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Historic records of phosphorus levels in the reef-building coral Montastrea annularis from Tobago, West Indies
Marine Pollution Bulletin P. R. and Reimnitz, E., eds), US Geological Survey Open File Report 90-39A. US Geological Survey, Menlo Park, CA. Douglas, G. S., Bence, A. E., Prince, R. C., McMillen, S. J. and Butler, E. L. (1996) Environmental stability of selected petroleum source and weathering ratios. Environmental Science and Technology 30, 2332-2339. Farrington, J. W. and Tripp, B. W. (1977) Hydrocarbons in western North Atlantic surface sediments. Geochimica et Cosmochimica Acta 41, 1627-1641. Gilfillan, E. S., Suchanek, T. H., Sloan, N. A., Page, D. S. and Boehm, P. D. (1995) Shoreline impacts in the Gulf of Alaska region following the Exxon Valdez oil spill. In Exxon Valdez Oil Spill." Fate and Effects in Alaskan Waters, ASTM Special Technical Publication No. 1219 (Wells, P. G., Butler, J. N. and Hughes, J. S., eds), pp. 444-481. American Society for Testing and Materials, Phildelphia. Lee, R. F. and Page, D. S. (1997) Petroleum hydrocarbons and their effects in subtidal regions after major oil spills. Marine Pollution Bulletin 34, 928-940. Long, E. R. (1992) Ranges in chemical concentrations in sediments associated with adverse biological effects. Marine Pollution Bulletin 24, 38-45. Magoon, L. B. and Anders, D. E. (1992) Oil-to-source rock correlation using carbon-isotopic data and biological marker compounds, Cook Inlet-Alaska Peninsula, Alaska. In Biological Markers in Sediments and Petroleum (Moldowan, J. M., Albrecht, P. and Philp, R. P., eds), pp. 241-274. Prentice-HaU, Englewood Cliffs, NJ. Maki, A. (1991) The Exxon Valdez oil spill: initial environmental impact assessment. Environmental Science and Technology 25, 24-29. Manen, C. A., Price, J. R., Korn, S. and Carls, M. G. (1993). Natural Resource Damage Assessment: Database Design and Structure. National Oceanic and Atmospheric Administration, US Department of Commerce, Rockville, MD, NOAA Technical Memorandum NOS/ORCA (in review). Miller, D. J., Payne, R. and Gryc, G. (1959) Geology of possible petroleum provinces in Alaska. U.S. Geological Survey Bulletin 1094, 9-131. NRC (1985) Oil in the Sea: Inputs, Fates, and Effects. National Research Council: National Academy Press, Washington, DC. Page, D. S., Boehm, P. D., Douglas, G. S. and Bence, A. E. (1995) Identification of hydrocarbon sources in the benthic sediments of Prince William Sound and the Gulf of Alaska following the Exxon Valdez oil spill. In Exxon Valdez Oil Spill." Fate and Effects in Alaskan Waters, ASTM Special Technical Publication No. 1219 (Wells, P. G., Butler, J. N. and Hughes, J. S., eds), pp. 41-83. American Society for Testing and Materials, Phildelphia. Page, D. S., Boehm, P. D., Douglas, G. S., Bence, A. E., Burns, W. A. and Mankiewicz, P. J. (1996) The natural petroleum hydrocarbon background in subtidal sediments of Prince William Sound, Alaska. Environmental Toxicology and Chemistry 15, 1266-1281. Page, D. S., Boehm, P. D., Douglas, G. S., Bence, A. E., Burns, W. A. and Mankiewicz, P. J. (1997) An estimate of the annual input of natural petroleum hydrocarbons to seafloor sediments in Prince William Sound, Alaska. Marine Pollution Bulletin 34, 744-749. Page, D. S., Boehm, P. D., Douglas, G. S., Bence, A. E., Burns, W. A. and Mankiewicz, P. J. (in press) Pyrogenic polycyclic aromatic hydrocarbons in sediments record past human activity: A case study in Prince William Sound Alaska. Marine Pollution Bulletin. Rapp, J. B., Hostettler, F. D. and Kvenvolden, K. A. (1990) Comparison of Exxon Valdez oil with extractable material from deep-water bottom sediments in Prince William Sound and the Gulf of Alaska. In Bottom Sediment Along Oil Spill Trajectory in Prince William Sound and Along Kenai Peninsula, Alaska (Carlson, P. R. and Reimnitz, E., eds). US Geological Survey Open File Report 90-39B. US Geological Survey, Menlo Park, CA. Rice, S. D., Spies, R. B., Wolfe, D. A. and Wright, B. A. (eds) (1996) Proceedings of the Exxon Valdez Oil Spill Symposium. AFS Symposium 18. American Fisheries Society, Bethesda, MD. Shaw, D. G. and Wiggs, J. N. (1980) Hydrocarbons in the intertidal environment of Kachemak Bay, Alaska. Marine Pollution Bulletin 11, 297-300. Short, J. W. and Harris, P. M. (1996). Petroleum hydrocarbons in caged mussels deployed in Prince William Sound after the Exxon Valdez oil spill. In Proceedings of the. Exxon Valdez Oil Spill
1012
Symposium (Rice, S. D., Spies, R. B., Wolfe, D. A. and Wright, B. A., eds), pp. 29-39. American Fisheries Society, Bethesda, MD. Short, J. W., Jackson, T. J., Larsen, M. L. and Wade, T. L. (1996) Analytical methods used for the analysis of hydrocarbons in crude oil, tissues, sediments and seawater collected for the natrual resources damage assessment of the Exxon Valdez oil spill. In Proceedings of the Exxon Valdez Oil Spill Symposium (Rice, S. D., Spies, R. B., Wolfe, D. A. and Wright, B. A., eds), pp. 140-148. American Fisheries Society, Bethesda, MD. Wells, P. G., Butler, J. N. and Hughes, J. S. (1995) Exxon Valdez Oil Spill: Fate and Effects in Alaskan Waters, ASTM Special Technical Publication No. 1219. American Society for Testing and Materials, Philadelphia. Wolfe, D. A., Hameedi, M. J., Gait, J. A., Watabayashi, G., Short, J. W., O'Claire, C., Rice, S. D., Michel, J., Payne, J. R., Braddock, J., Hanna, S. and Sale, D. (1994) The fate of the oil spilled from the Exxon Valdez. Environmental Science and Technology 28, 561-567. Wolfe, D. A., Krahn, M. E., Casillas, E., Sol, S., Thompson, T. A., Lunz, J. and Scott, K. J. (1996) Toxicity of intertidal and subtidal sediments contaminated by the Exxon Valdez oil spill. In Proceedings of the Exxon Valdez Oil Spill Symposium (Rice, S. D., Spies, R. B., Wolfe, D. A. and Wright, B. A., eds), pp. 121-139. American Fisheries Society, Bethesda, MD. Marine PollutionBulletin, Vol. 36, No. 12, pp. 1012-1018, 1998 © 1998 Elsevier Science Ltd Pergamon All rights reserved. Printed in Great Britain 0025-326X/98 $19.00+0.00
