Diversity of meiofauna and free-living nematodes in hydrothermal vent mussel beds on the northern and southern East Pacific Rise

The ecology and biogeography of meiofauna at deep-sea hydrothermal vents have historically received less attention that those of mega- and macrofauna. This study examines the composition of major meiofaunal taxa in beds of the mussel Bathymodiolus thermophilus at hydrothermal vents on the northern and southern East Pacific Rise (EPR) and presents the first comparison of species assemblages of the dominant taxon, the nematodes, among sites spanning 27 degrees of latitude. Meiofaunal samples were collected by submersible from three mussel beds at 9°N on the EPR and four mussel beds between 17 and 18°S in 1999. Estimated ages of the mussel beds at the time of sampling range from 4 to >20 years, enabling investigation of influence of mussel bed age on meiofaunal assemblages. Overall, the meiofauna of the mussel beds was dominated by nematodes, with copepods constituting the second most abundant meiofaunal group. There was variation in the ratio of nematodes to copepods between sites, however, with copepods more abundant than nematodes in the youngest mussel beds. Apart from polychaete larvae, other meiofaunal groups were generally present at very low abundance (< 1 %) in the samples and restricted in diversity to gastropod larvae, acari, foraminifera, ostracoda and turbellaria. Seventeen nematode species from 14 genera and 11 families were found in the samples, with no evidence of endemicity to hydrothermal vents at the generic level. Four genera present were not previously recorded at hydrothermal vents. Nematode species richness, species:genus ratios and abundances were low compared with other deep-sea habitats, though the ecological relevance of comparisons with soft-sediment benthos is discussed. Nematode assemblages exhibited high dominance by a few species, with one species of Thalassomonhystera most abundant at 5 of the 7 vent sites. Multivariate analysis of nematode assemblages reveals similarities among sites that do not match geographical proximity. The youngest mussel beds were most similar to each other and exhibited lower species richness than other sites, consistent with colonisation of mussel bed habitat by nematodes over time. Similarity in the composition of nematode assemblages among sites separated by ~3000 km indicates that they lie within a single biogeographic province, consistent with that proposed for mussel bed macrofauna. At a generic level, samples exhibited some overlap with nematode assemblages at vents elsewhere on the East Pacific Rise, on the Mid-Atlantic Ridge and in the North Fiji Basin

Research is needed to inform environmental management of hydrothermally inactive and extinct polymetallic sulfide (PMS) deposits

Polymetallic sulfide (PMS) deposits produced at hydrothermal vents in the deep sea are of potential interest to miners. Hydrothermally active sulfide ecosystems are valued for the extraordinary chemosynthetic communities that they support. Many countries, including Canada, Portugal, and the United States, protect vent ecosystems in their Exclusive Economic Zones. When hydrothermal activity ceases temporarily (dormancy) or permanently (extinction), the habitat and associated ecosystem change dramatically. Until recently, so-called "inactive sulfide" habitats, either dormant or extinct, received little attention from biologists. However, the need for environmental management of deep-sea mining places new imperatives for building scientific understanding of the structure and function of inactive PMS deposits. This paper calls for actions of the scientific community and the emergent seabed mining industry to i) undertake fundamental ecological descriptions and study of ecosystem functions and services associated with hydrothermally inactive PMS deposits, ii) evaluate potential environmental risks to ecosystems of inactive PMS deposits through research, and iii) identify environmental management needs that may enable mining of inactive PMS deposits. Mining of some extinct PMS deposits may have reduced environmental risk compared to other seabed mining activities, but this must be validated through scientific research on a case-by-case basis.FCT: IF/00029/2014/CP1230/CT0002/ UID/05634/2020/ CEECIND005262017/ UID/MAR/00350/2019; Direcao-Geral de Politica do Mar (DGPM) Mining2/2017/005/ Mining2/2017/001info:eu-repo/semantics/publishedVersio

Hydrothermal vents and methane seeps: rethinking the sphere of influence

Although initially viewed as oases within a barren deep ocean, hydrothermal vents and methane seep chemosynthetic communities are now recognized to interact with surrounding ecosystems on the sea floor and in the water column, and to affect global geochemical cycles. The importance of understanding these interactions is growing as the potential rises for disturbance of the systems from oil and gas extraction, seabed mining and bottom trawling. Here we synthesize current knowledge of the nature, extent and time and space scales of vent and seep interactions with background systems. We document an expanded footprint beyond the site of local venting or seepage with respect to elemental cycling and energy flux, habitat use, trophic interactions, and connectivity. Heat and energy are released, global biogeochemical and elemental cycles are modified, and particulates are transported widely in plumes. Hard and biotic substrates produced at vents and seeps are used by "benthic background" fauna for attachment substrata, shelter, and access to food via grazing or through position in the current, while particulates and fluid fluxes modify planktonic microbial communities. Chemosynthetic production provides nutrition to a host of benthic and planktonic heterotrophic background species through multiple horizontal and vertical transfer pathways assisted by flow, gamete release, animal movements, and succession, but these pathways remain poorly known. Shared species, genera and families indicate that ecological and evolutionary connectivity exists among vents, seeps, organic falls and background communities in the deep sea: the genetic linkages with inactive vents and seeps and background assemblages however, are practically unstudied. The waning of venting or seepage activity generates major transitions in space and time that create links to surrounding ecosystems, often with identifiable ecotones or successional stages. The nature of all these interactions is dependent on water depth, as well as regional oceanography and biodiversity. Many ecosystem services are associated with the interactions and transitions between chemosynthetic and background ecosystems, for example carbon cycling and sequestration, fisheries production, and a host of non-market and cultural services. The quantification of the sphere of influence of vents and seeps could be beneficial to better management of deep-sea environments in the face of growing industrialization

