Suspended sediments limit coral sperm availability

We have known for more than a decade that suspended sediments from dredging and other sources could impact coral fertilisation, but we didn’t know why. A WAMSI Dredging Science project is working to find the answers.

Lead researcher Gerard Ricardo from The University of Western Australia and the Australian Institute of Marine Science said the project team first designed an experiment to discover whether sediment was impacting the sperm or the eggs.

“We found that while the eggs were capable of fertilising in the presence of high sediment concentrations, far more sperm were needed to achieve adequate fertilisation success,” Gerard said. “This indicated that the sediment was ‘taking-out’ the sperm and preventing them from contacting the egg.”

“When we added sperm to the suspended sediments and noticed small flocs (flakes) appearing on the bottom of the containers, indicating the sediments were sticking to the sperm and both were sinking away from the floating eggs. We confirmed this hypothesis using microscopy to examine the flocs, as well as a sperm counts at the water surface which revealed a decrease in sperm numbers.

“Our results suggest that sediments may shrink the fertilisation window – a brief 1-2 hour period when sperm and eggs can fertilise before wind and waves dissipate them.

“The next step will be to determine what properties of the sediments cause the flocking and sinking of the sperm and subsequently which sediments present the greatest risk if dredging occurs during coral spawning events,” Gerard said.

The findings have been published in Scientific Reports: G. Ricardo, R, Jones, P. Clode, A. Humanes, A. Negri (Dec 2015) Suspended sediments limit coral sperm availability  doi:10.1038/srep18084

Fact File:

  • Sediments can reduce the amount of sperm available to fertilise the egg
  • Sperm can become tangled up in sediment flocs
  • Multiple lines of evidence were used including fertilisation assays, flow cytometry and optical and electron microscopy to determine the mechanism that is responsible for the decrease in fertilisation with elevated suspended sediments.
  • Sediment may further shrink an already brief (1-2 hour) ephemeral fertilisation window.

The work was carried out at the National Sea Simulator (AIMS) and the Centre for Microscopy, Characterisation and Analysis (UWA).

Naitonal Sea Simulator (SeaSim)

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.


Dredging Science

Comprehensive and accessible information to support science, policy making and public understanding

Australia’s northwest marine region is known for both its diversity and its remoteness. However, with increasing anthropogenic pressures within the region, there has been a growing need for accessible environmental and socio-economic information to support decision making. The North West Atlas was created in response to this need, providing comprehensive and accessible information for the greater northwest region.

The North West Atlas provides the infrastructure and tools to promote the free and open exchange of information to support science, policy making and public understanding of the region. These tools include a content management system for science articles and data, a mapping engine for spatial information and social media integration for promotion of content and interaction with a range of stakeholders. The North West Atlas provides a web portal to not only access and share information, but to celebrate and promote the biodiversity, heritage, value, and way of life of the greater northwest region.

Interactive Maps and Spatial Data

Interactive map on the North West Atlas summarising key research findings


The North West Atlas has links to a mapping engine used to both manage and visualise spatial data. Both raw data and prepared datasets can be uploaded. Raw data can be accessed and downloaded by researchers and managers to be included in analyses to inform decision making and management. While prepared datasets have been uploaded to provide an interactive summary of key research findings. Examples of prepared datasets include interactive maps for the North West Oceanic Shoals and Rankin and Glomar Shoals summarising these key ecological features.

Research Highlights

Research article summarising the WAMSI Kimberley Marine Research Program


Research articles provide an overview of key research undertaken within the region. Article are written for a general audience and summarise key research questions and findings. Articles to date describe current research for the WAMSI Kimberley Marine Research Program, feature outcomes from the Montara Environmental Monitoring Program and summarise the Woodside environmental survey of Rankin and Glomar Shoals. Highlights include exploring the deeper ‘hidden’ coral reefs of the Timor Sea and the finding these reefs, the north west oceanic shoals, support exceptional species richness.

