S. Kim Juniper

Long-term eruptive activity at a submarine arc volcano

Three-quarters of the Earths volcanic activity is submarine, located mostly along the mid-ocean ridges, with the remainder along intraoceanic arcs and hotspots at depths varying from greater than 4,000 m to near the sea surface. Most observations and sampling of submarine eruptions have been indirect, made from surface vessels or made after the fact. We describe here direct observations and sampling of an eruption at a submarine arc volcano named NW Rota-1, located 60 km northwest of the island of Rota (Commonwealth of the Northern Mariana Islands). We observed a pulsating plume permeated with droplets of molten sulphur disgorging volcanic ash and lapilli from a 15-m diameter pit in March 2004 and again in October 2005 near the summit of the volcano at a water depth of 555 m (depth in 2004). A turbid layer found on the flanks of the volcano (in 2004) at depths from 700 m to more than 1,400 m was probably formed by mass-wasting events related to the eruption. Long-term eruptive activity has produced an unusual chemical environment and a very unstable benthic habitat exploited by only a few mobile decapod species. Such conditions are perhaps distinctive of active arc and hotspot volcanoes.

Microbial‐mineral floc associated with nascent hydrothermal activity on CoAxial Segment, Juan de Fuca Ridge

Following a June 1993 seafloor eruption at CoAxial Segment, Juan de Fuca Ridge, extensive accumulation of microbial-mineral floc was observed in association with abundant diffuse venting on new lava flows, and around less extensive new venting on older basalts. Microscopic and SEM examination revealed a diverse assemblage of microbial forms contained within a poorly organized organo-mineral matrix. Samples more closely resembled microbial floc described from other hydrothermal areas than the layered bacterial mats observed after the eruption at 9°N on the East Pacific Rise. Iron and silica were the major compositional elements in all samples, with the latter likely important in preserving microbial remains. Organic carbon content was on the order of 3–4%. Enzyme assays indicated the presence of autotrophic CO2 fixation and potential for sulfide oxidation. Floc covered 7–14% of the seafloor on the hydrothermally active part of the new lava flow. We discuss the possibility that the CoAxial floc originated as ejecta from the sub-seafloor hydrothermal system rather than from in situ production around vent openings.

Crustal accretion and the hot vent ecosystem

We examine evidence for links between seafloor spreading rate and properties of vent habitat most likely to influence species diversity and other ecosystem properties. Abundance of vent habitat along spreading centres appears positively related to spreading rate while habitat stability shows an opposite relationship. Habitat heterogeneity is lowest at faster spreading ridges. Limited data indicate an increasing species diversity with spreading rate, complicated by historical factors. Ecosystem productivity and efficiency of resource utilisation may also reflect diversity differences.

Carbon flows through the microbial food web of first-year ice in resolute passage (Canadian High Arctic)

Abstract Ice algal communities are host to thriving populations of microheterotrophs whose trophic role remains poorly understood. We report here an inverse modelling analysis of the microbial food web associated with the spring bloom of ice algae at Resolute Passage in the High Arctic. Carbon flows among microbial components (ice algae, autotrophic and heterotrophic nanoflagellates, microflagellates and ciliates) and their exchanges with particulate and dissolved organic carbon (POC and DOC) were inferred from the observed changes in standing stocks of these compartments between 13 April and 22 May 1992. Calculations were made for three phases of the blooms development and for two sites under thin and thick snow cover. Observed DOC accumulations within the bottom ice originated largely from the ice algae. However, calculated production rates were too high to result strictly from normal physiological exudation. Mechanical or physiological stresses that disrupt the integrity of the cells and grazing by zooplankton at the ice-water interface may well be involved in this process. Inverse modelling confirmed field and experimental evidence that nanoflagellates may directly assimilate DOC to support their growth. Patterns in trophic flows between sites with thin and thick snow cover were similar. In contrast, trophic interactions changed as the bloom progressed: production of DOC and detritus from the ice algae were the only significant carbon flows during the early phase; bacterivory developed and peaked during the middle phase and was superseded by DOC utilization and herbivory by flagellates and ciliates during the late phase. Only ca. 20% of the DOC produced was utilized by the microheterotrophs. Direct links from DOC and ice algae to protists potentially increase the efficiency of C transfers within the ice-associated microbial food web; on the other hand, low recovery efficiency limits the role of the microbial loop in recycling DOC.

