Lighting question

[grasshopper]

Anthony -

Hi! First let me say that I missed you this past weekend. I will name no names except yours and mine so as to not get anyone in trouble. I am a mod on the site where you were supposed to be fragging, and was looking forward to talking to you about many things. As certain forces kept us apart - I am here to ask you a question...

In a post that someone on the our site quoted you in, (I hate being vague but I guess it's necessary) you were talking about lighting - specifically watts per gallon. Your quote was as follows, "Tip: provide at least 5 watts of daylight per gallon of water for a rough guide to illuminating reef corals properly. (do not count actinics or heavily blue colored bulbs)".

Now, granted I don't follow the watts per gallon rule other than as a very general concept, but I was wondering why we should not include actinics or heavily blue colored bulbs? I am guessing that it is because the PAR value it too low. Am I correct, or do you have a better explanation?

Thanks!
Grasshopper

[Anthony Calfo]

no worries my friend :) I'm sorry I missed the chance to see you too.

Very good question re: actinic lighting.

Indeed, we are necessarily making some generalizations here for "the masses" (garden reef keeping versus specific biotopes).

But the difference in lights for starters is that actinics are essentially a single wavelength of light (420 nm for example) and daylight lamps are "full spectrum".

We light are zooxanthellate corals to stimulate photosynthetic activity, of course. And we must ask ourselves to what extent do we want to drive photosynthesis? Well... we at least have to make it to the "compensation point" at which a coral can derive the minimal amount of "nutrition" (translocation of carbon) from the products of photosynthesis. And we know that we do not want/need to exceed the "saturation point" (the point at which no futher illumination will increase the yield from zooxanthellae).

Now where we fall in between re: lighting choices is somewhat up to you. Corals are largely, highly adaptable to a range of light. Many will grow faster with a warmer emphasis in the lamp spectrum (5 k K to 7000K , for example).

Other corals may get enough light ("compensation point" or slightly beyond) with more attractive color (subjective) for receiving heavier blue lamps (10k K to 20 k K).

But a majority of popular reef corals kept (shallow water species) will not fare well or even survive on dominant blue (actinic) color lamps.

In a nutshell... actinics are stimulating to corals indeed, but should not be relied upon as the principal light for zooxanthellate corals to grow/survive upon.

with kind regards,

Anthony

[grasshopper]

Anthony,

Thanks for the response. I was just reading about lighting in your vol.1 prop. book last night.

I was amazed to read that photosynthetic corals (sps spceifically) will actually "go brownish" due to lack of light or light very close to the compensation point. I had always read and thought that the browning of corals occurred when they received too much light and their zooxanthellae are increasing in number. I also never considered the coloration of corals as being a defensive reaction to light (similar to humans getting a tan). This would explain why when my corals (again sps) go brown I would move them down in the tank any they would become very stressed and in many instances die.

Regardless, it seems my 175W 10K over a 75 tank are just able to light my corals to a compensation point. This will have to be remedied as soon as possible. Thank you again for the response and clarifying my concerns about the watts per gallon generalization.

[Anthony Calfo]

always welcome my friend :)

and its true that corals can have seemingly similar responses ("going brown") to either side of the lighting dynamic. It depends to some extent on the coral.

For example... deep water corals sometimes have colorful reflective pigments used to reFRACT the minimal light received down into their tissue. But shallow water corals are often colorful to reFLECT excess light away. The presence or absence of UV light will influence these two opposite ends of the coral differently.

Deepwater corals like red Trachyphyllia may go brown with increased light because they do not need to manufacture refractive proteins for minimal light.

And shallow water corals can go brown under less light because they do not need to produce reflective proteins against excessive UV

food for thought :)

Anthony