Mactan Island, The Philippines
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Sponges are sessile animals that filter water through their porous bodies, and ingest food particles and dissolved materials. There are more than 7000 species alive today living in both freshwater and marine environments, and are the oldest known multicellular animals. Sponges live in all types of regions all over the world. 99% of all sponges live in the marine environment. There are a higher number of sponge individuals and sponge species in the tropics of all regions because the water is warmer. They do best in clearer waters as silt or sediment laden water may clog the pores of the sponges causing the demise of the sponge as it cannot get its nutrition and oxygen to survive. Sponges have strong structures that are able to handle the high volume of water that flows through them each day. By constricting certain openings, sponges are able to control the amount of water that flows through them. Scientists believe that some sponges are colorfull because the colors may act as protection from the sun’s harmful UV rays. Sponges in temperate oceans and perhaps some deep-ocean ones may live for 200 years or more. Some calcified sponges live for at most, a few years, but some tropical demosponges grow by only 0.2 millimetres (0.0079 in) per year and, if that rate is constant, specimens 1 metre (3.3 ft) wide must be about 5,000 years old. Some sponges start sexual reproduction when only a few weeks old, while others wait until they are several years old.
Sponges may reproduce sexually and asexually. Most sponges are both male and female. In sexual reproduction, they may play either role. The ‘male’ sponge would release sperm into the water, which would travel and then enter a ‘female’ sponge. After fertilization, a larvae is released into the water and becomes part of the plankton untill it finds a suitable surface on which to attach and begin its growth into an adult sponge.
They are also able to reproduce asexually through budding. This is when a small piece of sponge is broken off but is still able to survive and grow into another sponge, which may be the most common method of sponges spreading within our aquariums. Sponges are also able to repair damages to their bodies. These characteristics of sponges are ideal because even small parts of sponges may survive and spread within our aquariums.
Often, sponges are distinguished by the level of complexity exhibited by their bodies. The simplest form consists of a single tube two cell layers thick. Sponges with this type of architecture are necessarily very small due to surface area to volume constraints. In order for a sponge to attain greater size, the sponge wall must fold in on itself.
Like cnidarians (jellyfish, etc.) and ctenophores (comb jellies), and unlike all other known metazoans, sponges bodies consist of a non-living jelly-like mass sandwiched between two main layers of cells. Cnidarians and ctenophores have simple nervous systems, and their cell layers are bound by internal connections and by being mounted on a basement membrane (thin fibrous mat, also known as "basal lamina"). Sponges have no nervous systems, their middle jelly-like layers have large and varied populations of cells, and some types of cell in their outer layers may move into the middle layer and change their functions.
Most sessile or slow moving animals on tropical reefs have developed the means in which to produce a wide array of chemical compounds for self defense or to prevent other organisms from growing upon themselves. The brightly colored Nudibranch are a good example of an animal group that not only produces toxic, defensive compounds, but advertises that they do by being brightly colored. While many sponges do not advertise their toxicity through colorfull displays, they can and do produce some of the most elaborate compounds found anywhere on the world's reefs. For many years now, science has been collecting and analyzing a great many sponge compounds for use in the medical field to combat human cancers and for their use as antibacterials. It is also thought that many of these compounds may be used by the sponges as a form of chemical warfare (allelopathic) against other encrusting or encroaching organisms including other sponge species. This is where sponges can become a real problem in our aquariums should they feel the need to defend themselves or die and cause the release of these compounds. Which could of course cause the rapid demise of the other organisms we are trying to keep as part of our captive reef ecosystems. A number of times I have collected specific sponges with the thought of adding them to my aquarium only to find that they had released some form of toxin while in my collection bucket on the way home from our local reef which promptly killed any and all other creatures that I had collected and were sharing the same bucket. Over time and through trial and error I have come to learn which types or species are not prone to cause such harm and will try to include photos of those that I have found to be suitable for collection and keeping within an aquarium.
There are four different types of sponges from different classes: Calcarea, Hexactinellida, Demospongiae, and Sclerospongiae. They are split into the classes based on the type of spicules they have. This is an important fact when considering the sponge species we are attempting to keep within an aquarium setting as the materials needed, such as silicon, will need to be present in its dissolved form within the water in order for the sponge to create new spicules needed for support during growth.
In order to determine which type or catagory a sponge belongs to, a small piece of the sponge can be dissolved in household bleach which will seperate the spicules allowing them to be viewed under a microscope. You would of course need good references in order to determine what type and possibly what species of sponge you are examining although for our purposes in caring for a sponge, a simple catagory to determine its material make up is all that should be needed.