A year in hypoxia: epibenthic community responses to severe oxygen deficit at a subsea observatory in a coastal inlet.

Changes in ocean ventilation driven by climate change result in loss of oxygen in the open ocean that, in turn, affects coastal areas in upwelling zones such as the northeast Pacific. Saanich Inlet, on the west coast of Canada, is a natural seasonally hypoxic fjord where certain continental shelf species occur in extreme hypoxia. One study site on the VENUS cabled subsea network is located in the hypoxic zone at 104 m depth. Photographs of the same 5 m2 area were taken with a remotely-controlled still camera every 2/3 days between October 6th 2009 and October 18th 2010 and examined for community composition, species behaviour and microbial mat features. Instruments located on a near-by platform provided high-resolution measurements of environmental variables. We applied multivariate ordination methods and a principal coordinate analysis of neighbour matrices to determine temporal structures in our dataset. Responses to seasonal hypoxia (0.1–1.27 ml/l) and its high variability on short time-scale (hours) varied among species, and their life stages. During extreme hypoxia, microbial mats developed then disappeared as a hippolytid shrimp, Spirontocaris sica, appeared in high densities (200 m−2) despite oxygen below 0.2 ml/l. The slender sole Lyopsetta exilis was abundant in severe hypoxia and diminished as oxygen increased in the summer. This planktivore may be responding to changes in the depth of the diurnal migration of zooplankton. While the squat lobster Munida quadrispina was common at all times, juveniles disappeared in fluctuating conditions. Despite low oxygen conditions, animal densities were high indicating that the risk from hypoxia is balanced by factors such as food availability and escape from less tolerant predators. As hypoxia increases on the continental shelf, we expect benthic communities to become dominated by low diversity, hypoxia-tolerant species of low commercial significance.

Free-living bacterial communities associated with tubeworm (Ridgeia piscesae) aggregations in contrasting diffuse flow hydrothermal vent habitats at the Main Endeavour Field, Juan de Fuca Ridge.

We systematically studied free‐living bacterial diversity within aggregations of the vestimentiferan tubeworm Ridgeia piscesae sampled from two contrasting flow regimes (High Flow and Low Flow) in the Endeavour Hydrothermal Vents Marine Protected Area (MPA) on the Juan de Fuca Ridge (Northeast Pacific). Eight samples of particulate detritus were recovered from paired tubeworm grabs from four vent sites. Most sequences (454 tag and Sanger methods) were affiliated to the Epsilonproteobacteria, and the sulfur‐oxidizing genus Sulfurovum was dominant in all samples. Gammaproteobacteria were also detected, mainly in Low Flow sequence libraries, and were affiliated with known methanotrophs and decomposers. The cooccurrence of sulfur reducers from the Deltaproteobacteria and the Epsilonproteobacteria suggests internal sulfur cycling within these habitats. Other phyla detected included Bacteroidetes, Actinobacteria, Chloroflexi, Firmicutes, Planctomycetes, Verrucomicrobia, and Deinococcus–Thermus. Statistically significant relationships between sequence library composition and habitat type suggest a predictable pattern for High Flow and Low Flow environments. Most sequences significantly more represented in High Flow libraries were related to sulfur and hydrogen oxidizers, while mainly heterotrophic groups were more represented in Low Flow libraries. Differences in temperature, available energy for metabolism, and stability between High Flow and Low Flow habitats potentially explain their distinct bacterial communities.

