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Dolphin Enclosures and Algae
Distributions at Chankanaab, Cozumel:
Thomas J. Goreau, Ph.D. President, Global
Coral Reef Alliance
INTRODUCTION Even though Cozumel has been a major diving destination since the late 1960s, there have been few long-term studies of change in Cozumel reefs, as regular monitoring by the Cozumel Marine Park only began in recent years. Algae overgrowth that kills corals has been an increasingly severe problem around the Caribbean for several decades, but has not been reported to be a major problem in Cozumel until recently. In 1968, soon after the first dive shop, Aqua Safari, opened in Cozumel, a set of underwater photographs of Cozumel reefs were taken by the late Robert Harper. In 1999, his widow, Katherine Harper donated them to the Global Coral Reef Alliance. Soon afterwards, Harper's photographs of these sites, primarily from Paraiso and Palancar Reefs, were shown to groups of the oldest divers on the island, including those shown in the original photographs. They were able to identify all the sites precisely and to recognize many of the individual sponges, gorgonians, and corals shown in the photos as still surviving. These sites were recorded in digital video film by Thomas J. Goreau, in cooperation with Aqua Safari and the Cozumel Marine Park, along with sites at Colombia Reef and Micro Atolones, to develop a permanent record of long term change. Later, Dr. Goreau examined even older underwater photographs from Cozumel taken by the late Ramon Bravo, with the help of Maria Bravo. Comparison of the 2000 videos with the 1968 and older photographs indicated that although the reefs of Cozumel had changed less than any other sites known in the Caribbean, clear changes were nevertheless obvious. The most dramatic change was a clear increase in the abundance of sponges and a decline in corals. While most of the corals appeared to be very healthy, and showed low signs of disease overall, many were being over-grown, under-grown, or bored by sponges. This change is likely to be due to relative changes in the food supply of sponges with regard to corals. While corals rely on capturing zooplankton for their food, and on the photosynthesis of their symbiotic algae, sponges are extremely specialized filter feeders that eat bacteria, as shown by the work of Henry Reiswig in Jamaica around 1970. The dramatic increase of sponges in Cozumel, which has also been noted by the author in Jamaica, is therefore most likely due to increased concentrations of bacteria in the water. While in Jamaica the kinds of sponges on the reef have dramatically changed, in Cozumel the main change appears to be in increased abundance rather than different kinds of sponges. In Jamaica, ocean currents are slow and land runoff is high, so the source of bacteria feeding sponges is probably related to increasing coastal pollution. In contrast, Cozumel sponges and corals grow in very rapidly flowing open Caribbean waters with little surface runoff. The increase of sponges therefore suggests that large-scale, long-term changes in open water food chains has taken place in open Caribbean waters, leading to increases in bacterial food supplies for sponges. This hypothesis needs to be checked by direct studies of the bacteria, zooplankton, and nutrient availability in the waters flowing past Cozumel. Although algae cover in 2000 was still very low in comparison with other sites in Quintana Roo (Cancun, Isla Mujeres, Contoy, Puerto Morelos, and Banco Chinchorro) and other areas of the western Caribbean (such as Jamaica, Belize, Cuba, Florida, and Panama) fleshy algae had distinctly increased since the late 1960s. Very high levels of fleshy algae, that had overgrown and killed large amounts of large corals in shallow water, were found at only two sites, Colombia and Micro Atolones. The high algae levels at Colombia appeared to be localized in areas near the entrance to the Colombia Lagoon, and are thought to be due to elevated nutrient outflows from the lagoon probably caused by septic tank drainage into the lagoon from increasing development around it. In contrast, large dead corals overgrown by fleshy algae at Micro Atolones could not be ascribed to local nutrient sources. This area faces the open Caribbean, has no local population along the shore or water inputs from lagoons, and is subject to minor fishing effort due to its high wave exposure. This unusual pattern was also found at Banco Chinchorro, where the reefs along the protected and heavily fished western side, which faces populated mainland coasts, were coral dominated, while the eastern side of the atoll was almost completely dominated by fleshy algae. This suggests a remote nutrient source from the open Caribbean water. It was proposed that the most likely source was the massive erosion of soil and nutrients from Honduras following Hurricane Mitch, which caused catastrophic flooding and severe erosion of deforested mountain soils. Runoff from Honduras heads east in coastal currents, but then turns westward at Cabo Gracias a Dios when it encounters the main Caribbean currents, and heads directly towards Quintana Roo. If this is correct, long distance sources of nutrients, not local ones, may have caused the algae overgrowth of corals in eastern Cozumel and Banco Chinchorro, as well as the outer reefs of Belize, which