Bleached corals have reduced capacity to clear sediment

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An investigation into the ability of bleached corals to cope with dredging related stressors has found that several species of thermally bleached corals cannot clear sediment that has smothered them.

The study was undertaken as part of the Western Australian Marine Science Institution’s Dredging Science Node at the AIMS National Sea Simulator in specially developed tank systems.

Corals were subjected to elevated temperatures to cause bleaching and then exposed to various rates of sediment deposition, or smothering. Bleached corals were found to be able to remove about three times less sediment than those that were not bleached.

Lead researcher Pia Bessell-Browne from The University of Western Australia Oceans Institute, Centre for Microscopy, Characterisation and Analysis and Australian Institute of Marine Science said that as coral bleaching events become more common we need to increase our understanding of how these large scale pressures interact with more local pressures, such as dredging activities.

“This has important implications for management, as it demonstrates that precautions should be put in place to reduce the impact of dredging related pressures, and in particular sediment deposition, during periods of elevated ocean temperatures that could result in coral bleaching,” Ms Bessell-Browne said.

The full results have been published in  Scientific Reports.

Bessell-Browne P, Negri A.P., Fisher R, Clode P.L., Jones R, (2017) Cumulative impacts: thermally bleached corals have reduced capacity to clear deposited sediment Scientific Reports doi:10.1038/s41598-017-02810-0

The WAMSI Dredging Science Node is made possible through $9.5 million invested by Woodside Energy, Chevron Australia and BHP Billiton 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 Australia, Woodside Energy and Rio Tinto Iron Ore. The commercial entities had no role in data analysis, decision to publish, or preparation of the manuscript.

Category:

Dredging Science

New framework developed to assess coral resilience to dredging

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Results from a new dredging study in Western Australia’s Dampier Archipelago provide, for the first time, a framework for assessing likely impacts of dredging on coral populations, and for evaluating the timeframes and likelihood of population recovery from impacts.

In April 2014 and March 2015 studies of coral populations were undertaken at Enderby and West Lewis Islands in the Dampier Archipelago, outside the central Port of Dampier and largely unaffected by shipping or other port related activities.

The corals investigated in this study were Acropora millepora, Turbinaria mesenterina and massive Porites spp. (mainly P. lobata and P. lutea) because they were among the most common coral taxa on reefs of the Pilbara, and on many reefs globally.

Sampling locations in the Dampier Archipelago, Western Australia. Replicate sites with a permanent transects were established within each location at Enderby Island and West Lewis Island (Babcock et al 2017)

For each species, populations were carefully measured, mapped and tagged, then re-located and measured again one year later in order to compile measurements of colony growth, mortality and recruitment.  In total 737 colonies were tagged and relocated.

Tagged colonies of Acropora millepora, Turbinaria mesenterina and Porites spp. Each colony in the study was tagged and measured, then re-located and remeasured after 12 months to establish rates of growth and mortality (Babcock et al 2017)

Coral recruit, A. millepora.  All recruits (colonies less than 2cm diameter) within census transects were recorded, to establish rates of recruitment. (Babcock et al 2017)

A. millepora is fast growing and one of the more common Acropora species of the region. Turbinaria mesenterina has a vase-like growth form and is characteristic of inshore reefs in the Pilbara region, such as those commonly affected by development. Massive Porites spp. are encrusting to hemispherical, and slow growing to more than several metres in diameter. Because of their large size and life history strategy, they resist environmental disturbances such as severe cyclone impacts and provide important physical structure to reefs.

Three general disturbance scenarios were simulated, using the models:

i. size dependent mortality of the largest colonies (e.g. due to a cyclone);

ii. severe reductions in recruitment (e.g. due to an extended dredging campaign); and

iii. chronic reductions in recruitment (e.g. due to a shift in underlying environmental conditions).

More specific scenarios were also simulated to evaluate what levels of disturbance (general mortality combined with recruitment failure) could be sustained while still allowing recovery of populations to pre-impact levels within five years, consistent with the definition of the Zone of Moderate Impact in the Environmental Protection Authority’s impact zonation scheme (see Technical Guidance: Environmental Impact Assessment of Marine Dredging Proposals EPA [2016]).

