EXPLORING BONAIRE'S MESOPHOTIC CORAL REEFS

BONAIRE | OCTOBER 2024 | HYPOXIC TRIMIX REBREATHER COURSE + EXPLORATORY DIVES (75-100 METERS)

Bonaire’s reefs are among the healthiest in the Caribbean; they are world-renowned for their accessibility from shore, and some of its reefs extend down to the lower limits of known mesophotic zones (150m)[1]. In October 2024, my teammate Kevin and I completed our hypoxic trimix II course with our instructor Mauritius, and then we conducted exploratory dives at potential study sites (75 – 100m) after the course. Bonaire’s reefs face past and present threats due to their proximity to urbanized land and the entirety of these ecosystems warrant conservation measures[2]. However, marine protection in Bonaire currently ends at 60m[3]. To inform ongoing and future conservation endeavors to protect the entirety of the reef, we seek to expand the current understanding of mesophotic coral ecosystems in Bonaire.

[1] Keller, B. M. (2011). Imaging the Twilight Zone: the Morphology and Distribution of Mesophotic Zone Features, a Case Study from Bonaire. MSc thesis, University of Delaware, 168.

[2] Frade, P.R., Bongaerts, P., Baldwin, C.C., Trembanis, A.C., Bak, R.P.M., Vermeij, M.J.A. (2019). Bonaire & Curaçao. In: Loya, Y., Puglise, K., Bridge, T. Mesophotic Coral Ecosystems. Coral Reefs of the World, vol 12. Springer.

[3] STINAPA Bonaire National Marine Park. Retrieved November 27, 2024, from https://stinapabonaire.org/bonaire-national-marine-park/coastal-waters/ 

Instructor: Mauritius Bell (left)

Mauritius is a CCR Instructor Trainer, a cave instructor, and he has over 1000 hours on a rebreather! He is the Dive Safety Officer & Senior Manager of Dive Operations at the California Academy of Sciences, and the owner of Checklist Safety - a SCUBA and aquatic training and safety company.

Students: Kevin Rodriguez (middle) & Francheska Krysiak (right)

Kevin is a PhD candidate at the University of California, Los Angeles. His research in the Barber lab is focused on local adaptation and gene flow of mesophotic corals. He is also a USCG-certified boat captain and a Global Underwater Explorers Instructor Candidate.

Francheska is an advisor in marine conservation at the Department of Fisheries and Oceans Canada. She is a Young Professional Member of the IUCN World Commission on Protected Areas, a SCUBA instructor, brand ambassador, and an underwater photographer.

STUDYING BIODIVERSITY IN MESOPHOTIC CORAL ECOSYSTEMS

THE RATIONAL FOR DIVING DEEPER

Coral reefs provide a disproportionately large contribution to biodiversity for their given space occupied in the global ocean and their ability to support the well-being of millions of people who rely upon them for food (e.g., fisheries), livelihoods (e.g., tourism), and regulative processes (e.g., storm protection) is being diminished[4],[5]. Biodiversity can be assessed across three dimensions: taxonomic, phylogenetic, and functional[6] and within each dimension, it can be measured at various levels of specificity. Globally, the current understanding of the diversity in coral reefs is heavily biased towards information collected in shallow reefs (0-30 meters), and limited information exists about this diversity across the entire photic zone (0 - 200m)[7].

Because MCEs are subject to many of the impacts occurring in shallower waters (e.g., sedimentation, pollution, invasive species)[8], characterizing biodiversity across the three dimensions and assessing shifts in dominant species across the vertical gradient is critical for understanding reef ecosystems in their entirety. From a conservation standpoint, it is extremely valuable to understand how shifts in environmental variables can influence both the evolution of adaptive potential and the community composition across reefscapes[9]. More broadly, a deeper understanding of biodiversity patterns within and across MCEs is essential for testing ecological hypotheses (such as the deep reef refuge hypothesis) and for informing ongoing conservation initiatives to conserve and protect critical marine and coastal ecosystems across the global ocean.

[4] Eddy, T., Lam, V., Reygondeau, G., et al. (2021). Global decline in capacity of coral reefs to provide ecosystem services. One Earth 4 (9); 1278 – 1285.

[5] Sala, E., Mayorga, J., Bradley, D. et al. (2021). Protecting the global ocean for biodiversity, food and climate. Nature 592, 397–402.

