Small-scale variation in coral reef quality on the leeward side of Bonaire

In the last three decades, Caribbean coral cover values have been declining from 50% to 10% cover Caribbean wide. Several studies have researched this decreasing trend and assessed coral reefs throughout the Caribbean. These assessments often identify the coral reef of Bonaire as one of the most pristine reefs and describe the leeward coast of Bonaire as one of the healthier reefs of the Caribbean. However, the outcomes of these studies are based on pooled data, collected from multiple depths and locations and are presented as being valid for an entire reef while they have often been collected on a very small number of locations on each island. In a study on the ecosystem services of the reefs of Bonaire, Meesters et al. (2014) suggested that coral reefs show large variation in ecological quality on a small scale. This report investigates this small-scale variation in coral reef quality on the leeward coast of Bonaire. On the leeward side, we sampled the coral reef every 500 meters resulting in a total of 115 sampling sites. On each location, the reef was sampled at two different depths (~5 and ~10 meters) following the zonation pattern from Bak (1977). The reef quality is assessed with the Reefbudget methodology described in Perry et al. (2012). Carbonate production, bioerosion, and net production is calculated in kg CaCO3 m-2 year-1 for each site and depth. The net carbonate production reveals the quality of a reef. A positive value indicates the reef is growing while a negative value means a reef or site is flattening. Cluster analysis and TukeyHSD tests are used to analyse the spatial distribution of coral communities and to test if areas show a significant difference in coral reef quality. The shallow reef (depth ~5 meters) in front of Kralendijk shows clear signs of degradation. The area has a significant lower coral cover (3%, p=0.05) and a mean net carbonate production of -0.40 kg CaCO3 m-2 year-1. We found the marine reserve to have the highest coral cover and net carbonate production. The shallow reef of the marine reserve net produces 3.64 kg CaCO3 m-2 year-1, and the fringing deeper reef (depth ~10m) 4.04 kg CaCO3 m-2 year-1. A previous study found a net production of 3.63 kg CaCO3 m-2 year-1 for 5m depth zone. For the 10m depth, net carbonate production was 9.53 kg CaCO3 m-2 year-1. Both values were measured at the “no dive reserve” of Bonaire in Perry et al. (2012). This study finds a lower production for the 10 meters zone, but comparable values for the shallow reef at 5 meters depth. However, the values of the Marine Reserve in this study are the highest of the leeward side of Bonaire. The reef shows a large variation in reef quality along the coastline Net carbonate production ranged from a minimum of -8.70 to a maximum of 50.85 kg CaCO3 m-2 year-1 for one transect. This range is much larger than the range found by Perry et al. (2013). Perry et al. (2013) found a minimum net carbonate production of -2.3 kg CaCO3 m-2 year-1 and a maximum of 16.68 kg CaCO3 m-2 year-1. Comparing the calculated net carbonate production values in this study with data from the Caribbean region, we found that the variation between sites on the leeward side of Bonaire shows similarity with the variation throughout the area. Net production of reefs on Belize, Jamaica, and St. Croix show values of 1.42, 1.2-1.8, and 0.9 kg CaCO3 m-2 year-1 respectively. These values are similar to the 5 meters reef at Klein Bonaire, the South, and the North of Bonaire with 1.09, 0.49, and 0.18 kg CaCO3 m-2 year-1 production respectively. This study reveals a difference in coral community composition between the North and the South of Bonaire. The 10 meter reef of North Bonaire is merely Merulinidae spp where the South of Bonaire is more diverse with a larger cover of Agariciidae spp. Overall turf cover is high across the entire coastline with for the 10 meter depth reef a mean of 36.4% (± 1.8) cover. The 10 meter reef in front of the city shows a higher mean turf algae cover of 50% cover. This study shows that the reef in front of the Kralendijk is in a poor state and is, with a net negative carbonate production, flattening in topographic complexity. The Marine Reserve shows the best net production values in both the 10 meters depth reef as the 5 meters depth reef. The variation between sites along the leeward side is large. This large variation proofs that it is not legitimate to assess an entire coastline based on a limited number of sites. While parts of Bonaire Marine Reserve can indeed be viewed as belonging to the most pristine in the Caribbean, other areas, e.g. in front of the city, show similarities with known

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