Acropora millepora showed the most rapid recovery from mortality that affected adult colonies, while recovery was slower in T. mesenterina and slowest in Porites spp.

A. millepora however, was most affected by failure of recruitment, or sustained depression of recruitment rates. Recruitment rates did affect Turbinaria and Porites populations but the effects on adult numbers took much longer to manifest and their influence on population maintenance were smaller than in A. millepora.

Lead CSIRO researcher Dr Russ Babcock said modelling of coral populations under a range of scenarios representing likely impacts from dredging showed that, under a best case scenario, recovery within five years was only likely when impacts on live cover of A. millepora and T. mesenterina were less than 15 per cent.

“The results from the simulated impact events present a ‘best case’ scenario in that they represent a single impact,” Dr Babcock said. “In reality, there will usually be a range of impacts affecting individual corals, coral cover, and rates of recruitment, such as cyclones and/or coral bleaching that could affect communities within a decade.”

Babcock R, Gilmour J and Thomson D (2017) Measurement and modelling of key demographic processes in corals of the Dampier Archipelago. Report of Theme 4 – Project 4.7, prepared for the Dredging Science Node, Western Australian Marine Science Institution, Perth, Western Australia, 43pp.

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.

Category:

Dredging Science

Scientists test new sediment sensor that mimics coral reef

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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.

(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).

 

 

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.

Category:

Dredging Science

Can Environmental Windows be effective in managing effects of dredging?

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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.”

 

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.

 

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.

Category:

Dredging Science

Everything you ever wanted to know about how dredging impacts fish!

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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.

Category:

Dredging Science

Results released on seagrass responses to dredging in northwest Australia

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Three new reports have been released on the primary producer responses to dredging.

There is almost no knowledge of how seagrass primary producers in the northwest of Australia will respond to the environmental changes produced by dredging. Consequently, it is difficult to predict and then manage the impacts of dredging on these critical habitats with an acceptable level of certainty.

Research within the Western Australian Marine Science Institution (WAMSI) Dredging Science Node focuses on two of the most significant stresses produced by dredging: the reduction in light availability to plants; and the smothering of seagrass and algae as suspended sediments settle.

Project leader Kathryn McMahon from Edith Cowan University and team members from The University Australia, Department of Parks and Wildlife WA and The University of Adelaide have looked at three key areas:

  1. Seagrasses of the northwest of Western Australia: biogeography and considerations for dredging-related research;
  2. The current state of knowledge regarding the effects of dredging-related ‘pressure’ on seagrasses using information compiled from unpublished industry data, as well as published reports, articles and books; and
  3. Genetic variability within seagrass of the northwest of Western Australia

The first project identified five dredging related stressors that are likely to directly impact seagrass habitat and prioritised the top three in the following list that are of most interest for impact prediction and management of dredging events:

  • reduced benthic light quantity;
  • burial by sediment;
  • sediment anoxia and increased hydrogen sulfide production;
  • altered benthic light quality (i.e. spectral characteristics); and
  • increased suspended sediment

It identified knowledge gaps in three key areas:

  • How dredging affects environmental conditions that are likely to impact seagrass.
  • Thresholds for dredging-related stressor beyond which seagrasses will be affected; and
  • Monitoring during dredging campaigns.

The second project identified the seagrass species Halophila ovalis, Halodule uninervis and Cymodocea serrulata, as the focus of subsequent research into thresholds and indicators of response to dredging-related pressures.

The third study is the first of its kind to examine the patterns of genetic diversity in seagrasses in the Pilbara region which strongly influences their ability to adapt to, resist or recover from these pressures.

This study identified  that:

  1. Most meadows examined  had  relatively  high  clonal  diversity  (i.e.  many  unique  individuals in the meadow), so both sexual reproduction and vegetative growth are important for maintaining these populations; and
  2. There was a reasonably high level of migration of genes over distances of 2−5km, but lower levels over  greater  distances. The  study  also  showed  that  not  all  seagrass  meadows  and  species  in NW Australia  have  a  similar  level  of  genetic  diversity. This information should be incorporated into management decisions as the level of genetic diversity has implications for the ability of populations to resist and recover from disturbance.

