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Effects of dredging on filter feeder communities, with a focus on sponges

31 October 2016

A psammobiotic sponge (Photo: Christine Schönberg)

Sponges can filter up to 50,000 times their own volume of water in a day, making them an important link between the water column and seabed. They serve as habitat to other marine organisms and play an important role in the cycling of nutrients, making them a critical part of the marine ecosystem. So, understanding whether they can survive in turbid water, and being covered in sediment from dredging operations are important questions scientists are asking.

A report released by the Western Australian Marine Science Institution (WAMSI) evaluated sponge responses to acute and chronic sediment stress included elevated respiration, reduced or arrested pumping, pore closure, tissue retraction and changes in sponge morphology. Other responses included bleaching, disease and death. However, not all of these responses occurred in all species examined.

More than 900 articles were reviewed including those in peer-reviewed journals, grey literature, technical reports and theses for a Dredging Science Node project to define the thresholds and indicators of filter feeder responses to dredging-related pressures.

From an ecological perspective, turbidity and sedimentation were likely to alter the structure of filter feeding communities by reducing fitness and survival. There are, however, factors other than dredging (e.g. river inputs, cyclones) which have the potential to re-suspend sediment and increase turbidity.

There are sponges that are well adapt to living in turbid environments and may continue to survive at dredging sites. These include endopsammic sponges (living partially buried within sediments), fast growing species that are able to change their morphology (highly plastic), and species with erect growth forms. Sediment tolerance may also be related to species that are more capable of keeping their surfaces sediment-free.

Whilst little is known of responses to cumulative pressures, sponge vulnerability was found likely to be exacerbated during certain periods, e.g. when struggling to satisfy high energy demand for growth or reproduction, during thermal stress events or after tissue damage from e.g. spongivory, storms or reduced salinity.

The review found that sediment associated with dredging activity can affect the physiology of filter feeders in very complex ways, which are not yet adequately understood.

The high diversity and abundance of filter feeder communities in Australia, especially in Western Australia, combined with the lack of knowledge about their biology suggests two critical information needs:

  1. experimental research to improve the understanding of the ecophysiology of filter feeders and determine pressure:response relationships to dredging pressures; and
  2. identification of the dominant and habitat forming filter feeder species and their local and regional significance at possible future dredging locations.

This review also identified potentially sensitive sponge taxa, and summarised stress responses relevant to dredging-related pressures, which are necessary for the monitoring and management of this biodiversity resource.

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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