The results are in, the paper is out, and another sponge secret is unlocked!
Hello! I know it has been a while since we have posted an update, but we have been diligently working on data analysis and discussing our findings with other coral reef scientists and we have exciting news! First, our results are now published in a peer-reviewed journal article that is freely available here: Sponge DOM paper
If you recall, we were interested in testing the hypothesis that sponges alter the amount and types of organic nutrients in the seawater on coral reefs. Sponges act as a filter on coral reefs removing bacterial cells and dissolved nutrients from the water column. The nutrients we examined are metabolites like amino acids and vitamins that are dissolved in the water and collectively known as dissolved organic matter (DOM).
These nutrients are important to many coral reef organisms from microbes to the reef building corals. However, scientists still don’t understand the factors that influence the types and concentrations of nutrients on coral reefs. In our project, we examined the type and concentration of DOM in four main types of seawater:
1) “ambient seawater” collected on the reef but not immediately near a sponge
2) “exhalent seawater” that was released from a sponge that was host to a dense community of microbes
3) exhalent seawater from a sponge with few microbes
4) seawater collected away from the reef (“off reef”).
Schematic showing exhalent and ambient seawater
The results led us to a couple of main conclusions. First, the types of metabolites and their concentrations in exhalent seawater from both of the sponges were significantly different from that of the ambient reef water and the off reef water.
This was really exciting to see because it means that the sponges are impacting the chemistry of the seawater. We could also see that the sponges removed some compounds and added other compounds to the water. These included amino acids, the building blocks of proteins, and the building blocks of DNA called nucleosides. These are compounds are likely to be used by reef organisms in their metabolism. Just think about this, sponges are acting like highly complex chemical reactors on the reef!
Second, is that the two sponge species we investigated had a similar effect in terms of changing the types and concentrations of DOM in the water. This means that multiple types of sponges may exert a similar effect on the overall seawater chemistry. Because we sampled a relatively small number of sponges here, further research is needed to see if this “sponge signal” that we see in the DOM profile of exhalent seawater is similar to that of other sponge species. But, this work is unlike anything else that has been done in the field of coral reef science and it is incredibly exciting to see trends in the data!
What does all of this mean? It means that sponges have some role in determining the availability of important compounds like amino acids and other metabolites on coral reefs. This work that you funded is the first to demonstrate this specific role of sponges on coral reefs!
With our findings in hand, we have started discussing the implications of this for coral reef health. We presented our work at the International Coral Reef Symposium recently, a conference that includes coral reef scientists from all over the world and is held once every four years. This led to new collaborations and projects where we can address questions raised by our project. For example, we are discussing a new experiment to examine the effect of sponge exhalent seawater on the growth of corals in aquaculture. It is possible that the types of compounds removed and added to the seawater by sponges create a “healthy mix” of nutrients for other reef organisms like corals.
We have accomplished a tremendous amount of work and have discovered something entirely new about how nutrients are recycled and regenerated on coral reefs! We know that sponges have a role in altering nutrient availability on coral reefs and we can move forward with more targeted and in-depth experiments to look at the effects of this on coral reef health. None of this would be possible without your support and we are extremely grateful. We hope you have enjoyed the lab notes from this project and you are still welcome to post questions for us, we are happy to discuss the project and our findings. The next time you see a coral reef, remember to thank the sponges for being nature’s filtration system and know that these ancient animals still hold more secrets that we hope to unlock.
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