PII: S0025-326X(98)00086-1
Historic Records of Phosphorus Levels in the Reef-building Coral Montastrea annularis from Tobago, West Indies K I S H A N K U M A R S I N G H *~, R I C H A R D L A Y D O O * , J E F F E R Y K. CHEN* and A V R I L M. S I U N G - C H A N G *~ *Institute of Marine Affairs, p.o. Box 3160, Carenage Post Office, Chaguaramas, Trinidad *United Nations Development Programme, 19 Keate St. Port of Spain, Trinidad gLange PML Caribbean Ltd, Charles St. Port of Spain, Trinidad
Enhanced phosphorus concentrations in coral reef systems can be detrimental (Kinsey and Davies, 1979; Walker and Ormond, 1982; Fishelson, 1973). The deposition of aragonite (CaCO3) in coral skeleton material from the surrounding waters has led to the suggestion that coral skeletons may be used to determine the chemistry of the waters in which they grow (Br6ecker, 1963; Veeh and Turkeian, 1968; St John, 1974; Flor and Moore, 1977). A detailed review of corals as environmental indicators was published by Highsmith (1979). The presence of alternating bands of different density, as indicators of annual growth within the coral skeleton, provides a means of assessing historical trends (Knutson et al., 1972; Barnes, 1973; ~Present address: Environmental Management Authority, 2nd Floor the Mutual Centre, 16 Quenn's Park West, P.O. Box 150 Newtown, Port of Spain, Trinidad. ~Present address: Pan American Health Organisation, 49 Jerningham Ave., Queen's Park East, Port of Spain, Trinidad.
Volume 36/Number 12/December 1998 I
i
i IIo20'N--
c A R /
B
B
E
A
/V
Cullodenf
.
tt
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I
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60o50'W ]
5 I
km
60o40'w I
I
I
Fig. 1 Location of sampling sites, Culloden Bay and Buccoo Reef, in Tobago, West Indies.
Macintyre and Smith, 1974; Dodge et al., 1974; Dodge and Thompson, 1974; Barnes and Lough, 1989). Seasonal patterns are revealed when the coral is slabbed and X-radiographed (Dodge and Vaisnys, 1980; Barnes and Lough, 1989; Barnes et al., 1989). In the Caribbean, corals have been shown to preserve phosphorus records that are consistent with sewage impacts and other pollution sources of episodes (Dodge et al., 1984). It is therefore important to establish baseline levels and document enhanced eutrophication, for prediction and management purposes. There are no published accounts of phosphorus levels in corals in Tobago, although Risk et al. (1992) and Horvat et al. (1996) have investigated different aspects of coral sclerochronology locally. This paper documents the phosphorus content of corals collected from the island of Tobago, West Indies, from areas that are known to be stressed by sewage and domestic wastes, and compares these with corals from unpolluted, pristine areas. Buccoo Reef is located to the north of the southwestern tip of Tobago and covers an area of 7 km 2 (Fig. 1). It is characterized by an arc of five emergent reef fiats, dissected by seaward channels to the north; an extensive forereef; a shallow sandy backreef lagoon with a patchy distribution of coral communities; and the Bon Accord Lagoon fringed by a mangrove swamp to the south (Laydoo, 1996). The adjacent coastal area
of southwest Tobago is characterized by residential and hotel/guest house development, agriculture and animal farming. Buccoo Bay and Bon Accord Lagoon each receives effluents from a sewage treatment plant. Samples at Buccoo Reef were collected at Coral Gardens, which is in the reef lagoon. Culloden Bay is situated on Tobago's leeward coast (Fig. 1). The bay has a surface area of approximately 0.058 km 2. Because of the semi-exposed nature of the bay, anchorage and recreational swimming is limited, except for sporadic sport-diving for tourists. Culloden Bay may therefore be considered pristine. Samples from this site were collected in the forereef; there is no backreef. Cylindrical cores 30-36 cm long were obtained from Montastrea annularis colonies at 5-7 m depth at the Coral Gardens site in the Buccoo Reef area and at 8 m depth at the forereef of Culloden Bay. The cores were cut using a diamond-tipped rock corer which was attached to a pneumatic drill fed from a SCUBA tank. A guide-plate constructed from a 15 c m x 15 cm × 3 cm marine ply-board through which a circular hole was cut to accommodate the corer, was used to prevent the corer tip from skidding over the coral surface at the beginning of the core drilling. The guide plate was nailed to the coiony's surface, such that the corer was aligned with the growth axis of the colony. The core was drilled along the growth axis to a depth of approxi1013
Marine Pollution Bulletin
mately 35 cm. The guide plate was then carefully withdrawn. The core was broken near its base by forcing a diver's knife into the space around the core, and was then removed and labeled. The resulting cavity was filled with coral rubble and capped with cement to prevent invasion and destruction of the colony by boring organisms. Live tissue was later removed by soaking the cores in fresh water for approximately 1 h. After soaking, any remaining tissue was removed with a light jet of water. The cores were then air-dried for further processing. A slab approximately 0.5 cm thick was cut along the axis of each core using a circular geological saw. Each slab was X-rayed on Agfa Structurix D4 X-ray film, with a General Electric MPX X-ray machine set at 40 kVp for a period of 8 s, at a distance of 0.9 m. The X-radiograph was subsequently used to obtain a positive black and white print. The positive print of each X-rayed slab was overlain with a strip of clear acetate sheet and secured at each end with clear adhesive tape. A line was drawn on the acetate strip along the growth axis of the coral colony at the point at which it was cored. Where the orientation of the lines was not continuous over the length of the print, due to
