That sinking feeling: Suspended sediments can prevent the ascent of coral egg bundles

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New research has demonstrated a previously unrecognised event that can markedly reduce the probability that coral gametes (egg-sperm bundels) reach the water surface and come in contact with each other.

Inshore reefs are regularly exposed to higher concentrations of suspended sediments during storms, runoff and dredging. While it has been recognised that suspended sediments can negatively impact fertilisation and later life cycle stages, the vulnerability of the egg-sperm bundles during their journey to the water’s surface has not been considered.

Lead author of the WAMSI research published in Scientific Reports Gerard Ricardo (AIMS/UWA) explained many corals reproduce through synchronised broadcast spawning of gametes and the buoyancy of egg-sperm bundles is critical to fertilisation at the ocean surface.

“We demonstrated that during their ascent to the surface, the egg-sperm bundles can run into suspended sediment grains that stick to their mucous coating, and that under certain water quality conditions the sediment grains are enough to cause a significant number of bundles to sink and never reach the water surface, or be slowed in their ascent” Gerard said.

A coral colony releases egg-sperm bundles into the water column. (G. Ricardo)

The detrimental effect this has on the reproduction of corals is made worse by the fact that the bundles carry both eggs and sperm and the bundles need to reach the water surface and break apart for fertilisation to occur. So if less bundles make it to the surface, the coral spawn slick will be less concentrated and therefore there is less chance two compatible gametes will bump into each other.

“Even if the egg-sperm bundles do make it to the surface, they may arrive too late and miss the party; as wind, waves and currents can quickly dilute and disperse a coral spawn slick,” Gerard explained.

Microscopy image of a coral egg-sperm bundle after failed ascent through elevated concentrations of suspended sediments, revealing considerable attachment of sediment grains (yellow) to the bundles (purple). (Gerard Ricardo)

The observations were captured using a mathematical model that predicts the reduction in ascent probability and egg-sperm encounters as a function of sediment load, depth and particle grain size.

For reefs at 15 metres deep, the model predicts that a coarse silt could reduce 10 per cent of egg-sperm encounters at suspended sediment concentrations of 35 milligrams per litre, and for a reef at 5 metres deep, it could reduce 10% of the encounters at 105 milligrams per litre.

“This is the first study to examine the effects of environmental pressures on the success of coral gamete ascent, which can have important flow-on effects for the ability of a reef to maintain and recover its population,” Gerard said. “It adds to the list of stressors impacting early life history stages of corals and could prevent new corals from adding to the population on nearby reefs.”

It’s thought the mechanism and model used in this research could also be used to determine the effects of sediment grains on the reproductive success of other marine organisms that rely on positively buoyant eggs for fertilisation including some echinoderms, molluscs and fish.

Gerard Ricardo and researchers in the lab A microscopy image of an egg-sperm bundle showing eggs (orange) and sperm (white). (G. Ricardo)

Related Links:

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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Dredging Science

New type of reef identified in the Kimberley

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The remote Kimberley coast is characterised by its extreme tidal ranges, warm turbid waters and frequent cyclonic events, and is also home to a newly recognised form of coral reef, one which grows higher than any other reef type in the world.

Curtin University researcher Dr Mick O’Leary has been leading a Western Australian Marine Science Institution (WAMSI) project team that’s been characterising the surface morphology and internal architecture of Kimberley coral reefs using mutlibeam sonar and seismic profiling technologies, as well as collecting reef cores to establish growth histories and ecological change on thousand year time scales.

The findings, published in the journal Coral Reefs, provide new insights into the ability of Kimberley corals to survive, endure, and thrive, in what is generally considered to be environmentally challenging conditions for coral growth.

The seismic profiling revealed that the living coral veneer does not represent simple coral communities growing on rock foundations but are in fact the surface expression of massive and complex reef structures comparable to what we might see at Ningaloo or the Abrolhos or even the Great Barrier Reef.

Percussion coring on Bathurst-Irvine Island, core length up to six metres were recovered using this method. (Mick O’Leary)

The research team drove 6.5 metre lengths of aluminium tubing into the reef structure to recover a record of reef growth. Radiocarbon dating of corals collected from reef cores revealed that coral growth commenced in the Kimberley almost immediately after the continental shelf was flooded by rising sea levels that followed the end of the last ice age some 12 to 15 thousand years ago, with the oldest dated inshore corals returning ages of more than 9000 years.

The most unusual feature of Kimberley reefs is the elevation of their reef flats. Typically coral reefs will grow vertically until they reach sea level, then having used up all the available vertical space, they switch growth directions and begin to grow laterally into deeper water. The upper vertical limit of reef growth is the mean low water tide level, as corals can only tolerate exposure to the atmosphere for brief periods, which usually occurs around spring low tides.

However, the team’s multibeam sonar surveys have precisely measured the elevation of the reef flats and revealed that Kimberley reefs have grown vertically through the mean low water level limit up to the mean tide level.

