Entire Depth Range Research Articles

Distributional patterns of deep-sea coral assemblages in three submarine canyons off Newfoundland, Canada

Deep-sea corals are fragile and long-lived species that provide important habitat for a variety of taxa. The rarity of in situ observations in deep waters off Newfoundland, Canada, motivated the first extensive deep-sea research cruise to that region in 2007. We conducted 7 dives in 3 canyons (Haddock Channel, Halibut Channel, and Desbarres Canyon) with ROPOS (Remotely Operated Platform for Ocean Science). Over 160 000 coral colonies were enumerated and, of the 28 species found, Acanella arbuscula, Pennatula spp., and Flabellum spp. were most frequently observed. The largest coral observed was Keratoisis grayi at over 2 m in height. Corals spanned the entire depth range sampled (351 to 2245 m) and inhabited all bottom types surveyed, but boulder and cobble habitats were most species-rich. Assemblages differed significantly with depth class and bottom type. The unique assemblage at outcrops was strongly driven by the presence of Desmophyllum dianthus. Keratoisis grayi, D. dianthus, and Anthomastus spp. were largely absent in mud-sand habitats. Sea pen meadows covered large tracts of muddy seafloor spanning >1 km. Acanella arbuscula and Flabellum spp. characterised large coral fields with abundant corals but relatively low species richness. These results highlight not only the importance of hard structure in determining patterns of coral distributions, abundances, and assemblages, but also the need to focus conservation efforts on a variety of habitats to ensure protection for the full suite of deep-sea coral species.

Distribution and reproductive pattern of deep-water crangonid shrimps in the East Sea of Korea

In this study, we investigated the distribution patterns of two crangonid shrimps in the East Sea of Korea. The distributions of the shrimps differed significantly with depth. Neocrangon communis (Rathbun, 1899) was found at depths of 300-900 m throughout the survey area, with the greatest number of individuals at 300 m depth in the total sampling period. Argis toyamaensis (Yokoya, 1933) occurred over the entire depth range (300-900 m), with the greatest numbers of individuals at 800 m depth in the total sampling period. On average, the large females and ovigerous females of N. communis and A. toyamaensis were mainly distributed in shallow waters (300-400 m depth). The ovigerous females of the shallow-dwelling species N. communis mainly occurred in shallow waters. The deep-dwelling species, A. toyamaensis, differed slightly from N. communis in terms of the distribution of its ovigerous females. The ovigerous females of A. toyamaensis were widely distributed at all depths, and the gonadosomatic index did not differ significantly with depth. However, the deep-dwelling species, A. toyamaensis, had larger eggs than had N. communis. We suggest that life-history strategies are determined by many environmental factors, including depth, in the deep-water environment. The optimal distribution depths of these two species were closely related to their reproductive strategies.

Behavior of methane seep bubbles over a pockmark on the Cascadia continental margin

A newly modified acoustic method was used to derive time-dependent bubble emission size distributions and to monitor associated zooplankton behavior at a methane seep emitted from the northeast Pacific continental shelf in 150 m water depth near Grays Harbor, Washington State, USA. Instrumentation consisted of a seafloor mooring with an upward-oriented 200 kHz sonar that imaged the column's lower 100 m for 33 h during September 2009. The profiler observed several highly variable methane bubble streams venting from a large carbonate-lined pockmark. Other acoustic data and visual observations confirmed that the gas bubbles reached the sea surface and were highly variable in nature. Individual bubble traces in the acoustic sonar images were used to derive vertical bubble velocities with a mean value of 24.6 ± 2.5 cm s−1 over the entire depth range. Some bubbles entering the acoustic image at shallower water depths exhibited a slower rise velocity of 22.2 ± 2.4 cm s−1 and likely originated from adjacent emission sites. Measured rise velocities were too slow to be clean, uncoated bubbles. We therefore assumed that the bubbles were surfactant coated with a Gaussian-shaped size distribution peaking at an observed radius of 7500 ± 100 µm. If the flux derived from these measurements was assumed to be relatively constant over time, total methane issuing from only one of the ∼20 active bubble vents at the pockmark site is estimated as ∼9 kg yr−1, similar to the flux from other reported marine CH4 vent sites.

