Re-defining sediment transport models over coral reefs and seagrass meadows

Novel research within WAMSI’s Dredging Science Node will redefine how current dredged sediment transport models predict key pressure parameters such as sediment deposition rates within ecologically significant marine habitats.

Sediment deposition and subsequent smothering of marine habitats such as corals and seagrasses is one of the mechanisms by which dredging can impact on the environment.

However, according to Professor Ryan Lowe from The University of Western Australia, current sediment transport models are severely lacking in their ability to predict rates of sediment deposition and re-suspension over coral reefs and seagrass meadows with any degree of confidence.

Canopies formed by seagrass meadows impose drag forces that can trap sediment. This is not accounted for in sediment transport models.

“The first step in the Environmental Impact Assessment (EIA) process for proponents of new developments is to make predictions on the likely extent, severity and duration of their impacts on the environment,” Professor Lowe said. “To do this for projects involving dredging, proponents use sediment transport models that make predictions of where dredge plumes will go and what impacts they will have when they get there.”

“Current sediment transport models assume that the seafloor is essentially flat and that nothing is growing on it. However, in reality the large roughness, or canopies, formed by coral reefs, seagrass meadows and sponge gardens impose substantial drag forces that will alter turbulent flow structure over very small spatial scales and can trap sediment. As a consequence, current sediment transport models can grossly underestimate the rates of sediment deposition that occur in and around these important habitats.”

Sawhorse instrument frame deployed at Ningaloo Reef with hydrodynamic and sediment transport instrumentation. Photo: Andrew Pomeroy

Professor Lowe and UWA collaborator Dr. Marco Ghisalberti are leading a research program combining field and laboratory techniques to address this problem.

“In the field we are measuring turbulent flow structure and sediment concentrations above and within the coral reef and seagrass meadow canopies,” Professor Lowe said. “These direct measurements are compared with various conventional sediment transport models and highlight the major deficiencies.

“We are also conducting parallel and complementary laboratory experiments. The advantage of laboratory experiments is that we can examine in detail the mechanisms and processes in a controlled setting. We can control the densities and heights of canopies, and factors like whether they are completely submerged or not. In this way we can precisely measure transport rates, near bed turbulence, sheer stress and look at the effect of canopies on transport rates and subsequent deposition,” he explained.

Laboratory experiments of sediment transport through artificial canopies

The ultimate goal of this research is to develop new and improved transport formulations and algorithms that can more accurately predict rates of sediment deposition and the subsequent impacts to seabed communities.

“If we can achieve this, then both the Environmental Protection Authority and project proponents will have greater levels of confidence in the prediction of impacts during the EIA process,” Professor Lowe said. “And this is what the Dredging Science Node is all about.”

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

Coral embryos make next-gen mucous cocoons

By Gerard Ricardo, UWA

The phenomenon we call ‘coral spawning’ actually involves five primary early life-history stages, from the release of the egg-sperm bundle, fertilisation, embryogenesis, larval development until finally settlement – each with their own challenges to the impacts of sediment.

The development of the coral embryo occurs on the water’s surface and lasts about 36 hours from the point of fertilisation until the larvae become free-swimming. During this time, the embryos are part of a coral spawn slick, a buoyant slurry of sperm, fertilised and decomposing unfertilised eggs…it gives a smell that takes a while to get used to.

When we exposed the embryos to suspended sediment, we noticed an interesting response that took us a bit by surprise. The embryos cocooned themselves in a mucous sac which sunk to the bottom of the chamber. Within the confines of safety, the embryo maintained development until ciliation (fine-like hairs used for swimming). When the larvae were moved to clean sediment-free water, the larvae could be seen rotating within the cocoon and eventually would rupture and emerge from it – hardly a beautiful butterfly but amazing nonetheless.

Scanning electron micrographs of the mucous cocoon. Coloured backscatter image of an embryo with part of the mucous cocoon removed (left). Orange = sediment, purple = embryo and mucus. Inset A) Mucous web observed under secondary electron mode B) Sediment grains observed under backscatter electron mode.

