Porifera Life Cycle
The life cycle of a sponge is a relatively simple one. Sponges can reproduce sexually and asexually. There are many sponge species in which each sponge is considered male and female. When it comes to sexual reproduction, a sponge can play either role. The male sponge releases sperm into the water which travels towards and enters the female sponge. After fertilization occurs, a larvae is released from the female sponge into the water. The larvae floats around for several days until it can find a suitable substrate to stick to. At this point, the larvae will begin to grow into an adult sponge. Sponges become more diverse when different sponge species reproduce with one another (Myers, 2001). The sexual life cycle is depicted below in Figure 1.
When sponges go through asexual reproduction, it is by a system called budding. This occurs when a small piece of the sponge is broken off and is able to grow into a whole new sponge. Like in sexual reproduction, this small piece of the sponge must find a substrate to cling to in order to grow into an adult sponge (Myers, 2001).
Figure 1. The life cycle of a sexually reproducing sponge. Hermaphroditic sponges acting as “male” (A) release sperm into the water. A sponge acting as “female” (B) receive sperm through their pores. Sperm is directed into the sponge wall where the egg is located (C). Fertilization occurs and a zygote forms (D). The zygote is released into the water and uses its cilia to swim to a new location (E). Once the zygote settles into habitable substrate, it begins to grow into a mature sponge (F). Drawing by Sarah Petersen. Information from Myers (2001).
Sponges and their Associations with Other Organisms
Sponges make up an important component of coral reefs and filter the surrounding water and cycle nutrients (Hultgren, 2014). Sponges have a wide range of associations with other organisms, which can include facilitating primary production, providing a habitat for another organism, or even providing protection to organisms from predation. Sponges interact with a wide range of organisms, so it is sometimes difficult to understand the role sponges play in these relationships (Bell, 2008).
To facilitate primary production, sponges associate themselves with photosynthetic organisms. A review paper by Bell (2008) mentions that these photosynthetic relationships contribute between 48 and 80% of the sponge’s energy requirements and around 10% of the reef’s productivity. This paper also mentions that the role of sponges as primary producers may only be important for nutrient-poor waters, such as those found in the tropics. Sponges are also involved in secondary production because other organisms such as fish, crustaceans, and molluscs consume them. These predators vary over the differing ecosystems that sponges are found in (tropical, temperate, polar, etc.). Since sponges harbor photosynthetic organisms, the sponges being eaten by predators could be seen as a herbivorous interaction because the photosynthetic organisms may be of greater nutritional value than the actual sponge itself (Bell, 2008).
Sponges also provide microhabitats for smaller species. Costs and benefits to each organism in the relationship are not well studied. In an experiment by Hultgren (2014), the relationship between the Synalpheus species of snapping shrimp and the marine sponges they inhabit. It was found that the shrimp had varying effects on the sponges. When predators were present, the shrimp had positive effects on the sponges and negative effects during periods when the sponge was actively growing. These negative effects were likely the shrimp consuming the sponge as it grew. This study suggested a future study in which abiotic and biotic stressors should be manipulated to see if the relationship between shrimp and sponge changes. Sponges also interact with other organisms such as bivalves. When bivalves had sponges living on their valves, their risk of predation by starfish was reduced. The sponges benefit from the association by having an increased feeding efficiency. Sponges are also associated with crabs, which have been observed to use the sponges to cover their bodies as a form of camouflage (Bell, 2008).
Where Can Poriferans be Found?
Sponges have a global distribution that encompasses polar and tropical latitudes alike. They can be found from deep depths in the ocean to shallow rock pools. Poriferans have been known to occupy habitats that include marine thermal vents as well as freezing arctic waters. While many may associate sponges with a solely marine habitat, a portion of the phylum occupies freshwater as well such as the preserved specimen pictured below, found near a hatchery in New York. These freshwater sponges are represented by 219 out of the 15,000 species of Poriferans, all belonging to the suborder Spongillina of the class Demospongiae. While the diversity of freshwater sponges may be limited in comparison to their marine relatives, their abundance within their freshwater habitats is often greater. What is most amazing about freshwater sponge diversity is the specificity of the taxa found occupying a body of water. Around 47% of freshwater sponges originated from the body of water they inhabit, and new species discoveries can often been associated with new genre as well (Manconi and Bronzanto, 2008).
Figure 2. A preserved freshwater sponge from New York. Picture taken by Christine Koporc at the OSU Museum of Biological Diversity.