Temporal and spatial variation in the reproductive ecology of the vent-endemic amphipod Ventiella sulfuris in the eastern Pacific

Populations of the vent-endemic amphipod Ventiella sulfuris were compared from 6 East Pacific Rise (EPR) vent sites of different ages, 3 from the northern EPR and 3 from the southern EPR. Although vent age affected amphipod abundance, with no individuals at the oldest vent, other population/reproductive parameters were found to be site dependent rather than vent age dependent. There was little within-site variation in population structure and reproductive output, probably the result of high within-site motility. However, there were significant between-site and between-field differences, indicating a high degree of population and reproductive variability and a moderate degree of vent fidelity. Since population structure and reproductive output varied between sites, the possibility of their use as biomarkers of vent ‘condition’ is discussed. The reproductive ecology of V. sulfuris is described for the first time and compared to that of other vent amphipod species. Unlike other species studied, reproductive output is relatively high. Adults move to the periphery of vents to reproduce and brood; after brooding, they moult again, return to feed at vent habitats (e.g. mussel and tube worm beds), and undergo a new phase of gonad maturation and emigration

Reproductive ecology of Bouvierella curtirama (Amphipoda: Eusiridae) from chemically distinct vents in the Lucky Strike vent field, Mid-Atlantic Ridge

Populations of the vent amphipod Bouvierella curtirama were compared from two sites in the Lucky Strike vent field on the Mid-Atlantic Ridge. The two sites (Sintra and Eiffel Tower) are chemically distinct, fed by different hydrothermal sources, but separated by only about 400 m. Both sites are characterized by dense beds of the mussel Bathymodiolus azoricus, though the proportion of methanotrophic and thiotrophic endosymbionts supported by the mussel and its isotopic composition vary significantly between the sites. Such differences presumably reflect the availability of primary resources and would be expected to impinge on other members of the mussel bed community, such as B. curtirama, which was abundant at both sites. A detailed comparative study of the amphipod showed that, although the overall population structure (in terms of growth stages) was similar at the two sites, reproductive output was significantly greater at Sintra, a result of females maturing at a smaller body size and producing more broods of a greater size. The reproductive output at both sites was relatively low, with a proportion of surviving females failing to mature. The plasticity of response of the two populations is discussed in relation to food availability (quantity and quality). Grazing predation, resulting in loss of antennal flagellum articles, was high at both sites. Such damage is discussed in terms of predation impact. Damage to the antennae of the holotype has resulted in an inaccurate species description, which is remedied here

Structure and function of Halice hesmonectes (Amphipoda: Paraliscidae) swarms from hydrothermal vents in the eastern Pacific

Swarms of the pardaliscid amphipod Halice hesmonectes were sampled at low-temperature hydrothermal vents in the Venture Hydrothermal Fields of the East Pacific Rise. In excess of 3000 individuals were collected from a range of sites/habitats, and at two points in time (December 1991 and March 1994). The structure of swarms was described in terms of growth stages, the development of primary and secondary sex characteristics and the accumulation of nutritional reserves. The results demonstrated that swarms contained a wide range of growth stages, but that small juveniles and mature males and females were absent. Swarm structure was interpreted as an equilibrium dependent on the relative proportion of time spent by each growth stage in the swarm habitat. This equilibrium swarm structure was very similar at different sites and times. Swarms dominated by small juveniles occurred at the northern sites in December 1991 following a period of eruption and new venting in April 1991. Equilibrium swarm structure had become re-established at these sites by March 1994. The function of swarming was considered. The results indicated that swarming was not associated with reproductive activity. The available evidence, though not conclusive, suggested that swarms were associated with feeding

Evolution and biogeography of deep-sea vent and seep invertebrates

Deep-sea hydrothermal vents and cold seeps are submarine springs where nutrient-rich fluids emanate from the sea floor. Vent and seep ecosystems occur in a variety of geological settings throughout the global ocean and support food webs based on chemoautotrophic primary production. Most vent and seep invertebrates arrive at suitable habitats as larvae dispersed by deep-ocean currents. The recent evolution of many vent and seep invertebrate species (<100 million years ago) suggests that Cenozoic tectonic history and oceanic circulation patterns have been important in defining contemporary biogeographic patterns