Science and research
Below is a list of experiments being undertaken by the Benthic Acidification Consortium.
To date, our understanding of the likely effects of ocean acidification on inter-tidal organisms is limited. PML is addressing this knowledge gap by performing 18 month experiments in novel inter-tidal mesocosms. The health of inter-tidal environments is important as these productive environments serve important roles such as feeding and breeding grounds for commercially valuable species and ultimately provide a substantial carbon source for other benthic systems.
PML is performing multi-species experiments on the dog welk, Nucella lapillus, the macro algae Fucus serratus, the gastropods Osilinus lineatus and Littorina littorea, the barnacle Elminius modestus and the urchin Psammechinus miliaris. These complex experiments involve twenty separate cubic metres of seawater which are maintained at CO2 partial pressures of 380ppm, 750ppm and 1000ppm, and water temperatures of 10°C constant; ambient, ambient +4°C and a temperature treatments which follows the seasonal temperature.
The challenge of simulating a tidal environment in the laboratory was overcome by PML engineer Paul Mason, who designed and fabricated a unique mechanism which raises and lowers the test organisms in and out of the water. This controlled immersion simulates tidal conditions without the requirement of a holding facility for twenty tones of seawater when the “tide” is out.
The physiological aspects of test organisms are being measured at regular intervals and the results will be analysed in combination with the other participating organisations. The results from these experiments are expected to break new ground in terms of duration of exposure to conditions similar to OA and help us to understand of how our intertidal environments are able to withstand synergistic effects of global climate change.
To determine the impacts of ocean acidification and warming on a range of marine infaunal invertebrates, we are running long-term (18 month) experiments, which started in January 2011 and will end in July 2012.
Specifically, we are examining the effects of different levels of atmospheric CO2 (380 ppm, 750 ppm and 1000 ppm) and water temperature (10°C constant; ambient, following the seasonal temperature variations and ambient +4°C) on the behaviour and physiology of three benthic invertebrates (cockle Cerastoderma edule; brittlestar, Amphiura filiformis; ragworm, Nereis virens). We will assess the impact of these future climate scenarios on a variety of behavioural and physiological responses after 3, 6, 12 and 18 months of exposure. The invertebrates are being held in aquaria (12 × 12 × 30cm deep) containing sediment and seawater in three large water baths (one seawater bath for each temperature treatment). The temperature in the water baths is controlled (± 1°C) using aquarium heater and chiller units. The pH of the mesocosms is set by continuous bubbling with air of known pCO2, which is set and controlled through an air-gas CO2 mixing system. The experiment is being run and maintained by Drs Jasmin Godbold and Martin Solan at the University of Aberdeen.
Changes in invertebrate behaviour will be assessed by determining the amount of infaunal sediment mixing (bioturbation) and solute exchange between the water column and sediment (bioirrigation) at each time point. We can measure the amount of sediment mixing directly using brightly coloured sediment particles called luminophores. As the animals mix the sediment when they burrow and feed, they will move some of these particles deeper into the sediment and this can be visualised non-invasively, by taking an image of the side of each experimental tank and using imaging techniques to determining the pattern, rate and magnitude with which the different species move sediments under each of the future climate scenarios. Similarly, we can determine the rate and magnitude with which the different species pump water through their burrows, by adding a tracer (bromide) to the water column and measuring the change in concentration of bromide over 24 hours.
Physiological responses of the organisms (growth, resting metabolic rate, acid-base status and the health and structure of major body tissues) will be assessed at each time point by groups from the Universities of Southampton (Dr. Chris Hauton), Plymouth (Drs S. Rastick and P. Carlosi) and Bangor (Dr. N. Whiteley).
Flumes and percolation experiments
Two different types of sediment mesocosms, recirculating flume channels and vertically oriented percolation core liners, will be established at SAMS for the open use and benefit for members of the consortium and for collaborators from a complementing German national project on ocean acidification.
Overall, the recirculating flumes will serve as an ideal platform for studying effects of changing pCO2/pH for biogeochemistry and microbiology (including meiofauna) in a range of sediments. The flumes will successively be equipped with four sediment types: cohesive silty mud, silicate sand, carbonate sand and maerl to investigate impacts of acidification in all four systems.
A complementary approach will also be established consisting of a set of vertically oriented core liners or “flow through reactors”, that can be packed with different types of permeable sand. Measurements of the chemical constituents in the water before and after percolation will provide an overall measure of the carbon and nutrient turn-over rates, as well as the buffering capacity, of different types of permeable sediments.
Settlement panels, which incorporate gas permeable membranes, will be used to create and maintain high CO2 micro environments in the field. High CO2 treatments will be produced by altering the gas diffusion gradient through the membrane by controlling membrane thickness and gas pressure.
A significant benefit of this approach is the ability to measure biological responses to low pH conditions similar to those expected to occur as a result of ocean acidification, whilst maintaining the target community in the field under natural light, nutrient and larval supply conditions.
The European Regional Seas
Ecosystem Model (ERSEM)
ERSEM is a mature plankton functional type model that was initially developed by a framework 3 project.
It is related to NPZD type models but includes several refinements necessary to correctly represent the key processes of temperate shelf ecosystems; the main ones being some plankton community complexity, the microbial loop, variable nutrient stoichiometry, variable carbon : chlorophyll ratios and a comprehensive description of benthic biochemical and ecological processes.
Lophelia and maerl experiments
Long-term ocean acidification experiments will be established at the Centre for Marine Biodiversity and Biotechnology at Heriot-Watt University and the Department of Geographical and Earth Sciences at Glasgow University, to study the synergistic effects of ocean acidification and warming on biomineralisation in cold-water corals (Lophelia pertusa) and coralline algae (maerl). This will assess whether any changes in the growth, physiology and structural integrity of these species due to future high CO2 conditions will impede the ecosystem engineering function that cold-water corals and maerl perform.
Cold water coral cruises
In June 2011, Heriot Watt University researchers set out to Mingulay Reef (UK) as part of the UKOARP Pelagic Consortiums RRS Discovery Cruise. Here they collected L. pertusa colonies which are being used in the long-term multi-replicated ocean acidification system at HWU.
Further cruises in 2012, where L. pertusa reefs will be examined using remotely operated microlanders, will be key to contextualizing laboratory work to in situ systems.