Day 11: Dissolving balls

Today the blog is written by Seb Hennige (part of Team Coral) and is about clod cards (or clod balls as perhaps they should more accurately be named!).

As you can clearly see, there is a lot of life down at 860m, and these animals form a very complicated food web. Understanding this food web is critical for many long-term studies, as until we know how carbon and nitrogen cycle through these ecosystems, we cannot predict what will happen in the future. Clod cards can provide the key to this.

These balls were painstakingly made over many months by Christina Mueller from the Royal Netherlands Institute for Sea Research (NIOZ) by growing algae and bacteria in very dense cultures with traceable carbon and nitrogen. These cultures are then concentrated further and mixed with gypsum to form the ‘clod balls’, which look like the fat balls you buy for birds over the winter. These balls are then suspended in a plastic cage and deposited on an area of reef rich with live animals such as corals, sponges, sea urchins and starfish.

These balls then dissolve into the water over the next period of days and the surrounding animals will eat the released food and take up the traceable carbon and nitrogen into their tissue. Depending on how much they eat and respire, different animals will take up more or less of the carbon and nitrogen. After six days, we will return to the sites where we left these clod cards and carefully sample some of these animals to see how much of the nitrogen and carbon they have taken up.

Once we understand these complex food webs a little better, then we can start to think about how they will be affected by future changes in ocean conditions. Fingers crossed that when we return in six days that the visibility is good and we can find them again!