A sea sponge is a multicellular aquatic animal that belongs to the phylum Poriphera. The name of the phylum comes from the fact that these animals are filled with spores that help them circulate water in order to gain nutrients and oxygen and for excretion.
A sea sponge is an animal with a jelly-like structure that is covered in two thin layers of cells. They are full of pores and channels that allow water to move in and out, and they mostly are sessile or fixed into the substrate.
Sea sponges have undifferentiated cells that are capable of migrating between the cell layers and transform into specialized cell types. Because they do not have a circulatory, digestive or nervous system, they rely entirely on a constant flow of water to help them perform all the necessary functions.
The bodies have no defined shape or symmetry, as the cells can migrate through the non-living jelly matter in the middle and occupy other positions in the cell layers that form the exterior. While 5,000 to 10,000 species feed on food particles in the water and bacteria, some either collaborate with photosynthesizing endosymbionts or they are carnivorous, feeding on small crustaceans.
Sponges are distributed worldwide, and they live from the tropics to the polar regions. Many species of sponges live in relatively calm waters, as strong currents and waves could disturb the sediments, which would cover their pores. While most sponges live firmly attached to rocks, there are some species that have a root like structure which allows them to attach on soft sediments. While there are more sponges in temperate areas, they are less diverse, while at the tropics, the variety is greater, but less abundant. This could be linked to the fact that, in tropical waters, there are more predators that feed on sponges.
Although under the traditional system, there were only three sea sponge classes, there are now four admitted classes:
Calcarea or calcareous sponges
Hexactinellida or glass sponges
And the recently added Homoscleromorpha.
The differentiation between classes is mainly correlated to the composition of their skeletons, although recent classification also takes into account phylogenetical evidence.
While sponges themselves are not capable of photosynthesis, some species host photosynthesizing endosymbionts which not only provide them with enough food and oxygen – they also produce an excess which is beneficial to the ecosystem. Most such collaborations between a sea sponge and endosymbionts produce three times more oxygen and organic matter than they can consume.
Stove Pipe Sea Sponge
Aplysina archeri, commonly known stove pipe sponge, is s species of tube sponge common in the western parts of the Atlantic Ocean, especially around the Bahamas, in the Caribbean and around Florida, in depths up to 30 m. They are hardy and long-lived species – many of them live for several hundreds of years and they keep growing all their lives, especially if they can settle in an area with turbid waters (they seem to thrive better in turbulent waters).
These sponges look like stove pipes, indeed. The part that is visible over the substrate is a large tubular structure, in many cases 1.5 m tall and measuring over 7 cm in diameter, sometimes tube thickness exceeding 10 cm. The tube is rubbery and usually brightly colored, hues ranging from brown and gray to lavender, bright blue and fluorescent pink, with interiors of a different, usually much lighter color such as yellow or cream. The exterior surface of the tube has ridges and wart-like protuberances of the same color as the tube, but the interior of tube is completely smooth. These sponges can be found living alone or in groups, the tubes connecting to each other through a common base – the largest group found so far measured over twenty individuals.
Like many other sponge species, these animals are filter-feeders, too, obtaining the nutrients they need from the detritus and the plankton that floats around in the water. Though these creatures don’t have a mouth, using tiny pores on the exterior surface of their tube to draw in nutrients, they are very efficient while they are feeding – a single tube is able to filter several liters of water per second. The filtered water gets pumped out through a larger orifice on the other end of the tube.
Like many other sponge species, stove pipe sponges can reproduce both sexually and asexually. During sexual reproduction, fertilization takes place in the water column between the sperm released by the males and the eggs released by the females. The larvae that hatch from the fertilized eggs seek a suitable place for settling around the mother. Asexual reproduction happens through budding, a process during which a small piece becomes detached from the body of the sponge and settles to grow into a new stove pipe sponge individual.
Barrel Sea Sponge
The barrel sponge is one of the largest sponge species currently dwelling coral reef areas in the Caribbean, around the Bahamas and around Florida or in the Gulf of Mexico. These beautiful barrel-like creatures can be found on hard surfaces in relatively shallow, warm waters, at depths ranging from 10 meters to 120 meters and they are known to be among the longest-lived species of the world’s seas, their estimated lifespan being between several hundred and one thousand years.
Barrel sponges are instantly recognizable by their barrel-shaped bodies with a cone-shaped cavity in the middle and by the reddish-brown color that makes them stand out on the gray substrate, but individuals of a greyish pink hue have also been found. The color is provided by photosynthetic cyanobacteria that live inside the barrel, the skeleton of the sponge being glass-like without the bacteria to color it. The exterior surface of the barrel is hard and rough, but the skeleton fissures and breaks easily. The wall of the barrel can reach the thickness of 2.5 cm at the top and becomes thicker towards the bottom.
Barrel sponges are usually large, often growing to reach a diameter of 1.8 meters. The size and the bowl-shaped body make the sponge attractive to numerous other marine creatures – many invertebrates such as shrimps and crabs, as well as small fish species, including cardinalfish and gobies, use barrel sponges as hiding places or as their permanent habitat.
Barrel sponges are filter feeders – they pump water continuously through the sides of their body, filtering the water and drawing microscopic food particles out of it. The waste material produced by the sponge and the water that has been filtered are released into the inner cavity of the body and leave the body through the opening at the barrel’s top.
The species has distinct male and female individuals that release their respective reproductive fluids into the water column. They don’t have a preferred mating period, spawning can take place any time of the year and it occurs in groups. The fertilization of the eggs takes place in the water, following which the larvae become dispersed by the currents, thus ensuring wide coverage. When the floating larvae find a suitable patch of substrate, they attach themselves to it and start growing into beautiful, large barrel sponge individuals.
Vase Sea Sponge
The vase sponge is a family of medium sized sponges named after their vase-like shape. Common in the Indo-Pacific, especially in coral reef areas up to around 26-27 meters where they can live on walls, these sponges are frequently found living in areas populated by sponge brittle stars. Most of these sponges are solitary, living alone, but sometimes they form small groups, with one main tube and a few smaller, secondary tubes. Their lifespan varies from a few months to over two decades, depending on the species and on the living circumstances in the habitat.
Vase sponges are among the most colorful creatures in the world, the hues they display ranging from blue to pink, purple and red. Most species in the family have bumps and ridges on the exterior surface of their tube, usually 0.5-1cm high, but all of them have smooth interiors. Vase sponges vary in size from a few cm to over 20 cm in height.
Vase sponges are sessile, they spend all their life anchored to the chosen patch of substrate, therefore they need to obtain the nutrients they need from the water around them. They collect plankton and other food particles from the water, storing nutrients inside the vase tube. The water drawn in is filtered, then expelled through an orifice. Vase sponges can control the quantity of the water that passes through their body by closing the intake orifices.
These sponges, like many other species of sponges around the world, are able to proliferate both sexually and asexually. Asexual reproduction takes place by means of budding, a process during which a small part of the vase breaks off and floats in the water until it settles and grows into a new sponge. The process of sexual reproduction starts with the development of the unfertilized egg inside the parent body. When the eggs are sufficiently developed, sperm cells get released into the water and then introduced into the same parent body and the eggs are fertilized internally. The eggs also hatch internally, into larvae that have a flagella, a tail-like appendage that they use to leave the body of the parent. The larvae swim to find a place suitable for settling and when they find the right place, they start developing into new, colorful vase sponge tubes.