Lophelia pertusa at VK826

The Lophelia pertusa community at Viosca Knoll (VK826) is the most extensive found to date in the Gulf of Mexico. As part of a multi-disciplinary study, the physical setting of this area was described using benthic landers, CTD transects and remotely operated vehicle observations. The site was broadly characterised into three main habitats: (1) dense coral cover that resembles biogenic reef complexes, (2) areas of sediment, and (3) authigenic carbonate blocks with sparse coral and chemosynthetic communities. The coral communities were dominated by L. pertusa but also contained numerous solitary coral species. Over areas that contained L. pertusa, the environmental conditions recorded were similar to those associated with communities in the north-eastern Atlantic, with temperature (8.5–10.6 °C) and salinity (35) falling within the known species niche for L. pertusa. However, dissolved oxygen concentrations (2.7–2.8 ml l⁻¹) and density (σ_Θ, 27.1–27.2 kg m⁻³) were lower and mass fluxes from sediment trap data appeared much higher (4002–4192 mg m⁻² d⁻¹). Yet, this species still appears to thrive in this region, suggesting that L. pertusa may not be as limited by lower dissolved oxygen concentrations as previously thought. The VK826 site experienced sustained eastward water flow of 10–30 cm s⁻¹ over the 5-day measurement period but was also subjected to significant short-term variability in current velocity and direction. In addition, two processes were observed that caused variability in salinity and temperature; the first was consistent with internal waves that caused temperature variations of 0.8 °C over 5–11 h periods. The second was high-frequency variability (20–30 min periods) in temperature recorded only at the ALBEX site. A further pattern observed over the coral habitat was the presence of a 24 h diel vertical migration of zooplankton that may form part of a food chain that eventually reaches the corals. The majority of detailed studies concerning local environmental conditions in L. pertusa habitats have been conducted within the north-eastern Atlantic, limiting most knowledge of the niche of this species to a single part of an ocean basin. Data presented here show that the corals at VK826 are subjected to similar conditions in temperature, salinity, and flow velocity as their counterparts in the north-east Atlantic, although values for dissolved oxygen and density (sigma-theta: σ_Θ) are different. Our data also highlight novel observations of short-term environmental variability in cold-water coral habitat.

In press in Deep Sea Research vol 1.

Full Citation

Davies, A.J., Duineveld, G.C.A., van Weering, T.C.E., Mienis, F., Quattrini, A.M., Seim, H.E., Bane, J.M. & Ross, S.W. (in press) “Short-term environmental variability in cold-water coral habitat at Viosca Knoll, Gulf of Mexico.” Deep-sea Research Vol 1. DOI: 10.1016/j.dsr.2009.10.012.

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SAMS/Bangor Mini-lander

With my long standing collaborator Kim Last from SAMS and MSc student Harri Condie, we recently conducted a field trip to Sabellaria spinulosa habitats in the Wash. Sabellaria spinulosa is a polychaete worm that builds dwelling tubes out of suspended particles. As part of a project with Kim, funded by the Aggregate Levy, we are working to better understand these amazing reef-building creatures.

Armed with the best gear we could find at short-notice, we constructed a mini-lander system to be deployed near a S. spinulosa reef. We equipped the system with sensors that included a laser particle sizer set to provide information on the particle supply in the region, a current meter, temperature loggers and a CTD system logging not only temperature, salinity and depth but also light attenuation and dissolved oxygen.

Kim with the VideoRay ROV

We left the lander on the seafloor for 24 hours, providing a valuable insight into the particles that may be supplied to the S. spinulosa reef. To supplement this, we also placed out sediment traps on the amazing intertidal reef at Scotsman’s Sled. These traps are basically tubes that allow sediment to settle to the bottom, we then take the sediment back to the lab and look at the type and quantity of particles, including any organic food particles that land into the trap. These particles allow us to verify the readings from the particle sizer but also provide a vital clue to why S. spinulosa is found in that area.

We were out with the Eastern Sea Fisheries Joint Comittee on board their boat the Three Counties. They even let us have a go with their amazing little ROV, a VideoRay. Seriously, we’re thinking that we could do with one! Many thanks to ESFJC and the crew for supporting our research.