On the influence of earthquake energy range on the estimated seismicity parameters before the magnitude 7.9 Kronotskii earthquake of 1997

Results are reported from a detailed study of central Kamchatka seismicity for the period 1962–1997 based on a modification of the traditional approach. The approach involves (a) a detailed structure of the seismic region that recognizes the Kronotskii and Shipunskii geoblocks and two further blocks, the continental slope, and the offshore portion, (b) a study of variations in the rate of M = 3.0–7.2 earthquakes and the amount of seismic energy released at depths of 0–50 and 51–100 km, (c) a study of seismicity variability, and (d) separate estimates of the recurrence of crust-mantle earthquakes (depths 0–50 km) and mantle events (51–100 km). As a result, apart from corroborating the fact of a quiescence preceding the December 5, 1997 Kronotskii earthquake (M 7.9), we also found that a relationship exists between its beginning and the position of the earthquake-generating region relative to the mainshock epicenter. The quiescence dominates the seismic process during the pre-mainshock period and is characterized by a decreased rate of earthquakes (the first feature) and a decreased amount of seismic energy release (the second feature). Based on the first feature, we found that the quiescence started in 1987 throughout the entire depth range (0–100 km) in both parts of the Kronotskii geoblock close to the rupture zone of the eponymous earthquake. As to the Shipunskii geoblock, which is farther from the rupture zone, the quiescence began in the mantle of the inner area first (1988) and somewhat later at depths of 0–50 km within the continental slope (1989). By the second feature, the quiescence began at shallower depths in the inner area of the Kronotskii geoblock at the same time and later on (a year later) in the mantle (1988). Under the continental slope of the trench in the Shipunskii geoblock the shallower quiescence also began in 1987, while it was 3 years late in the inner zone (1990) and involved the earthquake-generating earth volume at depths of 0–100 km. These data are identical with or sufficiently close to the estimate for the beginning of this quiescence using a circular area of radius 150 km that combines the Kronotskii and Shipunskii geoblocks by the RTL method (1990).

Dependence of wedge transmission factor on co-60 teletherapy treatment depths and techniques

Measuring the wedge factor (WF) for radiation field of 10 x 10 cm2 at a specified depth and Source to Surface Distance (SSD), and applying the value to all treatment depths and technique could introduce errors > ± 5 % of threshold stipulated for patient radiation dose delivery. Therefore, some Treatment Planning Systems (TPSs) provide for inputs of separate Percentage Depth Dose (PDD) and Tissue Phantom Ratio (TPR) data for wedged fields to account for WF dependence of treatment depths and techniques. Hence, relatively more measurements than usual are taken per wedge filter and photon energy to establish a TPS and obtain dosimetric data for estima-ting treatment time for wedged fields, which required sophisticated equipment and procedures. While many On-cology Centres rely on International PDD and Tissue Maximum Ratio (TMR) data, benchmark data for wedged beams are not readily available. To provide radiotherapy dosimetry of high accuracy and expediency, two emp-irical equations were developed for a GWGP 80 Cobalt-60 teletherapy machine at the Oncology Department, Korle Bu Teaching Hospital (Ghana). The equations were validated via linear interpolations by measuring WFs at various treatment depths using Source Axial distance (SAD) and SSD treatment techniques. The approach required only measurements of WF for a 10 x 10 cm2 field at depth of 5 cm employing SSD treatment technique per wedge filter. Using the empirical equations, WFs were determined to within ± 0.50 % of the measured valu-es over the entire treatment depth range of 1.5 to 15.5 cm for SAD and SSD treatment techniques respectively; and WFs could be obtained for any treatment depth and technique.