The WAMSI Dredging Science Node is one of the largest single issue research programs in Australia meeting the needs of the State Government and industry to improve their understanding of how key primary producers are affected by dredging-related pressures.

The full reports can be found on the WAMSI DSN Primary Producer project page

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.

 

Category:

Dredging Science

Light limitation affects coral health more than sediment

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Researchers have compared the impact low light and suspended sediment particles have on coral and found that, of the two events associated with dredging, several coral species are more likely to be affected by the loss in light intensity.

The results, undertaken as part of the Western Australian Marine Science Institution’s Dredging Science Node at the AIMS National Sea Simulator in specially developed tank systems, have been published in the Marine Pollution Bulletin.

Lead researcher, Pia Bessell-Browne from The University of Western Australia Oceans Institute, Centre for Microscopy, Characterisation and Analysis and Australian Institute of Marine Science, said corals face increasing pressures from coastal development, particularly through dredging for ports.

“In order to appropriately manage these pressures, we need to improve our understanding of the key impacts of dredging on corals,” Ms Bessell-Browne said. “Sediments released from dredging activities can reduce or block light, clog feeding and smother coral. The sediments can also affect many aspects of coral reproduction and recruitment processes.

“High light levels are considered key to the health of corals as it allows for photosynthesis by algae that live within the coral. The products of this photosynthesis provide the coral with a food source.”

A range of light and suspended sediment concentrations were tested to determine their impacts on coral health.

Representative coral colonies from experimental manipulations that were exposed to no, low and high light, showing decreased colour in no and low light treatments (AIMS)

 

Exposure to low light conditions was found to result in coral bleaching, where algae that contribute to the nutrition of their partners, leave their coral host. Mortality of corals was only observed in low light levels, regardless of the amount of suspended sediment in the water column.

“When comparing experimental treatments with conditions experienced during dredging and natural sediment re-suspension events, such as storms and tidal currents, the results suggest that light reduction resulting from increased suspended sediments poses more of a risk to corals than suspended sediments alone,” Ms Bessell-Browne said.

Further work will determine the low light thresholds for corals.

 

PhD Completion Presentation: Lethal and sub-lethal impacts of dredge related stressors on corals, Thursday 02 March, IOMRC Auditorium, 4pm

Bessell-Browne P, Negri A.P., Fisher R, Clode P.L., Duckworth A, Jones R, Impacts of turbidity on corals: The relative importance of light limitation and suspended sediments Marine Pollution Bulletin 2017 http://dx.doi.org/10.1016/j.marpolbul.2017.01.050

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.

Category:

Dredging Science

Effects of dredging on filter feeder communities, with a focus on sponges

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Sponges can filter up to 50,000 times their own volume of water in a day, making them an important link between the water column and seabed. They serve as habitat to other marine organisms and play an important role in the cycling of nutrients, making them a critical part of the marine ecosystem. So, understanding whether they can survive in turbid water, and being covered in sediment from dredging operations are important questions scientists are asking.

A report released by the Western Australian Marine Science Institution (WAMSI) evaluated sponge responses to acute and chronic sediment stress included elevated respiration, reduced or arrested pumping, pore closure, tissue retraction and changes in sponge morphology. Other responses included bleaching, disease and death. However, not all of these responses occurred in all species examined.

More than 900 articles were reviewed including those in peer-reviewed journals, grey literature, technical reports and theses for a Dredging Science Node project to define the thresholds and indicators of filter feeder responses to dredging-related pressures.

From an ecological perspective, turbidity and sedimentation were likely to alter the structure of filter feeding communities by reducing fitness and survival. There are, however, factors other than dredging (e.g. river inputs, cyclones) which have the potential to re-suspend sediment and increase turbidity.

There are sponges that are well adapt to living in turbid environments and may continue to survive at dredging sites. These include endopsammic sponges (living partially buried within sediments), fast growing species that are able to change their morphology (highly plastic), and species with erect growth forms. Sediment tolerance may also be related to species that are more capable of keeping their surfaces sediment-free.

