UQx TROPIC101x 2.1.2 Species Diversity: Lower invertebrates - Lake Harding Association

UQx TROPIC101x 2.1.2 Species Diversity: Lower invertebrates

UQx TROPIC101x 2.1.2 Species Diversity: Lower invertebrates

By Micah Moen 0 Comment August 14, 2019


Looking at a drop of water on a coral reef reinforces how
biologically diverse tropical coastal ecosystems are. Within a
drop like this, there are literally hundreds of species
many of which are referred to as animal-like protists. These single-celled
organisms include groups such a cilliates and dinoflagellates and can be both heterotrophic and phototrophic at any one point in time. Now, during evolution, single-celled organisms began to live in
colonies and eventually form loose tissues in
which the cells making up a colony were in close contact and communication
with each other. Sponges are an ancient reminder of this evolutionary step which eventually led to
full-blown multicellular organisms. Sponges are fascinating creatures in
their own right, primarily filter feeders, sponges draw water through their porous colonies
and filter out tiny pieces of food. Some sponges
can play an important role in decalcification. This sponge is called Cliona and has the ability to drill into
the skeletons of both dead and living coral colonies. In doing so,
the sponge removes large amounts a reef calcium carbonate
representing a potent force in terms of the carbonate balance the coral reefs which
we will consider in a later lecture. The next group of
organisms which belong to the animal kingdom belong to the phylum Cnidaria. This is a
group of organisms that includes organisms such as jellyfish, hydroids, corals, and sea anemones. They are important particle feeders and in some cases carnivores in tropical
coastal ecosystems, trapping small particles and prey using
their tentacles and later digesting them in their
simple gastro-vascular cavities. In many cases Cnidarians
form mutualistic symbioses with dinoflagellates. We will be hearing much more about this symbiosis and its importance in later lectures.
Ctenophores are referred to as comb jellies, and may
be confused with jellyfish, however they’re not jellyfish. Rather they are gelatinous organisms which are distinct
from Cnidarians in that they don’t have true stinging cells. Many other organisms eat Ctenophores and they
form an important part of the connectivity between reef systems and can occur in very large numbers in
tropical waters. They are also the favourite diets of marine turtles and other planktivores.
Another group that you’ll see within tropical coastal ecosystems are Bryozoans or Ectoprocts. These
organisms form encrusting colonies and sometimes delicate lace-like
structures where thousands of individuals are
working together to form these tiny colonies. Bryzoans are an ancient group but they show an
increasing level of complexity when compared to Cnidarians and Ctenophores. Although they
do not have respiratory organs, blood vessels or even a heart they show
an increasing level of complexity in terms of the organs and tissues that they have in their bodies. They are however small in size which is a result of the limitations of diffusing oxygen in and carbon dioxide
and waste products out. The next group we’ll consider are the worms. There are large number organisms which
go by the name of “worm.” This term is largely non-taxonomic and has been applied to any animal that
is long and thin and which does not have a well-developed
head region. The first group of worms that we’ll consider here the flatworms, or the animals that belong to the
phylum Platyhelminthes. Like Cnidarians, flatworms have a simple
sack for a gut, no specialised respiratory or circulatory
systems. Some flatworms are parasitic while others
are active predators on the reef. Now many flatworms are also brightly-colored and this is because
they’re trying to advertise their distastefulness to predators such as
fish. Many of these flatworms actually have
toxic compounds in their tissues. The next group of worms are the ribbon worms or Nemerteans. The Nemerteans are a group that has a
well-developed digestive system, a primitive blood vascular system and
which can become quite large especially in cold water such as those associated
with Antarctica. In tropical coastal ecosystems, they’re
found underneath rocks or in mud or between gravel where they derive
nutrition from a range of different sources with
many species being carnivores, filter feeders and detritivores. Take the following quiz to check your
knowledge of the lower invertebrate organisms that we’ve been discussing.

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