Patterns of zooplankton diversity through the depths of the Arctic’s central basins

Metazoan zooplankton diversity is characterized for the oceanic environments of the Arctic Ocean, specifically the deep Nansen, Amundsen, Makarov and Canada Basins. Our species inventory is based on original records from 134 locations where stratified sampling of the entire water column was conducted from the surface to the bottom (or a maximum of 3,000 m) during seven icebreaker expeditions (RV Polarstern, 1993-2007, USCGC Healy, 2005) and two older expeditions of the Russian drifting ice stations North Pole 22 and 23 (1975-77). Representatives of eight large metazoan taxa, including Cnidaria, Ctenophora, Mollusca, Annelida, Nemertea, Crustacea, Chaetognatha, and Larvacea, all predominately oceanic species, are registered, with a total of 174 species. Crustaceans strongly dominate in terms of the species number (70%), and copepods are the most diverse group amongst them. Comparison with the historical data suggests that the composition of epi- and mesopelagic zooplankton is relatively well characterized to date, while a considerable number of species we encountered in the bathypelagic layers were either unrecorded before, or undescribed. There appears to be no zoogeographical barrier between the Eurasian and Canadian basins throughout the entire depth range. All deep-water and endemic species are found on both sides of the Lomonosov Ridge, suggesting effective exchange of the deep fauna across the ridge. Notable differences in the species composition in the upper and midwater layers are related to the occurrence of Atlantic and Pacific expatriates advected with their respective waters either into the Eastern or Western Arctic. A pronounced increase in Pielou’s evenness (J'), Shannon’s diversity (H'), and Margalef’s species richness (d) indices with depth, with a maximum occurring within the Atlantic layer, followed by a decrease in the deeper layers, was typical for all deep basins. Species-specific depth preferences and ranges result in statistically distinct communities at different depths with high within-depth similarity (60-80%). Differences were detectable between cruises in the epi- and mesopelagic layers (driven by the expatriates), but less so in the bathypelagic zone.

Azooxanthellate? Most Hawaiian black corals contain Symbiodinium

The ecological success of shallow-water reef-building corals (Hexacorallia: Scleractinia) is framed by their intimate endosymbiosis with photosynthetic dinoflagellates in the genus Symbiodinium (zooxanthellae). In contrast, the closely related black corals (Hexacorallia: Anthipatharia) are described as azooxanthellate (lacking Symbiodinium), a trait thought to reflect their preference for low-light environments that do not support photosynthesis. We examined 14 antipatharian species collected between 10 and 396 m from Hawai'i and Johnston Atoll for the presence of Symbiodinium using molecular typing and histology. Symbiodinium internal transcribed spacer-2 (ITS-2) region sequences were retrieved from 43 per cent of the antipatharian samples and 71 per cent of the examined species, and across the entire depth range. The ITS-2 sequences were identical or very similar to those commonly found in shallow-water scleractinian corals throughout the Pacific. Histological analyses revealed low densities of Symbiodinium cells inside antipatharian gastrodermal tissues (0–92 cells mm−3), suggesting that the Symbiodinium are endosymbiotic. These findings confirm that the capacity to engage in endosymbiosis with Symbiodinium is evolutionarily conserved across the cnidarian subclass Hexacorallia, and that antipatharians associate with Symbiodinium types found in shallow-water scleractinians. This study represents the deepest record for Symbiodinium to date, and suggests that some members of this dinoflagellate genus have extremely diverse habitat preferences and broad environmental ranges.

Admiralty Bay Benthos Diversity—A census of a complex polar ecosystem

A thorough census of Admiralty Bay benthic biodiversity was completed through the synthesis of data, acquired from more than 30 years of observations. Most of the available records arise from successive Polish and Brazilian Antarctic expeditions organized since 1977 and 1982, respectively, but also include new data from joint collecting efforts during the International Polar Year (2007–2009). Geological and hydrological characteristics of Admiralty Bay and a comprehensive species checklist with detailed data on the distribution and nature of the benthic communities are provided. Approximately 1300 species of benthic organisms (excluding bacteria, fungi and parasites) were recorded from the bay’s entire depth range (0–500 m). Generalized classifications and the descriptions of soft-bottom and hard-bottom invertebrate communities are presented. A time-series analysis showed seasonal and interannual changes in the shallow benthic communities, likely to be related to ice formation and ice melt within the bay. As one of the best studied regions in the maritime Antarctic Admiralty Bay represents a legacy site, where continued, systematically integrated data sampling can evaluate the effects of climate change on marine life. Both high species richness and high assemblage diversity of the Admiralty Bay shelf benthic community have been documented against the background of habitat heterogeneity.