variation in the growth direction, more than one line was necessary to define the growth axis along the length of the print. Annual growth bands comprising contiguous dark (high density skeleton) and light (low density skeleton) bands were then marked on the acetate strip perpendicular to the growth axis line. The annual band marks were labeled in decreasing years, starting from the end of the slab corresponding to the surface of the coral colony. This gave the approximate age of the coral up to the point corresponding to the base of the slab. The slab was then cut into skeletal segments corresponding to known years, and each segment was used for analysis. For Buccoo Reef, the coral was divided into 1-year intervals extending from 1968 to 1993, while the Culloden Bay sample was separated into 2-year intervals extending from 1961 to 1992. Coral sub-samples were sectioned using a diamondedge geological saw. Macroscopic holes from boring organisms were avoided while sectioning. Phosphorus analyses were carried out after Dodge et al. (1984). Briefly, a known weight of coral (approximately 0.5 g) was heated at 600°C for 12-15 h in a muffle furnace. After cooling, the residue was dissolved in a minimum
Total P Inorganic P Organic P
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-7-r178 81162 85186 89190 75176 79180 83184 87188 91182
Year Fig. 2 Variation of total, inorganic and organic phosphorus in core samples of Montastrea annularis collected at Culloden Bay, Tobago, West Indies.
1014
''v'/
/ / x..~....,,../"
Volume 36/Number 12/December 1998 of 4.5% HC1 and made up to a known volume. The resulting solution was analysed for phosphorus according to standard methods (ASTM, 1985). An additional fraction, operationally defined as inorganic material, was determined by omitting the muffling step (Dodge et al., 1984). This represents the 'acid available' fraction, and may include labile organic phosphorus. Dodge et al. (1984) concluded that the phosphorus in corals was in a form that was thermally unstable at
600°C or in concentrated nitric acid. Because of the large differences between the total determination and the inorganic determination, it is evident that a significant amount of the phosphorus is present in an organic form. This is supported by additional experiments performed (but not presented here) by first treating the samples with 30% hydrogen peroxide followed by dissolution in HCI. Phosphorus levels were significantly higher (p <0.05) by this method, and were comparable to those from the combusted samples. The difference between the total and inorganic fraction was taken to represent the organic fraction. Variations of total, inorganic and organic phosphorus for Culloden Bay and Buccoo Reef are illustrated in Figs. 2 and 3 respectively. For Culloden Bay, values of total phosphorus ranged from 2.36 to 4.87 lagg-1, organic phosphorus from 0.16 to 2.72 lag g 1, and inorganic phosphorus from 0,64 to 3.30 lag g - i . The ranges for the Buccoo Reef samples were greater: total phosphorus varied from 2.32 to 6.46 lagg-1, organic phosphorus from 0.02 to 5.56lagg -1, and inorganic phosphorus from 0.14 to 2.09 lag g - 1. It is evident from Fig. 2 that there has been minimal variation in phosphorus levels in the past three decades
TABLE 1
Comparison of mean values of phosphorus from this study with other values in the Caribbean (values are quoted in ~tgg-i).
St. Croix*
Mean Range Mean Range Mean Range Mean Range Mean Range
Bermuda* Curacao* Buccoo Reef Culloden Bay
Inorganic phosphorus
Total phosphorus
2.51___1.58 1.8-4.4 2.08+ 0.60 1.2-3.3 4.06___0.49 3.3-5.4 1.11+0.60 0.14-2.09 2.11 +0.67 0.64-2.89
5.96+ 1.82 3.8-13.1 8.21 + 1.30 5.6-10.3 5.25+ 0.47 4.6-6.6 4.15+ 1.01 2.32-6.46 3.45+0.62 2.36-4.87
*Dodge et al. (1984).
A "-/ /
_.
Total P OrganicP
_,,
Inorganic P
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72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 'lear
Fill. 3 Variation of total, inorganic and organic phosphorus in a core sample of Montastrea annularis collected at Buccoo Reef, Tobago, West Indies. 1015
Marine Pollution Bulletin for the CuUoden Bay samples. There is no obvious temporal trend and, in this case, the variation in total phosphorus level tends to be dictated by the inorganic fraction. This constitutes a direct contrast to the Buccoo Reef situation (Fig. 3), where the total phosphorus content is dominated by the organic
fraction. The latter may reflect sewage contamination. Dodge et al. (1984) reported levels of phosphorus of 1.8-4.4 lag g - t (inorganic) and 3.8-13.1 lag g - ~ (total) in areas of St Croix that they considered to be pollution-free and pristine. Table 1 gives mean values of phosphorus from this study, as well as other levels at
450-C"
400 -
350-
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(a)
76
84
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88
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YEAR
4500 4000350030002500200015001000500G
1~0
1~0
1990
(b) I~
No. of Households /
Population
Fig. 4 The total number of hotel rooms in the vicinity of the Buccoo Reef/Bay area, Tobago, West Indies, (a) and the total number of households and total population in the County of St. Patrick, Tobago, West Indies (b).
