Found! Nature’s Calcium Reactor

I’m sure the first thought when you saw that picture was not of a creature that is responsible for helping supply coral reefs with the building blocks they need to live and grow. Some recent findings have noted that these creatures actually may have a sizable impact on the environment around them. To the casual diver or snorkeler, sea cucumbers usually appear sedentary, sitting like a pair of shoes someone left on the sandy areas between stands of coral. It turns out that what goes in and out of sea cucumbers turns out to have a decent impact on the water chemistry of the entire reef ecosystem.

Our Torpedo Shaped Little Friends

Sea cucumbers are benthic creatures that live in much of the worlds oceans from sandy reef flats to the deep ocean areas and they come in many shapes, sizes and colors. They range in size from less than an inch to over 6ft in length and live generally 5-10 years. There are 1250 distinct species of these creatures throughout the oceans of the world. Biologically speaking, they are pretty simple, having a mouth at one end where small particles of sediment enter and then exit through their posterior end. They have small feet on their underside that help them to move along as they consume particles of food. Think about an ocean dwelling earthworm and you pretty much understand the lives of these creatures.

One Tree Island

Recently, Kenneth Schneider of the Carnegie Institution for Science at Stanford University and his team were studying CaCO3 dissolution on a reef near One Tree Island on the Great Barrier Reef. Ken’s team was there to study calcium carbonate levels on a reef near One Tree Island. As they made their measurements, they were noticing that the levels they were observing were quite a bit higher than their predictions. As they pondered these results, they noticed that there was a dense population of sea cucumbers in the area they were studying. Coincidentally, they happened to be on the small research island at the same time as another team who was actually knowledgeable on the biology and behavior of sea cucumbers.

These two teams combined efforts and were able to measure the density of sea cucumbers around One Tree Island. In addition, they were able to calculate the amount of CaCO3 that is released from the sea cucumber’s digestive system back into the water. Then results of this study showed that the acidic environment within the digestive system of a sea cucumber, which primarily aids in digestion, also was dissolving a good deal of this coral sediment back into its component calcium carbonate and other dissolved minerals. This dissolution of sediment which occurred predominantly at night was responsible for the increase in calcium carbonate that Ken’s
team was seeing. To anyone that keeps coral reef aquariums, this would remind them of a process that we do on a larger scale with a calcium reactor. In this case though, these sea cucumbers are like little calcium reactors that roam the sea floor.

Nature’s Calcium Reactor

Before anyone thinks they can go out and replace their calcium reactors with a handful of sea cucumbers, keep in mind that you would need quite a few of these creatures to supply the calcium need of most coral reef tanks. It is very interesting how many of the expensive and elaborate contraptions that are used in captive coral reef aquariums actually have their rooting in some natural process that has been occurring in the worlds oceans for millions of years.

It would be interesting as a follow up study to see if any of the other creatures that consume coral or coral sand on and around the world’s reefs have the same biological recycling effect on the water chemistry as the sea cucumbers do. Perhaps the trails of coral we see coming out the tail end of fish like the parrot fish contains a similar dissolution of these elements. Yet another topic that would be interesting to study would be how this process will play into the acidification we are seeing in the worlds oceans today. Will the added alkalinity of this digestive dissolution process help buffer against change in the oceans pH? It will be exciting to see what studies will be done in the future on all aspects of this biological process and see how both the scientific community as well as the reef aquarist can learn.

Schneider et al. (2011). Potential influence of sea cucumbers on coral reef CaCO3 budget: A case study at One Tree Reef. Journal of Geophysical Research VOL. 116, G04032, 6 PP. doi:10.1029/2011JG001755

You Tube video discussing the study