Different sponge species adopt different strategies to cope with sediments in turbid environments and while many of these alleviate pressure in the short-term, researchers have found that longer-term exposure may still compromise fitness and overcome the sponge’s ability to withstand sediment stress.
Sponges are ecologically important filter feeders that employ a wide variety of mechanisms to cope with turbid environments, such as those affected by dredging activity.
As part of a Western Australian Marine Science Institution Dredging Science Node project supported through co-investment from industry and the Australian Institute of Marine Science (AIMS), a team of researchers led by Dr Nicole Webster tested the sensitivity of sponges to poor water quality conditions. Five main experiments were performed by Dr Mari-Carmen Pineda and PhD student Brian Strehlow at the National Sea Simulator (SeaSim).
The researchers used tanks equipped with an automatic sediment delivery system in which all relevant environmental parameters were also electronically controlled. The latest results have been published in three separate articles in Scientific Reports.
|PhD student Brian Strehlow and intern Miriam Sternel working on effects of combined dredging pressures experiment at SeaSim (MCP)|
High concentrations of suspended sediments in the water column were found to interfere with suspension feeding, the strategy used by most sponge species to uptake their food from the seawater.
|Sponges smothered by sediments and mucus layer in Carteriospongia foliascens (MCP)|
Sediments were found to clog sponges’ internal chambers (aquiferous system), which affect their nutritional stores in the long term. In addition, light reduction associated with high turbidity also negatively affected the sponge photosymbionts, which are another source of nutrition for some species. However, most species also possessed an array of different mechanisms for coping with those pressures, such as the production of mucus that traps sediments or oscular closure and tissue regression to minimize the risk of clogging.
|Tissue regression in Ianthella basta (MCP)|
“Although sponges seem generally resilient to sediment pressures and can present several strategies to ameliorate their effects, we believe that long-term exposure will adversely impact their energetic resources which can certainly affect sponge population dynamics and their important roles in the oceans,” Dr. Pineda said.
Sub-lethal thresholds for suspended sediment concentrations and light intensity were also identified for some sponge species during the experiments.
“These thresholds can be used to help proponents to more reliably predict the effects of their dredging proposals on sponge communities and also to design dredging programs to minimise impacts overall,” Dr. Pineda said. “Also, where the sponge species we used in our experiments occur in the field, they could be used as sentinels in dredge environmental monitoring and management programs and, with knowledge of the thresholds and indicators of stress we have identified, used to reduce risks on these important benthic communities.”
Future experiments will focus on the effects of dredging pressures on sponge larvae and juveniles, as early life stages may be more vulnerable than adult sponges.
Pineda MC, Strehlow B, Sternel M, Duckworth A, Jones R, Webster N.S. (2017) Effect of suspended sediments on the sponge holobiont with implications for dredging management. Scientific Reports. doi:10.1038/s41598-017-05243-x
Pineda MC, Strehlow B, Sternel M, Duckworth A, den Haan J, Jones R, Webster N.S. (2017) Effects of sediment smothering on the sponge holobiont with implications for dredging management Scientific Reports 7, Article number: 5156 doi:10.1038/s41598-017-05243-x
Pineda MC, Strehlow B, Kamp J, Duckworth A, Jones R, Webster N.S. (2017) Effects of combined dredging-related stressors on sponges: a laboratory approach using realistic scenarios Scientific Reports doi:10.1038/s41598-017-05251-x
Project Page: www.wamsi.org.au/filter-feeder-responses-dredging
The WAMSI Dredging Science Node is made possible through $9.5 million invested by Woodside Energy, Chevron Australia and BHP Billiton 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 Australia, Woodside Energy and Rio Tinto Iron Ore. The commercial entities had no role in data analysis, decision to publish, or preparation of the manuscript.