Outreach and Communication

Instagram images providing a brief summary of research highlights

The goal of the North West Atlas is to provide a friendly site to engage all stakeholders including managers, research scientists, government, industry and the general public. The site has links to the blog site, Twitter, Facebook, YouTube and Instagram, These links provide an avenue to summarise and highlight research targeting different user groups and providing varying levels of scientific and technical detail.

The North West Atlas project builds on the e-Atlas project for the Great Barrier Reef and the Ningaloo Atlas covering Ningaloo World Heritage Area. It is a partnership between government organisations, non-government organisations, researchers, industry, and community groups. Funding for the North West Atlas project has been provided by PTTEP Australasia (a wholly-owned subsidiary of PTTEP, the Thai national petroleum exploration and production company) and the Australian Institute of Marine Science (AIMS).

Genetics, Connectivity and Recovery Potential of Pilbara Seagrasses

Research from the WAMSI Dredging Science Node has provided new insight into how seagrasses in the Pilbara may recover from disturbance events such as dredging.

While some seagrasses can potentially recover from dredging related pressures over a 200 kilometre radius, others require another meadow within five kilometres to survive, or need to be regenerated from a seed bank.

The research, which is important to the ongoing management of the region’s coastal biodiversity, has produced the first real insight into the genetic variability of the area’s seagrass and the level of connectivity among different seagrass populations.

Pilbara seagrass meadows are an important source of food and habitat for the endangered dugong, sea turtles and prawns, the latter of which makes up part of the region’s multi-million dollar commercial fishing industry.

Lead researcher, Edith Cowan University’s Kathryn McMahon, described how several WA Marine Science Institution (WAMSI) projects are revealing more about the genetic diversity and connectivity of Pilbara seagrasses and how this is revealing the possible ways seagrasses may resist or recover from disturbance, insights which are critical to better management of seagrass meadows.

“In one WAMSI project we determined where the seagrass meadows are, how much there is and how it varies seasonally throughout the year” Dr McMahon said. “In a complementary genetics project we examined which species had the higher genetic diversity and therefore a better chance to resist change and recover from dredging pressures.”

Of the 15 species of seagrass found in the Pilbara, the WAMSI team, including researchers from CSIRO, the University of Adelaide and Department of Parks and Wildlife, looked specifically at three of the most common; Halophila ovalis (6 populations), Halodule uninervis (8 populations) and Thalassia hemprichii (3 populations).

“What we found is that Halophila ovalis and Thalassia hemprichii have high genetic diversity in most meadows that we sampled,” Dr McMahon said. “Thalassia showed a high connectivity over distance; the fruit from one meadow can potentially float to a meadow up to 200km away and successfully recruit into that meadow.

“Whereas with Halophila ovalis and Halodule uninervis gene flow is over a much smaller scale. So a meadow which is completely lost could only recover if there was another meadow within about 5kms.

“So from a dredging perspective, if we lose a seagrass meadow, we can give an indication of when or if they are likely to recover within five years based on the WA EPA’s Dredging Guidelines of irreversible loss,” Dr McMahon said.

Seagrasses tend to be found in the coastal zone and grow in soft sand and muddy sediment but some species can also grow on reefs. They are found in more shallow water to a depth of 10 metres, but can be found in clear water down to 50-60 metres. In the Pilbara, seagrass meadows are mostly found in shallower water.

Based on genetic differentiation, two to three management areas were identified. Exmouth Gulf was distinct from Thevenard Island, Rosemary Island and Balla Balla, and Balla Balla was distinct from the island sites.

“Long distance migration was detected but this is likely to be rare based on the genetic differentiation among sites,” Dr McMahon said. “This long distance dispersal was occurring both in a northward direction, against the direction of the dominant oceanographic current, and southwards, with the direction of the dominant current. There was no association of genotypes with habitat. Some meadows appear to be resilient from a genetic perspective, but others not.”

Halophila ovalis genetic connectivity among sites over a local scale in the Exmouth region. This network analysis is stylised on the site map to show the major migration pathways (relative migration rates >0.8). 1=Exmouth Gulf 1, 2=Exmouth Gulf 2, 3=Mangrove Bay, 4=Muiron Is. North, 5=Muiron Is. South.