Stable isotopes reveal limitations in C and N assimilation in the Caribbean reef corals Madracis auretenra, M. carmabi and M. formosa

We used tissue δ 15 N and δ 13 C to elucidate nitrogen and carbon utilization in 3 branching coral species of the genus Madracis. Coral branches were sampled between 5 and 47 m water depth, and tissue was sub-sampled from the tips and sides of branches. Photosynthetically active radiation (PAR) ranged between 1 and 71% of surface PAR. There was a good correlation between δ 15 N and δ 13 C, and these had similar ranges of 5.6 and 5.2‰, respectively, suggesting that light-driven photo- synthesis is a strong factor in isotope fractionation. However, at shallow depths, δ 13 C decreased more strongly while δ 15 N remained constant, while at deeper depths δ 15 N decreased while δ 13 C remained constant. Comparisons of δ 13 C in polyps and zooxanthellae revealed that prey capture at the tips of branches was more pronounced than at the corresponding sideward-facing positions and that corals at deeper depths did not increase their food uptake to compensate for a decrease in photosynthetic carbon assimilation. This indicates that foraging in branching Madracis depends on current regimes and prey encounter rather than selective food capture. The systematic analysis of tissue δ 15 N along a steep depth gradient revealed that the shallow-water coral M. auretenra was nitrogen limited throughout its entire depth range.

Comparing Atlantic and Mediterranean populations of the velvet belly lanternshark, Etmopterus spinax, with comments on the efficiency of density-dependent compensatory mechanisms

Etmopterus spinax is a small-sized deep-water lantern shark that occurs in the Eastern Atlantic and the Mediterranean. Differences in depth distribution, densities, size at maturity and fecundity were compared between a population that has suffered high levels of fishing mortality during the last decades (Southern Portugal in the northeast Atlantic) and a population where low fishing pressure below 500 m occurs at present or has occurred in the last decades (Northern Alboran Sea in the western Mediterranean). The density of this species, as derived by experimental bottom trawl survey, off the coast of Southern Portugal, is substantially lower than in the Northern Alboran Sea throughout the entire depth range. The Atlantic population is maturing at smaller sizes than the Mediterranean population and has a lower mean fecundity. Specifically, sizes at maturity for Southern Portugal and the Northern Alboran Sea were, respectively, 25.39 and 28.31 cm TL for males and 30.86 and 34.18 cm TL for females, while mean fecundities for Southern Portugal and the Northern Alboran Sea were, respectively, 9.94 and 11.06 oocytes per mature female. This work demonstrated the possible presence of density-dependent mechanisms in the Southern Portuguese population of E. spinax that has lowered the size at maturity as a possible result of excessive fishing mortality. However, given that this is an aplacentary viviparous shark, where fecundity is dependent on female size, this compensatory mechanism seems to have a limited efficiency.

Oxidation state of the lithospheric mantle beneath Diavik diamond mine, central Slave craton, NWT, Canada

Oxygen fugacity (fO2) conditions were determined for 29 peridotite xenoliths from the A154-North and A154-South kimberlites of the Diavik diamond mine using the newly developed flank method modified specifically for measuring Fe3+ in mantle-derived pyropic garnets. The results indicate that the garnet-bearing lithospheric mantle beneath the central Slave craton is vertically layered with respect to oxidation state. The shallow (<140 km), “ultra-depleted” layer is the most oxidized section of garnet-bearing subcratonic mantle thus far measured, up to one log unit more oxidizing relative to the FMQ buffer [Δlog fO2 (FMQ) + 1]. The lower, more fertile layer has fO2 conditions that extend down to Δlog fO2 (FMQ) − 3.8, consistent with xenolith suites from other localities worldwide. Based on trace element concentrations in garnets, two distinct metasomatic events affected the mantle lithosphere at Diavik. An oxidized fluid imparted sinusoidal chondrite-normalized REE patterns on garnets throughout the entire depth range sampled. In contrast, a reducing melt metasomatic event affected only the lower portion of the lithospheric mantle. The fO2 state of the Diavik mantle sample suggests that diamond formation occurred by reduction of carbonate by fluids arising from beneath the lithosphere.