Once ciliated, the larvae seem to pretty capable of deflecting sediment grains with their new energy-efficient brooms, but while they are embryos, mucous cocooning maybe the only mechanism they have to protect against abrasive and sticky sediment grains. Overall, early-life stages of corals can be very sensitive to sediment, but for these two development stages, mucous cocooning and cilia beating bring a welcome reprieve.

The progression of the coral embryos through the cocoon formation stage

 

 

Ricardo GF, Jones RJ, Clode PL, Negri AP (2016) Mucous Secretion and Cilia Beating Defend Developing Coral Larvae from Suspended Sediments. PLoS ONE 11(9): e0162743. doi:10.1371/journal.pone.0162743

 

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

Sponges choose enigma over charisma

While sea sponges may not be as charismatic as corals, an industry funded WAMSI project is finding their strength may lie in their resilience to change.

One of the most important roles of the sponge is providing habitat for vertebrate and invertebrate species, but one of the most impressive is its ability to filter huge volumes of water – a one kilogram sponge can filter more than 20,000 litres of sea water every day. It makes them a critical link between what’s happening in the benthic environment (the ecological region at the very bottom of the sea) and what happens in the pelagic zone (mid to surface region).

Because they have a big influence on what’s happening around them, a team of researchers at the Australian Institute for Marine Science (AIMS) led by Dr Nicole Webster is testing their sensitivity to reductions in water quality.

Mari Carmen Pineda monitoring sponges in the AIMS SeaSim lab

“Field surveys of the filter feeding communities in the Pilbara region led by Drs Jane Fromont and Christine Schoenberg really highlighted the amazing diversity and abundance of sponges,” Dr Webster said. “It has confirmed that sponges are the dominant filter feeders.”

“This project is looking at sponges of different species, different morphologies and different nutritional strategies to see how they respond to the various dredging related pressures,” she said.

Little is understood about the effects of dredging pressures on sponges. However, some of the known effects include bleaching or the loss of photosynthetic microbes from low light conditions, clogging of their aquiferous systems from high levels of suspended solids or complete burial or smothering of the sponges due to high rates of sedimentation.

Sponge filtration capability

The sponge’s aquiferous system is made up of channels and small chambers lined with specialised cells (choanocytes) that create currents of water and retain nutritive particles.

It’s quite well known that sponges can reduce their pumping activity in response to high levels of particulates in the sea water, but how long they can maintain that reduction in pumping activity before their energy reserves, which they need for growth and reproduction, become entirely depleted is not yet known.

Dr Mari-Carmen Pineda and PhD student Brian Strethlow are testing the sponges under controlled conditions in the AIMS National Sea Simulator (SeaSim) to define cause/effect relationships to the dredging related pressures of light attenuation, sedimentation (smothering) and elevated suspended sediments (clogging).

Carteriospongia foliascens with  mucus and sediment layer sloughing
Cliona orientalis with brittle star inside its osculum cleaning the sediments

“To determine the sponge stress response we measure a whole suite of health parameters in our experimental animals including: changes to respiration rates, bleaching or loss of symbiotic microbes, changes to sponge pumping activity and cellular necrosis,” Dr Pineda said.

“Overall we are finding that sponges seem largely tolerant of short term dredging-related pressures and that light and suspended sediments on their own do not cause severe stress in the short time (days),” she said. “Sponges also demonstrate an array of different mechanisms for coping with sedimentation, such as the development of new oscula (exhalent pores), sediment sloughing and removal of sediment from the aquiferous canals by infauna

Coscinoderma matthewsi with open osculla through the sediment layer

such as brittle stars. “

“On the other hand, long-term exposure (>2 weeks) to dark conditions and high levels of suspended sediments (>30 mg/L), seems to have an impact on growth rates and symbiotic microbes, although most sponges can recover once conditions return to normal.

“Overall, cup shaped sponge morphologies and phototrophic species (ie those that rely on photosynthetic microbial symbionts for nutrition) are the most sensitive to dredging related impacts, and some of them do not possess the ability to recover,” Dr Pineda said.

The SeaSim experiments will add to data gathered from pre-dredging surveys by divers and towed video. The field surveys are also due to be repeated in July post-dredging off Onslow to determine what changes have occurred and how this can be applied to management of dredging operations in the future.

