Benthic Stations Research Articles

CAGE15-2 Cruise Report: Gas hydrate deposits and methane seepages offshore western Svalbard and Storfjordrenna: Biogeochemical and biological investigations

The main goal of CAGE 15-­2 cruise was to study the gas hydrate system and methane emissions off western Svalbard and in Storfjordrenna. We addressed this through a comprehensive scientific program comprising dives with the MISO-­‐Tow Cam adapted to the multicorer frame from UiT-­‐NPI (TowCam/Multicorer, TCM), methane measurements in sediments and water column, sediment coring (multicorer + gravitycorer), water column and sediment biogeochemistry, microbiology, micropaleontology, macrobiology, and bathymetric mapping. In addition, during the ecosounder and TCM surveys we collected data for selecting the locations for the CAGE observatories to be deployed during the cruise. The areas investigated were: W Prins Karls Forland (two sites at ca 90 m and 240 m water depth),An area located at the coordinate 78N 08E called “site 7808” (ca 90 m water depth; marker CAGE 882),Vestnesa Ridge (ca 1200 m water depth; markers CAGE 888 and 895),Storfjordrenna (two sites at ca 350, benthic station SR1, and 390 m water depth, Pingos site; marker CAGE 933),Craters area (ca 350 m water depth). We planned the following activities during the CAGE 15-­2 cruise: EM 300 Simrad swath bathymetry mapping to identify seabed morphologyMapping of flare distributionsCTD stations at different water depths and in different areas for measurements ofocean water masses characteristics, andwater sampling for water/gas chemistry and microbiology investigations across methane seeps.TCM surveys (video-­‐camera) to image seabed fluid flow expressions, sites of bacteria mats and gas bubbles. These results were used to define sampling stations and collect data for the future deployment of CAGE observatories (cruise CAGE15-­‐3)Repeated deployments with TCM to sample surficial and shallow sediments with respect to microbiology, geochemistry, biogeochemistry, and micropalentology.Gravity corer for studying sediment biogeochemistry, biomarkers, microbiology, and foraminifera.Van Veen grabs sampling for studying macrofauna.Scrape sampling to collect fauna communities and possible carbonate blocks. The cruise may be known as: CAGE15_2

Benthic Habitat Morphodynamics-Using Remote Sensing to Quantify Storm-Induced Changes in Nearshore Bathymetry and Surface Sediment Texture at Assateague National Seashore

This study utilizes repeated geoacoustic mapping to quantify the morphodynamic response of the nearshore to storm-induced changes. The aim of this study was to quantitatively map the nearshore zone of Assateague Island National Seashore (ASIS) to determine what changes in bottom geomorphology and benthic habitats are attributable to storm events including hurricane Sandy and the passage of hurricane Joaquin. Specifically, (1) the entire domain of the National Parks Service offshore area was mapped with side-scan sonar and multibeam bathymetry at a resolution comparable to that of the existing pre-storm survey, (2) a subset of the benthic stations were resampled that represented all sediment strata previously identified, and (3) newly obtained data were compared to that from the pre-storm survey to determined changes that could be attributed to specific storms such as Sandy and Joaquin. Capturing event specific dynamics requires rapid response surveys in close temporal association of the before and after period. The time-lapse between the pre-storm surveys for Sandy and our study meant that only a time and storm integrated signature for that storm could be obtained whereas with hurricane Joaquin we could identify impacts to the habitat type and geomorphology more directly related to that particular storm. This storm impacts study provides for the National Park Service direct documentation of storm-related changes in sediments and marine habitats on multiple scales: From large scale, side-scan sonar maps and interpretation of acoustic bottom types, to characterize as fully as possible habitats from 1 to 10 m up to many kilometer scales, as well as from point benthic samples within each sediment stratum and these results can help guide management of the island resources.