1016
92
Volume 36/Number 12/December 1998 control or pristine sites elsewhere in the Caribbean. Although the present study represents about 10 years more data than was considered by Dodge et al. (1984), the mean values of inorganic and total phosphorus for Culloden Bay and Buccoo Reef are below those quoted for the other sites. These values imply that the samples studied here are comparable to pristine sites elsewhere in the Caribbean. Figure 3 shows an interesting temporal trend. The phosphorus is mainly dictated by the organic phosphorus content, while the inorganic phosphorus levels appear to be relatively constant throughout the length of the core. There was a sharp decrease in total and organic phosphorus between 1969 and 1975, followed by a gradual increase since 1975. These trends observed for Buccoo Reef show some correlation to agricultural and tourism development in that part of the island. In 1965, the Government embarked on a Statelands Development Programme, that sought to expand livestock production. This resulted in completely intensive systems (Braithwaite, unpublished). Farms were set up in the St Andrew and St David counties which drain directly into the Buccoo Bay/Reef area. In the 1970s, a high inflow of revenue from petroleum exports increased the importation of livestock products (Braithwaite, 1991), and livestock production declined in the early to mid 1970s. The tourism industry as well as population growth have seen significant development in the last two decades (Fig. 4). Concurrent with this development was the commissioning of sewage treatment plants at Bon Accord and Buccoo in the mid 1970s. These events may have collectively contributed to the lowering and subsequent increase of phosphorus levels in the Buccoo Reef area. Several studies (Thames Water International et al., 1992; IMA, 1992, 1993a, 1996) concluded that the Buccoo Bay/Reef area is severely stressed by sewage and domestic wastes. IMA (1992) estimated a phosphorus loading to the Buccoo Bay/Reef area of 2.6 metric tonnes annually, while I M A (1996) found the highest nutrient levels at Bon Accord Lagoon and Buccoo Bay when compared with other areas in southwest Tobago. The variation of phosphorus levels at the Coral Gardens site strongly suggests the influence of effluent discharge as a result of land use development in the adjacent areas. Dollar (1994) asserted that the discharge of treated sewage effluent may have no negative effect on coral communities and may enhance growth by providing nutrient subsidies. The relatively low levels of phosphorus found at Buccoo Reef compared to other Caribbean sites (Table 1) may also be partially attributed to the flushing characteristics of the outer reef areas; I M A (1993b) reported that the outer reef area is well flushed. It is concluded that historic records of phosphorus pollution in coral cores of Tobago reflect conditions of their environment, as a result of adjacent land use
features and the associated effluent runoff. This is a preliminary study, and for a more thorough interpretation, supportive information such as calcium levels and organic carbon content are needed. Although the levels of phosphorus found in corals from this study are within the range of those quoted for pristine areas around the Caribbean, Buccoo Reef cannot be considered to be pristine. If recent trends as reflected in the coral cores continues, this area will become further stressed. It is important, therefore, that effective management be instituted to prevent pollution from developing further. The authors wish to thank Mr lndar Moonasar of the Marine Analytical Laboratory, Institute of Marine Affairs, for his assistance in sample analysis, the Seismic Research Unit of the University of the West Indies for assistance in coral sectioning, Mount Hope Medical Complex, Trinidad and Tobago for X-rays, UNEP/CEPPOL for funding and Dr Peter Swart of the Geology Department of the University of Miami. The support of the Tobago House of Assembly is gratefully acknowledged. ASTM (1985) American Society for Testing and Materials, Vol. 11.02. ASTM, Philadelphia. Barnes, D. J. (1973) Growth in colonial scleractinians. Bulletin of Marine Science 23, 280-298. Barnes, D. J. and Lough, J. M. (1989) The nature of skeletal density banding in scleractinian corals: fine banding and seasonal patterns. Journal of Experimental Marine Biology and Ecology 126, 199-234. Barnes, D. J., Lough, J. M. and Tobin, B. J. (1989) Density measurements and the interpretation of X-radiographic images of slices of skeleton from the colonial hard coral Porites. Journal of Experimental Marine Biology and Ecology 131, 45-60. Braithwaite, O. (1991) Overview of livestock production in Tobago. In FAO Report of the Round Table on Small Farmers' Livestock Development in the Caribbean. Port of Spain, Trinidad and Tobago,
24-26 July 1991. Food and Agriculture Organisation, Rome. Br6ecker, W. S. (1963) A preliminary evaluation of uranium series inequilibrium as a tool for absolute age measurements on marine carbonate. Journal of Geophysical Research 68, 2817-2834. Dodge, R. E. and Thompson, J. (1974) The natural radiochemical and growth records in contemporary hermatypic corals from the Atlantic and Caribbean. Earth Planet Science Letters 23, 313-322. Dodge, R. E. and Vaisnys, J. R. (1980) Skeletal growth chronologies of recent and fossil corals. In Skeletal Growth: Biological Records of Environmental Change, eds D. C. Rhoads and R. A. Lutz. Plenum Press, New York, pp. 493-517. Dodge, R. E., Aller, R. C. and Thompson, J. (1974) Coral growth related to resuspension of bottom sediments. Nature 247, 574-577. Dodge, R. E., Jickells, T. D., Knap, A. H., Boyd, S. and Bak, R. P. M. (1984) Reef-building coral skeletons as chemical pollution (phosphorus) indicators. Marine Pollution 15, 178-187. Dollar, S. (1994) Sewage discharge on coral reefs: not always pollution. Coral Reels 13, 224. Fishelson, L. (1973) Ecology of coral reefs in the Gulf of Aqaba (Red Sea) influenced by pollution. Oecologia (Berlin) 12, 55-67. Flor, T. H. and Moore, W. S. (1977) Radium/calcium and uranium/ calcium determinations for western Atlantic reef corals, in Proceedings, 3rd International Coral Reef Symposium, Vol. 2, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Florida, pp. 555-561. Highsmith, R. C. (1979) Coral growth rates and environmental control of density banding. Journal of Experimental Marine Biology and Ecology 37, 105-125. Horvat, M., Azemard, S., Mokhtar, M. B., Mandic, V., Bartocci, J., Readman, J. W. and Kumarsingh, K. (1996) The use of corals as historical recorders of mercury in the marine environment: a preliminary study. Poster presentation. In International Conference on Mercury as a Global Pollutant. Hamburg, Germany, 4-8 August, 1996. IMA (1992) Rapid Assessment of Solid and Liquid Wastes from Agricultural and Domestic Activities in Trinidad and Tobago, Vol. II. Technical report for UNEP Regional Co-ordinating Unit. Institute of Marine Affairs, Trinidad. 1017
