However, this adventure started long before that, with an odyssey to secure all the essential permits and equipment. In some cases, it actually meant engineering instruments to facilitate proper sample collection, such as stainless-steel drill bars and a frame used to aid the drilling process.

This frame facilitates drilling perpendicularly to the main growth axis of the corals – a crucial step to assess their growth density bands. In addition, it constrains drifts from the drill on the topmost surface of the coral, particularly common at the beginning of the drilling process, which can cause significant tissue damages. After months of thinking, elaboration, and eventually a leap of faith, the frame construction was a great success for which we must greatly thank Detlef Müller, his team from the Physics department at the Freie Universität Berlin, as well as Benjamin Rommel, from the Geology department at the Freie Universität Berlin.

On the 6th of March, with everything ready, we crossed the Atlantic Ocean and finally landed on Bonaire. At this point, it is a common misconception that scientific field work is a romantic combination of breath-taking dives intercut by naps under palm trees on the beach and immersion into the local culture. While there was some of that, the reality was quite different – certainly not because of Bonaire’s wonderful beaches which, interestingly, can have more coral rubble than white sand.

In fact, everyday would start at 6 o’clock, divers would be in the water by 8:30 the latest, and the days would be full of activities until 10 pm – so there was not much room for naps on the beach. Still, all the amazing dives and a couple of days off gave us the energy and motivation to keep accomplishing our goals.

The first challenge in the field was to find the coral chosen for the study – the coral Siderastrea siderea. It is a main reef-building species in the Atlantic reefs that produces seasonal growth bands (visible under X-rays), is long-lived (up to a few centuries) and stress-tolerant. However, during our recognition dives, we witnessed the spread of the Stony-Coral Tissue-Loss Disease (SCTLD), a new disease to the island that is severely impacting corals in the Caribbean since 2016. Filtering out those areas affected by the presence of SCTLD increased the challenge to find appropriate colonies of S. siderea.

Luckily, S. siderea corals were not affected by SCTLD, and we were able to determine relevant sampling sites based on their exposure to human impacts. The next step was to select a sufficient number of colonies, which should ideally be large enough to provide several decades of growth records. Additionally, they should appear healthy, so that biases associated with individual performance are avoided, and be isolated from other organisms, as it diminishes the chances of accidentally touching other organisms. After the coral colonies of interest were selected, the next step was to successfully retrieve cores from them.

This process proved to be challenging as the air supply was based on diving tanks – and our friend “Drill” can breath a lot! To provide air supply for the drill, snorkelling buddies replaced empty tank bottles on the surface while divers drilled and collected the coral cores underwater. The divers needed to find the correct angle for drilling, collect the core from inside of the colony, fit a cement plug into the hole left by the core, and bring the samples safely to the boat/coast. There, tissue samples were immediately collected for genetic analyses and cores were catalogued. The support of boats and their crew members allowed us to access more distant sites and improved our sampling effort, despite a limited number of days. All this effort could not have been possible without the invaluable support of STINAPA and its staff, as well as Charlie.

The cores were dried, labelled, stored, and transported back to Berlin. Their density growth bands will be identified with use of Computerised Tomography (CT) scans and X-rays, in collaboration with the Leibniz-Institut für Zoo- und Wildtierforschung (IZW) in Berlin and the Universität Leipzig. The annual growth rates of these corals may reveal temporal trends and associations with environmental changes documented over the past decades. The geochemical composition of their skeletons (i.e., trace element concentrations) will also be assessed, and may assist in the identification of chronic or episodic stressors potentially impacting these reefs. This information will contribute to conservation and management strategies aimed at protecting, conserving, and restoring these unique ecosystems.