Adaptive radiation in extremophilic Dorvilleidae (Annelida): diversification of a single colonizer or multiple independent lineages?

An Arctic natural oil seep investigated from space to the seafloor

Due to climate change, decreasing ice cover and increasing industrial activities, Arctic marine ecosystems are expected to face higher levels of anthropogenic stress. To sustain healthy and productive ocean ecosystems, it is imperative to build baseline data to assess future climatic and environmental changes. Herein, a natural oil seep site offshore western Svalbard (Prins Karls Forland, PKF, 80-100 m water depth), discovered using satellite radar images, was investigated using an extensive multiscale and multisource geospatial dataset collected by satellite, aerial, floating, and underwater platforms. The investigated PKF seep area covers roughly a seafloor area of 30,000 m2 and discharges oil from Tertiary or younger source rocks. Biomarker analyses confirm that the oil in the slicks on the sea surface and from the seep on the seafloor have the same origin. Uranium/Thorium dating of authigenic carbonate crusts indicated that the seep had emanated since the Late Pleistocene when ice sheet melting unlocked the hydrocarbons trapped beneath the ice. The faunal communities at the PKF seep are a mix of typical high latitude fauna and taxa adapted to reducing environments. Remarkably, the inhospitable oil-impregnated sediments were also colonized by abundant infaunal organisms. Altogether, in situ observations obtained at the site provide essential insights into the characteristics of high-latitude oil seeps and can be used as a natural laboratory for understanding the potential impacts of human oil discharge into the ocean.

Diversity, phylogeny, and bathymetric zonation of Sirsoe (Annelida: Hesionidae) from colonization experiments in the South China Sea, with the description of three new species

The South China Sea (SCS) basin is hypothesized to host distinct and bathymetrically differentiated fauna due to its semi-enclosed basin and three-layer circulation system. To test this hypothesis, three cow falls are artificially deployed at separate depths (655, 1604, and 3402 m) on Zhongnan seamount in the middle SCS, and the associated worms, Sirsoe spp. are selected as targets to explore their diversity, phylogeny, and zonation pattern. Analyses of collected specimens reveal three new Sirsoe species, which were then nominally described and named as S. polita sp. nov. (655 m), S. nanhaiensis sp. nov. (1604 and 3402 m), and S. feitiana sp. nov. (3402 m), and one known species (S. balaenophila lineage II). Metabarcoding analyses on cow-fall sediments reveal seven additional Operated Taxonomic Units (OTUs) assigned to Sirsoe, increasing the Sirsoe diversity to 10 species/OTUs in the middle SCS. Their distribution along depth shows increasing diversity toward the deeper sites. Phylogenetic inferences recover S. polita closely related to S. alucia from the Southwest Atlantic, forming a lineage deeply divergent from others. The nine deep-water species/OTUs are scattered in three distinct lineages showing closer phylogenetic relationships between 1604- and 3402-m counterparts. The lineage formed by S. naihaiensis and S. feitiana is distinct from other non-SCS congeners both morphologically and genetically. These results suggest multiple independent invasions of Sirsoe to the SCS, a new lineage potentially endemic to the SCS, and a strong zonation pattern related to depth, especially between the shallow (655 m) and the deep (1604 and 3402 m) sites. The semi-enclosed feature combined with the physical structure of the SCS may contribute to such a pattern. This work is registered in ZooBank under: urn:lsid:zoobank.org:pub:317771C8-42D717-4765-A168-B3BE99B09FBF.

The Current State of Eunicida (Annelida) Systematics and Biodiversity

In this study, we analyze the current state of knowledge on extant Eunicida systematics, morphology, feeding, life history, habitat, ecology, distribution patterns, local diversity and exploitation. Eunicida is an order of Errantia annelids characterized by the presence of ventral mandibles and dorsal maxillae in a ventral muscularized pharynx. The origin of Eunicida dates back to the late Cambrian, and the peaks of jaw morphology diversity and number of families are in the Ordovician. Species richness is heterogeneous among the seven recent families, with more than half of the valid species belonging to the Eunicidae + Onuphidae clade, one of the latest clades to diverge. Eunicidans inhabit soft and hard substrates from intertidal to deep waters in all oceans. The few freshwater species are restricted to Histriobdellidae, a family exclusively commensal/parasite of crustaceans. The reproductive biology, development and ecology of most families are poorly known and the information available suggests low dispersal ability. However, all families have records of widely distributed species. Scrutiny of these wide distributions has often revealed the presence of exotic species or more than one species. The exploration of the deep-sea and of new habitats has led to recent descriptions of new species. Furthermore, the revision of type specimens, the examination of new morphological features and the use of molecular data have revealed hidden biodiversity under unjustified synonyms, poor understanding of morphological features and incomplete descriptions. Molecular studies are still very few or nonexistent for the families Histriobdellidae, Hartmaniellidae, Lumbrineridae and Oenonidae. The integration of new methodologies for morphological and molecular study, along with information on biological and ecological traits appears to be the path to improve the knowledge on the diversity of Eunicida.