Marine Pollution Bulletin IMA (1993a) Biological Investigations and Water Quality Monitoring. Technical Report, Institute of Marine Affairs, Trinidad. IMA (1993b) Physical Oceanographic and Bathymetric Surveys of Buccoo Reef, Tobago. Technical Report, Institute of Marine Affairs, Trinidad. IMA (1996) Report of phase 1: an assessment of the biophysical environment of southwest Tobago. Document prepared for the Organization of American States. Technical Report, Institute of Marine Affairs, Trinidad. Kinsey, D. W. and Davies, P. J. (1979) Carbon turnover, calcification and growth in coral reefs. In Biogeochemical Cycling of Mineralforming Elements, ed. P. A. Trudinger and D. J. Swaine, Elsevier, New York, pp. 131-162. Knutson, D. W., Buddemeir, R. W. and Smith, S. V. (1972) Coral chronometers: seasonal growth bands in reef corals. Science 177, 270-272. Laydoo, R. S. (1996) Coral recruitment and transplantation in reef management: Buccoo Reef, Tobago. Master of Philosophy Thesis, Department of Zoology, University of the West Indies, St. Augustine, Trinidad. Macintyre, I. G. and Smith, S. V. (1974) X-radiograph studies of skeletal developments in coral colonies. In Proceedings, 2nd
1018
International Coral Reef Symposium, Vol. 2. Great Barrier Reef Committee, Brisbane, pp. 277-287. Risk, M. J., Van Wissen, F. A. and Beltran, J. C. (1992) Sclerochronology of Tobago corals: a record of the Orinoco? In
Proceedings of the 7th International Coral Reef Symposium, Guam, 22-27June 1992, Vol. 1, ed. R. H. Richmond. University of Guam Marine Laboratory, Mangilao, Guam, pp. 156-161. St John, B. E. (1974) Heavy metals in the skeletal carbonate of scleractinian corals. In Proceedings of the 2nd International Coral Reef Symposium, Vol 2, Great Barrier Reef Committee, Brisbane, pp. 461-469. Thames Water International, Reid Crowther and A De B Consultants (1992) Feasibility Studies and Preliminary Designs for
the Collection, Treatment and Disposal of Wastewater in Tobago. Document prepared for the Water and Sewerage Authority of Trinidad and Tobago. Veeh, H. H. and Turkeian, K. K. (1968) Cobalt, silver and uranium concentration of reef-building corals in the Pacific Ocean. Limnology and Oceanography 13, 304-308. Walker, D. I. and Ormond, R. F. G. (1982) Coral death from sewage and phosphate pollution at Aqaba, Red Sea. Marine Pollution Bulletin 13, 21-25.
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Symposium (Rice, S. D., Spies, R. B., Wolfe, D. A. and Wright, B. A., eds), pp. 29-39. American Fisheries Society, Bethesda, MD. Short, J. W., Jackson, T. J., Larsen, M. L. and Wade, T. L. (1996) Analytical methods used for the analysis of hydrocarbons in crude oil, tissues, sediments and seawater collected for the natrual resources damage assessment of the Exxon Valdez oil spill. In Proceedings of the Exxon Valdez Oil Spill Symposium (Rice, S. D., Spies, R. B., Wolfe, D. A. and Wright, B. A., eds), pp. 140-148. American Fisheries Society, Bethesda, MD. Wells, P. G., Butler, J. N. and Hughes, J. S. (1995) Exxon Valdez Oil Spill: Fate and Effects in Alaskan Waters, ASTM Special Technical Publication No. 1219. American Society for Testing and Materials, Philadelphia. Wolfe, D. A., Hameedi, M. J., Gait, J. A., Watabayashi, G., Short, J. W., O'Claire, C., Rice, S. D., Michel, J., Payne, J. R., Braddock, J., Hanna, S. and Sale, D. (1994) The fate of the oil spilled from the Exxon Valdez. Environmental Science and Technology 28, 561-567. Wolfe, D. A., Krahn, M. E., Casillas, E., Sol, S., Thompson, T. A., Lunz, J. and Scott, K. J. (1996) Toxicity of intertidal and subtidal sediments contaminated by the Exxon Valdez oil spill. In Proceedings of the Exxon Valdez Oil Spill Symposium (Rice, S. D., Spies, R. B., Wolfe, D. A. and Wright, B. A., eds), pp. 121-139. American Fisheries Society, Bethesda, MD. Marine PollutionBulletin, Vol. 36, No. 12, pp. 1012-1018, 1998 © 1998 Elsevier Science Ltd Pergamon All rights reserved. Printed in Great Britain 0025-326X/98 $19.00+0.00
PII: S0025-326X(98)00086-1
Historic Records of Phosphorus Levels in the Reef-building Coral Montastrea annularis from Tobago, West Indies K I S H A N K U M A R S I N G H *~, R I C H A R D L A Y D O O * , J E F F E R Y K. CHEN* and A V R I L M. S I U N G - C H A N G *~ *Institute of Marine Affairs, p.o. Box 3160, Carenage Post Office, Chaguaramas, Trinidad *United Nations Development Programme, 19 Keate St. Port of Spain, Trinidad gLange PML Caribbean Ltd, Charles St. Port of Spain, Trinidad
Enhanced phosphorus concentrations in coral reef systems can be detrimental (Kinsey and Davies, 1979; Walker and Ormond, 1982; Fishelson, 1973). The deposition of aragonite (CaCO3) in coral skeleton material from the surrounding waters has led to the suggestion that coral skeletons may be used to determine the chemistry of the waters in which they grow (Br6ecker, 1963; Veeh and Turkeian, 1968; St John, 1974; Flor and Moore, 1977). A detailed review of corals as environmental indicators was published by Highsmith (1979). The presence of alternating bands of different density, as indicators of annual growth within the coral skeleton, provides a means of assessing historical trends (Knutson et al., 1972; Barnes, 1973; ~Present address: Environmental Management Authority, 2nd Floor the Mutual Centre, 16 Quenn's Park West, P.O. Box 150 Newtown, Port of Spain, Trinidad. ~Present address: Pan American Health Organisation, 49 Jerningham Ave., Queen's Park East, Port of Spain, Trinidad.