“This basically means the corals on the reef flat spend half their life exposed above the level of the tide,” Dr O’Leary said. “The sight of water cascading off the edges of a Kimberley coral reef as the tide falls is something that you can experience nowhere else on Earth.”

Somehow Kimberley corals have managed to adapt over many thousands of years to these extreme tidal ranges, high levels of turbidity, really warm water temperatures and exposure, and are thriving in the Kimberley despite these conditions.

So as we see the beginnings of yet another major bleaching event on the Great Barrier Reef, we might look to these more robust Kimberley coral reefs and ask what is unique about these corals? How long did it take to adapt to the unique Kimberley marine environments and are there lessons here that can be applied to the more sensitive coral reef regions of the world?

Water cascading off the reef at Tallon Island (Tubagus Solihuddin)

Related Links:

The $30 million Kimberley Marine Research Program is funded through major investment supported by $12 million from the Western Australian government’s Kimberley Science and Conservation Strategy co-invested by the WAMSI partners and supported by the Traditional Owners of the Kimberley.

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Kimberley Marine Research Program

River Release | 9 News Perth

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New life is being breathed into Perth’s waterways with 400 thousand juvenile prawns being released into the Canning River. The restocking program has been running for the past four years, rejuvenating a dying hobby and getting families back on the water.

Government Media Statement: Four millionth prawn for Swan and Canning rivers

 

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Estuary Science

Science maximises prawn restocking success

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Estuary Science

Science for restoring and enhancing estuary values – Vasse Wonnerup

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The Vasse Estuary receives the highest nutrient loads of any estuary in WA.

Report from the National Estuaries Network Science Forum on Barrier Estuaries

The Department of Water, Water Science Branch and Busselton office together with Geocatch, hosted the National Estuaries Network Science Forum on Barrier Estuaries with special focus on the Vasse Wonnerup System (VWWS) – a wetland of international significance (Ramsar, 1990).

Around 60 estuary managers, researchers and interested community members met in Busselton to exchange information about the Vasse Strategy, science needs for estuary management and the current state of the VWWS. 

Opening comments highlighted that aligned and collaborative sciences, supported by robust baseline level data are essential for effective decision-making.

Implementing the Vasse Strategy includes a restructure of governance arrangements, development of a business case to fund the strategy, reviewing the drainage infrastructure and continued catchment management interventions.

The history of flow and drainage modifications designed to protect Busselton from flooding were also shown to have contributed to the eutrophic conditions in the lower rivers and estuaries.

Advances in hydrological modelling and smarter engineering solutions are being investigated to achieve essential flood protection as well as better water quality by increased dilution of lowland river flows, helping to reduce nutrient concentrations and the undesirable expression of nuisance algal blooms and fish kills.

Early stage research projects, part of the South West Catchment Council Research Node for the Vasse Wonnerup Wetlands will explore quantitative food web structure, nutrient sources and sinks and socio-economic factors.

The connection with and potential impacts on the receiving water body – Geographe Bay were also explored.  Geographe Bay has one of the largest seagrass meadows on the WA coast. A nation-wide risk assessment for seagrass meadows indicated that climate-driven temperature increase poses the greatest threat to South West seagrass integrity and that this is a greater threat than estuarine water nutrient discharge to Geographe Bay due to the drying climate pattern.

The feedback from members of the National Estuaries Network was that all of the elements needed for successful restoration appear to be in place but the integrated and thoughtful synthesis of all actions, progress and estuary health status updates would greatly assist communication between all stakeholders and sustain the momentum of support that has emerged.

Community interest is high, there has been 18 years of GeoCatch activity in catchment restoration and some highly visible media campaigns for behaviour change such as “Save the Crabs and Eat Them”.  Community members appreciated the opportunity to engage with estuary managers and researchers.

Vasse Wonnerup System and adjacent Geographe Bay are incredible natural assets; with the strong community interest, there are opportunities to greatly enhance eco-tourism activities around this wetland benefiting the economy, society and environment.


We thank all the people who participated in this event. The Abstract booklet includes the speakers and their contact information.


National Estuaries Science Forum on Barrier Estuaries (Busselton)

 

 

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Estuary Science

Marine mapping for a North Kimberley Marine Park

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Scientists on a mission to better understand the ecological biodiversity that thrives on the ocean floor in Australia’s remote northwest are about to head out on the fourth of five field trips, this time to uncover what lives in the area of the proposed North Kimberley Marine Park.

The results will be added to the data collected from the recent field trip aboard RV Solander to the islands of the Bonaparte Archipelago to investigate the coral reefs, sponges and other marine life inhabiting this remote area of the Kimberley.

The Solander voyages include researchers from AIMS, the Western Australian Museum, CSIRO and Curtin University.

The surveys focus on sampling in southern, central and northern sections of the Greater Kimberley proposed Marine Park. Researchers map the sea floor using multi-beam sonar technology, examine the distribution of habitats using towed video, make measurements of the water conditions (light penetration levels; temperature; salinity levels) and tidal ranges, and collect representative samples of the benthic flora and fauna using an epibenthic sled.