This research was funded by Woodside, Chevron, BHP and WAMSI partners

 

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

Researcher Q and A – Mari Carmen Pineda

Published in AIMS Waypoint

Mari Carmen Pineda talks sponges, dredging and the link between science and industry.

Q1: What brought you to AIMS from Spain?

I first came to AIMS to work in ecology and microbiology and I fell in love with AIMS amazing facilities, like the National Sea Simulator (SeaSim) as well as the scientific excellence of the staff here.

Q2: You are currently studying sponges and how dredging effects them. Can you explain more?

I am working with the ‘sponge team’ I am sponsored by the Western Australian Marine Science Institute (WAMSI) Dredging Science Node to test how sponges respond to sedimentation and dredging-related pressures.

Q3: Sponges are sometimes said to be ‘a window’ into the effects of sedimentation? How is this so?

Sponges are an important component in marine coastal ecosystems where dredging activity usually occurs. In the WAMSI Dredging Science Node, we are working to determine the effects of dredging-related pressures (e.g. sedimentation, total suspended solids and light attenuation) on sponges.

We are performing a series of experiments within SeaSim to do this, in order to develop a better idea about how to devise sound environmental assessments related to dredging programs.

Q4: How do you think industry and science can help each other?

I think that following the global economic crisis it is essential that scientists engage with society and industry to make our research applicable to sustainable development.

Science and industry working together is so important. There are still huge gaps in our basic knowledge of marine systems, so we can’t forget that fundamental science is still essential in order to progress with our more applied research.

And this is what I love about my current job at AIMS! Studying the effect of a potential stressor such as dredging on an important group of marine invertebrates is basic research that can also be applied to improve sustainable dredging programs, ultimately benefiting our oceans, industry and our society.

Q5: Why do you think science is important generally?

Because I can’t conceive of a world without science! Can you? Science contains both the questions and the answers to the environment around us. Science enables us to better understand the world we are living in. Science has improved our health and our quality of life. I truly believe that science is the answer to our current and future problems. Science is our future!

Q6: Can you tell us one fascinating fact about the way in which people need sponges apart from in the bath?

Actually, sponges of the family Spongiidae (order Dictyoceratida, class Demospongiae) have traditionally been harvested as bath sponges, although now days most of the sponges we use in our tubs are actually synthetic!

Sponges have a lot to offer! Some sponge chemicals have considerable potential as anticancer drugs, for example.

Additionally, sponges provide important bioservices within their habitats, including nutrient cycling and the purification of vast water masses. These services provided by sponges ultimately affect the water quality of our oceans and the quality of our fisheries, which are directly linked to our health and wellbeing!

 

Category:

Dredging Science

Northwest seagrass in a world of its own (in the lab)

In the second part of our report into measuring the effects of light reduction and sediment burial to determine the capacity for northwest seagrasses to withstand change, we move from the field to the lab for some surprising results.

The WAMSI Dredging Science Node project has brought together researchers from Edith Cowan University (ECU), The University of Western Australia (UWA) and the Commonwealth Scientific and Industrial Research Organisation (CSIRO) to test tolerance levels that have

UWA’s seagrass growth facility (Crawley campus)

previously never been determined for seagrass species in the far northwest.

Dr John Statton manages the research’s experimental tank system at UWA’s seagrass growth facility (Crawley campus) where the effects of light stress and sediment burial are being measured under controlled conditions on three commonly co-occurring northwest Australian

tropical seagrass species (Halodule uninervis, Halophila ovalis and Cymodocea serrulata).

“We’ve been keeping plants under different light intensities for a number of weeks now. It was quite clear that within the first three weeks the plants at low light intensities (4 and 11% surface irradiance) had lower photosynthetic rates and growth rates than unshaded plants.

“Some of the responses were as expected but what was interesting is that it took a long time for all except one of the species, Halophila ovalis, to die,” Dr Statton said.

Halophila ovalis

Halophila ovalis has the smallest leaf and storage reserves of the three seagrasses under observation and is the only variety of the three that can also be found off the southwest coast.

In the second stage of the research, the plants were subjected to fine sediment (Rocla Quarries WA sponsored UWA with high-grade fine sediments) burial at a depth of between 4mm to 70mm but the effects of light were found to have a far greater impact.