Volume 36/Number 12/December 1998 I
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Fig. 1 Location of sampling sites, Culloden Bay and Buccoo Reef, in Tobago, West Indies.
Macintyre and Smith, 1974; Dodge et al., 1974; Dodge and Thompson, 1974; Barnes and Lough, 1989). Seasonal patterns are revealed when the coral is slabbed and X-radiographed (Dodge and Vaisnys, 1980; Barnes and Lough, 1989; Barnes et al., 1989). In the Caribbean, corals have been shown to preserve phosphorus records that are consistent with sewage impacts and other pollution sources of episodes (Dodge et al., 1984). It is therefore important to establish baseline levels and document enhanced eutrophication, for prediction and management purposes. There are no published accounts of phosphorus levels in corals in Tobago, although Risk et al. (1992) and Horvat et al. (1996) have investigated different aspects of coral sclerochronology locally. This paper documents the phosphorus content of corals collected from the island of Tobago, West Indies, from areas that are known to be stressed by sewage and domestic wastes, and compares these with corals from unpolluted, pristine areas. Buccoo Reef is located to the north of the southwestern tip of Tobago and covers an area of 7 km 2 (Fig. 1). It is characterized by an arc of five emergent reef fiats, dissected by seaward channels to the north; an extensive forereef; a shallow sandy backreef lagoon with a patchy distribution of coral communities; and the Bon Accord Lagoon fringed by a mangrove swamp to the south (Laydoo, 1996). The adjacent coastal area
of southwest Tobago is characterized by residential and hotel/guest house development, agriculture and animal farming. Buccoo Bay and Bon Accord Lagoon each receives effluents from a sewage treatment plant. Samples at Buccoo Reef were collected at Coral Gardens, which is in the reef lagoon. Culloden Bay is situated on Tobago's leeward coast (Fig. 1). The bay has a surface area of approximately 0.058 km 2. Because of the semi-exposed nature of the bay, anchorage and recreational swimming is limited, except for sporadic sport-diving for tourists. Culloden Bay may therefore be considered pristine. Samples from this site were collected in the forereef; there is no backreef. Cylindrical cores 30-36 cm long were obtained from Montastrea annularis colonies at 5-7 m depth at the Coral Gardens site in the Buccoo Reef area and at 8 m depth at the forereef of Culloden Bay. The cores were cut using a diamond-tipped rock corer which was attached to a pneumatic drill fed from a SCUBA tank. A guide-plate constructed from a 15 c m x 15 cm × 3 cm marine ply-board through which a circular hole was cut to accommodate the corer, was used to prevent the corer tip from skidding over the coral surface at the beginning of the core drilling. The guide plate was nailed to the coiony's surface, such that the corer was aligned with the growth axis of the colony. The core was drilled along the growth axis to a depth of approxi1013
Marine Pollution Bulletin
mately 35 cm. The guide plate was then carefully withdrawn. The core was broken near its base by forcing a diver's knife into the space around the core, and was then removed and labeled. The resulting cavity was filled with coral rubble and capped with cement to prevent invasion and destruction of the colony by boring organisms. Live tissue was later removed by soaking the cores in fresh water for approximately 1 h. After soaking, any remaining tissue was removed with a light jet of water. The cores were then air-dried for further processing. A slab approximately 0.5 cm thick was cut along the axis of each core using a circular geological saw. Each slab was X-rayed on Agfa Structurix D4 X-ray film, with a General Electric MPX X-ray machine set at 40 kVp for a period of 8 s, at a distance of 0.9 m. The X-radiograph was subsequently used to obtain a positive black and white print. The positive print of each X-rayed slab was overlain with a strip of clear acetate sheet and secured at each end with clear adhesive tape. A line was drawn on the acetate strip along the growth axis of the coral colony at the point at which it was cored. Where the orientation of the lines was not continuous over the length of the print, due to
variation in the growth direction, more than one line was necessary to define the growth axis along the length of the print. Annual growth bands comprising contiguous dark (high density skeleton) and light (low density skeleton) bands were then marked on the acetate strip perpendicular to the growth axis line. The annual band marks were labeled in decreasing years, starting from the end of the slab corresponding to the surface of the coral colony. This gave the approximate age of the coral up to the point corresponding to the base of the slab. The slab was then cut into skeletal segments corresponding to known years, and each segment was used for analysis. For Buccoo Reef, the coral was divided into 1-year intervals extending from 1968 to 1993, while the Culloden Bay sample was separated into 2-year intervals extending from 1961 to 1992. Coral sub-samples were sectioned using a diamondedge geological saw. Macroscopic holes from boring organisms were avoided while sectioning. Phosphorus analyses were carried out after Dodge et al. (1984). Briefly, a known weight of coral (approximately 0.5 g) was heated at 600°C for 12-15 h in a muffle furnace. After cooling, the residue was dissolved in a minimum
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Year Fig. 2 Variation of total, inorganic and organic phosphorus in core samples of Montastrea annularis collected at Culloden Bay, Tobago, West Indies.
