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Scientists test new sediment sensor that mimics coral reef
Scientists have tested a breakthrough in sensing sediment risks to reefs that uses bundles of fibre optic sensors and hundreds of countersunk holes to mimic coral.
Sedimentation is considered one of the most widespread causes of stress on coral reefs, and researchers are working to understand the patterns of suspension and resuspension caused by wind, wave, catchment run-off and dredging related activity to better inform about the environmental risks.
The newly designed sediment sensor, has 15 separate fibre optic bundles that produce three separate measurements, each an average of five bundles, and the three-millimetre-thick plate is perforated with hundreds of countersunk apertures, the size and spacing designed to mimic coral. The shape allows sediment to be naturally resuspended by wave action in a similar way to that which would occur on a coral.
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| (Whinney J, Jones R, Duckworth A, Ridd P (Dec 2016) Continuous in situ monitoring of sediment deposition in shallow benthic environments Coral Reefs DOI 10.1007/s00338-016-1536-7) |
The sensor was tested as part of a Western Australian Marine Science Institution Dredging Science Node project against different conditions in the Australian Institute of Marine Science (AIMS) National Sea Simulator (SeaSim) laboratory and in the highly turbid inshore reef community of the Great Barrier Reef (GBR).
Researchers from James Cook University and AIMS were able to show previously undescribed patterns of sediment deposits on reef in the turbid coastal central GBR over periods of a few hours rather than averages over days or weeks, giving a greater understanding of the behaviour of one of the key pollutants on coral reefs.
“The in-situ deployment covered a range of physical conditions with peaks in sedimentation occurring after peaks in turbidity and waves when material began to settle out of suspension,” lead researcher, Dr James Whinney said. “The daily average sediment deposition rate was 19 ± 15 mg cm-2 d-1 over the deployment.”
“However, while Sedpods offer a low cost alternative to measure rates of sedimentation, they do not self clean and need to be changed over each day which involves the logistical and financial costs of daily boating and diving to collect and redeploy.
“The next stage is to carry out testing further offshore as well as during dredging campaigns to define the range of sediments rates corals are likely to experience,” ” Dr Whinney said.
Earlier versions of the deposition sensor used in this study have been deployed in Japan, Papua New Guinea and the inshore central GBR (Thomas et al. 2003a; Thomas and Ridd 2005).
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Whinney J, Jones R, Duckworth A, Ridd P (Dec 2016) Continuous in situ monitoring of sediment deposition in shallow benthic environments Coral Reefs DOI 10.1007/s00338-016-1536-7
The WAMSI Dredging Science Node is made possible through $9.5 million invested by Woodside, Chevron and BHP as environmental offsets. A further $9.5 million has been co-invested by the WAMSI Joint Venture partners, adding significantly more value to this initial industry investment. The node is also supported through critical data provided by Chevron, Woodside and Rio Tinto Iron Ore.
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Can Environmental Windows be effective in managing effects of dredging?
An examination of whether dredging operations suspended during generic windows of environmental sensitivity could reduce the impacts on marine life has found the marine invertebrates, seagrasses and macroalgae too diverse to be covered by a one-size-fits-all approach.
An international team of researchers were involved in the review for the Western Australian Marine Science Institutions’ Dredging Science Node. Lead researcher, Dr Matthew Fraser from The University of Western Australia’s (UWA) Oceans Institute, said the results helped to clarify whether there was enough scientific evidence to base the timing of dredging operations outside a set of generic Environmental Windows.
“The project was basically tasked with looking at whether avoiding or reducing dredging during sensitive life history periods may help to minimise dredging impacts, and we used Western Australia as a case study,” Dr Fraser said. “The problem is that we don’t know enough about reproduction, planktonic dispersal and recruitment for many benthic marine organisms in Western Australia.”
