ENCORE: the Eаect of Nutrient Enrichment on Coral Reefs
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Marine Pollution Bulletin Vol. 42, No. 2, pp. 91±120, 2001 Ó 2001 Published by Elsevier Science Ltd. Printed in Great Britain PII: S0025-326X$00)00181-8 0025-326X/01 $ - see front matter ENCORE: The Eect of Nutrient Enrichment on Coral Reefs. Synthesis of Results and Conclusions K. KOOP *,1, D. BOOTHà, A. BROADBENT§,2, J. BRODIE , D. BUCHERàà, D. CAPONE ,3, J. COLL§§,4, W. DENNISON , M. ERDMANNààà, P. HARRISONàà, O. HOEGH-GULDBERG ,5, P. HUTCHINGS§§§, G. B. JONES§, A. W. D. LARKUM , J. O'NEIL ,5, A. STEVEN ,6, E. TENTORI§§, S. WARDàà,5, J. WILLIAMSON ,7 and D. YELLOWLEESàààà School of Biological Sciences, The University of Sydney, Sydney NSW 2006, Australia àDepartment Environmental Sciences, University of Technology, Sydney NSW 2065 Australia §Department of Chemistry, James Cook University, Townsville, Qld 4810, Australia Great Barrier Reef Marine Park Authority, P.O. Box 1379, Townsville, Qld 4810, Australia ààCentre for Coastal Management, Southern Cross University, P.O. Box 157, Lismore NSW 2480, Australia §§Department of Biology, Central Queensland University, Rockhampton, Qld 4702, Australia Department of Botany, University of Queensland, Brisbane, Qld 4072, Australia àààP.O. Box 1020, Manado, Sulawesi, Indonesia §§§The Australian Museum, 6, College Street, Sydney, NSW 2010, Australia Chesapeake Biological Laboratory, University of Maryland, Box 38, Solomons, MA 20688-0038, USA ààààBiochemistry and Molecular Biology, James Cook University, Townsville, Qld 4811 Australia Coral reef degradation resulting from nutrient enrichment assessed a variety of factors focusing on nutrient dynamics of coastal waters is of increasing global concern. Although and biotic responses. A controlled and replicated experi- eects of nutrients on coral reef organisms have been ment was conducted over two years using twelve small demonstrated in the laboratory,there is little direct evi- patch reefs ponded at low tide by a coral rim. Treatments dence of nutrient eects on coral reef biota in situ. The included three control reefs $no nutrient addition) and ENCORE experiment investigated responses of coral reef three+N reefs $NH4Cl added),three+P reefs $ KH2PO4 organisms and processes to controlled additions of dis- added),and three+N+P reefs. Nutrients were added as solved inorganic nitrogen $N) and/or phosphorus $P) on an pulses at each low tide $ca twice per day) by remotely oshore reef $One Tree Island) at the southern end of the operated units. There were two phases of nutrient addi- Great Barrier Reef,Australia. A multi-disciplinary team tions. During the initial,low-loading phase of the exper- iment nutrient pulses $mean dose 11.5 lMNH4 ; À3 2:3 lMPO4 rapidly declined,reaching near-back- À3 *Corresponding author. ground levels $mean 0:9 lMNH4 ;0:5 lMPO4 ) E-mail address: [email protected] AK. Koop). within 2±3 h. A variety of biotic processes,assessed over a 1 Present address: New South Wales Environment Protection year during this initial nutrient loading phase,were not Authority, P.O. Box A290, Sydney South, NSW 1232, Australia. 2 Present address: Max Winders and Associates Pty Ltd, GPO Box signi®cantly aected,with the exception of coral repro- 3137, Brisbane 4001, Qld, Australia. duction,which was aected in all nutrient treatments. In 3 Present address: Wrigley Institute for Environmental Studies & Acropora longicyathus and A. aspera,fewer successfully Department of Biological Sciences, University of Southern California, 3616 Trousdale Parkway, AHF 108, Los Angeles, California 90089- developed embryos were formed,and in A. longicyathus 0371. fertilization rates and lipid levels decreased. In the second, 4 Present address: Chancellery, Australian Catholic University, 40 high-loading,phase of ENCORE an increased nutrient Edward St, North Sydney, NSW 2060, Australia. À3 5 Present address: Centre for Marine Studies, University of Queens- dosage $mean dose 36.2 lMNH4 ;5:1 lMPO4 de- À3 land, Brisbane, Qld 4072, Australia. clining to means of 11.3 lMNH4 and 2:4 lMPO4 at 6 Present address: School of Biological Sciences, University of New the end of low tide) was used for a further year,and a South Wales, Sydney, NSW 2052. 7 Present address: Environment Protection Authority, Victoria, variety of signi®cant biotic responses occurred. Encrusting G.P.O. Box 4395QQ, Melbourne, Vic 3001, Australia. algae incorporated virtually none of the added nutrients. 