Sponges

• Sponges

Types of Sponges

Calcareous sponges

This class of sponge includes over 400 species that vary in shape and size. The defining feature of this class is the skeleton of spicules, two to four pointed star shaped structural units.

Microbiology of Sponges

3 layers: central jelly layer surrounded on either side by live cells.

No nervous system (this makes them the simplest multicellular creatures in the animal kingdom, putting them above jellyfish, who have a similar cellular structure AND a nervous system).

Jelly layer is non-living, but contains a variety of other cells.

Outer cell layer is made of pinaccocytes, forms external skin.

Inner cell layer is made of Choanocytes, which regulate water flow

Porocytes regulate water filtration in the ostia, which cross the Jelly layer.

Archaeocytes are totipotent (can transform into any other type of cell in the body), useful for regeneration, reproduction, hazard removal, transport, and a variety of other tasks.

Sclerocytes secrete spicules (little sharp bits of a sponge, make it harder to eat).

The life of a sponge

Respiration

Sponges gain oxygen from the water through diffusion. The water enters through small pores called ostia and then is distributed throughout the sponge from areas of high concentration to areas of low concentration. The water flows throughout the sponge with the help of choanocytes, cells with flagella for movement. This simple process works without a more complex respiratory system because all cells of a sponge are within close proximity of exchange sites.

A study of the Red Sea coral reef sponge Negombata magnifica reveals the distribution of oxygen use. In this sponge, about 25.1% of oxygen was used for water pumping. Water pumping and maintenance together accounted for about 74% of all oxygen usage. The remaining 26% was used for other processes, mainly growth. This suggests that oxygen usage could contribute to controlling growth of sponges on the coral reef.

Reproduction

Sponges can reproduce both sexually and asexually. Most marine sponges don't willingly produce asexually, but shards can regenerate into new sponges if they are broken off of the main body.

Most marine sponges release sperm and hold onto eggs. When another sponge's sperm comes into their filtration system, it is absorbed and carried to their eggs. The new sponge grows out of the side of the parent and eventually removes itself.

River sponges reproduce asexually all the freaking time because it's an effective migration method in a river. They basically fertilized themselves, then let the "zygote" develop into a ball of archaeocytes with lots of food, then put it in a dormant state that's adaptable to super-wide temp+salinity+sediment+etc ranges, then release it. A few marine sponges do, but I don't think it's as effective when currents are circular in nature and always going towards the nearby shore.

Feeding/Diet

Sponges gain basically all of their nutrients and sustenance from the water filtration process outlined in the respiration section.

Any clogged ostia are cleaned by Archaeocytes.

Habitat

Sponges can survive in almost any habitat imaginable, due largely to their simple design and rudimentary requirements for subsistence, but they occur in the greatest proliferation on coral reefs.

Glass sponges rarely appear in reefs.

Because they are sessile, they have to compete for growing space. Because most competitors in this field are photosynthetic, sponges can often be found in shaded outcroppings of rock.

Most have to remain moored to a solid bottom, but some can moor themselves on soft bottoms (sand, etc) via a thick root system (looks a lot like a tap root in plants).

Defense

Sponges have a basic immune system that prevents cell movement in infected areas, and eventually kills all cells in the area by excreting toxin.

Sponges are very good at competing for space, which makes sense since they can't actually move. Some shed their spicules, making it hard for predators to approach them (think surrounding your tent with caltrops/upright nails/legos every night before going to sleep in the woods). They also produce toxins that make life difficult for other nearby sessile organisms.

Ecological Interaction of Sponges

Sponge filtration is actually a vital part of the coral ecosystem, as many sponges can cycle great amounts of nutrients back into the ecosystem very quickly after fish, corals, etc, die and degrade (normally disintegrated resources/floating detritivores might be carried away by the current, or any number of other things).

This is part of why Darwin's paradox is possible.

Many sponges form symbiotic relationships with photosynthetic algae. These sponges are great sources of Oxygen for the reef.

Common predators include nudibranchs, sea turtles, Wrasses, and parrotfish.

Human interactions

Humans used to harvest sponges for a variety of uses, from paint pigments to modern commercial sponge sales, but today most sponge-based products actually use synthetic sponges.

Reef sponges are often damaged by fishermen using weighted nets or even simply taut fishing lines. They are also often detached by storms.

Sponges are being affected by Climate change just like the rest of the reef.

Sponge pathogens seem to be on the rise. The largest sponges are the most vulnerable to these, since they filter the most water and most pathogens are caught by water filtration. This is especially notable because the largest sponges in a habitat are usually providing habitats for other creatures.

Resources

http://www.sciencemag.org/content/342/6154/108.full

http://www.nature.com/nature/journal/v413/n6857/full/413726a0.html

http://www.nature.com/news/2009/091116/full/news.2009.1088.html

http://news.nationalgeographic.com/news/2001/11/1107_keyholecoral.html

http://link.springer.com/article/10.1007%2Fs10750-011-0842-x

http://www.mareco.org/khoyatan/spongegardens/introduction/

http://www.coralscience.org/main/articles/climate-a-ecology-16/caribbean-sponges

http://www.qm.qld.gov.au/Find+out+about/Animals+of+Queensland/Sea+Life/Sponges/Unique+features+of+sponges#.UwA1doXPuh4 (this has a majority of the basic information in it)

NOTES

Freshwater sponges probably don't matter on here, but holy hay are they different.

Resource URLs can turn into actual citations later.