Phylogeny, biogeography and systematics of Pacific vent, methane seep, and whale-fall Parougia (Dorvilleidae : Annelida), with eight new species

Dorvilleidae is a diverse group of annelids found in many marine environments and also commonly associated with chemosynthetic habitats. One dorvilleid genus, Parougia, currently has 11 described species, of which two are found at vents or seeps: Parougia wolfi and Parougia oregonensis. Eight new Parougia species are recognised and described in this study from collections in the Pacific Ocean, all from whale-falls, hydrothermal vents, or methane seeps at ~600-m depth or greater. The specimens were studied using morphology and phylogenetic analyses of DNA sequences from mitochondrial (cytochrome c oxidase subunit I, 16S rRNA, and cytochrome b) and nuclear (18S rRNA and histone 3) genes. Six sympatric Parougia spp. were found at Hydrate Ridge, Oregon, while three of the Parougia species occurred at different types of chemosynthetic habitats. Two new species were found over wide geographical and bathymetric ranges. Another dorvilleid genus, Ophryotrocha, has previously been highlighted as diversifying in the deep-sea environment. Our results document the hitherto unknown diversity of another dorvilleid genus, Parougia, at various chemosynthetic environments. http://zoobank.org/urn:lsid:zoobank.org:pub:EC7EBBEA-2FB5-43D6-BE53-1A468B541A5C

Do ampharetids take sedimented steps between vents and seeps? Phylogeny and habitat-use of Ampharetidae (Annelida, Terebelliformia) in chemosynthesis-based ecosystems

BACKGROUND

A range of higher animal taxa are shared across various chemosynthesis-based ecosystems (CBEs), which demonstrates the evolutionary link between these habitats, but on a global scale the number of species inhabiting multiple CBEs is low. The factors shaping the distributions and habitat specificity of animals within CBEs are poorly understood, but geographic proximity of habitats, depth and substratum have been suggested as important. Biogeographic studies have indicated that intermediate habitats such as sedimented vents play an important part in the diversification of taxa within CBEs, but this has not been assessed in a phylogenetic framework. Ampharetid annelids are one of the most commonly encountered animal groups in CBEs, making them a good model taxon to study the evolution of habitat use in heterotrophic animals. Here we present a review of the habitat use of ampharetid species in CBEs, and a multi-gene phylogeny of Ampharetidae, with increased taxon sampling compared to previous studies.

RESULTS

The review of microhabitats showed that many ampharetid species have a wide niche in terms of temperature and substratum. Depth may be limiting some species to a certain habitat, and trophic ecology and/or competition are identified as other potentially relevant factors. The phylogeny revealed that ampharetids have adapted into CBEs at least four times independently, with subsequent diversification, and shifts between ecosystems have happened in each of these clades. Evolutionary transitions are found to occur both from seep to vent and vent to seep, and the results indicate a role of sedimented vents in the transition between bare-rock vents and seeps.

CONCLUSION

The high number of ampharetid species recently described from CBEs, and the putative new species included in the present phylogeny, indicates that there is considerable diversity still to be discovered. This study provides a molecular framework for future studies to build upon and identifies some ecological and evolutionary hypotheses to be tested as new data is produced.

The Evolutionary Ecology of Animals Inhabiting Hydrogen Sulfide–Rich Environments

Hydrogen sulfide (H2S) is a respiratory toxicant that creates extreme environments tolerated by few organisms. H2S is also produced endogenously by metazoans and plays a role in cell signaling. The mechanisms of H2S toxicity and its physiological functions serve as a basis to discuss the multifarious strategies that allow animals to survive in H2S-rich environments. Despite their toxicity, H2S-rich environments also provide ecological opportunities, and complex selective regimes of covarying abiotic and biotic factors drive trait evolution in organisms inhabiting H2S-rich environments. Furthermore, adaptation to H2S-rich environments can drive speciation, giving rise to biodiversity hot spots with high levels of endemism in deep-sea hydrothermal vents, cold seeps, and freshwater sulfide springs. The diversity of H2S-rich environments and their inhabitants provides ideal systems for comparative studies of the effects of a clear-cut source of selection across vast geographic and phylogenetic scales, ultimately informing our understanding of how environmental stressors affect ecological and evolutionary processes.

Are organic falls bridging reduced environments in the deep sea? - results from colonization experiments in the Gulf of Cádiz

Organic falls create localised patches of organic enrichment and disturbance where enhanced degradation is mediated by diversified microbial assemblages and specialized fauna. The view of organic falls as “stepping stones” for the colonization of deep-sea reducing environments has been often loosely used, but much remains to be proven concerning their capability to bridge dispersal among such environments. Aiming the clarification of this issue, we used an experimental approach to answer the following questions:

Are relatively small organic falls in the deep sea capable of sustaining taxonomically and trophically diverse assemblages over demographically relevant temporal scales?

Are there important depth- or site-related sources of variability for the composition and structure of these assemblages?

Is the proximity of other reducing environments influential for their colonization?

We analysed the taxonomical and trophic diversity patterns and partitioning (α- and β-diversity) of the macrofaunal assemblages recruited in small colonization devices with organic and inorganic substrata after 1-2 years of deployment on mud volcanoes of the Gulf of Cádiz. Our results show that small organic falls can sustain highly diverse and trophically coherent assemblages for time periods allowing growth to reproductive maturity, and successive generations of dominant species. The composition and structure of the assemblages showed variability consistent with their biogeographic and bathymetric contexts. However, the proximity of cold seeps had limited influence on the similarity between the assemblages of these two habitats and organic falls sustained a distinctive fauna with dominant substrate-specific taxa. We conclude that it is unlikely that small organic falls may regularly ensure population connectivity among cold seeps and vents. They may be a recurrent source of evolutionary candidates for the colonization of such ecosystems. However, there may be a critical size of organic fall to create the necessary intense and persistent reducing conditions for sustaining typical chemosymbiotic vent and seep organisms.