“Sponges represent up to 90 % of the benthic faunal biomass. At most, you can have five or six kilos of sponges per square metre. The Geodia barretti sponge can filter up to 1,000 litres of water per kilo of tissue each day. Over a year, this can add up to a large volume of water,” says Bannister.
Quite simply fascinating
Sponges can be found on the sea floor the whole way along the Norwegian coast and far up into the Barents Sea, and Geodia barretti is one of the most common species dominating the sponge fauna. Bannister has become fascinated by these simple creatures, which are the most primitive group of multi-cellular organisms, and are arguably just colonies of cells. Nevertheless, the sponge cells manage to work together so effectively that they become powerful pumps, allowing them to filter water and obtain nutrients. Sponges live off the particles that they filter out of the water and they can retail up to 95 % of bacteria present in the water column. Although they are simple organisms, they still have some foods they prefer to consume.
“They can block out certain particles, and let other ones in, even if the particles they prefer are bigger than the other ones,” explains Bannister.
Without the filtering done by sponges, there would be far more bacteria in the sea. Sponges are considered an important part of the benthic fauna, and they are classified as vulnerable organisms, but there is still a lotthat we do not know about their function in the ecosystem.
Oil pumps and water pumps
At The Institute of Marine Research’s station at Austevoll outside Bergen, Bannister is busy testing how much pollution from the oil industry the sponges can cope with before they stop pumping and filtering. Initially, the scientists are looking at the impact of the drilling fluids from the actual drilling process. In total, 200,000 tonnes of these fluids are released every year.
Since the oil industry is moving northwards, Geodia barretti seems a good species to study in terms of the impact of the industry. In spite of the fact that sponges are very common, there have been no studies looking at the oil industry’s potential impact on them.
Advanced sponge collection
While the laboratory experiments are going full steam ahead, scientists Tina Kutti and Jan Helge Fosså are out on the research vessel “Håkon Mosby” collecting sponges – ably assisted by the crew. They are using a remotely operated underwater vehicle (ROV) with a specially designed grab and container.
“We pick up sponges that are resting on sediments. That means we do not need to damage them by removing individuals attached to the substrate, which we would have to do if they were on a rocky bottom. It is important to keep the sponges in water the whole time, so first they are transferred to a large tank on the boat, before they are moved to a new tank on land,” says Fosså.
The sponges that are collected are left to acclimate for a few days, to make sure that they are still filtering. If they are, they can then be used in the experiments.
Then they are exposed to different concentrations and types of oil drilling wastes produced by the oil industry. Advanced equipment is used to measure their pumping activity and oxygen intake. After being exposed for a given amount of time, the sponges are taken out of the tanks for analysis. After carefully recording their weight and volume, the scientists look for different kinds of responses to pollution, including everything from the activation of stress genes to cellular death.
Next door, the sponges are cut up into small slices. Bannister and Professor Sally Leys, an expert on sponges from Canada, can often see differences in the internal colour of the sponges, depending on which of the different pollutants they have been exposed to.
“It is important to find out more about sponges. Not just in terms of their roles in the ecosystem, but also in terms of what happens when they become stressed, and are no longer able to perform these roles. When they suffer stress, their oxygen intake falls,” says Bannister, pointing at graphs showing oxygen intake versus pollution level.
PhD candidate Katelyn Edge has come all the way from Australia to work with Bannister and the rest of the sponge team at The Institute of Marine Research. She is looking more closely at cellular level changes as part of her PhD. The four-year project, which is funded by The Research Council of Norway, is providing us with a good foundation for understanding how sponges react to pollution caused by the oil industry. However, there are over 250 species of sponge in Norwegian waters, and we cannot assume that all of them react to changes in the same way. The scientists therefore want to expand their study to include other species as well. A new application for additional funding has been submitted, to allow work to continue.
“There is reason to believe that sponge communities play an important role in benthic ecology. In order to understand this properly, it is important to carry out studies on a larger scale than laboratory experiments,” says Bannister, who would like to continue studying sponges.