As mentioned earlier, sponge fossils have been found dating back to the Precambrian, where poriferan remnants have been identified in marine strata (Porifera: Fossil Record, 2006). Colonization of freshwater by sponges has been dated back to the Mesozoic period, which occurred some 220 million years ago. This theoretical date is based off of structures found in the oldest known freshwater sponge fossils, called gemmae. These are highly conserved features within Spongellina, and act as asexual propagules of the sponge which can become dormant if environmental conditions are not favorable. This is a feature that has been associated with the ability of sponges to occupy some of the unique inland habitats they are found in (Manconi and Bronzanto, 2008). Until relatively recently in Earth’s geological time scale, sponges have constituted a large part of the framework of oceanic reefs. Today, sponges still remain an important part of reef communities, however do not contribute nearly as much to mass as corals (Porifera: Fossil Record, 2006).
Diversity in Sponges
There are many times when it is difficult to differentiate between two sponge species. On more than one occasion, two sponge species were thought to be one until scientists took their observations of the sponges one step further and realized that there was a difference between the two. There are various ways in which sponge species can be distinguished from one another. Some are seen as a food source to certain animal species while other very similar sponges are not, such as seen in fire sponges (Tedania ignis) and volcano sponges (Tedania klausi). These two sponge species used to be seen as one diverse species, fire sponges, until scientists performed feeding choice experiments as well as a morphological and molecular study and determined that they were not the same species at all. Volcano sponges are eaten by sea stars, while fire sponges are not, leaving the species to live in very different habitats. These two species were also found to have a difference in their susceptibility to disease and ability to withstand a wide change in temperature and salinity. Molecular markers also helped scientists to see the difference between the sponge species Scopalina blanensis and Scopalina lophyropoda. S. blanensis responds positively to seasonal environmental changes in temperature and food availability, while S. lophyropoda responds similarly throughout these environmental changes (Wulff, 2012).
Differences in sponge species can be seen in many different aspects of the sponge and its life. They can be based upon the role that a sponge takes in its community, their association with other species, morphological (physical) characteristics, and their vulnerability to hazards. An example of the morphological differences between sponges can be seen below in Figures 3 and 4. Some of these contrasting features can be determined through observation, while others require the use of experiments (Wulff, 2012).
Figure 3
Figure 4
Figures 3 and 4. The physical diversity of sponges is clearly seen between these two dried marine sponge specimens. Pictures taken by Christine Koporc at the OSU Museum of Biological Diversity.
Freshwater and Saltwater Sponges
Sponges live in a wide variety of ecosystems. Sponges are such simple organisms that they have been able to adapt to many different environments, which is why they are able to be found in nearly every type of body of water. They are found in the deep sea, in coral reefs, near hydrothermal vents (which are 3,000 to 7,000 feet below the water’s surface), and in various freshwater environments (Masters, n.d.). While most live in marine environments, such as oceans, there are still some that live in freshwater environments, such as lakes, ponds, and streams. Around 200 of the 15,000 known species of sponges live in freshwater environments (Skelton & Strand, 2012). The important functions of marine sponges have been determined by their impact on substrate (reef creation and erosion of hard oceanic substrate), their coupling with other organisms living at the bottom of the sea (their role in the carbon cycle, silicon cycle, nitrogen cycle, and oxygen depletion), and their interactions with other organisms (Bell, 2008). Much less is known about freshwater sponges and the roles that they play in their ecosystems, though it is believed that their roles will be very similar to those that are seen in marine sponges (Skelton & Strand, 2012). Even with this limited amount of information for their functional roles, freshwater sponges are found to be very hardy creatures that can withstand a wide variety of situations, such as drought, chemical pollution, and fluctuations in water flow, pH, and temperature (Masters, n.d.).
How sponges are used today
Sea sponges have vast economic importance. The types used are mainly demospongiae because they possess spongin which is the flexible skeleton like structure of the sponge.
Video 1. Student demonstrates the flexibility of the spongin using a dissecting microscope.
The most popular sponge used is the Wool sponge; it is the softest and most durable sponge. Firstly, they are used in industry. There is a city in Florida called Tarpon Springs located in the Gulf that is the acclaimed Sponge Capital of the World. They harvest and export a majority of the worlds sponges. Before World War II, Florida produced 600,000 pounds that is 7,800,000 individual sponges on average for human use. In recent years they produce around 70,000 pounds, that is 910,000 individual sponges on average (Stevely & Sweat, 2015).
Figure 5. Freshly harvested wool sponge. Photo taken by Christine Koporc at the Sponge Docks in Tarpon Springs, Florida.
Sea sponges are very popular in the health and beauty field. They can be used for cleaning an array of surfaces and have better water retention than that of the artificial sponge. Most popular uses include car care, household cleaning, makeup application and removal, skin exfoliant for when bathing, and personal care. If taken care of properly, they can last years on end where an artificial sponge can fall apart and be riddled with bacteria after months of use.
