Coral Biology

[jakeosaur99]

Basically, I want to learn more about coral biology.

I'm reading a book (Aquarium Corals, Borneman) that discusses coral respiration, but I don't know what that means. Do corals have a mechanism to extract oxygen from SW? Where is this O2 stored or how is it transferred to where it is needed? Where is it needed?

There are so many other questions I have. For example what kind of nervous system do corals have? Other than for digestion and sexual reproduction, what organs do corals have, for example to store energy, eliminate toxins, and fight disease?

Where can I get more information about coral biology?

Thanks,

Jake

[jakeosaur99]

I thought this might be a tough question since I've never seen anyone ask anything like this, but I'd hoped for at least one good reply.

How about just sticking to respiration.

Can anyone describe the respiration process for a coral?

Jake

[Spanky]

Jake I'm hoping Chris will chime in on this, so we're sort of waiting it out. He's the best one to answer all these questions and can do it with both hands tied behind his back.

[galleon]

I knew you were going to do this to me Jerel . Oh well, it is a weekend.

Can anyone describe the respiration process for a coral?

Cnidarians such as corals have no circulatory organs or respiratory system. Therefore, the only way they can get CO2 out and O2 in is the same way that all unicellular life does it: diffusion. Oxygen diffuses into the coral's cells and CO2 diffuses out. Corals can get away with this technique (where as higher organisms need a circulatory system) because they have only two cell layers, ectoderm (outside) and endoderm (inside the ecotderm and the gastrovascular cavity), a very thin layer of non-living matrix called the mesoglea in between, and a very close ratio of body volume to surface area exposed to seawater.

Corals are essentially a bag. The top of the bag being the mouth and the bottom being where it would attach to the skeleton. The outside of the bag is made up of ectoderm and the inside of the bag is made up of endoderm. The inside of the bag is called the gastrovascular cavity. Divided into complete and incomplete lobes called mesenteries, it is where digestion takes place and gonads develop.

The top of the bag is constricted into a small mouth lined by tentacles (the tentacles are hollow, again with ectoderm making up the outside and endoderm making up the inside. The internal hollow is connected to the gastrovascular cavity). In this constricted space, the gastrovascular cavity forms a tube, called the actinopharynx. On either side of this tube are two canals that run the length of the tube called siphonoglyphs. These are lined with cilia and never close. The ectoderm is always exposed to surrounding (oxygenated) seawater, but the endoderm has to pump water to itself and inside the gastrovascular cavity via the cilia in the siphonoglyph.

As far as a nervous system goes, Corals and other cnidaria are believed to be some of the earliest organisms to have evolved some type of nervous system. In cnidaria, while the nervous system is not central or very advanced, it is efficient and effective. Modified epidermal cells called neurons contain long, thin strand-like processes, called neurites, that synapse into each other. This creates a neural network, of which corals and other cnidarians have two separate ones: one fast conducting and one slow conducting.

The slow conducting network generally has single, unfused neurites coming off of many sides of the cell (multipolar). Synapses can fire in a single direction or back and forth across the neural network, depending on how the neurites come together. The fast conducting network lies underneath the slow network and is formed by fused neurites coming from only two sides of the neuron cell (dipolar). This reduced branching of neurites and their fusing to a larger size allows for a faster and more direct movement of signal to the musculature. When neurons that are exposed to the water, “neurosensory cells,” are stimulated (by touch, etc.), waves of synapses fire, spreading across the animal and ending at a neuromuscular junction.

As far as storing energy, think of corals as a group of cells living together semi-independently, they recognize each other, help each other out, but in terms of storing reserves, its every cell as an individual, with the endodermal cells harboring zooxanthellae acting as a temporary host for the nutrients, as it is these cells that force the zooxanthellae to give up some of what they have made. The colony/polyp as a whole will distribute the lipids/sugars/etc. as is necessary, but there is no special organ (like our livers) that perform this function.

[galleon]

Any questions on musculature or cnidocytes?

[jakeosaur99]

Waiting gives me more time to nail down my question.

A closer look reveals I'm looking for coral physiology. I've found quite a bit of information on feeding, defense, reproduction, and immunology, just not much in the way of fundamental life processes.

