Presented by Charles & Linda Raabe
© 2009 All Rights Reserved
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
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.
Sponge bodies are diverse in form, ranging from encrusting sheets, to
volcano-shaped mounds, to tubes as small as one millimeter or as large as one
meter. In all cases, sponges have a canal system, through which they pump water. Water enters
through pores called ostia, flows through canals to a spacious chamber called a
spongocoel, and finally exits through large openings called oscula.
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
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
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.
Sponges filter food particles out of the water flowing
through them. Particles larger than 50 micrometres can not enter the ostia and pinacocytes
consume them by phagocytosis
(engulfing and internal digestion). Particles from 0.5 to 50 micrometres
(2.0×10−5 to 0.00197 in) are
trapped in the ostia, which taper from the outer to inner ends. These particles
are consumed by pinacocytes or by archaeocytes which partially extrude themselves
through the walls of the ostia. Bacteria-sized particles, below 0.5 micrometres,
pass through the ostia and are caught and consumed by choanocytes.
Since the smallest particles are by far the most common, choanocytes typically
capture 80% of a sponge's food supply.
Archaeocytes transport food packaged in vesicles from cells that directly digest food
to those that do not.
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
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
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.
( Sponge covering the top half of one of my clams )
( Ascidians ) 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
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