Ongoing ocean warming threatens the rich and diverse macrobenthic communities of the Antarctic continental shelf

Global warming is heating the Antarctic circumpolar deep water (CDW), which comes into direct contact with the diverse and abundant macrobenthic communities thriving on the continental shelf of the Weddell Sea (WS). A set of 16 current meters deployed along more than 3000 km coastline revealed that tidal currents drive CDW intrusions onto the WS continental shelf and they can increase the temperature near the seabed by ~2.7 °C. The ongoing ocean warming trend may expose macrobenthic assemblages to ambient temperatures >2 °C by the end of the century with dramatic consequences for communities which have evolved during millions of years in near geophysical isolation under rather constant environmental conditions with temperatures <0 °C. These stenothermal communities have long generation times (therefore, reduced opportunity to mutate) and require hundreds of years for adaptation.Results from 135 benthic stations along the study area showed that macrobenthic communities in the southeastern section of the WS are the most vulnerable to the increase of temperature near the seabed given their high component of sessile organisms. Besides a dramatic marine biodiversity loss, the eventual demise of these communities, which provide habitat structure for a large number of species that can build up >87 g C m−2, will cause the liberation of thousands of tons of carbon to the environment. Macrobenthic communities colonizing the recently opened shelf in the Larsen A and B bays may not have the chance to reach the type of mature assemblage inhabiting the eastern WS shelf. The highest temperatures derived from CDW intrusions were recorded in the Filchner-Ronne region, suggesting that the consequences of the thermal impact could develop faster here than in the rest of the WS. Thus, these macrobenthic communities may show the effects of warming earlier than those thriving in other regions of the WS shelf. Global warming seriously threats the abundant and highly diverse macrobenthic communities of the Antarctic continental shelf.

Bryozoa from the continental shelf off Tierra del Fuego (Argentina): Species richness, colonial growth-forms, and their relationship with water depth

As bryozoans have a rich fossil record, the analysis of their bathymetric ranges and the occurrence of different colonial growth-forms in living assemblages may be valuable for palaeoecological interpretation. The bryozoan fauna from 58 benthic stations (18–92 m) collected on the Atlantic continental shelf off Tierra del Fuego (Southwest Atlantic) was analyzed to assess its biodiversity and the relationship of species richness and colonial growth-forms with depth. In the 58 stations analyzed here, which covered an area of ∼5600 km2, 90 species were found. Of these, 43 species were already known for this area, whereas the remaining 47 are new records. Therefore, the present study increases by 87% the known biodiversity for the study area, which now reaches 101 species. There is a clear increase in bryozoan species richness with depth, but the ratio of erect-rigid/encrusting species remained unchanged, as all the growth-forms increased with depth. Stations were classified by cluster analysis in three groups differing mainly in species richness. Taxonomic turnover (beta diversity) increased with increasing differences in depth between stations. This was due to the presence of a new set of deeper species, but not to the demise of the shallower fauna in the deeper stations. Twenty-two potentially habitat-forming species were found along the bathymetric range surveyed in this study. They were absent at the shallowest station, its number was relatively low at intermediate depths (31–64 m) and then experienced a sharp increase at 70 m. Palaeoecological interpretations should take into account that fragile, calcareous growth-forms could be expected to occur at shallower depths in more protected areas.

High speed acoustic communication with orbital angular momentum multiplexing

Acoustic communication is critical for underwater application such as deep ocean scientific explorations, off-shore industrial controls, and ocean environment monitoring. This is because other techniques using electromagnetic waves such as RF communications are difficult for underwater applications due to the strong absorption of water in such a frequency. Optical communication, on another hand, suffers from the light scattering from micro-particles or marine life making long range underwater optical communication very challenging. Therefore, using acoustic waves to transmit information is currently the dominate technique for underwater applications including data collection and remote control of off-shore benthic stations. However, the low frequency bandwidth available for acoustic communication limits the data transmission rate and information capacity or content. We propose and experimentally demonstrate here a new approach using the orbital angular momentum (OAM) of acoustic vortex beams which provides a new and independent channel that enhances the data transmission rate by eight fold. The OAM multiplexing method demonstrated here will impact significantly on future underwater communications.

MoveIt!: Autonomous Underwater Free-Floating Manipulation

Today, autonomous underwater vehicles (AUVs) are mostly used for survey missions, but many existing applications require manipulation capabilities, such as the maintenance of permanent observatories, submerged oil wells, cabled sensor networks, and pipes; the deployment and recovery of benthic stations; or the search and recovery of black boxes. Currently, these tasks require the use of work-class remotely operated vehicles (ROVs) deployed from vessels equipped with dynamic positioning, leaving such solutions expensive to adopt. To face these challenges during the last 25 years, scientists have researched the idea of increasing the autonomy of underwater intervention systems.