We’ve only been back a few days, so our data is still being downloaded off our instruments. But these observations will hopefully be the first of many, as we attempt to determine the underlying environmental controls for S. spinulsa. This work was related to the MEPF/ALSF project (MEPF 08/p76), where we are using our novel VoRT tanks to better understand the impact of aggregate dredging on a range of different species.

Sabellaria spinulosa

Many aquatic organisms rely on the suspension of particulate matter for food or for building materials, yet these conditions are difficult to replicate in laboratory mesocosms. Consequently, husbandry and experimental conditions may often be sub-optimal. The VOrtex Resuspension Tank (VORT) is a simple and reliable system for the resuspension of food or sediments using an enclosed airlift. The particle rain from the lift is mixed in the tank by two water inputs that provide directional current flow across the study organism(s). The vortex mixing creates a turbulent lateral water flow that allows the distribution of particulate matter outwards from the sediment outflow. By calibrating a VORT it is possible to control sedimentation rate by manipulating water and air flow rates. As an example application, three VORTs were maintained under different sediment loading to assess the sediment fraction utilisation and tube growth rates of the tube-building polychaete worm Sabellaria spinulosa. S. spinulosa consistently utilised a lower mean particle size than that of the background sediment when provided with well sorted medium sands. Under sediment starved conditions, there was net erosion of colonies whereas under intermediate and high sediment rates there was consistent cumulative growth throughout a 15 d experiment. This highlights the importance of suspended sediment for S. spinulosa and also the suitability of the VORT system for maintaining organisms with suspended matter requirements.

Publication in Journal of Experimental Marine Biology and Ecology 370.

Full citation

Davies, A.J., Last, K.S., Attard, K. & Hendrick, V.J. (accepted) “Maintaining turbidity and current flow in laboratory aquarium studies, a case study using Sabellaria spinulosa” Journal of Experimental Marine Biology and Ecology 370, 35-40.

http://dx.doi.org/10.1016/j.jembe.2008.11.015

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One particularly notable attempt was to quantify and identify the fish community in the area, the water depth is nearly 1000 m. We used a timed bait release system mounted on the ALBEX lander and attached a new SAMS infra-red camera.

The results were pretty good. You can see a sneak preview below:

Published in JMBA UK 2009.

A three year study was undertaken during 2002 to 2004 from May to September to estimate abundance and density of harbour porpoises on the north coast of Anglesey, Wales, UK. There were no ecological data regarding the harbour porpoises in Anglesey waters so the ability to influence conservation measures was highly constrained.

Boat based transects using distance sampling techniques were applied so a robust estimate of density and abundance could be attained. The study area consisted of a block approximately 489 km2 extending from the east of Point Lynas to the west of South Stack on north coast of Anglesey. The study area was divided into 5 blocks consisting of 31 perpendicular transect lines to the shore. Each of the transect lines were surveyed 1–5 times by the end of the three year study.

Based on the assumption that g(0) = 1 the density of harbour porpoises for the 489 km2 study site was estimated to be 0.630 individuals/km2 (CV = 0.20) and the abundance is estimated to be 309 individuals (CV = 0.20). Heterogeneity in density and abundance was observed across the 5 blocks which showed Point Lynas and South Stack to have the highest densities. This distribution was closely associated to fine-scale oceanographic features which cause prey to be concentrated and may facilitate foraging for harbour porpoises. The study showed that Anglesey provides coastal habitats for the harbour porpoise and was the first study of this kind in North Wales, UK.

Full citation

Shucksmith R, Jones NH, Stoyle GW, Davies A, Dicks EF (2009) Abundance and distribution of the harbour porpoise ( Phocoena phocoena) on the north coast of Anglesey, Wales, UK. Journal of the Marine Biological Association of the United Kingdom, 89(5), 1051-1058.

