When we see Sea sponges, they appear to be doing not much of anything. This is because, with few exceptions, they remain on the same spot throughout their existence. The few that move, do so on a cellular level. Less than one millimeter a day is much slower than the rate in which grass grows. These sponges remain too slow to capture food or escape any threat. The sea sponge stands its ground through it all. It defends itself from predators and invaders with spicules and powerful chemical toxins.
In order to feed, the sea sponge creates a water current that drives the nutrient-rich sea water through its body. It extracts oxygen and minerals from the water while at the same time getting rid of carbon dioxide and waste. The sea sponges’ diet consists of the tiniest morsels imaginable. On the other hand, due to their natural habitat, some sponges have to resort to much larger prey.
Come to Me
Sea sponges are the simplest multi-cellular organism on earth. They are believed to be the first evolutionary leap from single cell to multi-celled organisms (NISL). They have no organs or nervous system – which means no need for a mouth to eat.
The food they require has to come to them and even when it does they cannot snare it like other sedentary animals, such as the Sea anemone . Sea sponges create an inward current using specialized cells called collar cells. These cells repeatedly beat a whip-like structure called a flagellum. Thanks to the action by these cells the nutrient rich water is sucked into the sponge delivering bacteria, plankton and other organic matter, as well as oxygen.
The water is finally expelled through a large opening called the ostium; carrying with it carbon dioxide and waste.
The sheer simplicity of their physical make up determines the sea sponges’ diet. One of the items on the menu is bacteria. Yes! the smallest prey on the planet. It makes sense, since sponges are just one level more complex than their food – the bacteria.
Bacteria are the tiniest (half micron) of the food that can fit through the numerous openings (ostia) that cover the surface of the sponge. That is about 10 times smaller than a plant cell (Seattlepi).
Eat Your Greens
Sea sponges also make plankton part of their diet, which include the many microorganisms that drift aimlessly in the sea water. This includes animals and plants. The phytoplankton are one-celled plants – they make their own food by using the sun’s energy (Plankton).
The zooplankton consists of microscopic animals, which feed on the phytoplankton. Some zooplankton spend their entire existence as such, while for others it is the initial part of their development.
The sea sponge can not consume plankton larger than 50 micrometers. Anything larger can’t fit through their ostia – the numerous openings that cover their entire surface, through which water-rich water is filtered.
A number of sea sponges live in such remote places that the sunlight is not able to reach, which means the sea water may be low on nutrients. Such low nutritional content forces the sponge to innovate. As a result predation has become the only option for these sponges to obtain their needed nutritional requirements.
Not unlike their counterparts, these predatory sponges passively wait for their prey. The Harp sponge (discovered in 2000 off the coast of California) contains from one to six vertical branches. Each has a number of vertical poles that extend the end of the limb. Each pole contains barbed hooks along its surface. The live prey become caught in the hooks. The meals consist mainly of crustaceans and other animals (Aquaviews).
Even carnivorous sea sponges don’t have a mouth or digestive system, or any organs at all. They digest their prey on a cellular level. Specialized cells travel to the captured prey; there they envelop and digest the kill (Curiosity). They consume what is needed and discard the rest. Not unlike the rest of the animal kingdom.
Diverse Eating Habits
Sea sponges are not only triumphant in evolutionary terms. They also have adapted to different ways of surviving in places where dissolved nutrients in the water are not readily available.
Most sea sponges sift the sea water for nutrition. They accomplish this with the help of specialized cells called collar cells. The nutrients include bacteria, plankton and other organic matter. These bits of food must be no larger than 50 microns in size. Anything bigger than that will not be able to enter through the opening on the sponges’ surface called ostia.
The incoming water delivers the minerals, as well as oxygen, to the waiting collar cells, as well as other cells within the sponge. When the water is expelled out through the ostium, carbon dioxide and waste are discharged.
Some sea sponges have to resort to other measures to meet their nutritional requirements. They live in such distant environment that the sun’s rays and their energy the sponge do not reach.
These sea sponges have to resort to other measures. They have evolved a more active method.
Even though these sea sponges still wait for their prey, they have a more predatory way of acquiring their food. When snails and other animals come close enough to the sponge’s trap, they become ensnared in their hooks.
The sponges’s cells move toward the prey and engulf it, while beginning the digestive process.
As you can see sea sponges are masters of survival and adaptability. Without the ability to move efficiently they can’t hunt their prey, but they have evolved some ingenious methods to meet their nutritional requirements.
They have been surviving much longer than us and it looks like they can offer us much-needed help. Only if we can help to protect them and their environment, may we fully reap the benefits they offer.
Do you own a sea sponge in your home aquarium? What do you feed it?
Would you perhaps like to own your own sea sponge someday? How do you feel about their amazing eating habits?
Please leave your comment below.
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