MARINFORSK-Marine ressurser og miljø

The main objective of the Sea Patches project was to determine the physical and biological mechanisms leading to the formation of zooplankton swarms. In the project we have found a new way of locating plankton swarms, using remote sensing from satellite. This gives us a significantly better starting point for understanding swarm formation, as we can now collect data on a much larger scale and over a much longer time than has been possible so far, with collection from research vessels. For zooplankton research, this is to be regarded as a major step forward that has already changed our view of the plankton's ecology. Also within ocean color remote sensing, these results have opened up many new research questions, mainly related to the ability to see larger particles than previously assumed from satellite. To understand the mechanisms behind swarm formation, we have developed an experiment in which we measured the vertical movement of plankton. These results were then fed into an advanced 3D model of ocean currents (FVCOM) and the first model runs show that the formation of plankton patches depends on both the movement of plankton and the patterns of the ocean currents. In the project, we also looked at the stock size of overwintering Calanus finmarchicus, and found that the stock increases as a delayed response to climatic effects in the North Atlantic, which also affects the herring stock. The project has significantly expanded our understanding of plankton patch formation. At the same time, we have found a new technological method that will make it easier to increase our understanding of the plankton's ecology further, and statistical methods for predicting stock fluctuations in Calanus finmarchicus.

Thanks to the collaborative effort during field work, experimentally and modelling we were able to verify our hypothesis that remote sensing of copepods is possible and greatly enhanced our understanding of zooplankton patch formation. Based on our results it might be possible to obtain numerical abundances of copepods from ocean colour remote sensing in the future. Our combined results will decrease the uncertainty in stock size estimates of harvested copepods and we might also become able to forecast stock size based on large scale climatic forcing. For the ocean colour remote sensing community our results strongly advise a major shift in thinking, large coloured particles are likely to contribute strongly to ocean color signals (absorption and reflection), despite those particles being relatively sparsely distributed (compared to phytoplankton).

The red feed Calanus finmarchicus is a key species in the North Atlantic that transfers primary production to commercially exploited fish species and to marine mammals and seabirds. Recently the Norwegian ministry released a management plan for this copepod based on a stock size of 33 million tons. However, stock size estimates are highly uncertain due to the challenges of sampling a marine species that is patchily distributed over a large geographical area. Recent observations show a high degree of patchiness in the red feed C. finmarchcius, but mechanisms for patch formation in the open ocean are poorly understood and remain a central issue in marine ecology. We thus propose an interdisciplinary project that will locate patches, and delineate physical and behavioural mechanisms responsible for zooplankton patch formation in the ocean. Understanding the extent of patchiness in the distribution of species is of crucial importance when sampling to determine the stock size, and is also transferable to new technologies for revolutionizing harvesting methods for a sustainable management of marine resources. Our approach is: 1) to locate patches of C. finmarchicus in summer based on proven, state-of-the-art methods (laser optical plankton counter, video plankton recorder, fish acoustics) and on novel technology (hyperspectral RAMSES radiometers) that will explore the optical contribution of C. finmarchicus to reflectance signals from satellite, 2) to analyse zooplankton patch structure in detail in order to provide the basic data necessary for stock size estimations, and 3) to delineate physical and biological mechanisms of zooplankton patch formation based on a combination of experiments and physical-biogeochemical behaviour models. Taking such an innovative approach based on contemporary instruments and models we will provide the new fundamental knowledge necessary to develop robust and well-founded models of stock-size estimates of an increasingly harvested species.