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.

Dredging Science