Resilience of deep-sea benthic fauna to sedimentation from seabed mining
The ROBES (Resilience of benthic communities to the effects of sedimentation) programme is funded by MBIE and runs from 2016 to 2021. The project involves a strong multidisciplinary team of scientists from NIWA, Victoria University of Wellington and the University of Waikato. It also links with European research initiatives.
Currently the effects of sedimentation on life in and on the deep-seabed are not well understood.
This programme looks at the impacts of sediment plumes (clouds of sand and other particles) created by disturbance to the seafloor and the discharge of processed waters. Understanding such impacts in the deep ocean is challenging but is important for evaluating the effects on the environment of human activities and developing options to manage them.
In the field
A combination of field surveys and on-site observations are being used along with laboratory-based experiments to determine the effects of seabed disturbance on benthic life.
The first field work started with a benthic disturbance survey in May-June 2018 on the Chatham Rise using NIWA’s research vessel Tangaroa.
An area of the seabed was disturbed with a specially designed tool (called a benthic disturber) to create a sediment plume. The suspended sediment created by the disturbance was tracked and monitored using a variety of survey techniques including conductivity temperature depth (CTD) samples, ship-mounted acoustic echo-sounders and NIWA’s ocean glider.
The effects on the animal community structure at this site and at increasing distances from the area of impact were examined by pre-and post-disturbance sampling using shipboard and moored instrumentation (including landers with sediment traps and optical sensors), sediment cores, and seafloor imagery. Baseline data were collected on bathymetry, topography, water column characteristics, sediment composition, and faunal community structure and abundance prior to disturbance, and then up to twice post-disturbance. Water current flow was assessed using the vessel sensors, moored current profilers, and the underwater glider. Experimental work on the properties of sediment cores was also carried out in onboard laboratories.
There were 254 discrete sampling events. Further sampling will be undertaken in 2019 and 2020 to determine the longer-term resilience and recovery dynamics of disturbed communities.
In the laboratory
The laboratory-based side of the programme involves holding live deep-sea corals and sponges in tanks and exposing them to various levels and durations of particle loads in the water (based on the field survey plume). This is to reveal acute and lethal thresholds as well as the chronic effects of settled and suspended sediment on survivors. Techniques are being developed in an associated project as part of the Sustainable Seas National Science Challenge. The responses to be measured include physical impacts, feeding and respiration efficiency, behaviour and physiological responses such as mucous production. This work will begin in 2019 with samples collected during the second survey.
In combination, the field and laboratory research will provide information on the concentrations and distances over which the impacts of suspended sediment on animals become ‘ecologically significant’. They will also assess the short-medium term resilience and recovery of species and communities from the initial impacts.
Data will be specific to the characteristics of the surveyed substrate and the type of plume created in the survey area (not to an actual mining operation). However, the results will also be useful for evaluating the reliability of sediment plume models, as well as more generic sedimentation impacts. The methods will be an important development that can be applied to other situations. For example, while seabed mining is the principal target industry, results will also be applicable to improving understanding of the effects of deep-sea trawling operations.
Results will be published in scientific papers, presented in separate seminars and workshops and posted on this page.
- The 2018 survey collected a large amount of oceanographic, sedimentological, and biological data that provide significant insights into plume effects and will support a wide variety of analyses in coming months.
- A plot of optical backscatter data collected by the glider shows a plume extending from the seafloor at 450m to 300m (circled on map). This was also detected at times by the CTD sensors.
- Water column chemistry appears to have been affected by the disturbance at the seabed.
- However, the disturber produced less extensive sediment plumes than expected as it did not stir up the heavier sandy component of sediments in the area.
- There was little immediate visual impact on the seabed as the fine sediments appeared to disperse rapidly in the relatively fast bottom current conditions.
- Onboard experiments showed that capping of normal sediment by fine particles from the plume reduced the depth of dissolved oxygen penetration below the surface.
Sponges collected for the experiment by benthic sled; a mooring array being deployed from Tangaroa. [Photo: NIWA]
Communication with tangata whenua is integral to this large Programme. Project Leader Malcolm Clark and NIWA Pou Ārahi Lee Rauhina-August visited Wharekauri/Rēkohu (Chatham Islands) in April 2018 to outline the project, methodology and opportunities for tangata whenua to be involved in this research. Further meetings were also held with Ngāi Tahu. This engagement helps researchers better understand the viewpoints and concerns of Māori and these learnings are on-going. NIWA’s Te Kūwaha (National Centre of Māori Environmental Research) Group continues to facilitate these partnerships.
The research programme has a user advisory group that provides feedback on the research and ensures the work remains relevant. The group has representatives from government agencies, the fishing industry, a commercial mining operator, the minerals industry, an environmental group and the research team. A wider stakeholder workshop is planned for 2019.
Reports and additional information
Information Flyer April 2019 [PDF 448 KB]
Information Flyer August 2018 [PDF 200KB]
Information Flyer September 2018 [PDF 200KB]