91 Marine Pollution Bulletin Organisms containing endosymbiotic zooxanthellae $cor- been identi®ed as one of the most threatened marine als and giant clams) assimilated dissolved nutrients rap- ecosystems AGoreau, 1992; Sebens, 1994; Wilkinson and idly and were responsive to added nutrients. Coral Buddemeier, 1994; Bryant and Burke, 1998; Wilkinson, mortality,not detected during the initial low-loading 1998; Hoegh-Guldberg, 1999). The loss of viable reefs phase,became evident with increased nutrient dosage, would have major consequences for the economies of particularly in Pocillopora damicornis. Nitrogen additions many small island nations in the Paci®c and Indian stunted coral growth,and phosphorus additions had a oceans and the Carribean. Economic impacts would variable eect. Coral calci®cation rate and linear almost certainly be seen in terms of declining ®sh pro- extension increased in the presence of added phosphorus duction, loss of tourism and amenity values. Reefs also but skeletal density was reduced,making corals more protect and stabilize coastlines. Hence, their loss could susceptible to breakage. Settlement of all coral larvae was have drastic consequences in the longer term because of reduced in nitrogen treatments,yet settlement of larvae coastal destablization and the loss of other associated from brooded species was enhanced in phosphorus treat- habitats like mangroves and seagrasses. ments. Recruitment of stomatopods,benthic crustaceans Anthropogenic impacts are the cause of the decline in living in coral rubble,was reduced in nitrogen and nitrogen the `health' of reefs in many areas of the world AWil- plus phosphorus treatments. Grazing rates and reproduc- kinson and Buddemeier, 1994). Increasing urbanization tive eort of various ®sh species were not aected by the of coastal areas, often associated with loss of important nutrient treatments. Microbial nitrogen transformations coastal habitats Ae.g. forests, coastal wetlands) and in- in sediments were responsive to nutrient loading with ni- creased intensive agricultural activities in the nearby trogen ®xation signi®cantly increased in phosphorus catchments have led to increases in the rate of land treatments and denitri®cation increased in all treatments runo, which is often loaded with sediment and nutri- to which nitrogen had been added. Rates of bioerosion and ents from fertilizers which are then discharged into grazing showed no signi®cant eects of added nutrients. coastal waters after heavy rains. For example, Demou- ENCORE has shown that reef organisms and processes get A1989) estimated that 1000 t of sediment were carried investigated in situ were impacted by elevated nutrients. into the lagoon of Tahiti annually where extensive reefs Impacts were dependent on dose level,whether nitrogen occur. Untreated sewage is also typically discharged into and/or phosphorus were elevated and were often species- coral reef lagoons in many developing countries. These speci®c. The impacts were generally sub-lethal and subtle same reefs may also be subjected to over®shing, and and the treated reefs at the end of the experiment were physical removal of the reefs to form marinas or ports, visually similar to control reefs. Rapid nutrient uptake and construction of major tourist complexes. Coral reefs indicates that nutrient concentrations alone are not ade- are important tourist attractions and loss or decline in quate to assess nutrient condition of reefs. Sensitive and the `health' of these reefs may have important economic quanti®able biological indicators need to be developed for consequences for many countries. All these anthropo- coral reef ecosystems. The potential bioindicators identi- genic impacts have the potential to degrade coastal coral ®ed in ENCORE should be tested in future research on reefs. coral reef/nutrient interactions. Synergistic and cumula- Increasing nutrient inputs and associated sediment tive eects of elevated nutrients and other environmental loads have been hypothesized as having the potential to parameters,comparative studies of intact vs. disturbed seriously impact coral reefs ACortes and Risk, 1985). reefs,oshore vs. inshore reefs,or the ability of a nutrient- Despite its importance, our understanding of how in- stressed reef to respond to natural disturbances require creasing nutrient loads impact on coral reefs is surpris- elucidation. An expanded understanding of coral reef re- ingly limited. The coral reef literature contains many sponses to anthropogenic impacts is necessary,particu- accounts of coral reef degradation associated with de- larly regarding the subtle,sub-lethal eects detected in the clining water quality Ae.g. Banner, 1974; Smith et al., ENCORE studies. Ó 2001 Published by Elsevier Science 1981; Walker and Ormond, 1982; Tomascik and Sander, Ltd. 1985; Hughes, 1994; Sebens, 1994; Hudson et al., 1994). While convincing, the complex nature of the inputs to coastal areas such as industrial and domestic euents Introduction and runo from land, however, has made it dicult to identify the components Ae.g. nutrients, sediment, heavy Coral reefs are among the most spectacular marine