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| Western Australia is a hotspot for macroalgal diversity. Slow growing macroalgae are considered as having higher vulnerabilities to dredging impacts. (Matthew Fraser) | Chromodoris westraliensis (Nudibranch) at Cottesloe Reef. (Matthew Fraser) |
“Combine this knowledge gap with species-specific timing of these events suggests a generic environmental window does not protect all species,” co-author UWA’s Professor Gary Kendrick said.
“What this means is that selection and management of Environmental Windows are best considered on a location by location basis with priority given to ecologically and economically important species that we know enough about,” Dr Fraser said.
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| Western Australian seagrasses form important habitat that supports diverse assemblages of marine animals. Slow growing seagrasses such as Posidonia australis (above) are at higher risk from dredging impacts than faster growing seagrasses. (Matthew Fraser) |
Fraser MW, Short J, Kendrick GA, McLean D, Keesing J et al. Effects of dredging on critical ecological processes for marineinvertebrates, seagrasses and macroalgae, and the potential for management with environmental windows using Western Australia as a case study Ecological Indicators http://dx.doi.org/10.1016/j.ecolind.2017.03.026
The WAMSI Dredging Science Node is made possible through $9.5 million invested by Woodside, Chevron and BHP as environmental offsets. A further $9.5 million has been co-invested by the WAMSI Joint Venture partners, adding significantly more value to this initial industry investment. The node is also supported through critical data provided by Chevron, Woodside and Rio Tinto Iron Ore.
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Everything you ever wanted to know about how dredging impacts fish!
Early stages of fish life, such as eggs and larvae, are most likely to suffer lethal impacts from dredging-related stress, while adult fish that migrate from fresh water to the sea to spawn (catadromous fishes) are more likely to change behaviour, according to new research.
A team led by University of Queensland postdoctoral researcher Amelia Wenger examined hundreds of studies to determine how dredging related stressors, including suspended sediment, contaminated sediment, hydraulic entrainment (organisms that get sucked up with the sediment) and underwater noise, directly influence the size of the effect and response in fish across all aquatic ecosystems and all life history stages.
The Western Australian Marine Science Institution Dredging Science Node project, found that across all dredging-related stressors, studies that reported fish mortality had significantly higher effect sizes than those that describe physiological responses, though indicators of dredge impacts should aim to detect effects before excessive mortality occurs.
“Both suspended sediment concentration and duration of exposure greatly influenced the type of fish response we observed, with both higher concentrations and longer exposure associated with fish mortality,” Dr Wenger said.
(Figure 1. A schematic diagram of categories of potential effects of dredging on fish. – Wenger AS, Harvey E, Wilson S, et al. A critical analysis of the direct effects of dredging on fish. Fish Fish. 2017;00:1–19. https://doi.org/10.1111/faf.12218)
“It’s well known that some fish avoid turbid waters but moving to a less ideal environment can affect their chances of survival. Increasing exposure to suspended sediment makes it harder for fish to find their food, elevates their stress levels, and causes damage to fish gills affecting growth, development and swimming ability.
“By analysing several studies, we were able to see clear evidence that fish from all aquatic ecosystems were sensitive to turbidity,” Dr Wenger said.
Studies examining the effects of contaminated sediment also had significantly higher effect sizes than studies on clean sediment alone or noise, suggesting combined dredging stressors produce an effect greater than the sum of their individual effects.
“The review highlights the need for in-situ studies on the effects of dredging on fish which consider the interactive effects of multiple dredge stressors and their impact on sensitive species of ecological and fisheries value,” Dr Wenger said.
The findings are expected to improve the management of dredging projects to ultimately minimise their impacts on fish.
Wenger AS, Harvey E, Wilson S, et al. A critical analysis of the direct effects of dredging on fish. Fish Fish. 2017;00:1–19. https://doi.org/10.1111/faf.12218
The WAMSI Dredging Science Node is made possible through $9.5 million invested by Woodside, Chevron and BHP as environmental offsets. A further $9.5 million has been co-invested by the WAMSI Joint Venture partners, adding significantly more value to this initial industry investment. The node is also supported through critical data provided by Chevron, Woodside and Rio Tinto Iron Ore.
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