“Only the deepest burial treatments resulted in in some adverse effects,” Dr Statton said. “The seagrasses adapted and grew vertically to new sediment heights then, much like suburban lawns, they put out runners spreading across the new sediment surface. So their initial response to being buried in sediment was to increase the length of their leaves then grow vertically.”

The next step to the lab work will be to install the combined sediment burial and light interaction experiment to look at answering the questions as to what synergies there are when the stresses are combined.

 

The first part of this story was published in the February WAMSI Bulletin:

WAMSI research finds northwest seagrass in a world of its own (Part 1 – in the field)

Related Links:

Tropical Seagrass examined for light pressures (article by Science Network WA)

 

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

WAMSI research finds northwest seagrass in a world of its own

Groundbreaking research into the sensitivity of seagrasses off the northwest coast has uncovered unique behaviour that could lead to a re-think in the way the region is managed.

The seagrasses off Western Australia are the most extensive and diverse of any region in the world with 26 species in 11 genera, accounting for more than 35 per cent of all species currently described globally.

The submerged flowering plants play a vital role in supporting biodiversity, filtering harmful chemicals and nutrients, and sequestering CO2 from the atmosphere. Tropical seagrasses are also a critical food source for fauna such as dugong and green turtles, but little is known about populations off the subtropical northwest .

A Western Australian Marine Science Institution (WAMSI) Dredging Science Node project has brought together researchers from Edith Cowan University (ECU), The University of Western Australia (UWA) and the Commonwealth Scientific and Industrial Research Organisation (CSIRO) to measure the effects of light reduction and sediment burial to determine the capacity for northwest seagrasses to withstand change.

Tolerance levels have previously been determined for seagrasses in the southwest but they are very different to the species off the far northwest coast according to ECU Professor Paul Lavery.

“In the southwest, the dominant species of seagrasses have large storage organs and carbon reserves, and produce large non-dormant seeds,” Professor Lavery said. “Because of their considerable carbon reserves, when they are placed under stress by dredging operations, they draw on those carbon reserves and can survive for several months.

James McLouglin and Roisin McCallum establish a field experiment at Thevenard Is. to determine the mechanisms and rate of seagrass recovery
James McLouglin and Roisin McCallum establish
a field experiment at Thevenard Is. to determine
the mechanisms and rate of seagrass recover

“The seagrass species up north are much smaller, producing small dormant seeds that lay waiting in sediments. They appear to be much more sensitive to changes in light and sediment cover. However we need to be cautious,” he said. “While they may show a rapid response to dredging-induced changes, we don’t really understand yet if they can recover quickly from those impacts. It’s possible that a few months after complete loss, the meadow returns from seed.”

The researchers are conducting a combination of field studies and controlled laboratory experiments.

“We’re working in the Pilbara areas around Exmouth Gulf and Thevenard Island (about 20km off Onslow),” Professor Lavery said. “We’ve been going up every few months to measure characteristics of the meadows, from when they grow, to when they die off and how much biomass there is. This is information we just don’t have for seagrasses in the north.”

Northern sites_Mick Haywood
Research sites in the Pilbara areas around Exmouth Gulf and Thevenard Island

The research program is focused on gaining information that is useful and relevant in a systematic way. An initial recommendation from the research is that pre-development surveys and ongoing monitoring programs for seagrass should consider the time of year. In the month of June, for example, there appears to be no seagrass meadows. It’s not until September that they start to grow back.

“This most basic and fundamental piece of information we didn’t understand before,” Professor Lavery said. “This in turn will save money for companies as they often conduct costly surveys when seagrass is not naturally present.”

We’ve now conducted field studies in several locations to see if the same sort of patterns exist in each location and so far we’re finding that different places have different patterns, which makes things more complicated and is going to make advising government and industry more challenging.”

Off Thevenard Island the researchers removed seagrasses from both shallow and deep water meadows to observe how the system recovers.

“We wanted to see if the meadows can recover from seed or by material drifting in from elsewhere,” Professor Lavery said. “So far we aren’t seeing any recovery by seed. There seems to be a need to have vegetative material available for it to grow back. So it’s back to the lab now to find out the capacity for the seagrasses to withstand change.”

 

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