MSM61: Dive into the deep

2 February 2017 / Mindelo
RV Maria S. Merian back in the EEZ of Cabo Verde

The deep sea is the largest environment on the planet. Most of the deep sea consists of the water column above the seafloor, the pelagic zone. In many parts of the pelagic ocean, no scientific sample or observation has ever been collected. Consequently, knowledge on deep-sea pelagic biodiversity and on the biology and ecology of organisms in this realm remain largely unknown.
During MSM61 we perform deployments with the pelagic in situ observation system or PELAGIOS. This ocean instrument collects high definition video during horizontal transects while being towed on a CTD cable at various depths of interest. The organisms on the collected video are identified and annotated and these results provide detailed insight in the distribution, abundance and diversity of pelagic organisms in relation to their environment. PELAGIOS is particularly designed to collect observations of gelatinous fauna. This group of organisms has been historically undersampled in surveys since their fragility prevents them from being captured intact in nets. In situ video observations are very suitable to study these organisms and pelagic video surveys, e.g. with ROVs, have revealed high abundance of gelatinous organisms from the surface to the deepest parts of the ocean, a pattern that we are now also revealing in the eastern Atlantic.

The area of our research is the Cape Verde region. In the past scientific expeditions using deep-sea trawls revealed a wide variety of deep-sea organisms including fishes, crustaceans and cephalopods. The PELAGIOS video surveys during MSM61 and during two other past cruises establish one of the first pelagic biological baselines in this area. Baseline data is important as it can be used to study ocean community response to climate change and other impacts. One specific goal is to understand the distribution and abundance of gelatinous fauna in relation to oxygen minimum zones, which are expanding as a result of climate change. Many gelatinous fauna have relatively low metabolic rates and one hypothesis that is being tested is whether some species of (gelatinous) fauna are abundant in the oxygen minimum zone in the eastern Atlantic. By establishing detailed vertical distributions, we can predict which pelagic species may be winners or losers of an expanding oxygen minimum zone. During MSM61 we are deploying PELAGIOS at the time series station CVOO (Cape Verde Ocean Observatory), a station that has also been visited during past cruises. The repeat observations at this station allow a temporal analysis of animal distribution, diversity and abundance, and its relation to oxygen variability. Additionally by performing mesopelagic surveys at other stations, we can investigate the spatial variation in pelagic community structure and vertical distributions.

During the PELAGIOS deployments on MSM62 we have been observing various gelatinous fauna, including siphonophores, medusae and ctenophores, but also fishes and crustaceans. Examples of some of the organisms that have been ‘captured’ on the video can be seen in the. I will follow up with more news on deep-sea fauna that we encountered.