Worm holes and snail trails

By Christina Wood 

My job on the RRS Discovery is to characterise the activity of the species that live in the sediment.

I look at a process called bioturbation, which is when species living in the sediment create burrows or move sediment particles up or down.  These activities stimulate microbial growth and encourage the cycling and release of nutrients and are important mediators of shelf sea processes.

To measure bioturbation we use coloured particle tracers we call luminophores, which are placed on top of sediment cores we collect in a 2 – 3 mm thick layer.  These are bright coloured particles that can be easily seen when they are mixed into the underlying sediment.

There are many small worms, shrimp and snails living in the sediment that are constantly moving, grazing, hunting, burrowing, and bioirrigating (moving water to keep burrows and the sediment oxygenated). They can create vast networks of burrows such as those created by Nephrops norvegicus, the Norwegian lobster. They can create mounds and pits on the sediment surface like the Angular crab, Goneplax. 

An Angular crab, which can create deep pits and large mounds around a burrow network.

We photograph the sediment under ultra-violet light, making the luminophore particles fluoresce so they can be easily identified compared to the surrounding sediment by an automatic computer program and the number of luminophore pixels per sediment depth calculated.

An example image of luminophore movement taken under ultra-violet light.  It is easy to see where the luminophores have been moved by species activity. These trails have probably been created by small worms creating burrows which the luminophores have fallen down. This is an easy and effective way to measure species activity in the sediment in the shelf seas and we can relate this activity to nutrient fluxes measured over time.