Modelling tidal current-induced bed shear stress and palaeocirculation in an epicontinental seaway: the Bohemian Cretaceous Basin, Central Europe

Lower to Middle Turonian deposits within the Bohemian Cretaceous Basin (Central Europe) consist of coarse-grained deltaic sandstones passing distally into fine-grained offshore sediments. Dune-scale cross-beds superimposed on delta-front clinoforms indicate a vigorous basinal palaeocirculation capable of transporting coarse-grained sand across the entire depth range of the clinoforms (ca 35 m). Bi-directional, alongshore-oriented, trough cross-set axes, silt drapes and reactivation surfaces indicate tidal activity. However, the Bohemian Cretaceous Basin at this time was over a thousand kilometres from the shelf break and separated from the open ocean by a series of small islands. The presence of tidally-influenced deposits in a setting where co-oscillating tides are likely to have been damped down by seabed friction and blocked by emergent land masses is problematic. The Imperial College Ocean Model, a fully hydrodynamic, unstructured mesh finite element model, is used to test the hypothesis that tidal circulation in this isolated region was capable of generating the observed grain-size distributions, bedform types and palaeocurrent orientations. The model is first validated for the prediction of bed shear stress magnitudes and sediment transport pathways against the present-day North European shelf seas that surround the British Isles. The model predicts a microtidal to mesotidal regime for the Bohemian Cretaceous Basin across a range of sensitivity tests with elevated tidal ranges in local embayments. Funnelling associated with straits increases tidal current velocities, generating bed shear stresses that were capable of forming the sedimentary structures observed in the field. The model also predicts instantaneous bi-directional currents with orientations comparable with those measured in the field. Overall, the Imperial College Ocean Model predicts a vigorous tide-driven palaeocirculation within the Bohemian Cretaceous Basin that would indisputably have influenced sediment dispersal and facies distributions. Palaeocurrent vectors and sediment transport pathways however vary markedly in the different sensitivity tests. Accurate modelling of these parameters, in this instance, requires greater palaeogeographic certainty than can be extracted from the available rock record.

Characterizing Spatial and Temporal Variability of Dissolved Gases in Aquatic Environments with in situ Mass Spectrometry

The TETHYS mass spectrometer is intended for long-term in situ observation of dissolved gases and volatile organic compounds in aquatic environments. Its design maintains excellent low mass range sensitivity and stability during long-term operations, enabling characterization of low-frequency variability in many trace dissolved gases. Results are presented from laboratory trials and a 300-h in situ trial in a shallow marine embayment in Massachusetts, U.S.A. This time series consists of over 15000 sample measurements and represents the longest continuous record made by an in situ mass spectrometer in an aquatic environment. These measurements possess sufficient sampling density and duration to apply frequency analysis techniques for study of temporal variability in dissolved gases. Results reveal correlations with specific environmental periodicities. Numerical methods are presented for converting mass spectrometer ion peak ratios to absolute-scale dissolved gas concentrations across wide temperature regimes irrespective of ambient pressure, during vertical water column profiles in a hypoxic deep marine basin off the coast of California, U.S.A. Dissolved oxygen concentration values obtained with the TETHYS instrument indicate close correlation with polarographic oxygen sensor data across the entire depth range. These methods and technology enable observation of aquatic environmental chemical distributions and dynamics at appropriate scales of resolution.

Physical limitations of dissolved methane fluxes: The role of bottom-boundary layer processes

In situ methane emission measurements from sediments are combined with water column backscatter anomalies recorded with an Acoustic Doppler Current Profiler (ADCP) integrated on a benthic observatory. During cruise SO191 to the Hikurangi Margin (New Zealand), the Fluid Flux Observatory (FLUFO) was deployed at a cold seep site at Omakere Ridge. The sediments incubated in the two benthic chambers of FLUFO contained seep-associated fauna, including small and larger tubeworms, juvenile bivalves of the genus Acharax and some juvenile clams. The first 26 h of in situ incubation revealed low to moderate methane fluxes of 0.01 to 0.4 mmol m − 2 d − 1 into the overlying water of the backup and flux chamber, respectively. In the following sampling sequence, however, the methane concentration in the flux chamber reached 3-fold higher concentrations whereas the methane concentration in the backup chamber remained low and unchanged. Simultaneous to the sudden methane increase, a significant backscatter anomaly was recorded and persisted for 30 min and covered the entire depth range (100 m) of the upward looking ADCP. Data analyses revealed that a single-phase plume (no bubbles) outburst likely occurred during this time. While bubbles appeared to be present during some periods, plume simulations revealed that the volume of gas required (rate of 8 ton/day) does not support a bubble plume. A second data set was obtained during lander deployments at Rock Garden where visual observations by ROV confirmed the transient pattern of free gas injection into the water column. Acoustic flares and methane concentration increase in the bottom water hint towards a pressure (tidal) induced discharge mechanism. The presented data demonstrate the temporal and spatial variability of seabed methane emission, and very short methane signal lifetime in the water column (hours to a few days) due to turbulent diffusion. Both have to be considered when methane budgets are extrapolated from single methane emission rates.

