Welcome to the abyss I’m Jaclyn and today
we are discussing coral reefs. Let’s dive in.
Coral reefs are often described as the rainforests
of the sea.
This is due to both ecosystems being rich,
productive and incredibly diverse.
However, at the phyla level of classification
coral reefs are the most diverse ecosystem
on the planet, with 32 of the 34 animal phyla
being represented.
This diversity includes an estimated third
of all marine fish species and a total species
estimate of 600,000 to 9 million.
This diversity is a remarkable feat considering
coral reefs only make up approximately
0.05 to 0.1% of the ocean floor.
Their small global cover can be seen when
looking at the world-wide distribution of coral reefs.
This limited area is due to their specific
physical requirements.
Coral reefs require tropical waters in a temperature
range between 18-20 degrees Celsius.
They are also limited by light and salinity,
so are found in shallow waters away from river mouths.
This again, makes their diversity impressive,
because this is an area of the ocean that
is not typically very productive.
Of course, one of the most defining features
of coral reefs are the corals themselves.
Corals are animals in the phyla Cnidarian,
which also includes the jellyfish and the anemones.
Within this phyla, is the class Anthozoan,
which is the corals.
The adult stage of Anthozoans is a polyp which
are soft-bodied, sessile organisms
attached to the seabed.
Within the Anthozoans there are many different
types of corals that are found all over the
world’s oceans not just on reefs.
The reef building corals make up the order
Scleractinia in the subclass Hexacoralia.
They are commonly referred to as the stony
corals.
This is because the polyps secrete a calcium
carbonate skeleton, which protects their soft body.
While many Scleractinian species are solitary,
many more are colonial, meaning that many
genetically identical polyps are all connected
together and act as one individual.
So when you think of the large corals that
dominate reefs such as the brainy corals or
large branching corals, these are actually
many identical individuals that act as one.
These Scleractinian corals are also the reef-building
corals.
They precipitate calcium carbonate from the
surrounding waters and secrete it as a skeleton,
later this forms the substrate on which the
reef sits.
When the corals die their skeletons are eroded
into sand, which settles into cracks and crevices
on the reef.
This sand is them cemented by other animals
into a hard limestone rock.
This process is referred to as reef cementation.
Overtime the reef grows larger and builds
upwards, allowing it to stay in the shallow
water that many of it’s species require.
This is one way that coral reefs are a unique
ecosystem,
because the substrate is biogenically created.
This process also creates a complex ecosystem
that results in a variety of habitats and
a larger diversity of species.
One of the main reasons why coral reefs are
so productive and diverse, and yet so environmentally
sensitive is because of a symbiotic relationship
between the corals and a single-celled algae
called zooxanthellae.
A symbiotic relationship is when two species
are dependent upon each other for survival.
Since corals are animals they are heterotrophic
and require food from external sources.
In the case of corals they are predators that
use their stinging nematocysts to filter feed
on zooplankton.
However, reef building corals live in tropical
waters, where there is not enough nutrients
and food in the water for the corals to survive.
This is where their symbiotic relationship
with zooxanthellae come in.
The zooxanthellae live in the endodermis,
or inner skin cells, of the corals.
Zooxanthellae are photosynthetic and can therefore
make their own food using energy from the sun.
This allows nutrients to be obtained in low
nutrient waters.
Zooxanthellae are so good at this that they
can photosynthesize 10 to 100 more times organic
matter than they need for their own metabolic
and growth needs.
They then provide the corals with the excess
food, allowing the corals to thrive and provide
more energy to the ecosystem overall.
Since this is a symbiotic relationship the
zooxanthellae also benefit.
The corals produce waste carbon dioxide and
ammonia as part of their respiratory and metabolic
processes, both of which the algae require.
The corals also protect the zooxanthellae
from grazers and provides them with a habitat
close to the sunlight, where they can photosynthesize.
This relationship is part of why reefs are
able to teem with life while the surrounding
waters are comparatively barren.
In conclusion corals are a rich, dynamic and
complex ecosystem.
In part due to how to ecosystem is formed
and where the energy is derived.
That’s it for today’s video, but it’s
just the tip of the reef when it comes to corals.
If you have any other questions leave them
in the comments down below.
As always if you like this video give it a
thumbs up and subscribe.
Until next tide, I will sea you later.
