Alex Re: [00:00:00] Hello, welcome to On Wildlife. I'm your host, Alex Re. On this podcast, we bring the wild to you. We take you on a journey into the life of a different animal every month, and I guarantee you you're gonna come out of here knowing more about your favorite animal than you did before. On today's episode, we're looking at animals that may remind you more of a plant.

They may be immobile, but that doesn't mean they're boring. These animals have amazing characteristics that have allowed them to survive on Earth for hundreds of millions of years. So hold your breath, because we're headed all the way to the sea floor to talk about sponges.

Despite what you might think, sponges are animals just like us. Although they don't exactly look like us, [00:01:00] they're more closely related to humans than they are to any plant. In fact, sponges were one of the first ever animals, with fossil records showing that they've been around for over 600 million years.

There are over 8,500 sponge species, all belonging under the phylum Porifera. In Latin, Porifera translates to having pores, and that's one of the main characteristics of sponges. They have holes and channels throughout their bodies. Sponges are always found underwater. Most species are found in the ocean, but there are some species that are able to live in fresh water, like the lake sponge.

Most adult sponges have a stem that attaches them to the bottom of the sea floor, and a lot of sponges look like tubes with one large hole at the end called the osculum. You can find them in every ocean in the world, and their large amount of species allows for tons of diversity. There are some species that live in shallow [00:02:00] waters, while others are found in the deep ocean.

The deepest sponge ever found was discovered in the Philippine Trench, which is over 32,000 feet below the ocean's surface. And they can come in a variety of shapes and sizes. They can be red, yellow, blue, green, purple, and more. One of the largest sponge species is the giant barrel sponge. It's found in the Caribbean and can grow to be around eight feet tall.

And many sponges have very slow growth rates, only growing at a pace of a few millimeters every year. It's hard to tell just how long they're able to live, but scientists can make estimates based on how quickly they grow per year and how large they are. The oldest individual sponge is an Antarctic sponge, which is estimated to be around 15,000 years old.

Unlike a lot of animals that we cover on this podcast, sponges don't have any internal organs like a brain, stomach, or [00:03:00] heart. So what are they actually made of? We'll talk about that right after the break.

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Now back to the episode. Even though the sponges that we use in the kitchen are soft, the animals actually have sharp rods that make up their inner skeleton, which are called spicules. The spicules are either made of calcium carbonate, the same stuff that makes up clam shells, or [00:04:00] silica. Some species can also have spicules made of a tough protein called spongin, which is not sharp and bony like the calcium carbonate and silica spicules.

And the species that are made of spongin actually used to be collected and used to make sponges that we use in our kitchen. Now, the sponges that we use are made of plastic or other synthetic materials. All of this to say, most sponges aren't as soft as they look on the outside, and if you see a living sponge in the wild, you should try not to touch it.

The spicules can even become embedded in your skin and cause irritation if they're touched. Spicules are surrounded by different specialized cells. The outer layer of the sponge is made of a layer of cells that kind of act like skin cells. The inner layer is made of collar cells, which help the sponge eat.

Since they don't have mouths or stomachs, sponges rely on the flow of water [00:05:00] to get their food. The way this works is that water flows through their pores in their outer cell layer and into the inner cavity of the sponge. This is where collar cells come into play. The collar cells have tail-like structures called flagella that move the water through them, and inside, they have microscopic hairs that trap food particles like bacteria, plankton, and other nutrients.

The water then gets pushed through the large hole at the end of the sponge. This is also where they emit their waste. Because of how they get their food, we classify sponges as filter feeders. What's really cool is that you can see this filter feeding in action. There are videos online where researchers will squirt non-toxic dye around the sponge, and you can watch the water get taken into their pores and pushed through their osculum.

And because there are so many species, there have to be [00:06:00] exceptions to the rule. Some sponges are carnivorous. Just this past year, researchers found a new species of sponge that they've named the death ball sponge. It doesn't really even look like a sponge. It has a base with multiple stems on it, and at the end of each stem is what looks like a translucent pink balloon.

Covering the surface of these balloon-looking structures are microscopic hooks that the researchers believe are used to catch their prey. There are also some animals that eat sponges. They're called spongivores. If we took a bite out of one, it would not be pleasant. They can be sharp, they don't have much nutritional value, and some can also be toxic.

But some animals have evolved to specifically eat sponges, like sea slugs. Certain species of sea slugs are even able to take the toxins from sponges to use for themselves. Other animals that eat sponges are hawkbill [00:07:00] sea turtles and pufferfish. Because sponges don't have a nervous system, they're unable to communicate with each other, but they do compete with each other and other organisms for space, which is the most valuable asset for a sponge.