Figure 6. Above is an example of how a wool sponge is implemented in a bar of soap for health/beauty purposes. Photo taken by Christine Koporc in North Port, Florida.
Other organisms use sponges
Dolphins will use marine sponge to protect themselves while searching for food. They will grab a sponge from the seafloor and fit it around their beak to protect it from chunks of coral or rock that could hurt them. It is hypothesized that they hunt the bottom dwelling fish instead of the ones out in the open ocean because the bottom dwelling fish are more nutritious (Morell, 2011). Also, a variety of microorganisms, worms, crabs and shrimp will inhabit the cavities in the sponges. Sponges also serve as a protection mechanism for scallops. The sponges will attach and live on the shell and protect it from organisms such as starfish which can damage it (Bean-Mellinger, 2015).
Human Impact
Sponges have been harvested since the 1800’s because they are beneficial and durable for many uses. They are a huge industry in Florida. The regeneration of the sponges that are harvested is important for the health of the ecosystem; there are now certain parts of Florida where harvesting sponges is illegal. In the beginning sponges were harvested using the hook method. This entails a diver using a pronged hook to grab the sponge then rip it free of its base. It was later discovered that the hook method inhibits the chance of that sponge fully regenerating. It is now a law that sponges have to be harvested using the cutting method, making sure to leave enough left at the base of the sponge for proper re-growth. This entails using a knife to cleanly cut the sponge away. Doing this brings the chance of survival for the sponge to 71% versus 41% for hooked ones (Stevely & Sweat, 2015).
Figure 7. Wool sponge laying on its side. Left side of the sponge is the bottom; it can be seen it is flat because it has been cut, not torn from its base. Photo taken by Christine Koporc in North Port, Florida.
Conclusion
It’s now easy to see why we can appreciate phylum porifera and its place in basal Metazoa. What may represent one of the first multicellular organisms that successfully survived and diversified to current day is also a reminder of Metazoa’s more humble beginnings in evolutionary history. While these hermaphroditic organisms may not have organized tissue, they certainly have specialized cells and organelles to carry out the functions that would otherwise be performed by more complex structures in higher animals. Though their mobility is limited to larval stages, gametes, and the occasional passive gemmae in freshwater specimens, these organisms have also managed to occupy an incredible diversity of habitats, all at varying depths, latitudes and longitudes.
Sponges have had a large impact on their environment as well. This includes not only their primary role in reef structure throughout geological history, but direct use by other animals. Animals like humans, who rely on marine sponges in particular as an industry, can also have a significant influence on their survival through overharvesting. Poriferans are certainly amazing creatures, and their ancient lineage in conjunction with their diversity in taxa, habitat, chemical production, and ecological utility represent the merit in appreciation of these organisms.
Literature cited
Bean-Mellinger, B. (2015). Relationship Between Scallops and Sponges. Animals. Retrieved from http://animals.pawnation.com/relationship-between-scallops-sponges-9329.html.
Bell, J. J. (2008). The Functional Roles of Marine Sponges. Estaurine, Coastal and Shelf Science, 79(3), 341–353.
Hultgren, K.M. (2014). Variable effects of symbiotic snapping shrimps on their sponge hosts. Marine Biology 161, 1217-1227.
Manconi, R., Masters, R. (2008). Global Diversity of Sponges (Porifera: Spongillina) in freshwater. Hydrobiologia, 595(1), 27-33.
Masters, M. (n.d.). Habitats of Sea Sponges. Retrieved from http://animals.pawnation.com/habitats-sea-sponges-2396.html.
Morell, V. (2011, July). Why Dolphins Wear Sponges. Science. Retrieved from http://news.sciencemag.org/environment/2011/07/why-dolphins-wear-sponges.
Myers, P. (2001). Porifera Sponges. Retrieved from http://animaldiversity.org/accounts/Porifera/.
Porifera: Fossil Record. (2006). Retrieved March 28, 2015, from http://www.ucmp.berkeley.edu/porifera/poriferasy.html.
Skelton, J., & Strand, M. (2012). Trophic ecology of a freshwater sponge (Spongilla lacustris) revealed by stable isotope analysis. Hydrobiologia, 709(1).
Stevely, J., & Sweat, D. (2015). Florida’s Marine Sponges: Exploring the Potential and Protecting the Resource. Retrieved March 28, 2015, from http://edis.ifas.ufl.edu/sg095.
Wulff, J. (2012). Ecological Interactions and the Distribution, Abundance, and Diversity of Sponges. In Advances in Marine Biology (pp. 273–344).
This article raises some crucial points that deserve more attention. The depth of analysis and the quality of writing are commendable. I’d love to see a follow-up article with more examples and possibly some case studies to further illustrate the points made.Gamesofunity