1014
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Volume 36/Number 12/December 1998 of 4.5% HC1 and made up to a known volume. The resulting solution was analysed for phosphorus according to standard methods (ASTM, 1985). An additional fraction, operationally defined as inorganic material, was determined by omitting the muffling step (Dodge et al., 1984). This represents the 'acid available' fraction, and may include labile organic phosphorus. Dodge et al. (1984) concluded that the phosphorus in corals was in a form that was thermally unstable at
600°C or in concentrated nitric acid. Because of the large differences between the total determination and the inorganic determination, it is evident that a significant amount of the phosphorus is present in an organic form. This is supported by additional experiments performed (but not presented here) by first treating the samples with 30% hydrogen peroxide followed by dissolution in HCI. Phosphorus levels were significantly higher (p <0.05) by this method, and were comparable to those from the combusted samples. The difference between the total and inorganic fraction was taken to represent the organic fraction. Variations of total, inorganic and organic phosphorus for Culloden Bay and Buccoo Reef are illustrated in Figs. 2 and 3 respectively. For Culloden Bay, values of total phosphorus ranged from 2.36 to 4.87 lagg-1, organic phosphorus from 0.16 to 2.72 lag g 1, and inorganic phosphorus from 0,64 to 3.30 lag g - i . The ranges for the Buccoo Reef samples were greater: total phosphorus varied from 2.32 to 6.46 lagg-1, organic phosphorus from 0.02 to 5.56lagg -1, and inorganic phosphorus from 0.14 to 2.09 lag g - 1. It is evident from Fig. 2 that there has been minimal variation in phosphorus levels in the past three decades
TABLE 1
Comparison of mean values of phosphorus from this study with other values in the Caribbean (values are quoted in ~tgg-i).
St. Croix*
Mean Range Mean Range Mean Range Mean Range Mean Range
Bermuda* Curacao* Buccoo Reef Culloden Bay
Inorganic phosphorus
Total phosphorus
2.51___1.58 1.8-4.4 2.08+ 0.60 1.2-3.3 4.06___0.49 3.3-5.4 1.11+0.60 0.14-2.09 2.11 +0.67 0.64-2.89
5.96+ 1.82 3.8-13.1 8.21 + 1.30 5.6-10.3 5.25+ 0.47 4.6-6.6 4.15+ 1.01 2.32-6.46 3.45+0.62 2.36-4.87
*Dodge et al. (1984).
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Fill. 3 Variation of total, inorganic and organic phosphorus in a core sample of Montastrea annularis collected at Buccoo Reef, Tobago, West Indies. 1015
Marine Pollution Bulletin for the CuUoden Bay samples. There is no obvious temporal trend and, in this case, the variation in total phosphorus level tends to be dictated by the inorganic fraction. This constitutes a direct contrast to the Buccoo Reef situation (Fig. 3), where the total phosphorus content is dominated by the organic
fraction. The latter may reflect sewage contamination. Dodge et al. (1984) reported levels of phosphorus of 1.8-4.4 lag g - t (inorganic) and 3.8-13.1 lag g - ~ (total) in areas of St Croix that they considered to be pollution-free and pristine. Table 1 gives mean values of phosphorus from this study, as well as other levels at
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Fig. 4 The total number of hotel rooms in the vicinity of the Buccoo Reef/Bay area, Tobago, West Indies, (a) and the total number of households and total population in the County of St. Patrick, Tobago, West Indies (b).
1016
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Volume 36/Number 12/December 1998 control or pristine sites elsewhere in the Caribbean. Although the present study represents about 10 years more data than was considered by Dodge et al. (1984), the mean values of inorganic and total phosphorus for Culloden Bay and Buccoo Reef are below those quoted for the other sites. These values imply that the samples studied here are comparable to pristine sites elsewhere in the Caribbean. Figure 3 shows an interesting temporal trend. The phosphorus is mainly dictated by the organic phosphorus content, while the inorganic phosphorus levels appear to be relatively constant throughout the length of the core. There was a sharp decrease in total and organic phosphorus between 1969 and 1975, followed by a gradual increase since 1975. These trends observed for Buccoo Reef show some correlation to agricultural and tourism development in that part of the island. In 1965, the Government embarked on a Statelands Development Programme, that sought to expand livestock production. This resulted in completely intensive systems (Braithwaite, unpublished). Farms were set up in the St Andrew and St David counties which drain directly into the Buccoo Bay/Reef area. In the 1970s, a high inflow of revenue from petroleum exports increased the importation of livestock products (Braithwaite, 1991), and livestock production declined in the early to mid 1970s. The tourism industry as well as population growth have seen significant development in the last two decades (Fig. 4). Concurrent with this development was the commissioning of sewage treatment plants at Bon Accord and Buccoo in the mid 1970s. These events may have collectively contributed to the lowering and subsequent increase of phosphorus levels in the Buccoo Reef area. Several studies (Thames Water International et al., 1992; IMA, 1992, 1993a, 1996) concluded that the Buccoo Bay/Reef area is severely stressed by sewage and domestic wastes. IMA (1992) estimated a phosphorus loading to the Buccoo Bay/Reef area of 2.6 metric tonnes annually, while I M A (1996) found the highest nutrient levels at Bon Accord Lagoon and Buccoo Bay when compared with other areas in southwest Tobago. The variation of phosphorus levels at the Coral Gardens site strongly suggests the influence of effluent discharge as a result of land use development in the adjacent areas. Dollar (1994) asserted that the discharge of treated sewage effluent may have no negative effect on coral communities and may enhance growth by providing nutrient subsidies. The relatively low levels of phosphorus found at Buccoo Reef compared to other Caribbean sites (Table 1) may also be partially attributed to the flushing characteristics of the outer reef areas; I M A (1993b) reported that the outer reef area is well flushed. It is concluded that historic records of phosphorus pollution in coral cores of Tobago reflect conditions of their environment, as a result of adjacent land use
