To understand how humans might impact life in the North Sea, we first need to understand where animals naturally live and why. Box coring and “SPI”-ing on crabs is part of the study process. A report of a day of sediment sampling.
This photogenic swimming crab (Liocarcinus sp.) was showing off his blue legs to us. Normally, crabs can’t really swim, but his species can use its flattened leg-ends to swim around! We were “SPI”-ing on this crab to study the sediment. A Sediment Profile Image (SPI) shows a cross section of the sediment structure beneath the seafloor. It reveals all types of features that can explain why some animals like to live there, and others don’t. You can see, for example, the sediment texture, different sediment colours that reveal the presence of chemicals like oxygen and iron, and burrows of organisms.
Understanding the habitat preference of fauna is important, because the North Sea has a great variety of habitats. In the immense area stretching between the Netherlands, the United Kingdom and Norway many processes are occurring that form these habitats. For example, there are tidal waves sweeping into the North Sea through the English Channel twice a day. These cause the formation of massive sand banks that provide slopes in a flat landscape. There are also processes on a smaller scale: some places have more food to eat, some places have more stones to live on, etc. All these variables determine where an animal with its own specific adaptations can live.
The Bruine Bank is one of the many large sand banks in the North Sea. The tidal currents and wind-induced waves move over the sand bank and push around the sediment. Therefore, the sediments get sorted by size which results in a variety of sediment types. The top of the bank will be sandy, while the troughs will be muddy with large stones and shells lying on top. For those interested in the methods of how we studied the distribution of animals in the sediment during the last couple of days: below is a step-by-step photo report.