James C. Hendee
hendee at AOML.ERL.GOV
Thu Jun 22 14:53:27 EDT 1995
The following was received from Professor Tony Larkum
(alark at extro.ucc.su.oz.au) for inclusion in the Coral Health and
"ENCORE, The Effect of Nutrient Enrichment of Coral Reefs and the Programme
of Prof Larkum (School of Biological Sciences, University of Sydney).
The amount of phosphorus and nitrogen pouring onto the Great
Barrier Reef from rivers and drainage off the land is now ten fold what it
was fifty years ago. The major source is intensive agriculture with lesser
contributions from sewage effluent and industry/urbanisation. In other
parts of the world coral reefs have been degraded by effluent from such
sources. Nutrients are high on the list of agents which may have caused
this effect. The conventional thinking is that natural algae grow faster
in the presence of added nutrients (N+P) and that they then overgrow and
smother the coral and other animals of a typical coral reef leading
eventually to the disappearance of coral and the formation of an algal
There is no consensus at the moment that the increased levels of
nutrient (N+P) on the Great Barrier Reef are at levels that may cause
concern or even that nutrients are the causal agent in decline of coral
reefs elsewhere, eg Kaneohe Bay, Hawaii; Philippines, Thailand.
Nevertheless nutrients must be building up in the Great Barrier Reef Lagoon
and this poses a potential threat to the GBR and its $1.4 billion
contribution to the Gross Nationa Product.
To answer the questions arising from the previous discussion an in
situ reef fertilisation experiment is being undertaken on the Australian
Great Barrier Reef (at One Tree Island), to investigate the response of
coral reefs to nutrient enrichment. This experiment, known as ENCORE, was
designed by Prof Larkum (University of Sydney) and Mr. Andy Steven (GBRMPA)
to quantify the fate of nitrogen and phosphorus within a coral reef, and
compare their impact on a variety of coral reef organisms. Coordinated by
the Great Barrier Reef Marine Park Authority, Townsville (GBRMPA), 30
scientists from 8 Australian and 3 overseas organisations are undertaking
research encompassing cellular through to community level responses.
This research will provide a scientific basis for developing appropriate
water quality management strategies in coral reef environments, and may
identify a number of sub-lethal indicators of nutrient stress.
Nine robots have been built and deployed in natural shallow pools
(microatolls) in the main lagoon at One Tree Reef. At each low tide these
robots squirt a dose of pollution (N or P or N+P) into the pool. The
following organisms are being studied in detail: a range of typical corals,
clams, sponges, fish, bacteria, and algae.
The results to the present time are surprising in that they show a
direct effect on coral growth and reproduction and on the growth of clams.
Most surprising is the lack of effect on the microscopic algae which are
generally considered to feed the animals of the reef. It seems that under
the conditions at One Tree (and maybe generally on coral reefs) they are
not limited by nutrients. The rates of primary production that have been
measured are at the upper range for any known alga and therefore it is
likely that the algae are limited by inorganic carbon supply rather than by
nutrients. Nutrient recycling within the epilithic algal community is
probably adequate to supply the N and P needs of these algae. Addition of
nutrients to these algae in tanks has not increased primary productivity.
Protection of the algae from grazing has also not enhanced productivity -
supporting the contention that the algae are limited by carbon supply. In
the longer term the biomass and possibly the primary productivity are
limited by grazing, particularly by grazing fish. However the levels of
nutrients that have been discharged into the pools over the last year are
very low. As a result it has been decided to treble the loading in 1995.
Under these conditions (the same concentration as before but delivered in
three injections 30 min apart) it is expected that there will be a response
of the microscopic algae in the form of a community shift whereby certain
green algae will dominate and grow excessively. However this has to be put
to the test.
Funding for ENCORE is at two levels. The GBRMPA (Great Barrier
Reef Marine Park Authority) funds the infrastructure of the project and
supports a minimal amount of research. Individual researchers are mainly
dependent therefore on grants that they can attract from funding bodies.
Prof. Larkum had an Australian Research Council grant for his work from
Detailed Results on the algae to the present time
The algae referred to as EAC are the epilithic algal community (which we
study on year-old dead Porites blocks). These have shown no response in
any of the experimental atolls to added nutrients. At first we thought
that this was due to the effect of severe grazing, but we found the same
effect when we caged the blocks for two weeks. We then thought that the
levels of added nutrients might be so low that this was the reason for no
effect. So we bathed the blocks in ten-fold nutrient concentrations for
24-48 hours. This was done both with our respirometers and the "Cheshire"
respirometer. Still we got no effect. So we have to conclude that the EAC
is not nutrient limited in the lagoon at One Tree. (We have repeated this
at several seasons so it is not a seasonal effect -although Hatcher and
Larkum 1983 did detect a small effect in Spring, and it is possible that
this does occur and we missed it).
No inhibition of growth of crustose coralline algae - Lithothamnion
and Lithophyllum spp. has been found.
My group has not been studying the macroalgae. These are not
common inside the microatolls but do occur on the outside rims of the
microatolls - particularly at the moment Laurencia spp. Ed Drew and Bill
Dennison have been studying effects of nutrients on these. Bill claims to
have found a definite stimulation of growth and Ed a non-statistical
Note that this update has concentrated on the free-living micro-
and macro-algae. Of course, corals and many other animals of coral reefs,
have symbiotic zooxanthellae. We are not studying these algae, but many
other workers are and particularly Drs. Ove Hoegh-Guldberg and Assoc.
Prof. D. Yellowlees of the ENCORE Project. In general past work seems to
suggest that increased nitrogen causes an increased gowth of the
zooxanthellae. This increased growth may adversely affect the growth of
corals. Current research in the ENCORE Project is directed towards testing
Larkum, A.W.D. and Steven, A.D.L 1994. ENCORE (The effect of nutrient
enrichment on a coral reef). 1. Experimental design and research programme.
Mar. Pollut. Bull. 29, 112-120
Professor of Plant Sciences,
School of Biological Sciences,
University of Sydney,
tel (02) 351 2069
fax (02) 351 4771
email alark at extro.ucc.su.oz.au"
Prof Tony Larkum
alark at extro.ucc.su.oz.au
Ph (02) 692 2069
Fax (02) 692 4771
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