DISCLOSE is a partnership between TU Delft RUG, NIOZ and the North Sea Foundation.
From the end of October until the first week of November DISCLOSE researcher were on an expedition with the NIOZ research vessel Pelagia in the North Sea. Here you can read the blog which was written by expedition member Danielle de Jong. Read more on the DISCLOSE website.
Blog 6 - Goodbye North Sea. Hello office
Today we have safely arrived back on Texel. The ship is clean. The equipment is unloaded. The data is ready to be analysed. We thank the crew for their hard work and good care.
Hopefully you have enjoyed following our blog. We hope we gave you a good idea of all our activities and what we hope to achieve with them. It definitely was a good cruise (perhaps with exception of the storm) and we managed to get a lot of work done. Now it’s time to return home, and start with the data analysis.
Life aboard is very different from life on land. At home, we don’t have to shower with a constantly tilting floor. We are not bumped out of our beds by a sudden wave. And personally, I will definitely not miss being seasick due to 5 meter waves. However, we will miss all the beautiful North Sea sunrises and sunsets, and we will definitely miss all the good care of the crew. They worked very hard to help us achieve our goals. The deck crew knew how to handle our equipment, and helped us solve unforeseen issues. Every day breakfast was prepared when we got up at 7 and we were treated with an amazing 3-course warm lunch.
We wish Leo, Afrizal and Patrick good luck adjusting back to a normal day-time rhythm. We say goodbye to the crew, and we say goodbye to you – our readers. We are already looking forward to present you the scientific papers that result from all our collected data!
Blog 5 - Be a scientist yourself: quest for sand mason reefs II
Acoustic techniques are used to efficiently study a large area. However, the interpretation of the data can be difficult. Learn to find sand mason reefs yourself in the landscape of the Bruine Bank!
The beauty of the DISCLOSE project is the multidisciplinary approach. The North Sea should be studied on different scales to understand the distribution of benthic fauna. And that’s exactly what we’re doing. We took box cores of 0.07 m2 resulting in a total studied area of about 4.9 m2. We filmed a total area of about 1350 m2. Finally, we tried to map the total area of 50 km2.
If you want to efficiently map a large area, acoustic mapping is the way to go. Basically, these maps are plots of the properties of reflected sound waves. Therefore, you only have direct information about the return speed and intensity of the wave reflection. Proper interpretation of these variables can result in information about the habitat. This is very useful for us, as one of the goals of DISCLOSE is to create comprehensive habitat maps of the North Sea. Within DISCLOSE, Leo tries to improve the interpretation of acoustic data for habitat mapping. To show you how exciting and useful acoustic maps are, I will guide you through interpreting some maps made during this cruise. In the landscape we will try to identify one of the habitats found in the North Sea: sand mason (Sabellaria spinulosa) reefs.
During this cruise we used the multibeam echosounder and side scan sonar (Figure 1). Both systems are based on the concept of sending out sound waves, which are reflected by the seafloor. The time between outgoing and returning waves is measured to calculate water depth. The change in wave intensity is measured to identify the material which reflected the waves. The multibeam is fixed underneath the RV Pelagia and could be used at night without supervision. In contrast, the side scan sonar (Figure 2) needs to be deployed into the water column and must be kept at a constant height (~10 meters) above the seafloor. Therefore, the cable length was constantly adjusted to deal with the irregular seafloor. It meant hard work for Leo, Afrizal and Patrick, who manually controlled the side scan sonar cable (Figure 3).
Blog 4 - Diving with Bruce: the quest for sand mason reefs
Bruce is the name of our camera system designed to film the seafloor. It allows us to directly observe the seafloor and study the distribution of larger animals living on and just above the bottom. We found beautiful tube worm reefs formed by Sabellaria spinulosa!
In the last blog, we explored the sediment using box cores and the SPI camera. With these methods, you study a small area of seafloor in great detail. The opposite is true for acoustic methods in which you study a large area of the seafloor, but with less detail. The acoustic maps show abstract features that are not easily interpreted. For example, it can show an irregularity at the bottom, but you have to make an educated guess about what it could be.
The findings of the above-mentioned methods can be ground-truthed with a camera. By directly observing an area you can study the expected bottom structures, sediment features, and animals living on and just above the seafloor. Is the whole area muddy just as the box core predicted? Or was it a sample of a muddy patch in an area that is mostly sandy? Is the irregularity on the map really a ship wreck, or perhaps a group of large stones?
As proud owners of our camera system Bruce, we took him diving on the Bruine Bank. Bruce has two cameras: a HD video camera for filming, and a photo camera that takes pictures. In all videos and pictures, you can see two laser points. These have a known distance, which later will be used to measure features. Bruce also has eight LED lamps for illumination of the seafloor.
After finding the optimal camera settings during some test runs, we started filming transects at the different box core locations. Each transect is a straight line of 150 meters intersecting with a box core station in the middle. We found that the top of the bank was very sandy, and in the troughs were more shells and stones lying on the bottom.
And we found spectacular life! Striped red mullets (Mullus surmuletus), dragonets (Callionymus sp.), sea stars (Asterias rubens), brittle stars (Ophiuroidea), hermit crabs (Pagurus bernhardus), Sabellaria spinulosa reefs and even a small-spotted dogfish (Scyliorhinus canicula) were present. The top of the sand bank seemed poorer in terms of life (figure 4) compared to the deeper troughs (figure 5).