Automated Image Analysis for the Detection of Benthic Crustaceans and Bacterial Mat Coverage Using the VENUS Undersea Cabled Network

The development and deployment of sensors for undersea cabled observatories is presently biased toward the measurement of habitat variables, while sensor technologies for biological community characterization through species identification and individual counting are less common. The VENUS cabled multisensory network (Vancouver Island, Canada) deploys seafloor camera systems at several sites. Our objective in this study was to implement new automated image analysis protocols for the recognition and counting of benthic decapods (i.e., the galatheid squat lobster, Munida quadrispina), as well as for the evaluation of changes in bacterial mat coverage (i.e., Beggiatoa spp.), using a camera deployed in Saanich Inlet (103 m depth). For the counting of Munida we remotely acquired 100 digital photos at hourly intervals from 2 to 6 December 2009. In the case of bacterial mat coverage estimation, images were taken from 2 to 8 December 2009 at the same time frequency. The automated image analysis protocols for both study cases were created in MatLab 7.1. Automation for Munida counting incorporated the combination of both filtering and background correction (Median- and Top-Hat Filters) with Euclidean Distances (ED) on Red-Green-Blue (RGB) channels. The Scale-Invariant Feature Transform (SIFT) features and Fourier Descriptors (FD) of tracked objects were then extracted. Animal classifications were carried out with the tools of morphometric multivariate statistic (i.e., Partial Least Square Discriminant Analysis; PLSDA) on Mean RGB (RGBv) value for each object and Fourier Descriptors (RGBv+FD) matrices plus SIFT and ED. The SIFT approach returned the better results. Higher percentages of images were correctly classified and lower misclassification errors (an animal is present but not detected) occurred. In contrast, RGBv+FD and ED resulted in a high incidence of records being generated for non-present animals. Bacterial mat coverage was estimated in terms of Percent Coverage and Fractal Dimension. A constant Region of Interest (ROI) was defined and background extraction by a Gaussian Blurring Filter was performed. Image subtraction within ROI was followed by the sum of the RGB channels matrices. Percent Coverage was calculated on the resulting image. Fractal Dimension was estimated using the box-counting method. The images were then resized to a dimension in pixels equal to a power of 2, allowing subdivision into sub-multiple quadrants. In comparisons of manual and automated Percent Coverage and Fractal Dimension estimates, the former showed an overestimation tendency for both parameters. The primary limitations on the automatic analysis of benthic images were habitat variations in sediment texture and water column turbidity. The application of filters for background corrections is a required preliminary step for the efficient recognition of animals and bacterial mat patches.

Changes in sea-ice phagotrophic microprotists (20–200 μm) during the spring algal bloom, Canadian Arctic Archipelago

Heterotrophic microflagellates and ciliates (i.e., 20–200 μm size fraction) were examined for evidence of their response to the spring accumulation of algal biomass in the bottom of the annual sea ice in Resolute Passage (Canadian High Arctic, 74°N, 95°W). The most abundant heterotrophic microflagellates were dinoflagellates in the water column and cryothe-comonad-type cells in the ice. Ciliates were exclusively represented by typical planktonic species in the water column while the ice community was characterized by the occurrence of benthic-type species. This contrasts with observations in the Antarctic and at the southern limit of sea ice in the northern hemisphere, where annual sea ice seems to serve as a temporary habitat for planktonic communities. Protist biomasses in Resolute Passage were one to two orders of magnitude higher in the ice than in the plankton. In the ice, a seasonal increase in the biomass of phagotrophic microprotists as well as in the number of micrometazoa (from our microprotist samples) followed the spring algal bloom. These observations (1) support previous suggestions of the existence of a functional microbial food web within sea-ice communities and (2) indicate that micrograzers may represent one of the basic levels of the ice food web that responds to the seasonal accumulation of algal biomass. Heterotrophic microprotists growing in the ice accumulated about 4 mg C m−2 d−1, a net production rate that is two to four times higher than those reported for sea-ice bacteria (both Arctic and Antarctic), and represented 1–9% of the net production of ice algea in the early season at resolute. A carbon budget exercise indicated that the required energy for microprotozoan growth in the later season, when algal biomass was declining, corresponded to 1–8% of the net biomass loss from the ice algal populations. The specific growth rates of microprotozoan populations within the ice (0.04–0.18 d−1) appeared to increase significantly with decreasing algal productivity. This may be critical for the protracted heterotrophic food web in multi-year ice and to many consumers during the long polar winter.

