WEBVTT
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Hello, my name is Meri Bilan, I'm a PhD
student from the University of Salento.
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My thesis is focused on the physiology and
ecology of cold-water corals in Blanes submarine
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canyon, located on the Catalan continental
margin in the Northwest Mediterranean Sea.
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We will be talking about cold-water
corals, which are not model organisms
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but there is a potential for the development
of this idea. The main reason for this is that
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they are not easily reared in the laboratory.
Most of the experimental studies on cold-
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water corals are done with wild individuals,
but there are significant improvements on
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how to keep them in the labs from all of
the studies that have been done so far,
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so we shall call them
potential model organisms.
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In any case, the laboratory methods
presented here can be used for other
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corals, and we will pass over some
basic concepts for corals in general.
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So to start with, corals are mostly colonial
animals, although their solitary species
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such as Desmophyllum dianthus. On the
other hand, coral colonies are made by
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numerous polyps, which are supported by
a skeleton as we can see here in the black
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coral Leiopathes glaberrima or in
a gorgonian Muriceides lepida.
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Each polyp is an individual and we will be
going into more detail on their anatomy
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in the following slides. Firstly let's
have a look at their classification.
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So the information on their taxonomy is taken
from WORMS, which stands for World Register
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of Marine Species. There you can find
information about any marine species
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you are interested in, and here is
an example for Lophelia pertusa
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which as you can see now it has a status
that is Unaccepted over new combination
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and the new name is Desmophyllum pertusum.
Besides this you can find more information in
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terms of in which environment you can find
it, when it was first described, what is the
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taxonomic citation, what are the synonymised
names, some notes on global distribution,
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and images, and so on.
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So now the class Anthozoa is
part of a phylum called Cnidaria.
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In Greek, Anthozoa means flower animals,
indicating their shape. There are three main
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subclasses, starting with Ceriantharia, tube-
dwelling anemonies. They are usually found
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in soft sediment and as their name suggests,
they produce a fibrous tube within which they
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can retract. Second is the subclass
Hexacorallia, which is composed of
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corals with 6-fold symmetry. The subclass
includes order Actiniaria which are sea
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anemonies, black corals - here we can see
a deep-sea species Leiopathes glaberrima.
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Then we have Corallimorpharia which
are similar to stony corals which are
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called Scleractinia here, and here we can
see Madrepora oculata as a representative
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of this order, and finally we have
Zoantharia which can be parasitic
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corals and that can invade other
corals, and in this case it is found
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on a gorgonian Callogorgia verticillata.
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The Hexacorallia are mostly found on rocky
substrates and some of them, in particular
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the order Scleractinia, can produce
complex calcium carbonate skeletons
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which can form reefs,
especially in tropical waters.
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The third subclass is Octocorallia, which
are corals that have 8-fold symmetry
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and the order Alcyonacea, also known as
soft corals, sea fans, gorgonians, et cetera
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they are presented here as Callogorgia
verticillata, another deep-sea species.
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Then we have Helioporacea, which resemble
stony corals due to their elaborate calcium
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carbonate skeleton, and finally
there Pennatulacea or sea pens
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that are mostly found in soft sediments.
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Right, so now that we have a grasp on class
-ification, we can focus more on their anatomy.
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The most prominent feature of a polyp are
the tentacles. So here we can see them and
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here as well, and their number and form
or shape can differ between species.
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Basically they're contractible extensions of
the oral disc, they're used for defense and
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for food capture and they also harbour
nematocysts or spirocysts, which are
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cnidae, and cnidae are organelles secreted
by the Golgi apparatus in a cnidocyte,
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which is an epithelial cell.
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Here on the left we can see a
scheme of a cnidae discharge.
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So when the pressure is detected here, it
triggers a discharge of a spear-like structure
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at very high speed. It can often contain
toxins that can harm the prey or the
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predator. Cnidae are specific for all Cnidaria
and there are many different forms and
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specifications depending on the species
or on the higher taxonomical level.
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On the tentacles of Sclerotinia there are
globular structures called acrospheres
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that contain high numbers of nematocysts.