Whilst little is known of responses to cumulative pressures, sponge vulnerability was found likely to be exacerbated during certain periods, e.g. when struggling to satisfy high energy demand for growth or reproduction, during thermal stress events or after tissue damage from e.g. spongivory, storms or reduced salinity.

The review found that sediment associated with dredging activity can affect the physiology of filter feeders in very complex ways, which are not yet adequately understood.

The high diversity and abundance of filter feeder communities in Australia, especially in Western Australia, combined with the lack of knowledge about their biology suggests two critical information needs:

  1. experimental research to improve the understanding of the ecophysiology of filter feeders and determine pressure:response relationships to dredging pressures; and
  2. identification of the dominant and habitat forming filter feeder species and their local and regional significance at possible future dredging locations.

This review also identified potentially sensitive sponge taxa, and summarised stress responses relevant to dredging-related pressures, which are necessary for the monitoring and management of this biodiversity resource.

Links:

Background:

The Western Australian Marine Science Institution is delivering one of the largest single-issue marine research programs in Australia. It will vastly improve the planning and regulation of major dredging operations in our precious marine environment.

This world-class marine research is enhancing capacity within government and the private sector to predict and manage the environmental impacts of dredging in Western Australia. The outcomes will increase the confidence, timeliness and efficiency of the assessment, approval and regulatory processes associated with dredging projects.

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.

Category:

Dredging Science

The rise and fall of seagrasses in the Pilbara

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By Jo Myers & Mat Vanderklift (CSIRO)

Dredging associated with large port developments can reduce the light required for seagrass photosynthesis and smother their growth. This can be caused by large plumes of sediment which some seagrasses are very sensitive to (along with natural disturbances such as cyclones), while others have the capacity to cope, or to recover quickly.

Relatively little is known about normal patterns in seagrass composition, abundance and distribution in north-western Australia, including whether they have natural cycles in abundance across seasons. Knowing more about seagrass ecosystems is important for designing or interpreting studies that aim to detect potential dredging-related impacts on seagrass, and when making predictions about whether they can recover from disturbances, and if so, how quickly.

Results from research on seagrasses in the Pilbara, funded by the Western Australian Marine Science Institution (WAMSI) Dredging Science Node, has found that the most common species of seagrass in the region have similar life histories (they tend to be relatively good at colonising new space) but tend to have different patterns of spatial and temporal variation in abundance and reproduction. This creates challenges for people who assess environmental approvals, because it means that the temporal dynamics of seagrasses in the Pilbara might be less predictable than those of seagrasses in adjacent regions (the Kimberley and the Gascoyne). Monitoring programs that are established to detect potential changes in abundance will need to ensure that their design accommodates this variability.

WAMSI Scientist monitoring recovery of seagrass from cleared experimental plots
(Photo: Paul Lavery, ECU)

Another key finding from the research, led by CSIRO and Edith Cowan University, was the main mechanisms by which seagrasses recover after disturbance. In tropical regions, such as northwest Australia, small-leaved species of seagrasses are often characterised by natural patterns of loss and recovery that can span months or years. Vegetative growth (extension of rhizomes by remaining plants) accounts for most recovery, though recovery from seeds has also been recorded. Understanding which of these mechanisms dominates at a particular location is important for predicting the potential for seagrasses to recover after loss or reduction in abundance.

A field experiment undertaken at Thevenard Island during 2014 and 2015 involved clearing areas of seagrass and the placement of partial and full barriers around the cleared areas — these barriers were designed to disentangle vegetative growth from regeneration from seeds. The experiment showed that the primary mechanism for recovery of cleared areas was vegetative growth.

Halophila ovalis seagrass. Tropical seagrasses are important habitats for marine turtles including the loggerhead turtle that feeds on fauna associated with seagrass beds such as ascidians, clams, mussels and other invertebrates (Photo: Mat Vanderklift, CSIRO)

The main seagrass species at the study site was Halophila ovalis, which is also the most widespread species in the Pilbara. One key implication of this finding is that recovery from disturbances that remove seagrass from relatively small areas should occur within months, provided that sufficient meadow remains for rhizomes to colonise from. When seagrass loss occurs over a larger area, recovery might rely more heavily on immigration of plant fragments or seeds from distant sites, which will take much longer.