Ice-brine and planktonic microheterotrophs from Saroma-ko Lagoon, Hokkaido (Japan): quantitative importance and trophodynamics

Copyright (c) 1996 Elsevier Science B.V. All rights reserved. Biologists have rarely had the opportunity to investigate the community characteristics and dynamics of heterotrophic microorganisms in highly productive first-year sea ice. In this study, sterile seawater was used as a salinity buffer to extract the ice-brine microheterotroph communities (bacteria, flagellates and ciliatesr from a coastal lagoon in Japan (Saroma-ko, Hokkaido; 44°N, 144°Er during the late winter (February−Marchr of 1992. This procedure reduced osmotic shock during the melting of ice cores and allowed the recovery of up to 323% more cells than the traditional melting method. Most of the organisms were concentrated in the bottom 3−4 cm of the ice, where abundances were up to 33 times higher than in the plankton. In ice and plankton samples, heterotrophic flagellates were dominated by small species (<8 μm, mainly choanoflagellatesr and cryothecomonad-type cells while ciliates were dominated by a photosynthetic species, Mesodinium rubrum. In contrast to higher latitudes, increased snow cover appeared to favor the development of protozoa beneath the relatively thin 30−40 cm ice cover of Saroma-ko Lagoon. Temporally, a successional sequence was observed between protozoa and the bacterial compartment. Bacteria decreased in abundance throughout the sampling period while protozoa increased or attained their maximum number in late winter, toward the end of the sampling period. These observations support previous suggestions of the existence of a functional microbial food web within the sea-ice community. Heterotrophic flagellate biomass greatly exceeded bacterial biomass in the sea ice (30−60×r. Coupled with similar potential growth rates, this suggests the utilization of additional (non-bacterialr food items by ice-brine flagellates. Finally, the effects of salinity variations (ranging between 15 and 120 psur on potential microheterotroph growth rates are discussed.

Environmental Drivers of Benthic Flux Variation and Ecosystem Functioning in Salish Sea and Northeast Pacific Sediments.

The upwelling of deep waters from the oxygen minimum zone in the Northeast Pacific from the continental slope to the shelf and into the Salish Sea during spring and summer offers a unique opportunity to study ecosystem functioning in the form of benthic fluxes along natural gradients. Using the ROV ROPOS we collected sediment cores from 10 sites in May and July 2011, and September 2013 to perform shipboard incubations and flux measurements. Specifically, we measured benthic fluxes of oxygen and nutrients to evaluate potential environmental drivers of benthic flux variation and ecosystem functioning along natural gradients of temperature and bottom water dissolved oxygen concentrations. The range of temperature and dissolved oxygen encountered across our study sites allowed us to apply a suite of multivariate analyses rarely used in flux studies to identify bottom water temperature as the primary environmental driver of benthic flux variation and organic matter remineralization. Redundancy analysis revealed that bottom water characteristics (temperature and dissolved oxygen), quality of organic matter (chl a:phaeo and C:N ratios) and sediment characteristics (mean grain size and porosity) explained 51.5% of benthic flux variation. Multivariate analyses identified significant spatial and temporal variation in benthic fluxes, demonstrating key differences between the Northeast Pacific and Salish Sea. Moreover, Northeast Pacific slope fluxes were generally lower than shelf fluxes. Spatial and temporal variation in benthic fluxes in the Salish Sea were driven primarily by differences in temperature and quality of organic matter on the seafloor following phytoplankton blooms. These results demonstrate the utility of multivariate approaches in differentiating among potential drivers of seafloor ecosystem functioning, and indicate that current and future predictive models of organic matter remineralization and ecosystem functioning of soft-muddy shelf and slope seafloor habitats should consider bottom water temperature variation. Bottom temperature has important implications for estimates of seasonal and spatial benthic flux variation, benthic–pelagic coupling, and impacts of predicted ocean warming at high latitudes.