[Coral-List] Nutrient thresholds for coral reefs

[Julian Sprung]

It may be news to some members of the list to know that aquarists growing corals in reef aquariums come to essentially the same recommended background level for phosphorus, about 0.015 mg/L being a threshold that seems to be important in managing the proliferation of algae in reef aquariums.

Some other observations about it - 

1. corals will grow at substantially higher phosphorus concentrations in aquariums, especially when grazers are present to control algae. 

2. Some corals will stop growing or bleach and die when the phosphate level is maintained not very much below the abovementioned threshold!
This is a point of great interest as aquarists balance food inputs and phosphate export. Apparently corals can acclimate to lower levels as long as the transition is not too fast. Acclimation to "higher" concentrations, but still close to the abovementioned threshold, does not kill corals, but may cause SPS corals to become less colorful. It should also be noted that the observations may have some relation to the loss of corals to bleaching events in the most nutrient poor waters in the natural environment.

There was already a long thread on this list about inorganic nitrogen in aquarium culture of corals, but suffice it to say that corals in aquariums grow well with background levels much higher than proposed for their natural environment. They also grow well at nitrogen poor conditions, but may bleach if the levels become too low in an aquarium, especially when food inputs are scarce. Maintaining low levels help promote bright color in (Indo-Pacific) SPS corals, as the "background" zoox brown color is reduced and other pigments become more obvious.

When discussing nutrients I like to make an analogy that I think is appropriate-- I compare nutrients to light availability. If you think about sunlight on the reef, it comes in 2 distinct forms: background sky light and light from the sun itself. Nutrients as a background level (the abovementioned thresholds) could be thought of as analogous to sky light- all around and just right for normal growth. There are other sources of nutrients that are like the point source of light from the sun-- more intense and focused. Fish living (and eliminating waste) among coral branches would be an example of a nutrient supply that far exceeds the "background." These point sources (light or nutrients) seem to enhance growth. The analogy works but does not correspond with respect to water movement effects on nutrient availability.

Julian


> ----------
> From: 	coral-list-bounces at coral.aoml.noaa.gov on behalf of DeeVon Quirolo
> Sent: 	Thursday, February 16, 2006 9:56 AM
> To: 	Fiona Webster; coral-list at coral.aoml.noaa.gov; coral-list-owner at coral.aoml.noaa.gov
> Subject: 	[Coral-List] Nutrient thresholds for coral reefs 
> 
> Dr. Brian Lapointe of Harbor Branch Oceanographic Institution and Dr. 
> Peter Bell of  University of Queensland/Australia both arrived at the 
> same thresholds from different perspectives, but they are:  1 mg/L 
> dissolved inorganic nitrogen, .01 mg/L soluble reactive 
> phosphorus.  You can contact either Lapointe or Bell for further 
> info.  These thresholds are far lower than any current water quality 
> regulations.
> 
> Best, DeeVon Quirolo, Reef Relief www.reefrelief.org
> 
> 
> 
> At 08:43 PM 2/15/2006, Fiona Webster wrote:
> >content-class: urn:content-classes:message
> >Content-Type: text/plain;
> >         charset="utf-8"
> >
> >Hi
> >I am a PhD student study coral reef ecology at the Ningaloo Reef in 
> >Western Australia.  I am interested in bottom up verses top down 
> >effects on the growth of algae and how this may affect coral 
> >health.  I am going to be looking at the role of nutrients on algal 
> >growth and would like to set my nutrient concentrations at a similar 
> >level to other coral reefs which are considered to be nutrient > 
> >enriched.   Can anyone advise what levels of inorganic nitrogen and 
> >phosphorous in the water column are considered enriched?  I am after 
> >references and/or unpublished data.
> >Thank you
> >
> >
> >Fiona Webster
> >
> >Phd student
> >
> >Marine Ecology
> >
> >School Biological Sciences
> >
> >Department of Science and Engineering
> >
> >Murdoch University
> >
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