http://dx.doi.org/10.1017/S0025315408002579

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Human activity in the deep sea is extending ever deeper, with recent research showing that this environment is more sensitive to human and natural impacts than previously thought. Some deep-water fish stocks have collapsed and fishing methods such as bottom trawling have raised international concern over the habitat damage they cause. It is likely that in its current form, deep-sea fishing is unsustainable. Diminishing reserves of hydrocarbons in shallow water are pushing exploration and production into deeper waters, which may cause damage to little known deep-sea habitats. The deep sea is also proposed as an environment where anthropogenic carbon dioxide could be stored to minimise the effect of its release into the atmosphere. At the same time, rising atmospheric carbon dioxide levels may be altering the chemical equilibrium of the global ocean by lowering pH. Many countries are now beginning to designate some deep-sea habitats as marine protected areas in measures to reduce the damage caused by fishing and other anthropogenic activities. This review examines these current and emerging issues in deep-sea conservation and discusses conservation status and the designation of protected areas. The enforcement of protected areas using satellite tracking of vessels is discussed and applied to an internationally agreed deep-water conservation area, which aims to protect cold-water coral habitats on the Darwin Mounds in the north east Atlantic Ocean.

Full citation

Davies, A.J., Roberts, J.M. & Hall-Spencer, J. (2007) “Preserving deep-sea natural heritage: Emerging issues in offshore conservation and management” Biological Conservation 138: 299-312.

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Published in Marine Ecology-Progress Series (2007)

The role of limpet grazing in preventing the development of algal canopies is a recurrent theme in intertidal ecology. Less is known about interactions of limpets with the long-term dynamics of established canopies. Aerial photographs indicate that intertidal canopy cover has declined over the past 44 yr in Strangford Lough, Northern Ireland. There has been a loss of the previously continuous cover of Ascophyllum nodosum (L.) Le Jolis in the mid-shore. A barnacle dominated assemblage now fills gaps in the A. nodosum canopy. The rates at which barnacle patches become established and grow have increased since 1990. Changes in canopy cover have been accompanied by increases in limpet densities since the 1980s. Measurements between 2003 and 2004 showed no increase in length of A. nodosum fronds when limpets Patella vulgata had access to the algal holdfasts. In contrast, when limpets were experimentally excluded from the holdfasts, there was net frond growth. In the Isle of Man, which is climatically similar to Strangford Lough but has fewer limpets, growth occurred regardless of limpet grazing. The breaking force for A. nodosum declined with increasing local densities of limpets. A. nodosum is a sheltered shore species, potentially vulnerable to changes in wave exposure. There is no evidence, however, that Strangford Lough has become windier over the past 3 decades. Variation in wave exposure among locations within the lough was not related to rates of barnacle patch creation or expansion. Limpet population density has increased following a series of mild winters. Climate change may have a role in causing canopy loss, not by direct effects on the growth of fucoids, but by increasing the severity of grazing through changes to limpet populations.

Full citation

Davies, A.J., Johnson, M.P. & Maggs, C.A. (2007) “Unexpected loss of Ascophyllum nodosum caused by limpet grazing” Marine Ecology-Progress Series 339: 131-141.

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Internal waves provide a food supply mechanism for cold-water coral reefs

Andrew J. Davies, Marc Lavaleye, Magda Bergman, J. Murray Roberts, Hans Van Haren and Gerard Duineveld

The cold-water coral Lophelia pertusa forms large biogenic reefs throughout the North Atlantic Ocean. The mechanics of food supply to these areas have been largely hypothesised, with topographical focussing of currents, breaking internal waves and retained matter above banks all put forward as potential mechanisms. However, at present, there has only been limited description of these processes from detailed in situ observations. During several HERMES cruises, numerous physical and biological observations have been made in the Mingulay Reef complex. Located between the Outer Hebridean Island chain and the Scottish Mainland, this reef complex is situated within a dynamic area with semi-diurnal tides and currents of up to 80 cm s^-1. In 2006 and 2007, multiple deployments of landers, recording moorings, ship mounted ADCP and CTDs were used to record the food supply processes and the physical habitat of the L. pertusa reefs in the area. The complex topography of the area retains a solitary internal wave which breaks as direction of the tide changes. The wave drives surface productivity and warmer waters to the reef in a regular pattern. This mechanism has a strong resemblance with the theory of Frederiksen et al (1992) that coral distribution could be in areas where the bottom slope is critical to semi-diurnal internal waves.

http://www.anddavies.co.uk/downloads/DaviesetalHERMES.pdf

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