Imagine swimming on a coral reef, the water is clear and you see some stands of live coral, colorful reef fish, and, less-well-thought-of but plenty colorful and very important to coral reefs – sponges!
Sponges, can be thought of as the glue that holds the reef together, but they are important members of coral reefs for several other reasons: they filter large volumes of water, and they provide habitat to other reef animals from brittle stars and crabs to fish. They also exert a major influence over nutrient availability on the reef – meaning that they determine what nutrients are available for other reef organisms like corals. But how do they do this, and what does this mean for the health and stability of coral reefs if sponges increase or decrease in abundance in the near future?
My name is Cara Fiore and I am a postdoctoral researcher at Woods Hole Oceanographic Institution (WHOI) in Cape Cod, MA. My postdoctoral mentor (Dr. Kujawinski), several colleagues, and myself are trying to answer these questions and we are relying on crowd-funding to obtain the necessary funds to carry out the project.
Here I want to share some more information on what we hope to accomplish and why! If you are interested in contributing to help make this project a success, please go to the website above. As a contributor, you will also be able to follow along with the project through blog updates on the project website. You can contribute to the project through January 16 2015, but you can always check it out after that too.
First, some more info on the organism of interest; sponges are sessile (mostly, some can move a few mm a day by a coordinating their cells to move in an amoeba-like manner!) filter-feeding animals that obtain food particles from the water and other nutrients that are dissolved in the water. The nutrients that are dissolved in the water are called dissolved organic matter (DOM) and this component is what we are most interested in. Sponges are very efficient at pulling food and nutrients from the water and can remove 80% of particles in the water column, but, because the water they live in is typically clear and nutrient poor, a typical sponge needs to filter a ton of water to obtain an ounce of food! Imagine drinking that much water to get an ounce of food!
Sponges are considered by most scientists to be the most ancient living group of metazoan (multicellular) animals. Sponge cells are totipotent, meaning they can become any kind of specialized cell within the sponge – they can produce spicules which are the skeleton of the sponge, or the proteinaceous fibers called spongin, or choanocytes (“collared” cells with a flagella that pump water), or cells that line the outside of the sponge or internal canals (both can engulf food particles), or gametes. Many researchers study how sponge cells coordinate with each other to form tissues or respond to stress to get a better idea of how multicellular organisms (such as ourselves!) function at a basic level!
Check out this YouTube video to see sponges pumping and what it is like to travel through a sponge as a particle in the water:
Sponges, like humans, are not comprised of just sponge cells though. Sponges have a “microbiome” that is often unique to different species of sponges. Microbial cells can be quite abundant in sponges; in fact, nearly half of the volume of a sponge is actually comprised of bacteria and other microbial cells!
The microbial community is typically considered symbiotic – here meaning that the symbionts form a relationship with the sponge that is consistent over time and geographic space, although not necessarily benefiting or harming the sponge. That said, some phototrophic symbionts do benefit the sponge by providing some of the nutrients produced from photosynthesis to the sponge.
Because sponges can filter so much water and they are highly abundant on coral reefs and they can be full of microbes that influence nutrient uptake differently, we want to see how exactly sponges and their microbes are influencing nutrient availability on coral reefs.
How Do Sponges Affect Nutrient Availability on Coral Reefs?
Both sponges and their symbionts can remove dissolved nutrients, called dissolved organic matter, from the water column. There are generally two main types of sponges: those with many microbes, called high microbial abundance sponges (HMA), and those with significantly fewer microbes, called low microbial abundance sponges (LMA).
Because both sponges and microbes can take up nutrients from the water we want to know:
- What compounds are being taken up by sponges, and does this differ between HMA and LMA sponges?
- How does the composition of organic matter in water released by the sponge after pumping (excurrent water) compare to the ambient reef water?
- Does the overall composition and concentration of nutrients in water on coral reefs reflect what sponges are removing and adding to the water (in other words: is ‘reef water’ different than ‘non-reef water’ in terms of nutrients)?