Diagenesis of the Devonian Southesk-Cairn Carbonate Complex, Alberta, Canada: Marine Cementation, Burial Dolomitization, Thermochemical Sulfate Reduction, Anhydritization, and Squeegee Fluid Flow

Abstract One of the largest geological features in the deep part of the Alberta Basin in western Canada is the Middle to Upper Devonian Southesk-Cairn Carbonate Complex (SCCC). The SCCC is located at depths of about 5000 m adjacent to the disturbed belt of the Rocky Mountains, rising to depths of 3000 m in a northeastward direction over a distance of 150 km. The SCCC produces oil and gas with up to about 30% H2S from several stratigraphic levels. The diagenesis of the SCCC was investigated by means of petrography and geochemistry. Stable isotope compositions were determined for fibrous calcite cements, matrix dolomite, saddle dolomite, and sparry calcite. Fibrous calcites have stable isotope values of δ18O = −7.5 to −4.5‰ PDB and δ13C = +2.0 +/− 1.0‰ PDB. Matrix dolomite samples have stable isotope values of δ18O = −8.1 to −4.9‰ PDB and δ13C = 0 to +1.0‰ PDB. Saddle dolomite samples range from δ18O = −9.8 to −7.1‰ PDB and δ13C = −1.0 to 0‰ PDB. Sparry calcite samples have δ18O = −13.7 to −7.2‰ PDB and δ13C = −24.0 to 0‰ PDB. The Sr-isotope values of all analyzed samples span a broad range from 0.7080 to 0.7320, showing considerable scatter but also one distinctive pattern, i.e., values higher than 0.7220 occur only at depths in excess of about 4000 m, whereas lower values scatter throughout the entire depth range. Furthermore, the Sr-isotope values of sparry calcites decrease northeastward. Similarly, the fluid inclusion homogenization temperatures of these calcites display a general decrease updip, whereas the salinities show no general spatial trends. The uncorrected homogenization temperatures range from about 85 to 180 °C, and the NaCl-equivalent salinities range from about 17 to 24 weight %. The δD values of brines obtained from seven wells range from −79 to −20‰ SMOW, and their δ18O values range from −1.5 to +8.7‰ SMOW. The sulfur isotope values of the dissolved sulfate ranges from δ34S = +10.1 to +24.5‰ CDT. The Sr-isotope values of the brine samples range from 0.7109 to 0.7255. Elemental sulfur isotope values cluster tightly around δ34S = +18.0 to +18.4‰ CDT. The values of secondary anhydrites range from δ34S = +18.4 to +26.7‰ CDT. Values for solid bitumen vary from δ34S = +19.5 to +20.2‰ CDT. Integration of all data reveals a complex diagenetic evolution from the Middle Devonian to the Recent. The paragenetic sequence consists of 24 distinct diagenetic phases, which have been grouped into 5 diagenetic stages: Stage I: density-driven convection in near-surface settings, likely superimposed on and/or aided by tidal pumping, facilitating marine cementation; Stage II: cellular convection, facilitating pervasive matrix dolomitization, aided by compaction; Stage III: hydrocarbon migration; Stage IV: thermochemical sulfate reduction forming sour gas, and regional squeegee flow forming sparry calcite cements, and localized flow through faults; Stage V: fluid flow driven by erosional rebound in the overlying Mesozoic strata, and remnant squeegee flow. This study yielded several important results. (1) The prolific repertoire of diagenetic textures found in the Southesk-Cairn Carbonate Complex serves as a means of comparison for petroliferous carbonate complexes elsewhere, especially in sour gas provinces close to orogenic fronts. (2) The diagenetic evolution contains long periods of relative tranquility that were punctuated by several episodes of intense diagenetic activity. (3) Both thermochemical sulfate reduction and squeegee-type fluid flow are recorded in late-diagenetic sparry calcite cements. (4) The effect of the various burial-diagenetic episodes on the hydrocarbon reservoir properties throughout the entire reef complex was highly variable. Specifically, matrix dolomitization, thermochemical sulfate reduction, and the emplacement of secondary and tertiary anhydrites affected the hydrocarbon reservoir properties throughout the entire reef complex. On the other hand, squeegee fluid flow was insignificant in terms of affecting the reservoir properties.