have also become algae dominated in recent years (McClanahan, personal communication). Nutrient measurements in these water masses are needed to confirm this hypothesis. In 2002, new problems were noticed in Cozumel by local divers and by the Marine Park staff. These included a dramatic increase in algae near Chancanaab, apparently after the new dolphin and sea lion enclosures had been established as tourist attractions, and the apparent "bleaching" and mortality of around 90% of the hard corals at reefs near Colombia Lagoon. On May 14 2003 the author worked with Jose Juan Dominguez Calderon to view the Cozumel Marine Park's photographic archive of "bleached" corals and algae, and a rapid survey was made of areas where algae problems were reported. OBSERVATIONS Algal species abundances were examined in the lagoon at Chancanaab, along the coast both north and south of the dolphin enclosures, and all around the enclosures. The lagoon (cenote) had clear water with low turbidity and phytoplankton, and while most of the bottom was clearly visible, there were large mats of algae visible in some shallow well-illuminated areas. These algae were of marine species, largely composed of Chaetomorpha linum and Hypnea sp. (probably H. valentiae). The first species is an indicator of high phosphorus, and the second of high nitrogen. However both species were senescent and dying back at the time they were observed based on their color and form. When they are growing fast in response to high nutrients the former is dark green and the latter is dark red. But when observed the first was pale yellowish green and the latter pale reddish brown. At the time they were observed it was late in the dry season. It is likely that these algae had grown rapidly in response to nutrients in the freshwater layer during the previous rainy season, and were dying back, but they could grow very rapidly again if nutrients are added in fresh water during the next rainy season. While there did not appear to be significant nutrient inputs to the cenote or the adjacent seawater from the overlying freshwater lens of the island at the time of thee observations, this is likely to have a strong seasonal variation. The area south of the dolphin cages showed high abundance of algae indicative of high nutrients. These increased steadily from the southern edge of the park towards the dolphin cages. By far the most abundant algae were large gelatinous clumps of the cyanobacteria (blue-green algae) Lyngbya penicilliformis. These were especially common covering the rock ledges as deep as 7-8 meters, perhaps because they are likely to be washed away by wave action in shallower water. Corals were being overgrown by Lyngbya, and there were large numbers of dead gorgonians overgrown by Lyngbya. High densities of cyanbacteria are indicative of excessive pollution, in particular of phosphorus, and are common near sewage inputs. Macro-algae that were common included species indicative of moderate or high nutrients like Hypnea musciformis, Enteromorpha flexuosa, Bryothamnion triquetrum, and Ulva fasciata. On deeper sand areas the algae were more typical of lower nutrients, primarily Halimeda, Udotea, and Penicillus species. The area to the north of the dolphin cages had a dramatically different algae population. Lyngbya was rare, and most corals and gorgonians had little algae overgrowth. The dominant macroalgae were species indicative of moderate or low nutrients, primarily Dictyota pinnatifida, Laurencia poiteaui, Halimeda sp., Udotea sp,. and Penicillus sp. The fencing material that made up the outer and inner parts of the dolphin cages were completely covered with thick mats of Lyngbya on the southern side, and along the western side except for the very northern end, where it was notably less thick. The northern side of the cages had much lower abundance of Lyngbya. Lyngbya mats were dislodged to see which way they were transported by the currents. On the northern side of the dolphin cages they moved slowly into the cages, from north to south. On the southern edge they moved in the same direction, that is away from the cages. On the western side they moved parallel to the cages. This shows that although there is a very strong south to north current offshore, the inshore areas have a weak countercurrent moving in the opposite direction, from north to south. This is supported by observations of water turbidity. Water turbidity south of the cages steadily increased from south to north and was highest next to the cages. In contrast the water to the north of the cages was much clearer. Large schools of fish were observed congregating around the southern side of the cages, but not on the north, presumably reflecting available food supplies being carried by the currents out of the dolphin cages. CONCLUSIONS The types of algae found and their spatial distributions, in conjunction with the turbidity and the movement of the water, suggest that there are excessive nutrients, especially phosphorus, that are coming directly from the dolphin cages. These are likely to be due to a mixture of dolphin excrement and the rotting of uneaten food. (frozen fish). Excess nutrients carried by the currents from the dolphin cages appears to be causing serious coral reef overgrowth by weedy algae (eutrophication), especially by cyanobacteria, in the reefs to the south of the Chancanaab dolphin