This information will give us a never before seen snapshot of how nutrients are removed and regenerated on coral reefs. This has relevant implications for managers of protected reefs as well as other coral reef scientists, because as sponges change in abundance due to disease, overfishing, or climate change, the nutrients available to other reef organisms like corals could shift dramatically by a change in sponge abundance or shift in the type of sponges that make up the community. We will be able to predict from data that we generate what types of nutrients will be available to other reef organisms if sponges increase or decrease in abundance.
In order to carry out this project, we are collaborating with Dr. Chris Freeman at the Smithsonian Marine Station in Ft. Pierce, Florida. There we will go out to a reef and collect water near sponges (ambient reef water), water coming out of a sponge (excurrent water), and water away from the reef (off reef water) – and we will do this for 3 HMA and 3 LMA sponges. Then we need to filter the water to remove all particles and microbes and we are left with the dissolved organic matter. Next we use laboratory techniques to extract and concentrate the dissolved organic matter and we can analyze this using two special instruments called mass spectrometers.
A mass spectrometer (MS) allows us to differentiate many compounds in one sample based on their mass and the time it takes for that compound to travel down a special column. From the time (called retention time) and the exact mass (up to 6 decimal places!) we have a good chance of identifying the compound. We use two approaches to characterize the organic matter using mass spectrometers. The first is a “targeted” approach, where we have a set of known standard compounds (e.g., sugars, amino acids, and nucleotides) and we can look for, and quantify, these compounds in our samples. The second is an “untargeted” approach were we collect all mass values in our sample between 100 and 1000 Daltons (up to the size of a small protein). By using both of these approaches we will be able to characterize how sponges are driving the water chemistry on a reef by seeing what compounds they remove or add to the water and find out which of these might be important in the health and survival of sponges and the overall health of the coral reef.
Threats to Coral Reefs
A recent report from the World Resources Institute found that 75% of coral reefs around the world are considered threatened and this will likely increase to 90-100% by 2030. In the Caribbean alone, coral populations have decreased by 50% since the 1970s! This is due to several factors including over-fishing or harmful fishing practices, coastal development which leads to sedimentation and high nutrient input, and thermal stress from global climate change.
Basically, these ecosystems have shifted so that algae, and in some areas, sponges have increased, while corals have decreased in population. This means that nutrient dynamics are very different from a healthy coral reef. But, there is hope, coral reefs have resilience and with the right management strategies and with help from us humans, we can shift coral reef ecosystems back to a healthy state!
There is a desire to implement ecosystem-based approaches in coral reef management set out by the National Oceanic and Atmospheric Association (NOAA). Nutrients and environmental factors can influence microbial community composition in both corals and sponges and this can impact overall coral health. This means that better understanding nutrient dynamics on corals reefs is needed to implement ecosystem-based approaches.
A better understanding of the influence that sponges have on nutrient availability will give us a better idea of how and to what extent they can couple water column and benthic ecological processes and how this contributes to maintaining a healthy coral reef ecosystem.
We need healthy coral reefs not only because they are beautiful, but because they provide an important source of food for millions of people, and they protect coastlines from hurricanes and other storms. Coral reefs are also a source of novel medicines as well as a major reservoir of biodiversity!
Below is a video from the World Resources Institute discussion the threats to coral reefs. They focus on corals and fish, but now you know that sponges are an important part to this system too! Just think the next time you snorkel or dive on a reef you will be swimming in water that has recently passed through a sponge!
Meet the Researcher
Cara Fiore considers herself a marine microbial ecologist, with interests in how microbes influence nutrient cycling, symbiosis (specifically sponge-microbe symbiosis), microbial physiology, and coral reef ecology. Cara has also worked in biomedical research at the University of Rochester (Rochester, NY). Cara received a B.S. in biology from SUNY Cortland, and graduated from the College of Charleston (Grice Marine Lab) and the University of New Hampshire before starting a postdoc at Woods Hole Oceanographic Institution (WHOI). During graduate school Cara spent 10 days underwater in the Aquarius habitat, which is sits in 50 ft of water off the coast of Key Largo, FL, and is operated by NOAA and Florida International University. Currently at WHOI, Cara is investigating how microbes influence nutrient cycling in the ocean including on coral reefs.