By Kelsey Archer Barnhill
As often happens on cruises, you don’t find your rhythm until the end of the trip. This sentiment is now being realised on board as everyone keeps mentioning how it feels like we have fallen into a routine. Everyone now has their sleeping schedule, is more than familiar with the ship, and knows where they fit into the team. Despite the novel science occurring every day it can sometimes feel difficult to share updates when everyone is so enveloped in their routine.
The lander team is always busy and it can be difficult to keep track of which landers are deployed or not. In the latest baited trap deployment, Prof. Andrew Sweetman, Alycia Smith, and Daniëlle De Jonge counted at least 13 fish in the trap and managed to retrieve 10 of them to process (three fell off during lander recovery). They found plenty of amphipods eating away at the captured fish, including some large ones. The trap has since been sent down a third and final time for its last deployment of the cruise. The sixth camera lander deployment has been recovered and the seventh is scheduled to be sent down tomorrow.
So far the team has seen a higher scavenging rate when squid is used as bait compared to fish. This means the fish come to eat the squid faster than they do with the fish. As squid are predicted to become more common under climate change, this observation has interesting implications, which Daniëlle tells me she is still working on untangling! The team are hoping there will be time for 9 deployments in total, with the final one focused on whether or not rat tail fish will scavenge on their own species. Rat tails collected in the previous baited trap have been frozen in order to conduct this experiment. The respirometer lander has completed all its deployments with normal algae, so the next two will focus on degraded algae. This way the team will be able to compare in situ rates of respiration at 4000m to the on board ex situ experiment.
So far we have done 19 CTD casts led by Angela Mosquera and Iván Mouzo. Angela devotes time each day to analyse the data collected. Across the 19 CTDs she found that the physical oceanographic properties are similar, meaning this area of the ocean is homogeneous. As we are not covering that large an area relative to the scale of the ocean basin, this is to be expected. The CTDs are collected with the main aim of being able to better understand the environmental conditions in the areas where ROV dives are happening and eDNA samples are being taken. With the latest CTD, there have been sufficient samples to cover and describe particulate organic carbon (food supply) at Cadamosto Seamount. This hopefully means the end of Bea Vinha and Andrea Gori’s sleepless nights filtering water. Susan Evans is also happy with the spread of water samples, which will allow her to compare the eDNA found in the CTD and ROV samples to the organisms observed by the ROV cameras.
Since the last update we have done two more ROV dives, both on Cadamosto Seamount. The first dive followed a transect close to the first one we completed at the site. The ROV video cameras showed more or less the same organisms to those we saw on the first dive. This meant brittle stars and sea urchins galore! We also saw some Anthomastus soft corals and collected one for Andrea Gori to trial in aquaria. We take the opportunity to sample corals that have not been worked on before in aquaria so we can observe how they respond to the sampling process, and assess whether they could potentially be used in future aquaria experiments. For corals to survive, they need to be hardy enough to be sampled with an ROV and be able to adjust to the new water in the on-board aquaria.
Yesterday we completed a transect along the north east section of Cadamosto. It was an incredible ROV dive with Metallagorgia gardens and high coral and sponge biodiversity. If the weather allows, we have two more ROV dives planned: one at Fogo continental shelf so that we complete the magic number of 3 dives for that area, and one final dive at Cadamosto where we aim to start in the middle of the transect so we can reach the summit, which we have only done once.
Whilst we’re processing all the imagery from these most recent dives, here are some photo highlights from the ROV’s outing on 16 August. All images © ROV Luso / iMirabilis2.
Two nights ago the Autosub6000 returned from her first 24-hour mission at 3000m to a spirited welcome back on board. After being plagued with technical issues, everyone was rooting for the AUV and her hardworking team. We were all happy to see her return to the ship! The sub was welcomed back to a sound from the ship’s horn and Iván Casal playing a song on the Galician gaita. Susan was able to collect 15 eDNA samples with RoCSI during the mission. However, there were unfortunately issues with the Autosub6000’s multibeam system so we didn’t get any bathymetric data. The AUV team have since been working hard to replace the multibeam system, which was overheating. After deconstructing a portion of Autosub6000 to access the multibeam, the spare system has been placed inside and they are now working on getting the sub to communicate with the new system. Once the AUV is ready to go back in the water, she will be able to survey a larger portion of seafloor as her 24-hour mission has proved she can stay on survey lines and fly between volcanic cones. The next AUV mission has multiple aims: to understand the seafloor morphology, collect backscatter data to derive information about sediment and substrata types, and to collect bathymetry data to safely identify a flat location for a photo survey close to the seabed.
Behind the scenes, cruise leaders Cova Orejas, Veerle Huvenne and Andrew Sweetman, along with the help of Andrea Gori, have been hard at work planning all the logistics. The cruise leaders spend time each day discussing the plan and backup plans for the coming days. They are continuously adapting to weather and equipment conditions. Two days ago a last minute decision was made that the ROV could not be deployed due to the weather, and the AUV team was asked to get ready in record time so they could complete a surface test. Part of the planning process is to make sure that each team has enough time to sleep in between operations, as well as process samples and get ready for the next mission. Veerle has been working on designing the AUV missions, following the mission as it is ongoing, watching the track it begins on and then leaving it alone once she is sure it is behaving properly. She is also the science team member most involved in ship multibeam surveys and has been coordinating watches or collecting the data herself. Veerle and Andrea hold the fort during the night and early hours of the morning. One of the two of them is always awake so there is someone in charge should an issue arise in the lab or the bridge needs to contact them for further direction. The times they need to be awake can fluctuate depending on what operations are ongoing. When I last asked Andrea at 22:30 if it was his evening or morning, he told me he did not know… such is life at sea!
