Re: Light intensity and water depth
To: Aquatic-Plants at actwin_com
Subject: Re: Light intensity and water depth
From: Charley Bay <charleyb at hpgrla_gr.hp.com>
Date: Fri, 17 Nov 95 16:53:46 MST
In-Reply-To: <199511172039.PAA30753 at looney_actwin.com>; from "Aquatic-Plants-Owner at actwin_com" at Nov 17, 95 3:39 pm
Mailer: Elm [revision: 70.85]
> I'm not sure if this is why but from the talk I have with a marine storekeeper,
> he mentioned that in reef, the light need to penetrate the corals to be useful.
> In planted tank, the light just need to fall on the leaves. That is why they
> need more intense lighting.
I think I follow, and this is mostly correct:
A plant like algae has chloroplasts. Light hits, penetrates cell wall,
and hits the chloroplast. There's the minimum for the photon to excite
activity as the initial point of photosynthesis.
With many corals, the invertebrate actually absorbs algae and holds
it within the coral itself. This is symbiotic mutualism: The algae
gets the advantage of protection from predation, and access to the
coral's nitrite waste for growth. In return, the coral partially
feeds off the sugars produced by the algae, and actually consumes
surplus algae. In effect, the algae's NPP "subsidizes" the
coral's diet. Thus, a coral individual can adapt to a lower external
feeding requirement if it has access to good light (and has
algae internally), or can depend more on external food sources if
lighting is inadequate (or it could not opportunistically acquire algae
for mutualistic retention). Recent studies show that algal/coral
relationships are highly species sensitive (a specific coral species
will retain only a specific species of algae).
However, because the algae resides INSIDE the coral, the photon must
go through the coral to the algal cell, through the cell wall, and
into the chloroplast as a first step in photosynthesis. That's more
Hence the need for brighter light in a reef.
--charley Fort Collins, Colorado USA
charleyb at gr_hp.com or charley at agrostis_nrel.colostate.edu