Consequences of a mass mortality in populations of Eunicella singularis (Cnidaria: Octocorallia) in Menorca (NW Mediterranean)

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 327:51-60 (2006) - doi:10.3354/meps327051 Consequences of a mass mortality in populations of Eunicella singularis (Cnidaria: Octocorallia) in Menorca (NW Mediterranean) Rafel Coma1,*, Cristina Linares1, Marta Ribes2, David Diaz3, Joaquim Garrabou4, Enric Ballesteros1 1Centre d’Estudis Avançats de Blanes, Accés Cala Sant Francesc 14, 17300 Blanes, Girona, Spain 2Institut de Ciències del Mar, Passeig Marítim 37-49, 08003 Barcelona, Spain 3Instituto Español de Oceanografía, Centro Oceanográfico de Baleares, C/ Moll de Ponent s/n, 07015 Palma de Mallorca, Spain 4UMR 6540-DIMAR CNRS/Université de la Méditerranée, Station Marine d'Endoume, rue de la Batterie des Lions, 13007 Marseille, France *Email: coma@ceab.csic.es ABSTRACT: At the end of the boreal summer of 1999, many invertebrates in hard-bottom communities in the NW Mediterranean Sea suffered an episode of mass mortality. Our study examined the effects of this event on populations of the temperate octocoral Eunicella singularis at Menorca (Balearic Islands). The event affected colonies over the entire depth range where the species is present (15 to 40 m). Four years after the occurrence of the event, 59% of the colonies still exhibited some damage. The extent of injury of the colonies varied among locations, ranging between 37 and 67% with a mean of 50% of the colony surface. The proportion of dead colonies also varied among locations from 26 to 62%, with an overall mean of 46% of the population. The proportion of dead colonies was inversely correlated with density. Current size distribution of the colonies indicated the occurrence of low recruitment during the years subsequent to the mass mortality event. Our study demonstrates that the 1999 mass mortality event was geographically more extensive than previously thought (Menorca is located about 400 to 700 km from areas where mass mortality was previously reported, along the coast of Provence and Ligury). The mortality rate of E. singularis estimated for the Menorca populations was the highest value recorded to date for this species, showing that the delayed effects of the mortality event exerted a much greater impact on these populations than the immediate effects. Additional impacts result from a reduction in recruitment. These delayed consequences may lead to important changes in community composition, structure, processes and function, as gorgonians are key structural and functional organisms within these communities. KEY WORDS: Coralligenous community · Gorgonian mortality · Injury · NW Mediterranean · Eunicella singularis · Partial mortality · Balearic Islands Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 327. Online publication date: December 07, 2006 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2006 Inter-Research.

Archaeal tetraether membrane lipid fluxes in the northeastern Pacific and the Arabian Sea: Implications for TEX86 paleothermometry

