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A Plunge into the Sponge!

Sponges are among the most mysterious creatures in our Coastal Bays. They stay stationary for most of their lives and look so much like a plant; it’s hard to believe they are an animal! However, these seemingly simple organisms play a big part in keeping marine ecosystems healthy, and we are lucky enough to have some right in our Coastal Bays!

Blue Crabs on sponge by Zac Garmoe
Blue Crabs on sponge by Zac Garmoe
Life History

Sponges spend the first few days of their life as tiny larvae floating through the water until they can find a substrate that will serve as their forever home. It seems like a big commitment for a  three-day-old, but it is an important moment in every sponge’s life. Hard surfaces such as rocks and pilings are most suitable for a sponge to anchor itself to. 

Once a sponge is anchored, they’re ready to grow! Despite the peculiar nature of sponges, they are quite simple creatures. They are invertebrates (meaning they have no backbone) and have no specialized organs, such as a heart or lungs. Their skeletons are made of a soft material called spongin, which is a form of collagen, and their skin is leathery with many pores. These pores serve an important function for the sponge, as they act as the entrances for its food.

Sponges are filter feeders, which means they feed by taking water into their bodies and picking out the edible particles in the water. Edible particles for the sponge include plankton, viruses, detritus, and bacteria. They are also able to absorb nutrients and oxygen through their pores. Wastewater is then expelled from their bodies through an opening called the osculum. The process of filter-feeding helps to clean and clarify the water, which is why filter feeders are often considered ecosystem engineers! Other notorious filter feeders in the Coastal Bays include oysters, clams, mussels, sponges, and a small, silvery fish called the menhaden. While we appreciate sponges for simply existing, they also act as a food source and provide structured habitat for many sea creatures.

It is always important to leave sponges be, as they are quite sensitive to their environment. Sponges are rarely found free-floating and rely on staying anchored to their substrate. Since sponges are filter feeders, they take in about 20 times their volume in water every minute. This means their pores can easily get blocked with stirred-up sediment or air if taken out of the water. All the water that sponges take in also makes them particularly sensitive to pollutants or toxins in the water, and they can be important indicators of water quality. 

Red Beard Sponge
Red Beard Sponge by Cailyn Joseph
Red Beard Sponge by Cailyn Joseph

We have several species of sponge that live in the Coastal Bays, including the sulphur, or boring, sponge, red beard sponge, halichondria sponge, and the fig sponge. You may recognize the red beard sponge, as it is easy to spot if the water is clear enough. They are perhaps the easiest sponge to spot in our bays, as they boast a bright fiery orange color with many branching fingers, giving them a bushy appearance. Red beard sponges start out encrusting its substrate, making it look like a large splotch of orange-red. They can also withstand lower salinities and may be found in waters with higher inputs of freshwater. 

Fun fact! Red beard sponges can recreate themselves even after intense disturbances! This was discovered after scientists squeezed a sponge through a fine mesh and the separated cells crept along to find each other. From this newly reformed mass, the cells were able to reproduce and regrow the sponge, making it the first animal observed to exhibit this behavior.

Sulphur (Boring) Sponge

Though sulphur, or boring, sponges are not quite as easy to spot, there is an indicator that makes it easy to know one has been around in the past.

Shell with Sponge Holes by Cailyn Joseph
Shell with Sponge Holes by Cailyn Joseph

Have you ever picked up a shell and seen many small holes in it? These holes are a tell-tale sign that a boring sponge was once present on it. Boring sponges create space in shells to grow throughout them by using acid to make tiny tunnels. While the sponge does not directly harm the animal living in the shell, the animal often dies as a result of a weakened shell. These sponges are a yellowish color and smell like sulphur when broken apart. 

Halichondria Sponge
Halichondria sponge by Cailyn Joseph
Halichondria sponge by Cailyn Joseph

Another yellow sponge present in our bays is the halichondria sponge. Since these sponges can withstand drying out more than other sponges, they can be found in very shallow intertidal zones. If you keep your eyes peeled, you may just be able to spot one walking along a shoreline or dock. Similar to the boring sponge, these sponges also give off a distinct smell that has been compared to gunpowder! It likely gives off this odor to ward off predators. 

Finger Sponge

Continuing on our sponge expedition, we have to look to slightly deeper waters for the finger sponge. These sponges can grow up to 30 centimeters tall and have long, velvety branches. These branches are what gives it the common name of the “mermaid’s glove”. Their colors can range anywhere from light brown, yellow, or reddish. There are many

Finger Sponge by Nudibranch Marine Discovery Productions (Peter van Rodijnen); Stichting Natuurbeelden
Finger Sponge by Nudibranch Marine Discovery Productions (Peter van Rodijnen); Stichting Natuurbeelden

forms in which these branches can grow, which is why long ago when scientists were trying to classify them, they classified each branching arrangement as a different species! 

Sponges are certainly unlike many other beloved creatures in our Coastal Bays, but they are special and important all the same! I hope this information demystifies the sponge for you, as they deserve some recognition for their hard work clarifying our waters, and while doing it, they add a nice pop of color to the shallows.

*Information obtained from the Maryland Coastal Bays Fisheries Identification Guide.

Author Background

Cailyn Joseph is a seasonal scientist and educator with the Maryland Coastal Bays Program. Cailyn works with both the science and education teams on programs such as wetland assessments, data entry, summer camp facilitation, lesson design, bird monitoring, public seining programs, and more. She is currently working on a fisheries heritage project called “Voices of the Coastal Bays” that will feature the history and culture of the OC Fisherman’s Marina located in West Ocean City, as well as highlight the vibrant stories of the local fishermen and women that operate out of the marina.  Cailyn graduated from Salisbury University in May 2021 with a B.A. in environmental studies and a B.S. in biology.

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