Sabellaria spinulosa is a species of tube worms that form their own tubes by cementing sand (hence the common name sand mason). The reefs are hard 3D structures, providing a complex habitat in an otherwise flat environment. The elevated structures provide shelter for other animals (Figure 6). When an animal creates a new habitat, like the sand mason, they are called ecosystem engineers. Ecosystem engineers are very important, because they often increase the species richness in an area. The tubes feel quite hard (figure 7), but disintegrate when handled too roughly. Bottom fisheries, which occur regularly at the Bruine Bank, may damage these reefs preventing them to grow into even larger structures. Analysis of all collected imagery will hopefully tell us more about the function of these reefs and the impact of human activities on the biodiversity in the area.
Blog 3 - Why we are spying on crabs
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.
Blog 2 - Storm! What doesn't kill you makes you stronger
We have arrived at the Bruine Bank and started mapping the study area. The coming days we live and work on the research vessel RV Pelagia of the Royal Netherlands Institute of Sea Research (NIOZ). Already, we have been allowed a glance into the lives of North Sea animals. Above water there are various species of gulls, Northern gannets, and we even found a lost sparrow in the bridge of the ship. On and within the seabed we find fish, sea stars, sea urchins, crabs, shellfish, and many worms. In the box cores taken so far, we can see clear differences in sediment type and biodiversity at different locations across the Bruine Bank.
Our goal is to study how natural and human disturbances affect these creatures. In order to do this, we had to face some disturbances ourselves. Leo Koop and Tengku Afrizal are working night shifts, and were up for 26 hours at some point. Also, this weekend there was a storm over the North Sea. Therefore, we were unable to work safely with our heavy and expensive equipment. The 5 meter waves occasionally crashed on deck and some of us (including the author) experienced serious sea sickness.
Luckily, the weather calmed down. Today we have the opportunity to continue our research with renewed motivation and optimism. The plan is to take pictures and videos of the seabed as long as the sea is calm. “What doesn’t kill you makes you stronger” applies to us in this case. Now we study if the same applies for the North Sea communities down below who experience regular disturbances.
Blog 1 - We plan to predict life at the Bruine Bank, and here’s how
DISCLOSE researchers are planning an autumn research cruise, and preparations are in full swing. Next week we’ll set sail to revisit the Bruine Bank and map the area in detail. We will report to you straight from the RV Pelagia. By following this blog, you can see how we work, what we find, and how we use our data to predict life on the sea floor. With this first post, we give you a bit of an introduction on our planned work.
The goal of the DISCLOSE project is to understand the communities living on the bottom of the North Sea. The Bruine Bank is a shallow sandbank in the North Sea flanked by two deeper troughs. The deeper and shallower areas attract different types of life. Therefore, it is quite interesting to study. We already know we might find majestic tubeworm reefs formed by the organism Sabellaria spinulosa (Figure 1).
To determine exactly where we want to go, we first have to make a detailed map of the sea floor. We will do this using acoustic techniques like side scan sonar and the multibeam echosounder. To use this technique, we have to sail over the research area in parallel lines from south to north or vice versa. We will send out sound waves as we go, and count how long the waves take to get back to the ship. Also, we measure backscatter. Backscatter is the change in intensity of the soundwaves due to complex interactions with the seafloor. This gives us detailed information on the depth and the type of sediment around the ship.
Then, we will collect data from three so-called “transects” oriented from south to north in the study area. A transect is basically a straight line through a study area where you collect data. Measuring along a transect is a useful method if you want to detect if communities change along a gradient. As you can see from the map (Figure 2), this means we will study different areas: the deeper troughs (blue) and the sandbank (red). In each area, we will film the sea floor, take a big bucket of sand, and take a sediment profile image. The latter is a picture of what the sand looks like below the surface.
Figure 2: This is the Bruine Bank in the North Sea. The green box is the area we will map in detail using acoustic techniques. The colours show how deep the sea floor is: towards blue is deeper, towards red is shallower. The small purple lines are examples of where we might film the bottom.
We will film at several locations along the transect while sailing in a northern or southern direction. This ensures that the depth will be constant throughout the video. Each video will cover about 200 meters of sea floor. The videos are watched to identify the life crawling about.
The buckets of sand are also called ‘box cores’, and these will preferably be taken at locations we’ve already observed on video. This is because these areas have been ‘ground-truthed’. This means we have already directly observed the sea floor, and can therefore better interpret the data from the box core. The box cores are sieved through to find all the tiny organisms living inside the sediment.
To understand the chemistry of the sediment, we analyse the chemicals from a separate box core. We also look at sediment profile images. A sediment profile image is like digging a hole at the beach, and then looking at the sand sideways. That way you can see if the sand changes colour or if the grains get coarser or finer with depth.
We then compare the life and habitats in all three transects. Back in the office, we will use computer techniques to predict life in each transect. For example, if you tell the computer what the first and second transect look like, it will predict how the third transect may look.
Of course, we know what the third transect looks like, so we can check it against the prediction.
We’ll set sail on Thursday October 26th and we want to write a blog every two to three days. In these blogs we will show you exactly how we work to collect this data and what we find in our samples. We hope you join us at sea!
Rob Witbaard