Some studies show that they're able to release toxins that inhibit the growth of other individual sponges. They're also able to produce antimicrobial chemicals that protect them against pathogens and disease. But they're able to use these chemicals against corals that are inhabiting the same space that they live in.

As you may know from previous episodes, coral rely on algae for nutrients. Studies have found that sponges nearby are able to decrease the amount of photosynthesis that these algae are able to perform. This, in turn, reduces the amount of nutrients that the coral gets. And similar to coral, sponges are able to have symbiotic relationships with bacteria [00:08:00] and other organisms.

Deep sea sponges were found to be the host of an organism known as archaea. Archaea are similar to bacteria, and they were actually the first living things on Earth, appearing around three and a half billion years ago. We still don't really know exactly what the sponges get from their relationships with archaea.

Okay, let's take a quick break before we talk about the crazy ways that sponges are able to reproduce.

Time for today's trivia question. What is a group of bird or reptile eggs called?

The answer is a clutch. Although sponges can't communicate with each other, they can reproduce with each other. They can [00:09:00] reproduce two different ways, sexually or asexually. There are no male or female sponges, as they can produce both sperm and egg cells, but they usually don't produce them at the same time.

In sexual reproduction, sponges release sperm into the water, and they're taken in by another sponge that has produced eggs. The sperm fertilizes the eggs in between the inner and outer cell layers of the sponge, and the eggs are retained inside the body until they hatch and are released out through their osculum Unlike the adult stage, the larval stage of the sponge is able to swim and move throughout the water.

During this stage, they're classified as zooplankton. The larva swims around the environment to look for a suitable area to attach to and grow on, which scientists would call a substrate. Once the substrate is found, the larva attach to it and begin to [00:10:00] grow into an adult sponge, where it will no longer be able to move.

The other way that sponges are able to reproduce is asexual reproduction. This is a much more simple process called budding. During budding, an area of the sponge begins to grow outward and eventually detaches from the sponge. That small growth then becomes its own individual, and what's really interesting is that individual is genetically identical to the parent.

Also, if a piece of a sponge is broken off for any reason, that piece is able to form its own individual as well. That can be a really great way to make sure your genes survive to the next generation, especially if you're not able to move. Sponges do so much for the ecosystems that they live in. One of the most important things that they do is filter feeding.

If you've ever owned a fish tank, you'd know that you need a filter to keep the water [00:11:00] clean. Well, sponges basically act as that filter, removing particles from the water. They also cycle nutrients throughout the environment when they produce waste, making these nutrients available to other organisms who need it.

They also provide shelter for thousands of different marine organisms, like brittle stars, shrimp, and a bunch of different fish species. Certain sponge species, like the glass sponge, can act as the foundation of the reef ecosystem, not to mention sponges help in the fight against climate change. One of the main drivers of the warming of the planet is carbon dioxide.

A lot of carbon dioxide that humans produce is actually absorbed by the ocean, but that causes its own problems, mainly that it makes the ocean water more acidic. Sea sponges are able to take in the carbon that was absorbed by the ocean and use it to produce organic material. All of the benefits that I [00:12:00] just mentioned either directly or indirectly help humans, and sponges can also make a difference in the creation of new medicines.

This year, scientists from Florida State University have identified a molecule in a specific bacteria that could help create drugs that fight against rare cancers. This bacteria lives in the Pacific sea sponge. So even though they don't move, sponges are really amazing animals. As a whole, sponges aren't threatened, but there are specific species that have declining populations.

Some of this is due to the fact that in the 1800s and early 1900s, humans harvested a huge amount of sponges from the ocean for our own personal use. There's also a commercial fishing technique called bottom trawling that can be extremely harmful to sponges. Fishing boats will drop a heavy net to the bottom of the sea floor and drag that net across the ocean.[00:13:00] 

This pretty much rips up anything that's in its path, and since sponges aren't able to move, they get ripped up from their substrates. This practice is restricted in some areas throughout the United States, but it's not completely illegal. A newer threat to sponges is deep-sea mining, where people will drill through the bottom of the ocean in deep-sea habitats, looking for different metals or minerals.

This hasn't been put into practice yet, so we don't even know all of the effects that it could have on ocean animals, and as of right now, multiple companies are pursuing permits to do deep-sea mining. Luckily, there are organizations working to help prevent these harmful practices and to help the ecosystems that sponges call home.

You should check out the Deep Sea Conservation Coalition, Reef Life Foundation, and Marine Bio Conservation Society. Thank you so much for coming on this adventure with me as we explored the world [00:14:00] of sponges. You can find the sources that we used for this podcast and links to organizations that we referenced at onwildlife.org.

You can also email us with any questions at onwildlife.podcast@gmail.com, and you can follow us on Instagram @on_wildlife or on TikTok

@onwildlife. And don't forget to tune in next month for another awesome episode, and that's On Wildlife.