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

29 September 2016

Reef flat at Scott Reef (AIMS)

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.

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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