The newly introduced temperature proxy, the tetraether index of archaeal lipids with 86 carbon atoms (TEX86), is based on the number of cyclopentane moieties in the glycerol dialkyl glycerol tetraether (GDGT) lipids of marine Crenarchaeota. The composition of sedimentary GDGTs used for TEX86 paleothermometry is thought to reflect sea surface temperature (SST). However, marine Crenarchaeota occur ubiquitously in the world oceans over the entire depth range and not just in surface waters. We analyzed the GDGT distribution in settling particulate organic matter collected in sediment traps from the northeastern Pacific Ocean and the Arabian Sea to investigate the seasonal and spatial distribution of the fluxes of crenarchaeotal GDGTs and the origin of the TEX86 signal transported to the sediment. In both settings the TEX86 measured at all trap deployment depths reflects SST. In the Arabian Sea, analysis of an annual time series showed that the SST estimate based on TEX86 in the shallowest trap at 500 m followed the in situ SST with a 1 to 3 week time delay, likely caused by the relatively low settling speed of sinking particles. This revealed that the GDGT signal that reaches deeper water is derived from the upper water column rather than in situ production of GDGTs. The GDGT temperature signal in deeper traps at 1500 m and 3000 m did not show a seasonal cyclicity observed in the 500 m trap but rather reflected the annual mean SST. This is probably due to a homogenization of the TEX86 SST signal carried by particles as they ultimately reach the interior of the ocean. Our data confirm the use of TEX86 as a temperature proxy of surface ocean waters.

Effect of unloading strain rate on the elastic modulus of a viscoelastic solid determined by nanoindentation

The elastic modulus of an amorphous polymer was investigated by nanoindentation using combinations of ten total penetration depths and three constant unload rates. This experimental design provided a range of unloading strain rates coexisting with a range of depths. The elastic modulus of the material was found to correlate strongly with the unloading strain rate, whereas its correlation with the indentation depth was statistically nonsignificant. Thus, the increase of elastic modulus that occurred with decreasing depth at each constant unload rate was merely due to the increasing unloading strain rate associated with the decreasing depth. The true depth dependence of a rate-dependent material can therefore be studied only by maintaining a constant unloading strain rate across the entire depth range. The implications of these results to the continuous stiffness measurement technique are considered.

EVIDENCE OF RECENT RECRUITMENT IN THE OCEAN QUAHOG ARCTICA ISLANDICA IN THE MID-ATLANTIC BIGHT

Abstract We report results of a survey explicitly focused on ocean quahog recruitment in the Mid-Atlantic Bight. The recruitment survey resampled all NMFS survey sites south of Hudson Canyon and a selection of sites north and east of Hudson Canyon off the Long Island coast over the entire depth range of this species with the exception of the most inshore reaches off Long Island. More ocean quahogs were encountered, on a per tow basis, in the vicinity of and north of Hudson Canyon. The proportion of recruits in the size-frequency distribution was higher in the south and the most recent recruitment events were concentrated there. Analysis of the 104 size-frequency distributions delineated regions of recent recruitment, areas that have not seen significant recruitment for many decades and areas that received heavy recruitment some decades previously but not recently. Overall, the survey suggests that three regionally distinctive processes determine the size-frequency distributions of ocean quahog assemblages...

Regulation of root anaerobiosis and carbon translocation by light and root aeration in Isoetes alpinus

ABSTRACTThe activity of alcohol dehydrogenase (ADH) was measured in corms and roots of the submerged freshwater macrophyte Isoetes alpinus Kirk. growing in situ, and related to its capacity for internal oxygen transport and to carbohydrate translocation. ADH activity was present in roots but not corms at uniform activity (0.15–0.35 × 10−6 mol g−1 fresh weight s−1) over the entire plant depth range (3–7 m depth), and was intermediate to that developed in excised roots after 1‐week exposure to either dissolved oxygen at air‐saturation or to anoxia. Responses of photosynthesis and root oxygen release to light intensity confirmed that shoot‐to‐root oxygen transport saturated at similar light intensities to photosynthetic oxygen evolution, but was positive in the dark and at irradiances below the compensation point for photosynthesis, due to contributions to transport by oxygen diffusion from the external medium. Transport of 14C‐labelled photo‐assimilates to roots nevertheless ceased when intact plants were exposed to a combination of leaf darkness and root external anoxia, even when high 14C concentrations were present in shoots, but remained high when the roots were provided with external oxygen. The lack of any control over permeability of the root surface to gases in this species suggested that ADH activity and reduced translocation is most likely caused by development of hypoxic tissues in the apical tissue. These results suggest that reductions in ambient light intensity may have indirect effects on I. alpinus viability by increasing the degree of root hypoxia and impairing carbon partitioning.