[6] Magurran, A. (2021). Measuring biological diversity. Current Biology 31 (19); 1174 – 1177.

[7] Perez-Rosales, G., Pichon, M., et al. (2022). Mesophotic coral ecosystems of French Polynesia are hotspots of alpha and beta diversity for scleractinian assemblages. Div & Distributions 28 (7); 1345-1511.

[8] Rocha, L., Pinheiro, H., Shepherd, B., et al. (2018). Mesophotic coral ecosystems are threatened and ecologically distinct from shallow water reefs. Science 361, 281-284.

[9] Pinheiro, H., MacDonald, C., et al. (2023). Assembly rules of coral reef fish communities along the depth gradient. Current Biology 33 (8) ; 1421 – 1430.

Photo credits: All underwater photos in this document were captured by F.Krysiak (Scuba Franny Photography | scientific diving) and the photos of the three divers were taken by Adam Beard Photography (Underwater Photography | Adam Beard).

HIGHLIGHT: THE WINDJAMMER SITE

The biodiversity of the mesophotic coral reef at The Windjammer wreck or Mairi Bahn is of particular interest. The Windjammer sank at a depth of 60m off the coast of Bonaire while transporting a load of asphalt, which spilled out of the holds like lava and hardened on the seafloor. This site has ecological significance based on the circumstances surrounding the sinking of the vessel and the environmental impact it has on the local system. Survey dives conducted on the wreck in November 2024 provided baseline information about the site, including the maximum depth of the asphalt field at 80m - 90m. Interestingly, there is a significant amount of healthy coral cover growing atop the asphalt and many coral reef fish were observed using the coral-covered asphalt as habitat. There is no other known system like this in the scientific literature, and we will investigate how an environmental disaster has given way to this unique mesophotic coral ecosystem.

We hypothesize that extant biodiversity at the Windjammer site (Mairi Bahn) has been influenced by unique biomarkers since the incident in 1912. Contaminants can be released from asphalt pavement and lead to water pollution and potential harm to aquatic animals; for example, leachates from asphalt pavements could induce notable stress and inflammation responses in zebrafish [10]. However, initial observations show a healthy coral (e.g., Madracis spp., Montastrea spp., and Agaricia spp) and fish community (e.g., Liopropoma spp., Chromis spp. and Serranus spp.). Therefore, we seek to understand the mechanisms by which healthy mesophotic coral and fishes settled and are thriving atop the asphalt spill from the 1912 wreckage.

[10] Zou, F., Wu, M., Tan, Z., et al. (2024). Ecotoxicological risk of asphalt pavements to aquatic animals associated with pollutant leaching. Science of the Total Environment 944: 173985.

DIVING SAFELY TO 100 METERS

M.Bell and K.Rodriguez during a decompression stop in a shallow coral reef on Bonaire

All dives were conducted on rebreathers and diver equipment included safety gear (e.g., lights, cutting tools, signaling devices), exposure protection (drysuits), and underwater camera/ video equipment. Each diver had two cylinders for onboard gas supply, including: diluent (at a ratio of 10/70 oxygen/helium) and 100% O2, and 3 bailout cylinders with the following gas mixes: 1) 12/68; 2) 50/20; and 3)100% O2. The average bottom time was 15 minutes and the maximum depth for all dives was 100 metres / 330fsw.

COLLABORATORS & PARTNERS

A model of a rebreather diver at the Twilight Zone exhibit at the California Academy of Sciences

My journey to dive into the mesophotic zone was inspired by the Hope for Reefs team at the California Academy of Sciences. This global initiative aims to reverse the rapid decline of earth’s reefs through research and restoration. The team conducts science activities at great depths (100-500 feet below the ocean’s surface) in support of biodiversity studies, and they share their findings through innovative exhibits (right), educational programs, and collaborative engagement.

Lastly, the dives we conducted in Bonaire would not have been possible without the technical dive support from Area 9 Mastery Diving Research Center. Exploration is at the heart of Area 9’s mission, they are committed to uncover, document, and study Bonaire’s most remarkable and challenging dive sites. They prioritize safety and learning, and equip divers with the tools, skills and knowledge needed to navigate these demanding sites with confidence and care. I'm looking forward to working with Area9 the next time I'm in Bonaire!