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On the other hand, in octocoral species,
the tentacles have pinnules, which are
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lateral structures, and that help capture
prey and you can see them right here.
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So going further into coral anatomy, we will
use an example of a sclerotinian coral polyp.
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So as we already mentioned, the tentacles are
located on the oral side around the mouth
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which continues into the gastrovascular
cavity. Within it, there are mesenteries
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or here they are shown as digestive filaments.
They develop by infolding of the mesoglea -
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which is a connective tissue. The digestive
filaments or the mesenteries are radially
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arranged in the gastrovascular cavity and
their role is increasing the surface available
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for nutrient absorption. At the aboral end,
the gonads develop among the mesenteries.
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In colonial corals, the polyps are connected
by a connective tissue, coenosarc, which is
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a series of tissues presented here
surrounding the coral. They are made
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by the surface body wall, made by
epidermis, mesoglea, and gastrodermis.
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In the middle there is a gastrovascular
canal that is connected to the
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gastrovascular cavity. This way,
the corals can exchange nutrients
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and communicate better. Below it we have
gastrodermis, mesoglea, and calicodermis,
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which is a specialised layer of tissue that
produces the exoskeleton in scleractinians.
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Ok, so corals are known for their bio-
mineralization abilities, producing
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impressive calcium carbon skeletons in
tropical waters. In scleractinian corals,
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the calcified exoskeleton is built by
calicodermis, a part of the basal body wall.
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It is a thin layer of ectodermal stem cells
that surrounds the exoskeleton and lays
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on the mesoglea. Calicoblasts are specialized
cells found in the calicodermis that produce
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an organic matrix with all the
materials needed for calcification.
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In octocorals, the main support is the axis,
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which is made of a collagenous protein,
such as gorgonin. The axis is further
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supported by the surrounding tissue,
including gastrovascular panels and
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the mesoglea which contains
sclerites. We can see them here,
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these are specialised sclerites
from a species Acanthogorgia.
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They are small magnesium calcite
structures that are neatly packed
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and organised in the mesoglea that
support the skeleton and the polyps.
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The sclerites are produced by specific cells
called scleroblasts and their shape depends
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on the species and localization in the
colony. Sclerites are mostly made of
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magnesium calcite, while scleractinians'
exoskeleton is made of aragonite.
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In black corals, they don't have
any calcium carbonate support.
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Their skeleton is made of protein and
chitin, which together make antipathin,
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which is called the black coral skeleton.
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Reproductive strategies in corals are diverse.
Gametogenic cycles, planulae release, and
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maturation are controlled by various
environmental conditions such as
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temperature, seasonality, food
availability, lunar phases, et cetera.
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Asexual reproduction is a form of
increasing the same genetic material.
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Budding is the most common way where new
polyps develop close to the existing polyps.
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Fragmentation and polyp bail out include
detachment from the colony and some
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forms of spatial dispersion.
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Sexual reproduction produces new genetic
material, which is crucial for species' survival.
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There are four main reproductive strategies:
hermaphroditic broadcast spawners or
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hermaphroditic brooders, which means
that the males and females are found
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on the same colony. That means hermaphro
-ditic, and further on broadcast spawners
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means that the gametes are released
in the seawater while brooders
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have internal fertilisation.
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The second two ways are gonochoric
broadcast spawners or gonochoric brooders
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which means that the females and
males are found on separate colonies
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and again broadcast spawners have
external fertilisation, they release gametes
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into the sea, while brooders
have internal fertilisation.
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After fertilisation, there is a relatively
brief period of planktonic planulae.
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Planulae is coral larvae, which searches
for a suitable place for settlement,
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and where, once settled, it undergoes
metamorphosis into a primary polyp,
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which then grows into a mature colony.
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Today we got introduced to the World Register
of Marine Species, also called WORMS.
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We had a brief look at the orders of
Anthozoa. We learned what are the
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main features of a polyp, focusing mostly
on the tentacles, various forms of cnidae,
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as well as their discharge mechanism.
And finally we discussed the reproductive
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strategies and life cycles.
Thank you for listening.