Impacts of Tropical Beaches by Tourists and Island Residents Result on Fringing Coral Reefs

To determine whether lower percent coral cover is correlated with increased human activity, Juhasz et al. (2010) studied the relationship between the numberof visitors to a beach and the condition of the reef adjacent to that beach. The authors compared the amount and types of human use at five beaches on Moorea in French Polynesia to the total coral abundance, relative abundance of branching versus massive coral species, size distribution, and nutrient levels. The authors found a significant difference in the number of people per 1000 m across the five sites, with site 1 having the most visitors by a factor of 4. The other 4 sites had about the same number of visitors. The percent coral cover was lowest at site 1 (4.8%), which was significantly lower than sites 24 but not significantly different than site 5. The relative cover of branching and massive coral also varied significantly, with almost no branching coral at site 1 and only between 1% and 5% at the other sites. Small corals dominated the reef composition, though site 4 exhibited a more even distribution of sizes than the other sites. The nutrient levels were not found to vary significantly among the sites studied. The results of this study support the relationship between coral community composition and the number of visitors to a beach. High use areas are more likely to have damaged and weak coral communities, though more research needs to be done to determine exactly which activities harm the coral reefs. — Rachel King
Juhasz, A., Ho, E., Bender, E., Fong, P., 2010. Does use of tropical beaches by tourists and island residents result in damage to fringing coral reefs? A case study in Moorea French Polynesia. Marine Pollution Bulletin, doi:10.1016/j.marpolbul.2010.08.011.

            The sites in this study were selected because they were either highly used beaches or beaches in relatively pristine condition, to provide contrast in the data between high- and low-use areas. The reefs studied were “fringing” reefs, or reefs in shallow enough water that they could be walked on. All the sites experienced similar wave action, wind, and flow because they were all located on the north shore of the island. To quantify the number of beach users at each study site, the authors counted the number of people on the beach and in the water up to a depth of 2 m. Counts were done on a Sunday, Monday, and Tuesday every 30 min between the hours of 10:00 am and 4:00 pm. They also measured the length of the shoreline, and took the average of the counts and divided them by the shore length to get the number of people per 1000 m.
Benthic cover was determined by laying four 25 m transects at random compass bearings and randomly placing five quadrats (1×1 m) along the transect. The percent cover of each coral species or algae was determined and then the average percent coral cover was found for each site, and the authors used a single-factor ANOVA to determine if percent cover of total coral, branching and massive, and algae were significantly different between sites. The number and sizes of corals within 1 m of the transect on either side was also recorded, although only Porites lobata and Acropora spp. were counted since they were the most common coral species at all sites. The last part of Juhasz et al.’s study involved a nutrient analysis of the five sites. They collected samples of the algae Acanthophora spicifera, which they used because it responds quickly to increased nutrient supply, from one site along the north shore of Moorea. The algae were cultured in low nutrient, flowing seawater and then spun in a salad spinner to remove excess water. Five grams of the algae were then placed in each of five mesh bags, sewn shut and then placed at each site. The bags were attached to a hard substrate and collected after five days, then weighed again to determine the growth. A two-factor ANOVA was performed to determine if the growth rates differed significantly between algae at different sites. However, the results for the macroalgae growth did not vary significantly between any of the sites, therefore it is unlikely that nutrient supply varied significantly between the sites.
            The counts of people showed that site 1 had more visitors by a factor of four, and that the other four sites did not display significantly different numbers of visitors. However, site 4 was mainly visited by local residents, not tourists, and was mainly used for picnicking, so the potential for human impact on the reefs was lower. Site 1 also had the lowest percent coral cover (4.8%), while sites 2, 3, and 4 all had 21.451.5% percent coral cover. Site 5 was not significantly different from site 1, with coral cover of 15.6%. The differences in percent coral cover between the sites correlated with the differences in the numbers of people visiting each site, since site 1 was the most visited site and also had the lowest percent coral cover. There were also significant differences in the composition of the coral communities. At site 1, there were almost no branching coral, while other sites had between 1% and 5% percent coral cover. The massive coral was more abundant, and also had the lowest percent cover at site 1, while the other sites ranged between 12% and 51% percent coral cover. The number of massive coral colonies, Porites lobata, at each site varied, but was not correlated with human use, while the number of branching colonies was significantly smaller at site 1 than at the other four sites. The size frequency distribution for P. lobata also varied, but still was not correlated with human use. For the Acropora spp., site 1 had only the smallest size class present, and smaller corals also dominated sites 2, 3, and 5 even though they possessed some colonies of larger size. Site 4 was unique in respect to both coral species because it had a more even distribution of size classes.

The results of this study show a significant correlation between a high use area (a large number of visitors) and lower percent coral cover. The low amount of the branching coral and the lowest ratio of branching to massive coral present at the highest use site also suggests that branching corals may be more sensitive to human activities and may decline faster unless protective measures are taken. Though the authors do not know which specific activities have the most impact on corals, if further studies determined which activities were the most detrimental, restrictions could be placed on certain beach activities to help preserve coral colonies near high use areas. 

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