Ecologist Rob Witbaard studies the seafloor ecosystems of the North Sea. ‘These include the structure of the seafloor, the animals that live in it and the processes it is influenced by. I try to understand how the system works; how species influence each other, but also what the influences are of human activities, such as commercial fishing that disrupts the seabed, large-scale construction of wind parks and beach nourishments. All of these have an effect on the seafloor and seafloor life.’
‘I use the ocean quahog to investigate the influence of the climate on the seafloor ecosystem. The ocean quahog is a shellfish that can become extremely old. Ages exceeding 100 years are quite normal. The oldest known specimen was 507 years old and was found by English colleagues off the coast of Iceland. Just like a tree, an ocean quahog has growth rings. The width and chemical composition of these growth rings allow you to look back in time. In my work, it is important to understand aspects such as the role of temperature and food supply on the growth of the ocean quahog.’
‘Between 2014 and 2018, with a team of international colleagues, we followed sixteen different ocean quahogs over a period of five years by measuring every minute how wide their valves were opened as measure for their feeding activity. We used an instrument developed by NIOZ. We subsequently analysed the data containing more than 40 million measurements to examine which factor, food or temperature, is the most important for the ocean quahog’s activity.’
‘The ocean quahog occurs in all temperate shelf seas of the North Atlantic Ocean, as long as the water temperature remains between 0°C and 16°C. It is a filter feeder: it filters food particles directly out of the water column. This makes the ocean quahog an attractive research species. Examining the growth lines of the shell provides indirect insight into the processes in the water column that determine algal production, such as ocean currents, weather conditions and climate. Its potentially extremely high age makes the ocean quahog an ideal model to investigate the seafloor ecosystem in the broader sense.’Read more +
I was trained as a limnologist at the University of Amsterdam between 1982 and 1988. During that study I became involved in work at the open North Sea and found this so fascinating that "workwise", I never left the open Sea. The challenge of sampling at unknown places and the technological challenges connected to in-situ measurements hooked me to this kind of research. Up to now I have worked from coastal subtidal areas to full oceanic depths. The emphasis of the work lies mainly in the processes affecting and structuring the benthic communities and experimental autecological studies. In respect to the latter I have special interests in the technological challenges related to in situ experimentation.
I started with a study on the effects of bioturbation by the burrowing mud shrimp Callianassa subterranea . A common species in the muddy bottoms of the central North Sea. I managed to make a quantification of burrow volume and surface area on basis of resin casts of the burrows.
Later I got involved in the age determination and longevity of bivalves with special emphasis on the ocean quahog (Arctica islandica) which resulted in a Ph.D titled "Tree of the Sea". It explored the use of internal shell growth lines as means to reconstruct marine environmental/climatological change and was the first published long time series (>100 years) based on the growth lines of a bivalve. Various other applications of the growth lines have been demonstrated among which the reconstruction of fishing intensity on basis of scars in shells.
The study generated awareness about the vulnerability of large long living molluscs and their use as environmental health indicators for benthic ecosystems. Within OSPAR and the EU water frame work, ocean quahogs (Arctica islandica) are nowadays seen as an important indicator species for sea floor integrity.
Since my Ph.D I kept on working on the ecology of the ocean quahog. At the moment I am doing an behavioural study in northern Norway. With a so called "Valve-Gape-Monitor". Withinf the Marie Curie Trainings Network (Aramacc) the filtration response of 16 individuals at a minute resolution since february 2014 is followed. This study gives insight in the seasonality and the important environmental factors which control the behavior.
Besides work on the growth of bivalves have I been involved in various EU "deep - sea" projects, measuring in situ fluxes and oxygen consumption up to depths of 4800 meter at the Porcupine abyssal plain. Recently I participated in two cruises, one to the Black Sea and one to the Baltic. Last summer we used the equipment in the Whithard Canyon south of Ireland. The in situ lander technique is also used in shallower water such as the North Sea where the technique was used to study the ecosystem effects of beamtrawling versus puls-wing trawling in June 2017.