[Coral-List] Nutrients on coral reefs

Anthony Larkum alark at mail.usyd.edu.au
Fri Oct 27 15:32:25 EDT 2006

Dear Listers,

I have not seen a comment from any other team 
members of ENCORE, so as instigator of the 
project I will just add a few comments about 
nutrients on coral reefs and the results of the 
ENCORE experiment.  The major results are written 
up or referred to in:
Koop, K., Booth, D., Broadbent, A., Brodie, J., 
Bucher, D., Capone, D., Coll, J., Dennison, W., 
Erdman, M., Harrison, P., Hoegh-Guldberg, O., 
Hutchings, P., Jones, G. B., Larkum, A.W.D., 
O'Neill, J., Steven, A., Tentori, T., Ward, S., 
Williamson, J., Yellowlees, D. 2001. ENCORE: The 
effect of nutrient enrichment on coral reefs. 2. 
Synthesis of results and conclusions. Mar. Poll. 
Bull. 42: 91-120.

A few important results have been published elsewhere, since.

The ENCORE experiment remains the only experiment 
that has released nutrients (N, P N+P) onto 
replicated and significant-sized patches of coral 
reef (at One Tree Island).  At the end of 2 years 
the experiment was concluded.  The results were:

1.No effect on standing communities of macroalgae 
or epilithic algal communities (EAC).
2. Decreased calcification and growth in corals.
3. Decreased coral larval production and settlement.
4. No effect on crustose coralline algal growth or calcification.

These results have been questioned by others. 
And indeed the levels of significance were not 
always as good as we could have wished.

Nevertheless those are the results, take it or 
leave it., apart from throwing brickbats at a 
group of dedicated scientists

The lack of effect on standing communities of 
macroalgae and EAC is explained by the following 

a) Grazing was not controlled.  It continued at 
the background rate for the reef, since the size 
of the patch reefs was insignificant in relation 
to the whole reef, and thus any increase in 
growth of algae was was outweighed by the mass of 
grazers (but for the following reason there was 
probably no great increase in algal growth);
b) While normally one can stimulate the growth of 
macroalgae and EAC by addition of nutrients, this 
is not the case under the low stirring conditions 
on the average shallow reef, where growth is 
controlled by the uptake of carbon dioxide:
Larkum, A.W.D., Koch, E.C. and Kühl, M.  2003 
Diffusive boundary layers and photosynthesis of 
the epilithic algal community of coral reefs. 
Marine Biology 142,1073-1082.

Thus even with nutrient enrichment, in lagoonal 
situations there may be no enhanced of growth or 
standing crop, if grazing pressure is high and 
algal photosynthesis is high, under control 

The direct negative results on corals are easily 
explained by a wealth of experiments on the 
effect of N and/or P on coral physiology.

So that is the bottom line for coral lagoons.  On 
the outside of coral reefs where currents and 
wave-action are much higher, nutrients may cause 
and increase in algal growth.  However, that is 
yet to be experimentally tested.  Since there is 
very intense grazing on the outer reef slopes of 
coral reefs there might not be much effect on 
standing crop.  Nevertheless on the reef crest 
there is often a zone of high densities of 
macroalgae and one might expect an effect there.

With best wishes,

Tony Larkum

>Hi Jamie et al:
>I do not understand your comment about the Kuffner et al 2006 paper.
>For one there is no mention of any nut

>rient effects of any kind.  Thus
>the patterns of algal distribution and biomass that these authors report
>are what are found out there but there are no data to show that they
>have anything to do with nutrient (or grazing) levels.  The areas they
>surveyed are directly offshore of where Florida Bay water exits onto the
>Florida reef tract and are best characterized as hard bottom.  There has
>been little coral and lots of sediment on those hard bottom over
>Holocene time frames (reviewed by Ginsburg, Shinn and others)
>Secondly, if you read the paper carefully and study the figures, their
>results show that some (not all) algae have a small but variable effect
>on coral settlement.  In some cases there was more settlement in
>treatments with the algae, in some not, thus not a strong indictment of
>algal inhibition of coral settlement. Furthermore, while some of the
>differences between treatments were statistically significant the
>differences were not biologically/ecologically significant given natural
>variability in coral settlement patterns.  My work has shown a strong
>preference of several species of coral larvae for the undersides of
>field conditioned substrates (Szmant and Miller 2006, 10th Coral Reef
>Proc) regardless of presence of macroalgae. In fact, larvae avoid
>surfaces covered by algae, encrusting inverts, and some types of
>crustose corallines too.  They mostly settle on microfilm and there is
>plenty of that available at the scale of a coral larva, even when
>macroalgal cover is high. 
>The likely negative effect of macroalgal cover on coral recruits likely
>shows up later when the corals grow out of their cryptic settlement
>I know that excess nutrient enrichment, as well as too little grazing,
>as well as too much grazing, can all damage small corals, affect reef
>substrate composition etc etc etc.  But I hate to see the literature
>misquoted for any reason, and your post is a perfect example of how easy
>it is for scientists to prostitute the literature.  This is not
>acceptable scientific behavior and should be avoided even if the
>intention is laudable (e.g. to deter people from polluting coastal
>Dr. Alina M. Szmant
>Coral Reef Research Group
>UNCW-Center for Marine Science
>5600 Marvin K. Moss Ln
>Wilmington NC 28409
>Tel: (910)962-2362 & Fax:  (910)962-2410
>Cell:  (910)200-3913
>email:  szmanta at uncw.edu
>Web Page:  http://people.uncw.edu/szmanta
>-----Original Message-----
>From: coral-list-bounces at coral.aoml.noaa.gov
>[mailto:coral-list-bounces at coral.aoml.noaa.gov] On Behalf Of Dr. James M
>Sent: Tuesday, October 10, 2006 2:40 PM
>To: coral-list at coral.aoml.noaa.gov
>Subject: [Coral-List] About time!
>Dear Ilsa & Devon,
>Congrats on a thorough well put together manuscript! It is about time
>that these data are beginning to get published, I will use this for
>my class this next semester.
>The sad point is that the people that think urchin grazing and other
>dwindling herbivores/landscapers swimming on reef system control the
>algal lawns that smother corals.  This says to the developers that
>claim  "hey our point source" that is spewing secondary treated
>sewage out into a reef is not the reason for the reefs to become
>algal dominated, its because the spiny urchin died off that used to
>be a proficient landscaper and kept the corals "macro-algae free".
>Devon what I am not saying that top down controls are not
>significant, they are. However, what I am trying to say is that the
>levels of nutrients that induce algal blooms cannot be controlled
>with more grazers.
>Cheers, James
>Dr. James M. Cervino, MS, Ph.D.
>Marine Pathology
>Department of Biological & Health Sciences
>Pace University New York NYC
>Phone: (917) 620-5287
>Web site: http://www.globalcoral.org
>Coral-List mailing list
>Coral-List at coral.aoml.noaa.gov
>Coral-List mailing list
>Coral-List at coral.aoml.noaa.gov

Anthony W. D. Larkum
Emeritus Professor
School of Biological Sciences (A08)
and SUBIT - Sydney University Biological Informatics and Technology Centre
(Rm 141, Medical Foundation Building)
University of Sydney
NSW 2006,

Tel +612 9351 2069/+612 90363306
Fax +612 9351 4119
Email: alark at mail.usyd.edu.au


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