Inkfish Cayman Islands Leg 1

After yesterday's dive, everybody was excited to get back in the water again and start the work. The first day of photogrammetry is always a bit more challenging but luckily the divers were able to capture all the 100m2 plots at 60, 40, 20, 10 and 5 m depth. Unfortunately one of the rebreather divers had some issues with quite a bit of water in the loop, and had to bail out for a while during decompression - fortunately with adequate open-circuit gas on hand the problem was manageable, although definitely turned it into a more strenuous dive. The ROV team had finished assembling the new imaging payload skid but unfortunately soon after deployment the 300m-long tether started playing up. The AUV team had more luck and was able to complete most of the imaging of the reef between 20-60 m depth.

Deep divers about to descend on the first data collection dive with the ASV ready to track them

Orange Canyon at 40 m depth

Today we headed to the eastern side of the island to scout a location called High Rock Drop Off for the following days’ diving operations. With the tether working again, the ROV team managed to complete transects from 60 to 130 m depth. However, the swell was too substantial to allow diving there the next day, so we relocated to the more protected north-east side of the island, to a site called Lemon Wall. There, the ROV team conducted another set of deep transects, followed by the AUV team, who began imaging the site.

The Lemon Wall site was a stark contrast with the previous site, in that it had noticeably more macroalgal cover with coral cover being quite poor across depths but particularly in the mesophotic. Photogrammetric data collection went well for both the dive and AUV team, with everybody back in their regular routines. The shallow dive team also started the coral tissue collections and managed to come back with 99 samples.

Given the low coral cover at mesophotic depths, the dive team had to adapt the collection plan to reach the target number of coral samples. Rather than sampling only within the photogrammetry plot, the team extended collections to the eastern side of the plot, with one diver carrying an additional camera to photograph any unusual or rarer species encountered. With three deep divers and two shallow divers collecting, the team managed to obtain the vast majority of the anticipated samples, with around 350 corals collected during the 4.5-hour dive.

Meanwhile, the ROV team returned to Orange Canyon, the first site, to conduct transects from 60 to 130 m depth. The goal was to assess the lower mesophotic coral community, beyond the Marine Park boundary at 50 m, and document the lower depth limit of zooxanthellate corals, which we would normally do using the submersibles. The team also attempted to survey an additional site, but the currents were far too strong and caused the tether to become tangled early in the dive, so the attempt had to be aborted.

Leaving Grand Cayman with pretty comprehensive bathymetric mapping coverage

After a relatively smooth transit to Little Cayman, the ROV team headed out early in the morning to scout two potential dive sites: Paradise Plunge on the north shore and Coral City on the south shore. Phaedra and Maxine from the shallow dive team also assessed Paradise Plunge and the surrounding area by snorkel to determine whether it would be suitable for coral tissue collections. After the ROV team confirmed Coral City as the next dive site, the AUV team headed out to begin mapping the location. In the evening, the dive team gave a presentation to the crew about the scientific objectives and an explanation of the different methods that are being used.

The team decided to focus on Coral City for the next two days, as the wind was forecast to pick up after the weekend and this was likely the only opportunity to work on the south side of Little Cayman. The site is known for its relatively high coral cover in the shallows, but unfortunately coral cover at mesophotic depths was low, with much of the reef covered by macroalgae. The shallower depths appeared to have suffered substantial recent coral mortality, and at 20 m depth the team unfortunately found only dead Agaricia colonies. To make the transit back to 10 m, the divers were again assisted by Skye’s diver recall system, which communicated heading and range to the shallow buoy. As they approached, there was a clear transition into brownish water with substantially reduced visibility, making it even more important for the team to stay close together. Meanwhile, the AUV team followed their usual routine of mapping the site, although again were limited to ~50 m depth due to the steep terrain beyond that. After the dive and AUV team were done, the ROV team headed out to survey lower mesophotic depths at two additional sites: Black Hole and Lappy's Leap.

For today’s dive, the deep dive team took a similar approach to the previous collection dive, given the relatively low coral cover at mesophotic depths. They first sampled within the 100 m² plot, then searched beyond its boundaries to ensure sufficient representation of each species. Although the collections went well, the team was a little slow to wrap up sampling at 60, 40, and 20 m, resulting in some additional decompression making for a lengthy dive. By that time, the wind and swell had also picked up, making recovery more challenging. This was managed by having the zodiac collect all cylinders and science gear from the divers in the shallows, after which the divers scootered farther offshore so they could safely return to Skye. After the dive team returned, the ROV team headed out to survey the final two sites on the southern side of Little Cayman: The Edge and Rock House Wall.

A dry day for the divers, but a busy one on the water for the AUV and ROV teams. The ROV team completed transects at four different locations, with two in the morning and two in the late afternoon. Meanwhile, the AUV team relocated to “Paradise Plunge” to get a head start on mapping the area where the divers will be conducting photogrammetry and collections over the next two days. In the evening, the AUV and ROV teams gave presentations to the crew to talk about the evolution of the autonomous vehicles used during the Inkfish expeditions, and share same of the observations of the current leg.

Norbert and Pim conducting photogrammetry at 60 m

Today is the last day of coral tissue collections - with several shortages that still need to be covered to get proper representation across the coral genera. Luckily we knew from the photogrammetry dive yesterday that there is great representation of some of the rarer species (Helioseris, Mycetophyllia and Scolymia) in the 60 m plot. Luckily, it all went very smoothly and although coral cover was again much sparser at 40 m depth (with substantially higher abundance of macroalgae than at 60 m), we were able to tick most of the collection goals. During the long stop at 5 m depth, we had the AUV keeping us company as it was mapping the shallow reef, and it was interesting to watch all the obstacle avoidance behaviors in action. After the divers were out of the water, the ROV team took over and re-surveyed the site from 60-130 m depth (as there were some issues with the data collected during the first attempt), and then relocated to McCoy's wall to also conduct surveys there.

In transit to the shallow reef (~150 m away from the drop-off)

Today was set aside for AUV and ROV R&D trials aboard Skye. With help from Chad and Liam from the Hydra dive team, a range of colour-calibration targets was deployed, allowing the AUV and ROV teams to collect ground-truth data for new colour-correction algorithms being developed for the vehicles. The teams also had the opportunity to iterate on the AUV’s obstacle-avoidance capabilities, using the ROV to closely monitor the vehicle’s responses underwater. Meanwhile, the dive team spent the day curating the collected specimens and preparing for the final day of photogrammetry operations tomorrow.

For the final day of operations, the science team focused on Bloody Bay Marine Park, known for its spectacular vertical walls that rise to as shallow as 10 m depth. The dive team had a smooth and efficient dive at Great Wall West, photographing plots at 60, 40, 20, 10, and 5 m depth, with negligible transit times between depths thanks to the steepness of the terrain. The AUV team was still able to map the broader area between 5 and 20 m depth, but the steep vertical walls meant that coverage of the 60–130 m depth range had to be completed by the ROV team instead. Overall, it was a fantastic final day, with beautifully calm conditions and everyone enjoying the spectacular wall and abundant marine life.