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The acorn barnacleSolidobalanus hesperius, which has a broad subtidal distribution in the North Pacific, often lives as an epibiont on bivalves and commercially important decapod crustaceans. In comparison to other non-epibiotic barnacle species in the same region,S. hesperiushas an abbreviated lifespan averaging 6-7 mo. AlthoughS. hesperiuscommonly occupies crab carapaces, details of the relationship remain unknown. Using barnacles collected monthly from host crabs, we describe the reproductive seasonality and settlement patterns forS. hesperiusin relation to the molting patterns of 2 host crabs,Metacarcinus magisterandCancer productus, off the Pacific coast of Oregon, USA. Brooded embryos and mature gonads were observed throughout the year, although broods had a higher prevalence in the spring and mid-summer. Embryos developed quickly, hatching within 1 wk, and individuals as small as 3.8 mm in diameter were found with mature ovaries. We observed a large larval settlement peak in August. The spatial distribution of epibiotic barnacles was correlated with the microtopography of the host crab carapace, with most barnacles occurring in depressions and grooves. These findings indicate that the abbreviated life cycle ofS. hesperiusis well adapted to life on ephemeral crab carapaces that are molted frequently, and the spatial distribution of settlers may reduce the likelihood that barnacles are lost to abrasion. 

Study of stable isotopes in seep mussel shells to determine possible dispersal modes of larvae 

Abstract Mass mortality of marine animals due to volcanic ash deposition is present in the fossil record but has rarely been documented in real time. Here, using remotely-operated vehicle video footage and analysis of ash collected at the seafloor, we describe the devastating effect of the record-breaking 2022 Hunga submarine volcanic eruption on endangered and vulnerable snail and mussel species that previously thrived at nearby deep-sea hydrothermal vents. In contrast to grazing, scavenging, filter-feeding, and predatory vent taxa, we observed mass mortality, likely due to smothering during burial by thick ash deposits, of the foundation species, which rely on symbiotic chemosynthetic bacteria for the bulk of their nutrition. This is important for our broad understanding of the natural disturbance of marine ecosystems by volcanic eruptions and for predicting the effects of anthropogenic disturbance, like deep-sea mining, on these unique seafloor habitats. 

In highly fragmented and relatively stable cold-seep ecosystems, species are expected to exhibit high migration rates and long-distance dispersal of long-lived pelagic larvae to maintain genetic integrity over their range. Accordingly, several species inhabiting cold seeps are widely distributed across the whole Atlantic Ocean, with low genetic divergence between metapopulations on both sides of the Atlantic Equatorial Belt (AEB, i.e. Barbados and African/European margins). Two hypotheses may explain such patterns: (i) the occurrence of present-day gene flow or (ii) incomplete lineage sorting due to large population sizes and low mutation rates. Here, we evaluated the first hypothesis using the cold seep musselsGigantidas childressi, G. mauritanicus, Bathymodiolus heckeraeandB. boomerang. We combined COI barcoding of 763 individuals with VIKING20X larval dispersal modelling at a large spatial scale not previously investigated. Population genetics supported the parallel evolution ofGigantidasandBathymodiolusgenera in the Atlantic Ocean and the occurrence of a 1-3 Million-year-old vicariance effect that isolated populations across the Caribbean Sea. Both population genetics and larval dispersal modelling suggested that contemporary gene flow and larval exchanges are possible across the AEB and the Caribbean Sea, although probably rare. When occurring, larval flow was eastward (AEB - only forB. boomerang) or northward (Caribbean Sea - only forG. mauritanicus). Caution is nevertheless required since we focused on only one mitochondrial gene, which may underestimate gene flow if a genetic barrier exists. Non-negligible genetic differentiation occurred between Barbados and African populations, so we could not discount the incomplete lineage sorting hypothesis. Larval dispersal modelling simulations supported the genetic findings along the American coast with high amounts of larval flow between the Gulf of Mexico (GoM) and the US Atlantic Margin, although the Blake Ridge population ofB. heckeraeappeared genetically differentiated. Overall, our results suggest that additional studies using nuclear genetic markers and population genomics approaches are needed to clarify the evolutionary history of the Atlantic bathymodioline mussels and to distinguish between ongoing and past processes. 

Abstract Most volcanic eruptions on Earth take place below the ocean surface and remain largely unobserved. Reconstruction of past submerged eruptions has thus primarily been based on the study of seafloor deposits. Rarely before the 15 January 2022 eruption of Hunga volcano (Kingdom of Tonga) have we been able to categorically link deep‐sea deposits to a specific volcanic source. This eruption was the largest in the modern satellite era, producing a 58‐km‐tall plume, a 20‐m high tsunami, and a pressure wave that propagated around the world. The eruption induced the fastest submarine density currents ever measured, which destroyed submarine telecommunication cables and traveled at least 85 km to the west to the neighboring Lau Basin. Here we report findings from a series of remotely operated vehicle dives conducted 4 months after the eruption along the Eastern Lau Spreading Center‐Valu Fa Ridge. Hunga‐sourced volcaniclastic deposits 7–150 cm in thickness were found at nine sites, and collected. Study of the internal structure, grain size, componentry, glass chemistry, and microfossil assemblages of the cores show that these deposits are the distal portions of at least two ∼100‐km‐runout submarine density currents. We identify distinct physical characteristics of entrained microfossils that demonstrate the dynamics and pathways of the density currents. Microfossil evidence suggests that even the distal parts of the currents were erosive, remobilizing microfossil‐concentrated sediments across the Lau Basin. Remobilization by volcaniclastic submarine density currents may thus play a greater role in carbon transport into deep sea basins than previously thought.