Glider monitoring of shelf suspended particle dynamics and transport during storm and flooding conditions

Transfers of particulate matter on continental margins primarily occur during energetic events. As part of the CASCADE (CAscading, Storm, Convection, Advection and Downwelling Events) experiment, a glider equipped with optical sensors was deployed in the coastal area of the Gulf of Lions, NW Mediterranean in March 2011 to assess the spatio-temporal variability of hydrology, suspended particles properties and fluxes during energetic conditions. This deployment complemented a larger observational effort, a part of the MOOSE (Mediterranean Ocean Observing System of the Environment) network, composed of a coastal benthic station, a surface buoy and moorings on the continental slope. This set of observations permitted to measure the impact of three consecutive storms and a flood event across the entire continental shelf. Glider data showed that the sediment resuspension and transport observed at the coastal station during the largest storm (Hs>4m) was effective down to a water depth of 80m. The mid-shelf mud belt, located between 40 and 90m depth, appears as the zone where the along-shelf flux of suspended sediment is maximum. Besides, the across-shelf flux of suspended sediment converges towards the outer limit of the mid-shelf mud belt, where deposition of suspended particles probably occurs and contributes to the nourishment of this area. Hydrological structures, suspended particles transport and properties changed drastically during stormy periods and the following flood event. Prior to the storms, the shelf waters were weakly stratified due in particular to the presence of cold dense water on the inner- and mid-shelf. The storms rapidly swept away this dense water, as well as the resuspended sediments, along the shelf and towards a downstream submarine canyon. The buoyant river plumes that spread along the shelf after the flooding period provoked a restratification of the water column on the inner- and mid-shelf. The analysis of glider's optical data at different wavelengths suggests that the coastal area and the bottom nepheloid layer during the largest storm are primarily composed of coarse particles, probably macroflocs, and that the size of particles decreases further offshore. A similar trend, albeit less contrasted, is observed after the flooding. This work provided a unique synoptic view across the entire shelf of the impact of a typical Mediterranean storm on bottom sediment erosion and particulate fluxes. Repeated glider transects across the south-western part of the Gulf of Lions shelf permitted for the first time to measure continuously the thermo-haline structures, the suspended particles concentrations and size, the current speed, and to estimate the particulate transport before, during and after typical Mediterranean storm events. Glider data complement and compare well with concomitant high frequency time series at fixed stations along the coast and in a downstream submarine canyon.

The carbonate mineralogy and distribution of habitat-forming deep-sea corals in the southwest pacific region

Habitat-forming deep-sea scleractinian and alcyonacean corals from around the southwest Pacific were analysed for their calcium carbonate mineralogy. Scleractinian coral species Solenosmilia variabilis, Enallopsammia rostrata, Goniocorella dumosa, Madrepora oculata and Oculina virgosa were all found to be 100% aragonitic, while some members of the alcyonacean taxa Keratoisis spp., Lepidisis spp., and Paragorgia spp. were determined to be high magnesium (Mg) calcite (with 8–11mol% MgCO3) and Primnoa sp. is bimineralic with both aragonite and Mg calcite. The majority of these habitat-forming deep-sea corals are found at intermediate depths (800–1200m) in the Antarctic Intermediate Waters (AAIW) with low salinities (~34.5), temperatures of 4–8°C and high oxygen concentrations (>180μmol/kg) and currently sitting above the aragonite saturation horizon (ASH). However, habitat-forming corals have been recorded from greater depths, in cooler waters (2–4°C) that are undersaturated with respect to aragonite (Ωaragonite<1), but with oxygen levels still >160μmol/kg. To address the sampling depth bias the coral records were normalised by the number of benthic stations (sampling effort) in the same depth range. This shows that the highest number of corals per sampling effort is between 1000 and 1400m with corals present in over 5% of the stations at these depths. The normalised records and Boot Strap analyses suggests that scleractinian corals, especially S. variabilis should be present in >1% of stations down to 1800m water depth, with E. rostrata, M. oculata and G. dumosa slightly shallower. While alcyonacean corals are found in >1% down to 2600m, with Keratoisis spp. the deepest down to 2600m, while Lepidisis spp. and Paragorgia spp. found down to 1800m. This suggests that most species can probably tolerate some undersaturation of aragonite (Ωaragonite=0.8–0.9), with several species/genera (S. variabilis; Keratoisis spp.) even more tolerant of lower carbonate concentrations ([CO32−]), down to Ωaragonite of 0.7. With this tolerance for some carbonate undersaturation it is unclear how deep sea habitat-forming corals might respond to future ocean acidification. It is likely that some species/genera will cope better than others. However, future changes in oxygen concentrations and food availability, are also going to have a strong influence on the depth and spatial distribution of deep-sea corals in the southwest Pacific.

