Most people aren't familiar with sea sponges beyond a certain inaccurate cartoon character. Because of that our lab is often asked the same questions, so we tried to answer a few of the more frequent ones below.
Are sponges an animal or plant? Are they even alive?
Sponges are animals! They are thought to be either the first, or one of the first animals to have ever evolved. They have multiple cells that serve different functions and can elicit a whole body response to external stimuli (such as sediment, physical touch, and flow).
Is my dish sponge the same as a sea sponge?
The sponges we buy for our dishes are synthetic, and have nothing to do with marine sponges. However, sponges around the world have been harvested for centuries for use as body sponges. Not all sponges can be used for this, since some sponges have glass skeletons made of sharp "spicules" that would act like fiberglass on your body (ouch!). Even working with these "glass" sponges (Class Hexactinellida), we have to be careful and handle them with gloves. Only sponges in the group Demospongiae can be used on our bodies. Even then, in many places sponge over-harvesting has depleted sponge populations beyond recovery, so using natural sponges is not a great "alternative" or "green" option.
WHy are sponges important for the environment?
Sponges are prolific filter feeders, and as they filter they take out bacteria to feed on, and excrete wastes such as CO2, ammonia, and nitrates. In areas where there are a lot of sponges, this can massively change the water chemistry around them. Many animals can't feed on bacteria, but they can feed on sponge wastes; this is why sponges have been called the "screen between the used and the unused". By turning un-usable materials into something other organisms can use, sponges form the base of an entire food web. Perhaps as importantly, the complex structure and open crevices within sponges form the perfect hiding spot and habitat for animals. Many juvenile commercial species, such as rockfish, find their home around sponges. Research has shown that in areas where there are more sponges, there is a higher biodiversity of other animals.
Are sponges the first ever animal to evolve?
This is very complicated question, and one that is currently hotly debated among evolutionary biologists. Until very recently, sponges were more or less uncontested as the first animal to have evolved; however, it was with recent genetic analysis that things became complex. A group of animals called ctenophores (or, comb jellies) turned out to have fewer genes in common with later animals than sponges did. This means that sponges seem more closely related other animals, and ergo evolved later than ctenophores. This is interesting, because sponges have no nerves and no gut, while ctenophores do. If this new hypothesis is correct, that means sponges could have lost these intricate traits that we consider a hallmark of more 'derived' animals.
how is sponge research useful for humans?
Sponges have been instrumental in the invention of many of our pharmaceuticals, such as Acylovir (which is an antiviral cream) and many cancer drugs. Sponges have bacterial symbionts, and these bacteria produce organic molecules. Synthesizing organic molecules is a complicated process because out of all the possible combinations it's almost impossible to know which will have biologically relevant properties. Because sponges have many different organic molecules, it becomes much easier to find molecules that are likely to have some biological function. After the molecule has been identified it can easily be synthesized. Additionally, sponges have been used in pottery all around the world to improve the durability of clay structures. Sponges are also a habitat for many commercial species, like a forest is a home to birds (read more in sponge importance for the environment)
are there any human caused dangers to sponges?
One of the things we've studied extensively in our lab is the effect of sediment on sponges. As filter feeding animals, sponges pull water through a fine mesh to feed on bacteria in the water. If something unwanted, such as sediment, makes its way into the feeding mesh sponges either sneeze it out (as is the case in demosponges), or they stop pumping entirely (as is the case in glass sponges). Trawling the ocean floor for fish is a practice that started within the last two centuries, and in addition to tearing up the sea floor, it re-suspends massive clouds of sediment that can travel for kilometers. Because the deep sea is rarely disturbed and the waters are crystal clear, the deep sea sponges are not used to handling high sediment concentrations, which could negatively impact their survival. Additionally, sponges in tropical waters have been harvested for human use as, well, sponges for thousands of years. In many places where this practice is common, sponge populations have not recovered.
is it true that sponges can be pushed through a sieve and re-form?
Yes, but not all. This feature of sponges was first described over 100 years ago by H.V. Wilson, and has fascinated naturalists since. Not only were sponges able to reform, but if two dissociated sponges were mixed together, they would dissociate back into the two individuals that formed them. Based on our research, this capability is possible in some but not all sponges. Out of the 7 sponges we tested, only 2 were able to fully reaggregate, while the other 5 showed some signs of regeneration before they dissociated. This question is fascinating to study from the point of view of immunology and evolutionary biology.
How old can sponges get?
This is a surprisingly difficult question to answer, but one we get very often. Unlike humans, we can't ask a sponge how old it is. Many sponges live in an environment that is difficult to reach, and our monitoring techniques and practices are relatively new. Based on growth rates, some sponges are estimated to be hundreds of years old.
Where do sponges live?
Here! There! Everywhere! Sponges live in almost every water environment on the earth. Among the first animals to have evolved, sponges had at least 500 million years to adapt to the earth's diverse environments. From the deep cold oceans, to tropical reefs; from the Arctic to the Antarctic. Sponges live in freshwater and salt water, they live in crevices on rocks exposed during low tides, and moist branches of mangroves in Panama. We even have them in the header tanks of our water supply!
what is the biggest sponge?
Xestospongia muta, also known as the Giant Barrel Sponge is so big that it can fit an entire human in it. They are mostly found in the tropical regions of the Atlantic (i.e. in the Caribbean).
do sponges even have behaviours?
Absolutely! Sponges are multicellular animals that respond to their environment. As filter feeders, sponges use cells with undulating flagella to pull water from the environment into their bodies, and take out bacteria to feed on using a fine mesh filter. If there is sediment in the water it can clog their filter, and sponges will either rhythmically contract their body in a coordinated "sneeze" response (demosponges), or stop pumping entirely (glass sponges). Even without sediment, sponges have been shown to rhythmically contract and expand over periods of two weeks. Based on our research, we also see that sponges can respond to the flow around them, potentially in order to take advantage of "passive flow".
What do sponges eat?
The majority of sponges filter water to eat bacteria. Some sponges, however, also have algal symbionts (which makes them green) and it is thought that they eat the sugars the algae produce. Other "carnivorous" sponges have abandoned filter feeding entirely! Instead, they bare sharp bits of their glass skeleton, and snare small animals that happen to float by.
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