Understanding Zooxanthellae

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Sometimes aquarists are frustrated with corals changing corals. In my personnal quest to understand by i begun reading a chapter i have neglected.

Here is something to share:Zooxanthellae ("Zoos")= a strain of single celled algae or more correctly known as dinoflagellates, photosynthetic protists)

A colony of coral can have thousand, millions or billions of these Zoos. These mircoscopic cells allow corals to thrive and build reef structures in our wildest dreams amongst NUTRIENT STARVED tropical waters.

Possessing chlorophyll, these zoos synthesize O2 and energy rich products using SUNLIGHT n Co2.

Basically, the symbiosis (algal cells and coral polyp) exists that allow algae to exist in a stable environment with the predation in the open sea. The zoos benefit from the constant phyical n chemical conditions inside the cell where exchange of nutrients and wastes is provided

The Zoos benefit firectly from dissolved that the polyps absorbs; NO3 and PO4. Plus the corals will provide NH4 for Zoos to feed. Then Zoos in return for their symbiosis nourish the polyys with energy rich products of Photosynthesis. Mutualism they call this.

~~~~~~~~~~~~~~~Though coral could in theory survive on captured Zooplankton alone, in actual reef this food is limited therefore Zoos are needed. An experiment was done where Zooplankton were offered but corals shaded from light, the corals eventually expel their Zoos and died, despite have Zooplankton available.~~~~~~~~~~~

Presence or absence of Zoos can be used to divide all corals into 2 groups.
Its impt that aquarist understand corals that are Symbiotic possessing Zoos and Aposymbiotic having lack of Zoos n can live in darkened conditiond relying on their abilities to catch Zooplankton and or absord nutrients from water

Generally corals with Zoos thrive better in aquariums.

Note: Credits goes to Eric H Borneman for this above info, further reading is encouraged.

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Anyway, Zoos are reproduced when swallowed into the gastrovascular cavity of a new coral polyp and are transported into the gastrodermal tissues.

In a few coral (Litophyton, porites, monitpora, pocillopora, efflatounaria), The young polyps is brooded and provided with a small starter culture of Zoos by its parent. However most other corals are release in the wild without Zoos, therefore acquires them from the water and the mutliplication begins.

Zoos are able to supply energy natural products of photosynthesis, Zoos themselves generates > 150% of metabolic carbon energy needs of corals. In fact, 78% to 99% of all photosynthate is normally passed on to the host animal in a process call TRANSLOCATION

To date the prinicpal known products of translocation are glyceric acide, glucose, AMINO ACID, lipids, etc.

Lipids are stored by the polyp as reseve energy in less sunny days and may last for a month. The rate of food release is dependent of various chemical factors and dependent on needs

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Energy Budgets

C + PS = (Pz+Pa) + Rz+Ra) + F + U +G

where

consumption + Photosynthesis from Zoos EQUALS to

(Production of Zoos and Animal) + (Respiration of Zoos and Animal) +

Energy lost in feces "shit" + energy lost in other excretion + energy used in gonad output.

SO NOW WE ARE MORE AWARE

This equation shows the flow of energy as it is produced and consumed in corals.

If the sum of LIGHT and FOOD availability decrease , the balanced equation tell us either the photosynthesis, respiration, excretion or reproduction of coral will also decline.

Generally reproduction ability disappears 1st.

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LIGHT And Photosynthesis

The light gathering and photsynthetic machinery of Zoos are known as Photosynthetic Unit (PSU).

The rate of photosynthesis rises in corals with increasing light levels up to max rate called saturation level of light.

This means that above a certain level of irrdadiance , photosynthesis rates (all processes of a coral that are light dependent) will not be increased by higher light levels

The fact is that many corals can reach their max rate of photosynthesis in light that is much less intense than than by Sunlight!

Coles and Jokiel also confirmed this in long term studies with
montipora species where light levels higher than those to which corals were normally exposed caused not only reduced growth rates, bu also increased coral mortality when combined with other stress such as reduced salinity or temperatures increase.

The POINT for CORAL KEEPERS to remember is simple : MORE LIGHT is NOT ALWAYS BETTER Eric Borneman

Corals can adapt to higher or lower light levels to max the photosynthetic adv. This is call photoadaptation.

Photoacclimation on the other hand is when the actual changes that occur in the photoadaptive response. This usually involve a change in the pigment content of Zoos.

So is this why in sub saturating light conditions, corals tend to change the PSU components, while in super saturating light, they tend to increase the amount of photoprotective xanthophylls within the algal chromophores?

Answer by Eric Borneman is Yes