Video of sponge gardens at Nick’s Rock.

The current ship based surveys have a focus on the deeper areas, from around 10m below low tide, where little information is available from previous Kimberley studies.

The project anticipates that complimentary work will also be conducted to build on existing information of nearshore shallow and intertidal habitats.

Ultimately all available data will be drawn together to provide an overview of the large scale trends in habitats along the Kimberley and highlight the principle factors determining the presence or absence of key biota.

The locations for investigation have been selected with the WA marine park initiatives in mind, in particular Lalang-garram/Camden Sound Marine Park and the proposed North Kimberley Marine Park in the Cape Bougainville-Cape Londonderry region.

Scientists on the voyage collect benthic specimens to characterise the marine biodiversity of the area and create a reference collection at the WA Museum. This sampling and identification process will help the scientists determine what species of animals and plants occur there and what types of habitats each species is associated with.

What does a coral reef sound like?

“The Kimberley is an increasingly active, multiple-use marine region, with a growing need for accessible environmental and socio-economic information,” WAMSI Project leader, Dr Andrew Heyward (AIMS) said. “These are voyages of discovery, which is inherently exciting for the scientists. We expect the project will reveal much about life on the seabed in this region and make a useful contribution to planning and management.”

“The Kimberley region has a vast array of habitat types with a stunning array of biodiversity, much of which has not been studied or collected before,” CSIRO scientist Dr John Keesing said. “The macro tidal range and working in previously unchartered waters makes surveys of this type particularly challenging, but also exciting and rewarding in terms of the scientific discoveries waiting to be made.”

Work is now underway on the analysis of species assemblages, biomass and abundance in relation to habitat types encountered during the surveys.

Related Links:
Marji Puotinen (AIMS) captured the daily highlights of the voyage on the Northwest Atlas blog http://blog.northwestatlas.org/category/expedition-to-the-kimberly-coast/

The $30 million Kimberley Marine Research Program is funded through major investment supported by $12 million from the Western Australian government’s Kimberley Science and Conservation Strategy co-invested by the WAMSI partners and supported by the Traditional Owners of the Kimberley.

Category:

Kimberley Marine Research Program

Providing an evidence base to support decommissioning of offshore infrastructure

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When an oil and gas project completes, the infrastructure that was installed on the seafloor needs to be managed properly. Decommissioning this infrastructure is very expensive, but companies do it to leave the site in good order as the company moves on.

There are many strategies that can be employed to decommission offshore infrastructure from removal of all infrastructure, through to minimal removal required to make safe and environmentally acceptable. 

However, different stakeholders have different views on how far decommissioning should go. Oil and gas companies want to meet community expectations while minimising costs, recreational fishers like infrastructure to be left as it creates new environments and can enhance fish stocks, some commercial fishers want it removed as it can damage their fishing equipment and environmental groups want to be absolutely sure the environment is protected.

”Unfortunately we don’t have a clear and broadly accepted understanding of what the effects of different decommissioning strategies are in our Western Australian marine environment,” CEO of the Western Australian Fishing Industry Council John Harrison said. “This means everyone reverts to their own perspectives and opinions and can lead to conflict between sectors, to difficulties in regulation and policy, and in companies adopting precautionary strategies that may not be the most effective. So we want to work together to come up with a shared position we can all agree with.”

At the Premier of Western Australia’s Marine Science Round-table meetings, senior representatives of the interested sectors suggested that a collaborative project would make business sense to all parties to better inform regulatory policy and operational management of decommissioning.

 “The Blueprint Initiative has been an excellent process to allow the different sectors that share the ocean to work together on common issues,” Bruce Lake Chairman of APPEA and a member of the round-table said. “Decommissioning is clearly one of those issues that is imminent and is also important to many sectors so it’s a great exemplar project for this collaboration with real value to all.  APPEA is pleased to be able to support this multi-sector approach and particularly to have WAMSI run the project to ensure the outputs are genuinely independent.”

APPEA, RecFishWest, Western Australian Fishing Industry Council, National Energy and Resources Australia, along with NOPSEMA, the Office of the EPA, and Department of Mines and Petroleum and Department of Fisheries are supporting and advising the independent WAMSI project.

“We are also discussing with some other key stakeholder groups to ensure proper representation across the different views,” Patrick Seares CEO said.

The six month project is focussed on ensuring all stakeholders are involved in the conversation about decommissioning through workshops and other forums to understand and document everyone’s issues.  A review of global knowledge and experiences against those questions will then be completed before a consultative approach to deciding what is reasonable to adopt right now, and what are the knowledge gaps we need to do further work in.

“The projects follows in line with the approach tested successfully during the establishment of the WAMSI Dredging Node,” Patrick Seares said. “We will take the time to properly bed down the actual, instead of perceived, questions that need answering before planning a science program. This ensures that science, if required, is targeted and leads directly to the development of guidance that addresses management priorities.”