LINKS:

For further information about WAMSI and the Dredge Science Node, including access to the final reports (Theme 5.3 and Theme 5.4) see wamsi.org.au/dredging-science-node

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.

Category:

Dredging Science

DSN Report 4.3: Corals of the northwest of Western Australia: biogeography and considerations for dredging-related research

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WAMSI dredging science research has delivered the first guide to the choice of coral species for laboratory experiments to determine the effects of dredging activities on adult and juvenile corals in Western Australia.

Identifying scientifically appropriate coral species that will help to determine the overall ecosystem response to dredging-related pressures is one of three key research areas under the WAMSI Dredging Science Node, along with studies into primary producers such as seagrass and algae, and filter feeders such as sponges.

In Australia, and especially in sub-tropical and tropical north-western Australia, there are many examples of current and planned major dredging projects where millions of cubic metres of sediments require removal. These volumes are significant by global standards and since the released sediments can reduce or block light, clog filtering and feeding apparatus and smother benthic organisms they carry a significant environmental risk.

At the Australian Institute for Marine Science’s National Sea Simulator (SeaSim) laboratory in Townsville, Queensland, researchers are able to ‘pressure test’ for ecological responses. And so the criteria for identifying the best type of coral from the WA coast to test not only had to prove to work well under laboratory conditions but also be readily available for collection from the SeaSims lab doorstep, the Great Barrier Reef (GBR).

In order to identify which corals best fitted the criteria to achieve the most useful results the biogeographic distribution of hard corals was examined over ~2,500 km from Ashmore Reef (12°S) in the Timor Sea to the Recherche Archipelago near Esperance (34°S).

Using data mainly from studies conducted in association with the Western Australia Museum, together with digital records from the east coast held by the Museum of Tropical Queensland ~3,500 records were grouped to 19 locations and then sorted according to family, genus and species.

Of the WA records, the total hard coral species count was 361 species from 17 Families and 83 genera. The highest species count (253 species) was recorded at Scott Reef (North and South Scott Reef and Seringapatam Reef).

Another important criterion was that the corals were reasonably abundant, not just for collecting/permitting purposes but because they are an important part of the species in that habitat.

(Source: Jones R,  Corals of the north west of Western Australia: biogeography and considerations for dredging-related research)

Nine coral species were selected for study Each of these species is found in the central GBR and at each of the sites from Shark Bay to Ashmore Reef and Cartier Islet (i.e. the tropical/reef building territories).

The species represent five families including Poritidae and Acroporidae which are abundant in the Pilbara and commonly used in tagged-coral monitoring program in the Pilbara (Hanley 2011) and in the central GBR (Jones 2008).

The selected species have a range of forms and structures (morphologies):

  • Acropora millepora which “broadcast spawn” by releasing gametes—eggs and sperm—into the water to spread offspring. Broadcasters represent the majority of all reef-building corals.
  • Pocillopora damicornis is a brooder, which are most often not reef-building. Brooders release only sperm, which is negatively buoyant, sinking on to the waiting egg carriers.
  • Acropora tenuis is also a broadcast spawning species but it spawns just after sunset a few hours earlier than A. millepora allowing for more experiments to be performed on the night of spawning. It is a very common species with a similar widespread distribution pattern as Acropora millepora.

Both Pocillopora damicornis and Acropora tenuis will also be used in DSN studies (Theme 7) to help manage the risk of dredging projects around coral reefs where many (though not all) coral species spawn at predictable times of the year.

Links:

Background:

The Western Australian Marine Science Institution is delivering one of the largest single-issue marine research programs in Australia. It will vastly improve the planning and regulation of major dredging operations in our precious marine environment.

This world-class marine research is enhancing capacity within government and the private sector to predict and manage the environmental impacts of dredging in Western Australia. The outcomes will increase the confidence, timeliness and efficiency of the assessment, approval and regulatory processes associated with dredging projects.

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.

Category:

Dredging Science