In the underworld city of the coral reef ecosystem exist thousands of
species of plants and animals, all of which co-exist with each other.
These living organisms are either dependent on each other for food or for
protection from predators, or both. One such animal, the sponge, is the
definition of a symbiotic species, one that has working relationships
with many plants and animals. Despite the fact that the sponge is the
simplest form of a multi-cellular animal, containing no tissues or
organs, this often brightly colored animal plays many important roles in
the reef ecosystem.
There are over 5,000 species of sponges throughout the
world, the majority of which occur in saltwater. The sheer variety of
shapes and sizes in which this animal appears is a unique characteristic
- no other invertebrate (animal lacking a backbone) comes close. Some
brightly colored sponges are even mistaken for coral. The tube sponge,
one of the most common varieties on the reef, is distinguished by long
tube-shaped growths, ranging in color from blue to purple. Another
species that inhabits the Caribbean is the vase sponge, characterized by
a large bell shape, either purple or red, which can grow to two feet wide
by three feet high.
There are essentially two main categories that sponges
can be divided into: encrusting or free-standing sponges. Encrusting
sponges tend to cover the exterior of rocks, while free-standing sponges,
the type most commonly known, grow into odd shapes and tend to be quite
large (up to six feet in diameter). Both types of sponges are known to be
bottom-dwellers, and most attach to a solid surface in an area where
sufficient food exists, allowing it to grow. Covered with pores, by which
water is sucked in, sponges feed by filtering out microscopic nutrients
of plants and animals and expelling the remaining water through a large
opening at the top of their head. While feeding, sponges usually seek out
cavities of the reef to avoid predators such as the sea hare. At the same
time, sponges often provide an ideal habitat for invertebrates, such as
shrimp and brittle stars.
If sponges don't have organs or tissues, how can they
possibly reproduce? Sponges have evolved the ability to mate as either a
female or a male, increasing their odds for success. When it comes time
to mate, one sponge assumes a female role, while the other plays the role
of a male. Throughout their lifetime, sponges are capable of playing both
the female and male role. Just like typical reproduction, the male sponge
releases sperm, which enters the female sponge. Internal fertilization
takes place, and after the larvae is released and has drifted for a few
days, they descend onto a surface and begin growing.
Sponges are commonly observed throughout
the coral reef ecosystem. Of the vast amount of species that exist, only
17 species of sponges are commercially valuable, comprised of the
colorless variety seen in kitchens and bathrooms around the world. The
majority of sponges, however, are vividly colored contributing to the
rainbow of life that exists below the sea. And like most other
inhabitants of the coral reef ecosystem, the valuable role of sponges
cannot be underestimated.
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