I've found that coral respiration is "gas exchange through the surface" but I'm looking for a few details. What gasses are exchanged, through what channels are they transmitted (how does that work through the skin), what products result and how are those products stored or used?

Seems strange reef aquarists make such large investments in an animal most don't know the basic life process for.

Jake

[jakeosaur99]

Disregard that last post. You guys are fast!

Jake

[jakeosaur99]

The thread got moved! I didn't think this was theoretical enough for the Think Tank. Probably what it took for an answer.

Chris, all I can say is "wow" and "ummm..." I should probably add "Thank you!" That explanation far exceeded my hopes.

Did I mention you guys are fast?

Jake

[jakeosaur99]

After re-reading several times, I think I understand all that. I believe Oxygen is used for cell growth, etc.

Is the musculature essentially a synthesis of the endoderm and neural networks, thus also not very advanced, or is there more cell specialization?

Jake

[tdwyatt]

Originally posted by jakeosaur99
After re-reading several times, I think I understand all that. I believe Oxygen is used for cell growth, etc.

Well, actually...

Oxygen is primarily used for respiration in corals. This means that the O2 is used to combine with the Carbon in carbohydrates to release the chemical energy stored in Carbon to Carbon bonds for cellular activities varying from the manufacture of cellular proteins to supplying energy for motion and differing biological pumps. A good deal of energy is used in making the skeleton at the calcioblastic endothelium (the area where the polyp joins the skeleton and the skeleton is actually laid down). Oxygen is also a waste product of the endosymbionts (Symbiodiniium spp. of dinoflagellates responsible for the autotrophic portion of the organism's metabolism, or zooxanthellae ) which may be used by the animal portion of the coral as well as the oxygen diffused from seawater for respiration. The carbohydrates produced by the symbiotic algae usually consists primarily of glycerol, but may include glucose and occasionally levels of alanine (depending on speciation and the amount of nitrogen ingested/fixed from the water column). Prey captured by the animal portion of the coral probably supplies nitrogen to both animal tissue and algal symbionts, and is cycled back and forth between the two. Zooxanthallae are also capable of directly fixing nitrogen from the water column (one of the reasons that closed systems with 10 PPM or more of nitrate ion cause corals specimens to "brown"), but in oligotropic waters, coral predation on the water column becomes the primary source of nitrogen for both algal symbiont and coral tissue. This symbioisis is the mainstay of coral calcification as well, as the photosynthesis and its byproducts are essential to skeletalization and calcification, and although there is someskeletalization occuring in the absence of light, it is much, much slower. This discussion is geared toward the Scleractinian corals, anemone, Ceriantherians and Zoanthideans in general. Although related, the morphology and physiology of the octocorals is distinctively different.

This topic could take on a forum of its own, good book suggestions on the topic would be the Sorokin or Tomas Tomascik books on coral reef ecology, as they delve into the fine details of these processes. Also, any good Invert Zoo book will cover the gories in detail.

[SPC]

Thanks Chris and Tom, excellent posts!
Steve

[tdwyatt]

Originally posted by tdwyatt
Oxygen is primarily used for respiration in corals. This means that the O2 is used to combine with the Carbon in carbohydrates to release the chemical energy stored in Carbon to Carbon bonds for cellular activities varying from the manufacture of cellular proteins to supplying energy for motion and differing biological pumps...

we can persue this further it you'd like, down to the base level where phosphorylation of adenosine is the major end of respiration for chemical means of energy storage.

[tdwyatt]

or cnidocytes, or specialization of tissue cells in the ectoderm like epitheliomuscular cells for example, or my favorite, that 100 micron space involving the calcioblastic ectoderm and translocation...

Then there's reproduction

and my other fave, Coral Zooxanthellae symbiosis...

[Doug1]

YARP
pass the Thorazine, i am having bad flashbacks

[photobarry]

Originally posted by tdwyatt
and my other fave, Coral Zooxanthellae symbiosis...

Oooh, oooh! Back in grad school I took a symbiosis seminar with one of the fathers of coral symbiosis, Bob Trench. What I remember most is him getting upset whenever anyone used the term zooxanthellae.