A new device to follow temporal variations of oxygen demand in deltaic sediments: the LSCE benthic station

A new benthic station equipped with oxygen microelectrodes and environmental sensors was developed by Laboratoire des Sciences du Climat et de L'Environnement (LSCE) and Division Technique of the Institut National des Sciences de L'Univers (DT‐ INSU) to perform in situ time series monitoring of sediment oxygen demand, linked to the mineralization of organic matter. The time series typically cover periods of 2‐ 3 months, with a base frequency of 1 set of oxygen profiles per day. The profiling head assessed the lateral heterogeneity of the sediment oxygen demand at the beginning of the time series over a 0.8‐ m long rectangle to discriminate spatial and temporal variability. A continuous recalibration is performed using a moored oxygen optode anchored to the benthic station together with a set of environmental sensors. These sensors (turbidity, temperature, salinity, and oxygen) can trigger a high‐ frequency profiling mode to investigate the fate of particulate organic matter delivered during floods, resuspension, and deposition events. Deployments of the benthic station were performed in the Rhone River subaqueous delta (Mediterranean Sea). We show that “stable” periods (when neither floods nor storms occur) were characterized by a stable oxygen demand. In the case of resuspension events, an increase of the sediment oxygen demand by a factor of 2‐ 3 with a relaxation time of 1 day was observed, indicating that the new benthic station can adequately capture the impact of resuspension events on the oxygen demand in deltaic sediments.

Habitat-Specific Effects of Fishing Disturbance on Benthic Species Richness in Marine Soft Sediments

Around the globe, marine soft sediments on continental shelves are affected by bottom trawl fisheries. In this study, we explore the effect of this widespread anthropogenic disturbance on the species richness of a benthic ecosystem, along a gradient of bottom trawling intensities. We use data from 80 annually sampled benthic stations in the Dutch part of the North Sea, over a period of 6 years. Trawl disturbance intensity at each sampled location was reconstructed from satellite tracking of fishing vessels. Using a structural equation model, we studied how trawl disturbance intensity relates to benthic species richness, and how the relationship is mediated by total benthic biomass, primary productivity, water depth, and median sediment grain size. Our results show a negative relationship between trawling intensity and species richness. Richness is also negatively related to sediment grain size and primary productivity, and positively related to biomass. Further analysis of our data shows that the negative effects of trawling on richness are limited to relatively species-rich, deep areas with fine sediments. We find no effect of bottom trawling on species richness in shallow areas with coarse bottoms. These condition-dependent effects of trawling suggest that protection of benthic richness might best be achieved by reducing trawling intensity in a strategically chosen fraction of space.

Spatial and seasonal population dynamics of sympatric Jassa species (Crustacea, Amphipoda)

