While sea sponges may not be as charismatic as corals, an industry funded WAMSI project is finding their strength may lie in their resilience to change.
One of the most important roles of the sponge is providing habitat for vertebrate and invertebrate species, but one of the most impressive is its ability to filter huge volumes of water – a one kilogram sponge can filter more than 20,000 litres of sea water every day. It makes them a critical link between what’s happening in the benthic environment (the ecological region at the very bottom of the sea) and what happens in the pelagic zone (mid to surface region).
Because they have a big influence on what’s happening around them, a team of researchers at the Australian Institute for Marine Science (AIMS) led by Dr Nicole Webster is testing their sensitivity to reductions in water quality.
|Mari Carmen Pineda monitoring sponges in the AIMS SeaSim lab
“Field surveys of the filter feeding communities in the Pilbara region led by Drs Jane Fromont and Christine Schoenberg really highlighted the amazing diversity and abundance of sponges,” Dr Webster said. “It has confirmed that sponges are the dominant filter feeders.”
“This project is looking at sponges of different species, different morphologies and different nutritional strategies to see how they respond to the various dredging related pressures,” she said.
Little is understood about the effects of dredging pressures on sponges. However, some of the known effects include bleaching or the loss of photosynthetic microbes from low light conditions, clogging of their aquiferous systems from high levels of suspended solids or complete burial or smothering of the sponges due to high rates of sedimentation.
|Sponge filtration capability
The sponge’s aquiferous system is made up of channels and small chambers lined with specialised cells (choanocytes) that create currents of water and retain nutritive particles.
It’s quite well known that sponges can reduce their pumping activity in response to high levels of particulates in the sea water, but how long they can maintain that reduction in pumping activity before their energy reserves, which they need for growth and reproduction, become entirely depleted is not yet known.
Dr Mari-Carmen Pineda and PhD student Brian Strethlow are testing the sponges under controlled conditions in the AIMS National Sea Simulator (SeaSim) to define cause/effect relationships to the dredging related pressures of light attenuation, sedimentation (smothering) and elevated suspended sediments (clogging).
|Carteriospongia foliascens with mucus and sediment layer sloughing
|Cliona orientalis with brittle star inside its osculum cleaning the sediments
“To determine the sponge stress response we measure a whole suite of health parameters in our experimental animals including: changes to respiration rates, bleaching or loss of symbiotic microbes, changes to sponge pumping activity and cellular necrosis,” Dr Pineda said.
“Overall we are finding that sponges seem largely tolerant of short term dredging-related pressures and that light and suspended sediments on their own do not cause severe stress in the short time (days),” she said. “Sponges also demonstrate an array of different mechanisms for coping with sedimentation, such as the development of new oscula (exhalent pores), sediment sloughing and removal of sediment from the aquiferous canals by infauna
|Coscinoderma matthewsi with open osculla through the sediment layer
such as brittle stars. “
“On the other hand, long-term exposure (>2 weeks) to dark conditions and high levels of suspended sediments (>30 mg/L), seems to have an impact on growth rates and symbiotic microbes, although most sponges can recover once conditions return to normal.
“Overall, cup shaped sponge morphologies and phototrophic species (ie those that rely on photosynthetic microbial symbionts for nutrition) are the most sensitive to dredging related impacts, and some of them do not possess the ability to recover,” Dr Pineda said.
The SeaSim experiments will add to data gathered from pre-dredging surveys by divers and towed video. The field surveys are also due to be repeated in July post-dredging off Onslow to determine what changes have occurred and how this can be applied to management of dredging operations in the future.
This research was funded by Woodside, Chevron, BHP and WAMSI partners
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.