Sponges are made of four simple and independent cells. The first are the collar cells, which line the canals in the interior of the sponge. Flagella are attached to the ends of the cells and they help pump water through the sponge’s body. By pumping water, they help bring oxygen and nutrients to the sponge while also removing waste and carbon dioxide. It is when we expose sponges to air that causes many of their deaths during transport into our aquariums as the flagella are unable to perform in trapped air bubbles within the sponge, kind of like trying to row a boat by keeping the oar out of the water. Such exposure causes the death of the surrounding cells which can lead to necrotic tissue spreading untill all cells are affected.
The second cells are the porocytes, which are cells that make up the pores of the sponge. Epidermal cells form the skin on the outside of the sponge.
Finally, the amoebocytes exist between the epidermal and collar cells in an area called the mesohyl. They carry out functions of the sponge and help transport nutrients. They also form spicules, which are the sponge’s skeletal fibers. They work together with the collar cells to digest the food for the sponge and produce gametes for sexual reproduction.
Adult sponges lack neurons or any other kind of nervous tissue. However most species have the ability to perform movements that are coordinated all over their bodies, mainly contractions of the pinacocytes, squeezing the water channels and thus expelling excess sediment and other substances that may cause blockages. Some species can contract the osculum independently of the rest of the body. Sponges may also contract in order to reduce the area that is vulnerable to attack by predators. In cases where two sponges are fused, for example if there is a large but still unseparated bud, these contraction waves slowly become co-ordinated in both of the sponges.
The coordinating mechanism is unknown, but may involve chemicals similar to neurotransmitters. However glass sponges rapidly transmit electrical impulses through all parts of the syncytium, and use this to halt the motion of their flagella if the incoming water contains toxins or excessive sediment. Myocytes are thought to be responsible for closing the osculum and for transmitting signals between different parts of the body.
Sponges contain genes very similar to those that contain the "recipe" for the post-synaptic density, an important signal-receiving structure in the neurons of all other animals. However in sponges these genes are only activated in "flask cells" that appear only in larvae and may provide some sensory capability while the larvae are swimming. This raises questions about whether flask cells represent the predecessors of true neurons or are evidence that sponges' ancestors had true neurons but lost them as they adapted to a sessile lifestyle.
It was recently discovered by that the Halisarca caerulea sponges that grow in the deep cavities beneath reefs, obtained 90% of their diet by consuming dissolved organic carbon, which is inedible for most other reef inhabitants. When the amount of carbon that sponges consumed was measured it was found that they consume half of their own weight each day, yet they never grew. So what were the sponges doing with the carbon? As it turns out, the sponges were growing, but discarded so many of their own cells that it offset new growth, with the discarded cells becoming food for many other organisms. Essentially, the sponges recycle carbon that would otherwise be lost to the reef.
Most hobbyist seem to have very poor success rates with purchased sponges since any exposure to air will kill most species and those few types that are commonly sold are simply not suited for aquarium life as our providing the exact particle size and type of food, which for many species consists of phytoplankton and/or bacteria, are not usually available in any great quantity in a typical reef aquarium due to heavy filtration by skimmers. However, there are a few species that live in waters where the supply of food particles is very poor and instead, prey upon crustaceans and other small animals. Most belong to the family Cladorhizidae, but a few members of the Guitarridae and Esperiopsidae are also carnivores. In most cases little is known about how they actually capture prey, although some species are thought to use either sticky threads or hooked spicules. Most carnivorous sponges live in deep waters, up to 8,840 metres (5.49 mi) making it highly unlikely that we will ever find them within our aquariums but I thought it worthy to note simply to show how diverse this group of animals are.
The Urochordata, sometimes known as the Tunicata, are commonly known as "sea squirts." The body of an adult tunicate is quite simple, being essentially a sack with two siphons through which water enters and exits. Water is filtered inside the sack-shaped body. This is a very diverse family of marine animals, not only in size and shape, but there is also a great diversity in life style, some being pelagic, free floating along with the ocean currents and others either being lone individuals (as shown below), or living in tightly packed colonial groups. The diversity of form and function is just far to great for me to do any explanation of them any justice within a single webpage, but believe me, if you take the time to do a bit of research as I have done, you will be amazed at what appears to be a very simple animal, and one that may be related to us humans! That should get your interest.
I have yet to collect any tunicate species from the reefs that have done well for me over the long term, although I am attempting to keep a collected species as shown in the above photo. The few that I have been able to maintain so far, all appeared as hitch hikers on live rock and have to assume that it was only by chance that the species that happened along did well for me. I also have to note that there were more species that did not do well than those that did. In short, if you do find a tunicate species thriving in your aquarium system, count yourself lucky that your system and what it provides just happens to have met the needs of that specific species. For more information and photos concerning the Tunicates, please see the relevent section within my Hitch Hikers Guide to the Reefs.