cages. Although this decreased southward, it extended as far as observations were carried out (the point at the edge of the park), and the southern limit of its effects were not determined. During the dry season there appeared to be little nutrient input to the coastal zone from the freshwater lens of the aquifer. But such inputs could be significant during the rainy season, especially wherever the aquifer is polluted from septic tank overflows. The "bleached" corals in Cozumel in 2002 were in fact not bleached but killed by White Plague disease. This bacterial disease is rapidly spreading across the Caribbean, and is of great concern because it kills more species of corals, at a much faster rate, than any other coral disease. Outbreaks tend to be localized and most intense in the warmest times of year. The fact that this outbreak was limited to a small area that had unusually high water temperatures, according to the surveys made by the Cozumel Marine Park, fits this pattern. The epidemic appears to have ended, but killed about 90% of the corals in the affected area, according to Jose Juan Dominguez Calderon. Continued monitoring of diseases and water quality is needed to understand the impact of such diseases, but few management recommendations can be made at this time. RECOMMENDATIONS The dolphin cages appear to be a point source of nutrients that are damaging the coral reefs to the south, based on the species of algae, their abundances and distributions, the turbidity of the water, the water movement patterns, and the fish distributions. This should be confirmed by direct measurements of nutrients (ammonium, nitrate, and phosphate) in the cages, and in north-south transects north of the cages and south of them. Chlorophyll measurements would indicate if phytoplankton growth is being stimulated, as well as bottom-living algae. Oxygen measurements would indicate if decomposition is depleting oxygen in the water. The patterns of nutrients from land offshore should also be measured, especially during the rainy season, to determine if land-based sources of nutrients are also contributing. Nutrients should also be measured on the eastern side of Cozumel to determine if the algae overgrowing corals at Micro Atolones result from transport from long distance nutrient sources. The distribution of algae in west Cozumel reefs indicates that nutrient sources are limited to the vicinity of local point sources. Systematic water quality studies should be carried out at different seasons of the year to identify all point sources of nutrients, and the backgrounds of nutrients from groundwater and from ocean currents should be determined. These data should be used to devise management strategies to reduce nutrient inputs to the reef and prevent the sort of severe eutrophication that now is typical of most western Caribbean coral reefs. Such steps are important to maintain Cozumel's reputation as a superior quality diving destination. The most cost-effective way of making such measurements would be to use portable, real-time, continuous monitoring devices (see appendix). One instrument is needed to measure temperature, salinity, oxygen, chlorophyll, turbidity, and possibly hydrocarbons. A second instrument is needed to make instantaneous measurements of ammonium, nitrate, and phosphorus nutrients on extremely small samples. These instruments, which would cost approximately around $20,000, would allow each source of nutrients to be determined all along the coastline, using small boats. Nutrient pollution could be tracked directly to the sources (such as sewage pipes, lagoons, and cruise ship dumping) and the instruments could be used to determine if management measures to reduce sources are having the desired effects. Such instruments could be used to rapidly measure all major water quality parameters along the entire western coast of Cozumel in a few hours. They would be very cost effective if they were shared between the Cozumel Marine Park, the Isla Mujeres Cancun Marine Park, the Contoy Marine Park, the Banco Chinchorro Biosphere Reserve, the Sian Ka'an Biosphere Reserve, and the Puerto Morelos Marine Park on a rotating basis. Such instruments would allow the Parks to rapidly monitor the water quality along the entire coast and determine the effectiveness of control strategies for the first time, revolutionizing the practice of coastal zone management. These observations indicate that dolphin enclosures, which are increasingly common in tropical tourist areas, are a significant local source of nutrient pollution and ecological damage to coral reefs. There appear to be only two ways of reducing their impact. The first is to close them down. The second is to enclose them with solid walls to prevent nutrients escaping into the coastal zone. Fresh seawater could be pumped into them, but the effluents should not be permitted to flow back into the sea until they have been treated to remove the nutrients. This could be accomplished by pumping the effluent into large shallow tanks or flow-through raceways, exposed to full sunlight, in which marine algae are grown at high densities to take up the nutrients. To prevent the nutrients entering the coastal zone these algae could be used on land. Composted algae make an excellent source of nutrient rich fertilizer for agriculture or ornamental plants once the sea salts have been leached out by