Marine fouling communities are often characterised by dense aggregations of tube-building amphipod species of the genus Jassa. Although some species of this genus coexist in high densities, the development and relationships of sympatric populations are largely unknown. The current field study tested for the effects of exposure duration, seasonality and spatial heterogeneity on community composition, population structure and recruitment of three coexisting Jassa species. The establishment and succession of Jassa-dominated fouling communities on artificial substratum (PVC panels) were studied over two one-year periods off the island of Helgoland (German Bight, North Sea). At different seasonal times, and for different periods of time, panels were exposed at three stations: an exposed station (near water surface), a benthic station in 10m water depth, and a sheltered station (near water surface). Jassa falcata was the dominant species at the benthic station in 10m water depth, whereas Jassa marmorata and Jassa herdmani were more abundant on panels which were positioned near the water surface (exposed and sheltered station). The two latter species showed higher abundances at the exposed than at the sheltered station, although J. marmorata was always clearly the dominant species. The differences in the spatial distribution patterns of the three species may partly result from direct interspecific competition for space. Populations of all three Jassa species exhibited strong temporal changes in both abundances and population structure (sex ratio, proportions of reproductively active individuals, male morphs), most likely caused by seasonal factors. Rapid colonisation of free artificial surfaces was observed nearly throughout the year. Intensity of colonisation, however, followed a distinct seasonal pattern with a maximum in the summer months. Recruitment probably occurred via drifting juveniles which originated from amphipod communities in the surroundings. The observed differences among the species may mainly reflect adaptations to different environmental conditions. These differences, however, may also contribute to a stable long-term coexistence via some degree of resource partitioning along with ‘intermediate disturbance’ events.

Intervention AUVs: The Next Challenge

Abstract While commercially available AUVs are routinely used in survey missions, a new set of applications exist which clearly demand intervention capabilities. The maintenance of permanent underwater observatories, submerged oil wells, cabled sensor networks, pipes and the deployment and recovery of benthic stations are a few of them. These tasks are addressed nowadays using manned submersibles or work-class ROVs, equipped with teleoperated arms under human supervision. Although researchers have recently opened the door to future I-AUVs, a long path is still necessary to achieve autonomous underwater interventions. This paper reviews the evolution timeline in autonomous underwater intervention systems. Milestone projects in the state of the art are reviewed, highlighting their principal contributions to the field. To the best of the authors’ knowledge, only three vehicles have demonstrated some autonomous intervention capabilities so far: ALIVE, SAUVIM and GIRONA 500, being the last one the lightest one. In this paper GIRONA 500 I-AUV is presented and its software architecture discussed. Recent results in different scenarios are reported: (1) valve turning and connector plugging/unplugging while docked to a subsea panel, (2) free floating valve turning using learning by demonstration, and (3) multipurpose free-floating object recovery. The paper ends discussing the lessons learned so far.

Sediment Dynamics in the Bay of Marseille, Gulf of Lions (France): Hydrodynamic Forcingvs.Bed Erodibility

The present contribution aims to provide an insight into the sediment dynamics of the Bay of Marseille (BoM), France, an area characterised by a mostly rocky, steep-sloped, and protected shoreline. In terms of sediment composition, the northern part of the study area is dominated by fines, whereas sands of mean grain size 0.2 < d50 < 1 mm occur at most other locations. Posidonia oceanica meadows occupy many nearshore areas. Critical bed-shear stress was determined through tests in a unidirectional flume using 15 natural cores. Measured values ranged from 0.04 N/m2 to 0.46 N/m2 and were expressed as a function of the logarithm of d50. Mud content had no observable effect on sediment cohesion, whereas a weak positive trend between critical shear stress and clay content was discerned. Autonomous benthic stations (Acoustic Doppler Current Profiler/Conductivity, Temperature, Depth/Turbidity/ALTUS Data Collection System) were deployed for periods of 2–3 months, and several suspension and erosion events were identified for significant wave heights exceeding 1.5 m. Grain-size trends showed that the protected BoM appeared to favour accumulation of sediments advected from the surrounding areas. The southern sector of the BoM was found to be the area with the highest sediment agitation and erosion rates but with weak transport trends. The northern sector, exposed to dominant SW waves, was shown to be the second most active area in terms of sediment dynamics, whereas the several Posidonia oceanica meadows and sheltered locations along the study area appeared to be possible sediment sinks. The latter included locations close to port installations and the western part of the Cortiou area, known to have water quality issues, which, according to the present findings, are linked to low sediment mobility and/or dispersion of pollutants.

