A closer look at sponge symbionts

Just like we have bacteria that live on our skin and in our guts that help keep us healthy, sponges also host a diverse community of bacteria that make up a healthy sponge. In our project we looked at two types of sponges - one species that has a high abundance of bacteria and another species that has a low bacteria abundance.

We want to know how these two types of sponge might change the availability of nutrients differently. Let's first look a little closer at the sponge-bacteria relationship, where there are a few interesting facts that might surprise you.

Some sponges will keep certain types of bacteria enclosed within special chambers in the body of the sponge. Scientists have found that these sponges maintain a "supply" of these bacteria that are healthy and reproducing, but that they also eat some of the bacteria. In other words these sponges are basically "farming" a bacterial food supply! Farming such as this has been found in some carnivorous sponges described in another labnote and in shallow-water filter feeding sponges.

In humans, babies often receive beneficial bacteria from their mother - in a somewhat similar notion, many sponges transfer bacteria from the adult to their gametes so that the next generation of sponges will have a healthy set of bacteria with which they begin life!

 

Photo courtesy of Dr. Christopher Freeman (Smithsonian Marine Station, Ft. Pierce, FL) and Dr. Cole Easson (University of Alabama, Birmingham)

The photo above shows a section of sponge tissue that has had special fluorescent compounds added to it so you can see sponge cells and bacterial cells. You can see the canals of the sponge as the black spots and the green that you see are all sponge cells that make up the tissue of the sponge. The thousands of tiny orange dots that you see are all bacteria!

The bacteria that are found in sponges are very diverse. Some can photosynthesize like algae, and some of the food generated by this process can be shared with the sponge, while others feed off waste generated from the sponge or from nutrients in the water. Because the community of bacteria often differ from one species of sponge to another, this could have a big impact on how different sponges change the chemistry of the water as they pump this water through their bodies.

Now, because of support from all of you, we will be able to start to see how these two sponges that we sampled influence nutrient availability on coral reefs. While the data analysis we are working on now takes some time, we are looking forward to sharing with you what the results of our experiment mean for managing and conserving coral reefs.