features and the associated effluent runoff. This is a preliminary study, and for a more thorough interpretation, supportive information such as calcium levels and organic carbon content are needed. Although the levels of phosphorus found in corals from this study are within the range of those quoted for pristine areas around the Caribbean, Buccoo Reef cannot be considered to be pristine. If recent trends as reflected in the coral cores continues, this area will become further stressed. It is important, therefore, that effective management be instituted to prevent pollution from developing further. The authors wish to thank Mr lndar Moonasar of the Marine Analytical Laboratory, Institute of Marine Affairs, for his assistance in sample analysis, the Seismic Research Unit of the University of the West Indies for assistance in coral sectioning, Mount Hope Medical Complex, Trinidad and Tobago for X-rays, UNEP/CEPPOL for funding and Dr Peter Swart of the Geology Department of the University of Miami. The support of the Tobago House of Assembly is gratefully acknowledged. ASTM (1985) American Society for Testing and Materials, Vol. 11.02. ASTM, Philadelphia. Barnes, D. J. (1973) Growth in colonial scleractinians. Bulletin of Marine Science 23, 280-298. Barnes, D. J. and Lough, J. M. (1989) The nature of skeletal density banding in scleractinian corals: fine banding and seasonal patterns. Journal of Experimental Marine Biology and Ecology 126, 199-234. Barnes, D. J., Lough, J. M. and Tobin, B. J. (1989) Density measurements and the interpretation of X-radiographic images of slices of skeleton from the colonial hard coral Porites. Journal of Experimental Marine Biology and Ecology 131, 45-60. Braithwaite, O. (1991) Overview of livestock production in Tobago. In FAO Report of the Round Table on Small Farmers' Livestock Development in the Caribbean. Port of Spain, Trinidad and Tobago,
24-26 July 1991. Food and Agriculture Organisation, Rome. Br6ecker, W. S. (1963) A preliminary evaluation of uranium series inequilibrium as a tool for absolute age measurements on marine carbonate. Journal of Geophysical Research 68, 2817-2834. Dodge, R. E. and Thompson, J. (1974) The natural radiochemical and growth records in contemporary hermatypic corals from the Atlantic and Caribbean. Earth Planet Science Letters 23, 313-322. Dodge, R. E. and Vaisnys, J. R. (1980) Skeletal growth chronologies of recent and fossil corals. In Skeletal Growth: Biological Records of Environmental Change, eds D. C. Rhoads and R. A. Lutz. Plenum Press, New York, pp. 493-517. Dodge, R. E., Aller, R. C. and Thompson, J. (1974) Coral growth related to resuspension of bottom sediments. Nature 247, 574-577. Dodge, R. E., Jickells, T. D., Knap, A. H., Boyd, S. and Bak, R. P. M. (1984) Reef-building coral skeletons as chemical pollution (phosphorus) indicators. Marine Pollution 15, 178-187. Dollar, S. (1994) Sewage discharge on coral reefs: not always pollution. Coral Reels 13, 224. Fishelson, L. (1973) Ecology of coral reefs in the Gulf of Aqaba (Red Sea) influenced by pollution. Oecologia (Berlin) 12, 55-67. Flor, T. H. and Moore, W. S. (1977) Radium/calcium and uranium/ calcium determinations for western Atlantic reef corals, in Proceedings, 3rd International Coral Reef Symposium, Vol. 2, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Florida, pp. 555-561. Highsmith, R. C. (1979) Coral growth rates and environmental control of density banding. Journal of Experimental Marine Biology and Ecology 37, 105-125. Horvat, M., Azemard, S., Mokhtar, M. B., Mandic, V., Bartocci, J., Readman, J. W. and Kumarsingh, K. (1996) The use of corals as historical recorders of mercury in the marine environment: a preliminary study. Poster presentation. In International Conference on Mercury as a Global Pollutant. Hamburg, Germany, 4-8 August, 1996. IMA (1992) Rapid Assessment of Solid and Liquid Wastes from Agricultural and Domestic Activities in Trinidad and Tobago, Vol. II. Technical report for UNEP Regional Co-ordinating Unit. Institute of Marine Affairs, Trinidad. 1017
Marine Pollution Bulletin IMA (1993a) Biological Investigations and Water Quality Monitoring. Technical Report, Institute of Marine Affairs, Trinidad. IMA (1993b) Physical Oceanographic and Bathymetric Surveys of Buccoo Reef, Tobago. Technical Report, Institute of Marine Affairs, Trinidad. IMA (1996) Report of phase 1: an assessment of the biophysical environment of southwest Tobago. Document prepared for the Organization of American States. Technical Report, Institute of Marine Affairs, Trinidad. Kinsey, D. W. and Davies, P. J. (1979) Carbon turnover, calcification and growth in coral reefs. In Biogeochemical Cycling of Mineralforming Elements, ed. P. A. Trudinger and D. J. Swaine, Elsevier, New York, pp. 131-162. Knutson, D. W., Buddemeir, R. W. and Smith, S. V. (1972) Coral chronometers: seasonal growth bands in reef corals. Science 177, 270-272. Laydoo, R. S. (1996) Coral recruitment and transplantation in reef management: Buccoo Reef, Tobago. Master of Philosophy Thesis, Department of Zoology, University of the West Indies, St. Augustine, Trinidad. Macintyre, I. G. and Smith, S. V. (1974) X-radiograph studies of skeletal developments in coral colonies. In Proceedings, 2nd
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International Coral Reef Symposium, Vol. 2. Great Barrier Reef Committee, Brisbane, pp. 277-287. Risk, M. J., Van Wissen, F. A. and Beltran, J. C. (1992) Sclerochronology of Tobago corals: a record of the Orinoco? In
Proceedings of the 7th International Coral Reef Symposium, Guam, 22-27June 1992, Vol. 1, ed. R. H. Richmond. University of Guam Marine Laboratory, Mangilao, Guam, pp. 156-161. St John, B. E. (1974) Heavy metals in the skeletal carbonate of scleractinian corals. In Proceedings of the 2nd International Coral Reef Symposium, Vol 2, Great Barrier Reef Committee, Brisbane, pp. 461-469. Thames Water International, Reid Crowther and A De B Consultants (1992) Feasibility Studies and Preliminary Designs for
the Collection, Treatment and Disposal of Wastewater in Tobago. Document prepared for the Water and Sewerage Authority of Trinidad and Tobago. Veeh, H. H. and Turkeian, K. K. (1968) Cobalt, silver and uranium concentration of reef-building corals in the Pacific Ocean. Limnology and Oceanography 13, 304-308. Walker, D. I. and Ormond, R. F. G. (1982) Coral death from sewage and phosphate pollution at Aqaba, Red Sea. Marine Pollution Bulletin 13, 21-25.