“As a result, we feel that incorporating analysis of genetic diversity of seagrass meadows (clonal richness, allelic diversity, heterozygosity) into pre-dredging surveys would allow dredging proponents to identify sites, which are more resilient and hence better able to cope with or recover from dredging related pressures, or conversely, less resistant and in need of more stringent management measures,” Dr McMahon said.

A summary of the genetic resilience of seagrass meadows in the Pilbara based on clonal richness, allelic diversity and heterozygosity. The potential to adapt to pressures over generations was based on allelic richness, to recover from declines in a generation was based on heterozygosity and to recover from complete loss using seed banks was based on clonal richness.

The WAMSI research has also found that the diversity of Thalassia hemprichii is higher in the Pilbara than in the Kimberley, which was unexpected.

“The hotspot for seagrass in this region is in the Coral Triangle of Indonesia and since the Kimberley is closer to this hotspot, we expected to find higher diversity there than in the Pilbara.  However, it may be that the massive tides in the Kimberly result in it being more isolated from the rest of the coast.” Dr McMahon said.


Seagrasses are clonal, marine flowering plants that form critical habitat in coastal waters. They are found in coastal waters of all continents except Antarctica, where they provide significant ecosystem services including: primary productivity; a food source for critically endangered fauna; habitat for many marine flora and fauna; sediment stabilisation; and carbon storage.

Globally, seagrasses are threatened with 29 per cent of the known areal extent estimated to be lost.  Since 1990 the loss rate is reported to have increased from 0.9% per year to 7% per year, comparable to loss rates reported for mangroves, coral reefs and tropical rainforests.

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.


Dredging Science

New era for Indian Ocean research

The disappearance of flight MH370, the devastation caused by the 2004 Boxing Day Tsunami, the profound societal impact of monsoons which are so strongly linked to the Indian Ocean and the fact that so many island groups, states and territories rely on its little understood ways has helped to renew a global drive to find out more about the only ocean to be blocked by land to the north.  

Indian Ocean research came into focus in Goa, India, recently when researchers from around the world presented their findings ahead of a Second International Indian Ocean Expedition (IIOE-2), launched 50 years after its predecessor.     

A group of researchers from WAMSI partner organisations (CSIRO; Murdoch University, Curtin University, The University of Western Australia, Bureau of Meteorology and IMOS) attended the ‘Dynamics of the Indian Ocean: Perspective and Retrospective’.

The symposium provided a forum for marine and related scientists from countries bordering the Indian Ocean, as well as those from further afield, to present results of their latest research in the Indian Ocean; review the progress made in understanding the unique characteristics of the region; and plan future research to address outstanding issues.

“The symposium papers and the work to be undertaken now through IIOE-2 are particularly relevant to Western Australia and Australia more broadly,” Head of the Perth Programme Office of the Intergovernmental Oceanographic Commission (IOC) of UNESCO and IOC Second International Indian Ocean Expedition (IIOE-2) Coordinator Dr Nick D’Adamo said.

The work WAMSI partners are doing on the west coast of Australia contributed significantly to the event in synergy with the work of the broader regional and international scientific community. Presentations were made by: Professor Chari Pattiaratchi and Dr Eric Raes (UWA); Dr Alicia Sutton (Murdoch University); CSIRO’s Dr Francois Dufois, Dr Ming Feng and Dr Andreas Schiller; and IMOS Director Tim Moltmann.

Dr Pattiaratchi and Ms Su are examining the dynamics of the central northern Indian Ocean and contributing to the East Indian Ocean Upwelling Research Initiative of IIOE-2, which includes areas off N-NW Australia.

Tim Moltmann highlighted IMOS’s contribution particularly to Eastern Indian Ocean marine and related research.

Dr Feng’s area of research focus has been on the marine heatwave events off Western Australia in the Leeuwin Current system over the past few years and how they are linked to the Indo-Pacific climate variability.

“There were a lot of discussions about marine heatwaves and the Ningaloo Niño phenomena in particular, and the focus for the next IIOE expedition,” Dr Feng said. “So there will be a joint effort from scientists from Australia, China and Japan to investigate the dynamics of the Ningaloo Niño – marine heatwave.

