Day 5: Feeding Corals

After one week on board, we already have healthy corals in our tanks, and will use these corals to learn more about their ecology.
Today's blog has been written by Covadonga Orejas, from the Instituto Espanol de Oceanografia, Spain. During this cruise, exciting in situ experiments will be performed by some of the scientist. Another way to learn more about the ecology of deep sea organisms is to conduct aquaria experiments on the ship. Knowing what the animals feed on will help us to better understand their role in the ecosystem.

Yesterday, we started some of the feeding experiments that will be carried out during the Changing Oceans Expedition. Previous studies at home showed us that the coral Lophelia, the main “star” of this cruise, feeds on zooplankton and algae. However, we still do not know much about the other food sources in the ocean that could be consumed by this coral. At the depth of the reef, zooplankton could be scarce in some periods during the year, and phytoplankton is available in sufficient amounts, particularly during spring and summer. However, other particles (like bread crumbs…) are constantly present in the oceans, and even if they don't supply much energy due to their small size, they could be consumed in large amounts and constantly. Therefore, these particles, which scientists call particulate organic matter, could be one of the “secure” food sources for this organism in times when obtaining other prey is difficult. So we want to look at the uptake rates by Lophelia of these very small organic particles that float in the plankton.

Feeding chambers

Cova preparing chemicals

Healthy corals, filtered seawater and 9°C temperatures are the main ingredients for the 'feeding experiments recipe”. Once the aquaria are filled with chilled filtered seawater, and the corals feel comfortable in their chambers, we just need to add our “main course” so that we can later analyse what the corals actually ate.

In the natural environment, sea animals live under different current regimes, and animals that don't move around and filter particles out of the surrounding water are very dependent on these currents, which move the food to their tentacles. With this in mind, we developed experiments using different current speeds so that we can see which current speed is best for the corals to capture their food.

When we go back home, we will analyse the samples obtained from the experiments, and then know what the corals are eating. This will help us to better understand the ecological role that these animals play in the ecosystem. Many other things are going on board! The ROV has been in the water collecting corals, we have been box coring for benthic samples and we have had success with the microbial collection chambers! We will keep you updated!