Imagine diving on a tropical coral reef and seeing all sorts of colorful sponges, some large, some small, some barrel shaped and some tube shaped. You might wonder: are all of these sponges functioning in a similar way? Do all sponges look like these? The answer is no, not even close.
There are three classes of sponges, all within one phylum called Porifera. Almost all of these filter water to obtain food - like the ones we focus on for our project exploring how sponges change the water chemistry on coral reefs - but some use a different life strategy altogether.
Sponges in all three classes have microbes that live within them as symbionts (symbionts are organisms of different types that live/exist together). This is an important relationship for sponges and an important concept for our project!
First, the class Demospongia comprises the largest and most widespread group of sponges and these are what people typically think of when they think of sponges. Demosponges have silica (glass) spicules that help give structure to the sponge body (like a skeleton) and protein fibers called spongin, which gives them a resilient quality. Demosponges come in all sorts of sizes, shapes and colors as shown in the photo below.
Photo courtesy of Saspotato on Flickr under the creative commons license
They are found in tropical, temperate, polar, shallow, and deep water, and in freshwater. The sponges that were harvested (and still are on a smaller scale) for bathing belong to the genera Spongia and Hippospongia, are also a demosponges but these have no spicules.
Historical photo of sponge auction in Key West. Photo courtesy of Florida Sea Grant on Flickr under the creative commons license.
One unique demosponge I want to mention here is the carnivorous kind. Yes, I said carnivorous sponges! These typically live in deep water were there is less food in the water column. Theses sponges have hooked spicules that help them capture small crustaceans – like shrimp and amphipods, and even small fish! You can think of these as a sponge version of the venus fly trap plant.
The harp sponge is carnivorous and was discovered in 2012 off the coast of California at over 3,000 m depth by Monterey Bay Aquarium Research Institute. See more info here
Pictured below is one kind of carnivorous sponge, courtesy of NOAA photo library, that can trap small animals with filaments (typically seen with long filaments not shown here) that readily capture small animals that have fine hair-like appendages called setae.
NOAA photo library, creative commons license
The second class is Hexactinellida, or the glass sponges. These have silica spicules, which are often quite large and beautiful with 4 to 6 points on each spicule. The glass sponges are typically found in deeper waters (>1,000 ft or 300 m) and can form large reefs, such as found in deep water off the coast of British Columbia and Washington state.
Rather than pumping, these sponges rely on current to move water through their bodies so they can capture particles of food. They have a unique characteristic of being able to rapidly send electrical signals across their bodies so that they can respond to stimuli- perfect for grabbing that fast moving piece of detritus!
Venus’s flower basket glass sponge. Photo courtesy of NOAA photo library on Flickr under the creative commons license
One unique example of a glass sponge is the species known as Venus’s flower basket (pictured above). This sponge has a symbiotic relationship with a small shrimp. Two shrimp, one male and one female, live inside the sponge their entire lives. When the shrimp produce offspring (larvae), the larvae are released and travel to find another sponge to settle in. The shrimp get a great home with constant food supply and they help clean the sponge.
The last class is Calcarea – the calcareous sponges. The spicules in these sponges are made of calcium carbonate rather than silica. These are less common than demosponges but still found in marine waters worldwide, even in shallow water that you might dive in.
The photo below is from a NOAA Ocean Exploration cruise that I participated in that was organized by researchers at The South Carolina Department of Natural Resources and the College of Charleston’s Grice Marine Lab. The lovely looking calcareous sponge we collected using the submersible The Johnson Sea Link II was from ~150 m depth off the coast of Georgia and South Carolina is pictured below (On the left side of the calcareous sponge is another kind of sponge).
This guest-post is written by Cara Fiore (@clfiore). Cara is a post-doctoral researcher at Woods Hole Oceanographic Institute. Among other things, she studies how sponges influence water chemistry in reefs (and elsewhere). You can learn about her ongoing research at experiment.com/sponges.