“There are a few research cruises being proposed from Australia and Japan to collaborate on this topic.

“Also there are on-going discussions to enhance our capability to monitor the Leeuwin current through IMOS, which is an important component of the Indian Ocean heat balance,” Dr Feng said. “We would link with the United States/South Africa monitoring programs off Africa to understand the Indian Ocean basin wide circulation and heat balance.” 

The International Symposium also celebrated of The Golden Jubilee of India’s National Institute of Oceanography (NIO), which was established in 1966 following the first International Indian Ocean Expedition (IIOE).  the launch of the Second IIOE on 4 December 2015; and the start of the first multi-national IIOE-2 research cruise (ORV Sagar Nidhi (India), Goa to Mauritius, 4-22 December 2016).

The IIOE-2 is an interdisciplinary oceanographic research effort over five years. It aims to build on the scientific understanding of the Indian Ocean region in order to enhance the economic and social benefits of Indian Ocean rim nations, which includes Australia.

The UNESCO/IOC Perth Programme Office has helped plan the IIOE-2 since 2012, and now hosts one of the two Joint Project Office (JPO) nodes for the IIOE-2, led by Dr Nick D’Adamo. This facility works closely with the other major JPO node in Hyderabad, India and with UNESCO/IOC HQ in France, and connects with the broader international IIOE-2 constituency. The IIOE-2 website at provides links to key IIOE-2 reports and information.

Murdoch University’s Professor Lynnath Beckley, who was on the IIOE-2 Science Plan Development Committee, described the first Indian Ocean expedition in the 1960s as, “the biggest exercise ever in marine science.”  

“We live in a remarkably different world than we did 50 years ago,” Professor Beckley said. “Exclusive economic zones (EEZ) prescribed by the UN convention, some countries weren’t independent in the 1960s, not to mention computer modelling.

“So we developed a broad science plan for the Indian Ocean consisting of six major themes and countries are now trying to slot in to those themes over the next five years,” Professor Beckley said.  

The six research themes for the IIOE-2 are:

  1. Anthropogenic impacts (Human impact)
  2. Boundary current dynamics, upwelling variability and ecosystem impacts
  3. Monsoon variability and ecosystem response
  4. Circulation, climate variability and change
  5. Extreme events and their impacts on ecosystems and human populations
  6. Unique geological, physical, biogeochemical, and ecological features of the Indian Ocean

“If you’re a country that abuts the Indian Ocean, bringing together other countries to work in the Indian Ocean is quite a good idea,” Professor Beckley said. “It focusses people in one area of the planet and attracts others to work there.”

CSIRO’s Dr Nick Hardman-Mountford chaired a session on ecosystems covering from plankton and nitrogen cycling to fish, seabirds and citizen science.

“I think there was a real sense we’ve started something new,” Dr Hardman-Mountford said. “It started by paying tribute to the first Indian Ocean Expedition achievements and, looking forward, this is the start of a major endeavour for the Indian Ocean as a whole.”

“I think the momentum is there, there’s a lot of countries starting to work in the Indian Ocean; the US Germans, Dutch, UK all have interests there. We know many of the Indian Ocean rim nations are onboard – South Africa is getting a new ship. This has been a good meeting for forming partnerships between those nations with the best capacity and those with an interest.

“A lot of standard oceanographic rules have been developed in areas such as the North Atlantic and it’s not the same in the Indian Ocean. It is not an open basin, there are monsoons, it has the Leeuwin Current and massive biodiversity and things don’t behave the way we expect. This, coupled with the fact it has some of the poorest countries on its boundary and a huge dependence on it by local populations for food, climate and weather systems, makes the Indian Ocean interesting to study. 

“There is a real sense of excitement about the next phase of work in the Indian Ocean and WAMSI/CSIRO being able to be part of this research,” Dr Hardman-Mountford said.



Dr Nick Hardman-Mountford and colleague in front of  ORV Sagar Nidhi (India) at the launch of the first multi-national IIOE-2 research cruise (Goa to Mauritius 4-22 December 2016)