Escaping the flow: boundary layer use by the darter Etheostoma tetrazonum (Percidae) during benthic station holding

Aquatic habitats characterized by directional water flow (lotic environments) pose numerous challenges to their inhabitants, including the constant threat of dislodgement and downstream transport. As a result, many organisms exhibit morphological and/or behavioral adaptations that facilitate midwater or benthic station holding in these environments, such as the ventral sucker disc of armored catfishes. However, a few groups, including the species-rich group of small (7-8 cm long and 1-2 cm high) North American stream fishes called darters, exhibit no obvious morphological adaptations to life in lotic habitats. We therefore asked whether small size itself facilitates benthic station holding in these fish. We first used digital particle image velocimetry to quantify the fluid dynamics of flow over a variety of substrates. We then visualized the patterns of flow over the darter Etheostoma tetrazonum during benthic station holding. The thickness of the region of decreased water velocity (i.e. the boundary layer) associated with several types of rocky substrate was large enough (∼2 cm high in some cases) for E. tetrazonum and many other darter species to escape the oncoming flow. We also found that, despite the large size of its pectoral fins, E. tetrazonum is capable of producing only very weak negative lift forces with fins. These substrate-directed forces likely act in conjunction with upstream-directed frictional forces between the tail, anal and pelvic fins and the substrate to facilitate station holding. Thus, we hypothesize that, in darters, small size is an adaptation to life in the benthic boundary layer of lotic environments.

Tanaidacea (Crustacea, Peracarida) of the North-east Atlantic: the Agathotanaidae of the AFEN, BIOFAR and BIOICE projects, with a description of a new species of Paragathotanais Lang

The tanaidacean fauna of the Iceland-Faroes-Shetlands sector of the North-east Atlantic was studied using material from the BIOFAR, BIOICE and AFEN surveys. Seven agathotanaid species were recorded from the genera Agathotanais, Paragathotanais and Paranarthrura, a total comparable to those from a similar bathymetric range in the Rockall-Biscay area and the Gulf of Mexico. A new species of Paragathotanais is described. All records of this family were from benthic stations with a mean bottom temperature of &gt;= 2 degrees C, with none from the 'cold-water' region north of the Iceland-Shetlands ridge complex. An analysis of North-east Atlantic agathotanaid sex-ratios shows that these are not highly skewed in favour of females and are consistent with the status of the males as relatively non-dimorphic and long-lived entities.

GEOSTAR deep seafloor missions: magnetic data analysis and 1D geoelectric structure underneath the Southern Tyrrhenian Sea

From 2000 to 2005 two geophysical exploration missions were undertaken in the Tyrrhenian deep seafloor at depths between -2000 and -3000 m in the framework of the European-funded GEOSTAR Projects. The considered missions in this work are GEOSTAR-2 and ORION-GEOSTAR-3 with the main scientific objective of investigating the deep-seafloor by means of an automatic multiparameter benthic observatory station working continuously from around 5 to 12 months each time. During the two GEOSTAR deep seafloor missions, scalar and vector magnetometers acquired useful magnetic data both to improve global and regional geomagnetic reference models and to infer specific geoelectric information about the two sites of magnetic measurements by means of a forward modelling.

Effects of light, temperature and habitat quality on meroplanktonic diatom rejuvenation in Lake Erie: implications for seasonal hypoxia

Rapid sedimentation of phytoplankton cells following seasonal blooms is common in lakes and coastal zones throughout the world, yet the fate of these cells is uncertain. Ascertaining the fate of seasonal blooms may be particularly important in ecosystems that experience hypoxia. Benthic stations were sampled seasonally inside and outside of the hypoxic area in Lake Erie to test for differences in chlorophyll a concentrations, algal physiological condition (cell viability) and diatom rejuvenation rates (from enclosure experiments). Hypoxic areas did sustain higher chlorophyll a concentrations compared with oxic sites; however, diatom growth and physiological capability did not differ significantly. Hypoxic areas exhibited exponential growth rates as high as 0.56 day 21 (compared with the oxic station at 0.53 day 21 , P ¼ 0.000) and chlorophyll rejuvenation rates as high as 0.30 day 21 (compared with the oxic station at 0.36 day 21 , P ¼ 0.964). Therefore, sedimentation of phytoplankton cells may not only contribute to the seasonal hypoxia observed in Lake Erie, but those diatoms able to withstand low oxygen concentrations during the summer, once reintroduced into the water column, may also seed subsequent diatom blooms. Initial estimates indicate that the algal pigment present on the bottom of the central basin, likely sedimented from the overlying water, contributed significantly to hypolimnetic oxygen depletion (11‐33%).

