Jassa can be so readily found, but species discrimination has had a problematic history, the purpose of this monograph is to assist researchers to identify species through illustrations, descriptions, keys and habitat summaries. Seven species which were named in the 19th century but whose names have lapsed are placed in the context of currently known species. Two new species, J. laurieae n. sp. and J. kimi n. sp. are described, and J. monodon (Heller, 1866) and J. valida (Dana, 1853) are resurrected. Jassa mendozai Winfield et al., 2021 is submerged under J. valida, and J. cadetta Krapp et al., 2008 and J. trinacriae Krapp et al., 2010 are submerged under J. slatteryi Conlan, 1990. Morphological differences are related to current understanding of growth, behaviour and ecology. CO1 analysis suggests a Southern Hemisphere origin with diversification northward and an evolutionary direction toward greater physiological plasticity, leading to success in long distance transport and establishment in exotic locations. Correct identification of Jassa world-wide will facilitate further research on this ecologically important genus and will allow for differentiation of indigenous from exotic introductions.

Description: Epibiotic associations can result in co-introductions of non-indigenous species, which may affect ecosystems in several ways. In fouling communities of three estuaries in southern Brazil, a number of amphipods was found to harbour a dense coverage of epibionts. Three different species, the two globally widespread caprellids Caprella equilibra and Paracaprella pusilla, as well as the ischyrocerid Jassa valida, had been colonised by diatoms. Further scanning electron microscope analyses assigned these diatoms to 14 different species that had previously been reported from benthic habitats. This is one of the scarce records of diatoms attached to amphipods. The occurrence of the diatom Amphora helenensis represents the first report for Brazilian waters as well as the second record for the whole SW Atlantic Ocean. As some diatoms were associated with common fouling amphipods, a possible regional spread aided by these crustaceans seems likely. Possible effects of this amphipod-diatom association on the animals and their implications for the underlying ecosystems of this remain to be elucidated.

Description: Microbial composition and diversity in marine sediments are shaped by environmental, biological, and anthropogenic processes operating at different scales. However, our understanding of benthic microbial biogeography remains limited. Here, we used 16S rDNA amplicon sequencing to characterize benthic microbiota in the North Sea from the top centimeter of 339 sediment samples. We utilized spatially explicit statistical models, to disentangle the effects of the different predictors, including bottom trawling intensity, a prevalent industrial fishing practice which heavily impacts benthic ecosystems. Fitted models demonstrate how the geographic interplay of different environmental and anthropogenic drivers shapes the diversity, structure and potential metabolism of benthic microbial communities. Sediment properties were the primary determinants, with diversity increasing with sediment permeability but also with mud content, highlighting different underlying processes. Additionally, diversity and structure varied with total organic matter content, temperature, bottom shear stress and bottom trawling. Changes in diversity associated with bottom trawling intensity were accompanied by shifts in predicted energy metabolism. Specifically, with increasing trawling intensity, we observed a transition toward more aerobic heterotrophic and less denitrifying predicted metabolism. Our findings provide first insights into benthic microbial biogeographic patterns on a large spatial scale and illustrate how anthropogenic activity such as bottom trawling may influence the distribution and abundances of microbes and potential metabolism at macroecological scales.

Description: Estuaries are highly dynamic, spatially complex systems showing large daily fluctuations in salinity. Estuarine organisms, especially small animals with limited locomotory capacities, are thus expected to have variable ecological and morphophysiological strategies. This paper evaluates the responses to salinity challenges in four species of neotropical annelids along a subtropical estuarine gradient by assessing mortality (i.e., tolerance) and changes in body weight (proxy for water fluxes). We selected the nereidids Alitta sp. and Laeonereis acuta, with broad salinity niches, and the nephtyid Nephtys fluviatilis and the melinnid Isolda pulchella, with either narrow salinity niches or a more restricted spatial range. Worms were weighed, exposed to salinities ranging from fresh water to full-strength seawater (0, 5, 15, 25, and 35) for 1, 6, 12, and 24 h, and weighed again after these exposure times. Their mortality (as absence of body movements or vascular circulation) rates were recorded to assess their ranges of tolerance to these treatments or their degree of euryhalinity. Their integument was characterized histologically to show possible morphological links to their tolerances. Both nereidids displayed stable body weights and thick integuments, compatible with the wide range of salinity tolerance and capacity to maintain body hydration. Body weight of Alitta sp. returned to initial values after 1 h at salinities ≥5. Body weight did not change in L. acuta at salinities ≥15; mortalities occurred only at salinity 0 after 12–24 h. Nephtys fluviatilis showed a thin integument and less variation in weight throughout the whole range of tested salinities, but mortality occurred after 24 h at salinity 0, at its reference salinity (3) and at 35. Isolda pulchella showed a lower capacity to maintain body weight/hydration and a thin integument, compatible with its relative stenohalinity and presence restricted to polyhaline marine sectors. Its weight variation was significant at all salinities except 35; mortality occurred at extreme salinities: 0 and 35. Responses of the four species were compatible with their distribution along the estuarine gradient, as an interesting outcome of their autecological traits, morphophysiological adaptations and evolutionary histories.