Bonaire National Marine Park Hurricane Matthew Reef Damage Assessment Hurricane Matthew passed north of Bonaire on September 23 rd, 2016. After it passed Aruba, it decelerated, and then it slowly began heading north-northeast (Figure 1), causing waves to start heading towards Bonaire. On September 29 th, waves from Hurricane Matthew reached the leeward shore of Bonaire. The largest waves (3.1 m according to Windguru, Appendix 1) reached Bonaire on the evening of September 29 th and larger waves (larger than 2 m) continued to hit parts of the leeward shore of Bonaire on September 30 th. Immediately after the waves subsided, STINAPA sent survey forms to dive operators requesting information on reef conditions as well as offering to assist in removing large debris. Bonaire National Marine Park rangers took photos of damage to piers, docks, ladders, etc. and began removing large debris from the reef. On October 6 th, 2016, STINAPA staff, interns and volunteers began surveying sites along the leeward shore of Bonaire to assess reef condition. Figure 1. Path of Hurricane Matthew Methodology A total of 18 sites were surveyed. At each site, a 20 m x 4 m area was surveyed at three depths (20m, 10m and less than 10m). In each transect, the total number of corals and the number of broken and/or toppled corals in three size classes (>10 and
<30 cm, 30 cm 100 cm, and >100 cm in diameter) was recorded. The total number of sponges and damaged sponges was also recorded in each transect. Observers also estimated the percent of sand/silt covering living coral tissue and made general observations at depths of 30 m, 20 m, 10 m and less than 10 m. Additionally, divers fanned sponges and righted toppled corals when possible. Results The corals at depths of 10 m and deeper were mostly undamaged (Figure 2, Appendix 2). In the shallows (less than 10 m depth), an average of 25% of the coral colonies were damaged (Figure 3). Most of the damaged corals were fire corals (Millepora complanata). Several stands of branching corals (Acropora species) were also reported as damaged. Smaller colonies (between 10 and 30 cm in diameter) were damaged more than larger colonies (Figure 4) and this supports the written observations that many of the larger boulder/mound corals were undamaged in the shallows. Although eight sites had no sponge damage in the survey areas, the average sponge damage at all sites and depths was 12% with little difference by depth (Figure 3, Figure 5 and Appendix 2). Sponges, if they don t move about, may reattach to the substrate and continue growing. From general observations and photo documentation, there were many sites where the sand in the shallows had been scoured away and seemed to be flocking the rest of the reef. A week after the heaviest wave action, most of the corals had cleaned themselves of the sand cover. There was an average of less than five percent sand/silt covering corals at all depths. Corals, unless smothered, are often able to clean themselves using their tiny cilia. Figure 2. Percent corals damaged at three different depths at eighteen locations on the western shore of Bonaire and Klein Bonaire.
Figure 3. Overall Percent Damage of Corals and Sponges and Sand Cover by Depth. Overall % Damage and Sand Cover by Depth 30 25 20 15 10 5 0 Corals Sponges Sand/Silt <10 m 10 m 20 m
Figure 4. Percent of small (>10 and <30 cm), medium (30-100 cm) and large (> 100 cm) coral colonies damaged at three different depths. Percent Coral Colonies Damaged by Size Class and Depth 30 25 20 15 10 5 0 <10 m 10 m 20 m % small colonies % medium colonies % large colonies Figure 5. Percent sponges damaged at three different depths at eighteen locations on the western shore of Bonaire and Klein Bonaire.
Conclusions Bonaire has had a series of impacts to its leeward reefs in recent years. In 1999, waves from Lenny completely destroyed many of the shallow coral reefs of Bonaire, causing particular damage to branching corals. Some sites that had high coral cover before Lenny were completely bare down to a depth of 15 m. Lenny changed the underwater landscape of the island. In 2008, waves from Tropical storm Omar hit the leeward coast and also caused extensive damage to depths of 10m and more and some sites, also heavily damaging branching corals. The results of this damage assessment show that, although the waves from Hurricane Matthew damaged an average of 25% of shallow corals (less than 10 m deep) and 10% of sponges on the leeward side of the island, Bonaire s corals were mostly undamaged. The sites that showed the most damage in the shallows were some of the same sites that had been damaged by previous storms (Lenny, Omar) and many of the broken corals were fire corals (Millepora complanata). Although most of Bonaire s corals were spared from breakage and toppling, coral recovery at some of the sites most heavily hit by Lenny and Omar was reset and must begin anew. Also, there may be indirect effects of these types of disturbances
such as nutrients being released from the sediment/sand into the water column, death of small corals or coral recruits from abrasion of sand and/or rubble (small corals were not included in this assessment), and a decrease in immunity of corals due to stress, possibly resulting in more susceptibility to disease. Coral reefs are declining in most areas of the world and climate change is predicted to result in more storms and more coral bleaching events. Doing everything possible at the local level to safeguard Bonaire s coral reefs is essential. October 11 th, 2016 Prepared by: Caren Eckrich and Hannah Rempel STINAPA Bonaire Appendix 1. Archive data from Windguru for Bonaire. Appendix 2. Percent coral and sponge damage by depth at each site. Percent Coral Damage Depth <10m 10m 20m
Bachelor's Beach 43.33% 1.59% 0.00% Bellafonte 20.00% 0.00% 0.00% Bise Morto, WSNP 60.00% 14.06% 3.13% Boka Bartol, WSNP 38.30% 4.88% 0.00% Boka Slagbaai, WSNP 17.86% 8.57% 4.17% Buddy's Reef 86.05% 2.13% 0.00% Forest, Klein 0.00% 0.00% 0.00% Jeff Davis 0.00% 0.00% 0.00% Karpata Reserve 0.00% 0.00% 0.00% Mi Dushi, Klein 51.28% 37.50% 0.00% Monte's Divi 0.00% 0.00% 0.00% Ol' Blue 0.00% 0.00% 0.00% The Lake 25.93% 1.32% 0.00% Small Wall 0.00% 0.00% 0.00% Tori's Reef 79.17% 5.13% 0.00% Vista Blue 13.33% 0.00% 0.00% White Slave 0.00% 0.00% 0.00% Windsock 27.91% 1.45% 0.00% Percent Sponge Damage Depth <10m 10m 20m Bachelor's Beach 0.00% 0.00% 0.00% Bellafonte 0.00% 0.00% 0.00% Bise Morto, WSNP 50.00% 50.00% 0.00% Boka Bartol, WSNP 0.00% 16.67% 0.00% Boka Slagbaai, WSNP 40.00% 26.32% 33.33% Buddy's Reef 1.00% 62.50% 21.43% Forest, Klein 0.00% 0.00% 21.43% Jeff Davis 0.00% 0.00% 0.00% Karpata Reserve 0.00% 0.00% 0.00% Mi Dushi, Klein 33.33% 0.00% 0.00% Monte's Divi 0.00% 0.00% 0.00% Ol' Blue 0.00% 0.00% 0.00% The Lake 0.00% 0.00% 0.00% Small Wall 0.00% 20.00% 0.00% Tori's Reef 1.00% 33.33% 0.00% Vista Blue 13.33% 0.00% 0.00% White Slave 0.00% 0.00% 23.53% Windsock 0.00% 0.00% 0.00%
Photo documentation: Sand/silt covering all but living coral at 30 m. Sand and silt covering sponge.
Sand piling up against coral.
Sand scoured away from shallow sites exposing old dead corals. Diver doing 30 x 2 m survey.
Diver attempting to right toppled fire coral.
Diver fanning sand/silt off sponge.
Broken fire coral (Millepora complanata).