One of the goals of RRS James Cook cruise 120 is to sample and describe the communities of animals living on the seafloor of this seabed mining reserve area. There are several ways you can approach this for deep-sea biology: to sample large animals living on the sea surface (called megafauna) we use photographic techniques and trawls. When it comes to the animals that are too fragile for trawling, too small to see in videos, or live beneath the sediment surface, we take samples of sediment and sieve them until we are left with the animals.

We hope to understand how animal communities connect with other areas by taking samples for DNA analyses. Two important things to know about a reserve area are; a) are animals that live in threatened areas also found in the reserve area? and b) how well linked are the communities in each area? By sequencing DNA samples from this cruise and others from areas that will be mined, we hope to understand how closely linked the communities are and help assess how effective the reserve area is likely to be at preserving the biodiversity of the area as a whole.

To get the very best DNA samples, we have to act quickly. As soon as the cores of sediment are on the deck, we bundle them into the cold room and sieve them in cold seawater. We have to chill seawater especially for this since the surface temperature here is around 27˚C and quickly destroys animals that are used to 2˚C. Once we’ve sieved them, we can leave them in a fridge for a little while until we’re ready to take some mug shots, some of which are featured here (taken by me and Sergio Taboada). The best preservative for DNA is ethanol, but unfortunately this isn’t so great for preserving the animals shape and appearance, particularly colour. To get round this preservation effect, we take photos of the animals under a microscope before they get dropped in the alcohol. Formalin is a much better preservative for animals but it destroys DNA so that’s no good.

Combining the photos and DNA analyses is also incredibly useful for making a species catalogue of the area that can then be used to help other scientists working in other areas of this vast, and largely unexplored, part of the world.

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