rainfall on concrete platforms. Recycling the nutrients on land would have many environmental benefits, including preventing pollution and damage to coral reefs, eliminating the need to import costly fertilizers, and greatly improving the organic material, nutrients, and water holding capacity in poor soils such as those found on Cozumel. The cenote should be monitored for increases in algae (and nutrients) during the rainy season. This would indicate if there are significant inputs of nutrients to the sea from freshwater flow from the Cozumel aquifer. This would be highest in areas where septic tanks leach into the aquifer. ACKNOWLEDGMENTS The author thanks Maria Bravo of Isla Mujeres for first bringing this problem to his attention; Jose Juan Dominguez Calderon, Subdirector of the Cozumel National Park, for showing photographs and discussing field observations; Robert Cudney Bueno, Director of the Cozumel National Park, and Elvira Carvajal, previous Director of the Cozumel National Park for detailed discussions and encouragement; Ignacio Cureno Munoz, Juan Carlos Gonzalez Hernandez, and the staff of the Fundacion de Parques y Museos de Cozumel for discussions and help viewing the site and other locations on Cozumel; Bill Horn and the entire staff of Aqua Safari for discussions and help diving around Cozumel to examine long term reef change; Jens Ambsdorf of the Lighthouse Foundation of Hamburg Germany, and Rudolf Bittorf, Honorary Consul of Germany in Cancun, for assistance getting to Cozumel and suggestions. I also thank Prof. Robert K. Trench who first encouraged me to look at environmental problems in Cozumel, Roberto Iglesias Prieto of UNAM in Puerto Morelos for discussions, and Katherine Harper for donating the old photographs of Cozumel reefs taken by her late husband Robert Harper. I also thank Gerardo Garcia for the invitation to work in Quintana Roo, and the entire staffs of the Cozumel Marine Park, Parque Marino Isla Mujeres Cancun, Banco Chinchorro Marine Biosphere Reserve, the Contoy MarinePark, and the Universidad Nacional Autonomo de Mexico Mairne Lab at Puerto Morelos for assitance in the field. This project would not have been possible without all their help. APPENDIX
The appendix below regarding instrumentation
for a portable water quality monitoring facility was written more than three
years ago. It needs updating regarding the latest instruments and costs.
PORTABLE WATER QUALITY ANALYSER FOR QUINTANA ROO
May 14 2000 To:
Franciso Ursua, Parque Nacional Isla
Mujeres-Cancun
From: Thomas Joaquin Goreau Arango A real-time portable system for analyzing nutrients (ammonium, nitrate, and phosphate) along with chlorophyll, oxygen, temperature, and salinity is proposed for regular monitoring of changes of all land and ocean based nutrients to the coastal zone of the Mexican Marine Parks and related waters. This system will consist of two instruments packaged into a portable waterproof case, which can be deployed from a small boat. With addition of a GPS system, the results can be used to map, in real time, water quality and pollution sources on GIS maps. This equipment would allow continuous recording T, S. O, and Chl, and nutrients to be analyzed within a few minutes at any chosen site. It could be used in a small boat to produce complete records along 10s of kilometers in a day all along the coastline, identifying every source of nutrients, whenever needed. The instruments recommended for this are: a) A YSI-MA Model 6600 Multi-parameter water quality monitor, measuring temperature, salinity, oxygen, and chlorophyll simultaneously. Uses C batteries or 12V DC. With 12 hour data collecting and logging capability downloadable to a laptop computer, this costs around $9,000. NOTE: Newer versions of this instrument now also allow simultaneous turbidity and hydrocarbon analysis, and the cost has come down. b) A portable nitrate, ammonium, and phosphate analyzer using a pumped through 12 v DC system to analyze these nutrients in-situ in near real time, using flow injection analysis with fiber optics spectrophotometer with computer datalogging capability, from Constellation instruments, around $30,000. This system would fit in a weatherproof suitcase and be powered by 12 Volt batteries, and would contain the housing for the other instrument as well. The sensitivity to nutrient levels would be to oceanographic levels, i.e. less than 0.1 micromoles per liter. The nitrate analysis would use an enzymatic reduction method, eliminating the costly and failure prone copper-coated cadmium columns, which generated toxic wastes and were a major cost and lab problem to maintain in top condition. These instruments, which use miniature fibre-optics spectrophotometers use very small samples, but give the full analytical sensitivity needed, using amounts of chemical reagents that are hundreds to thousands of times smaller than used in conventional labs, while eliminating all sample storage and handing errors. They are therefore far more economical and accurate. NOTE: There are now many more manufacturers of this sort of equipment, and the costs for a basic field instrument (without telemetry features needed only for long term remote deployment) have come down considerably since the above was written. I can look into current prices and capabilities if there is real interest. |
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