Nearshore macrobenthos of northern Kotzebue Sound, Alaska, with reference to local sewage disposal

Macrobenthos of the shallow (\10 m) near- shore marine waters of northern Kotzebue Sound was examined in 2002-2004 to (1) determine nearshore com- munity structure and (2) assess the influence of sewage disposal. A variable number of benthic stations were sampled during three summers, with extensive effort at the disposal zone in 2003. The benthic community structure is similar to other nearshore Arctic locations, and was similar to a previous benthic study done in 1986-1987. The potential of sewage impact was assessed at the request of the community, because sewage is occasionally discharged into the Sound, in volumes of up to 38 million liters, typ- ically through the ice in early spring. Only minimal effects of disposal on the benthos were evident and the effects could not be separated from the impacts of low salinity and relatively high water pigments. Low diversity (H 0 ) and species richness (d) and high biomass characterized sta- tions in the sewage area. Parameters often associated with extreme sewage pollution, particularly hypoxic and/or anoxic conditions and high abundance of opportunistic taxa, were not observed. Local traditional ecological knowledge was solicited throughout the study, and was used to help define the area potentially affected by sewage disposal.

Modelling the impact of cod ( Gadus morhua L.) farming in the marine environment—CODMOD

The environmental impact of Atlantic cod ( Gadus morhua L.) farming was quantified by assessing the benthic effects of a large cod farm in Shetland, UK and by parameterising a mathematical model based on an existing salmon model (DEPOMOD, [Cromey, C.J., Nickell, T.D., Black, K.D., 2002a. DEPOMOD—Modelling the deposition and biological effects of waste solids from marine cage farms. Aquaculture 214, 211–239.]) to predict solids deposition from farmed cod to the seabed. Benthic physico-chemical and macrofaunal data for three consecutive years provided synoptic data for model validation, allowing model testing throughout the growing cycle, from low biomass to near maximum. A video technique for quantifying the particle size and settling rates of cod faeces was further developed (weighted mean settling velocity for cod faeces was 3.7 cm s − 1 ), and faecal output experiments yielded temporal data on post-prandial faecal output (faecal output was 8.5% of feed input d − 1 by mass), which was lower than faecal output rates that have been used in modelling salmon impacts. Feed settling experiments showed large and significant differences between three proprietary cod feeds. At most benthic stations, there was a good fit between modelled and measured benthic Infaunal Trophic Index (ITI) but it failed to reproduce the moderate to heavy impact observed at an inshore transect. Possible reasons for the underperformance of the model in this area include the hydrographic data available and unreported cage movements in the area of the transect. When these factors were taken into account in the model, performance improved. Surveys of the sea bed surrounding the cod farm indicated that over a cod growing cycle up to near maximum biomass, there is a biological response to organic enrichment of the near-field sediments. This enrichment is not excessive in terms of the biomass present, and is comparable to salmon culture sites of similar scale in similar environments. Provided that species-specific parameters are used for particulate wastes no special considerations for modelling of this relatively new aquaculture species are necessary.

BRANCH DIAMETER AND DEPOSITIONAL DEPTH IN CYCLOSTOME BRYOZOANS: TESTING A POTENTIAL PALEOBATHYMETRIC TOOL

Branch diameters within some species of sponges, corals, and bryozoans are known to decrease with depth. This relationship is here tested for inferring relative depth of deposition using three ramose, bushlike cyclostome bryozoans— Cinctipora elegans , Diaperoecia purpurascens , and Erksonea sp.—that are abundant on the continental shelf around New Zealand. Diameters were measured in broken branches of these species dredged from 15 benthic stations ranging in depth from 38–668 m. The expected inverse correlation between diameter and depth was apparent only in C. elegans and even then at a low level of significance and only at relatively shallow depths ( D. purpurascens or Erksonea sp. Further research is needed to ascertain exactly which depth-related environmental factor(s) influences branch diameter in cyclostome bryozoans and whether different species respond differently before bryozoan branch diameter can be used in paleobathymetry.