## 4 Discussion  
In this paper, we presented results from the GLIDER project in which two surface and one subsurface vehicle were deployed to collect ecological and environmental data throughout the LoVe region, from March to September 2018. In these months, the gliders recorded data during a period of increased biological activity starting prior to the onset of the spring phytoplankton bloom, zooplankton overwintering ascendance and reproduction, and cetacean migrations. Previously, four operational factors were identified as limiting the use of ocean observatories in ecological and fisheries applications: \"(1) limited spatial coverage, (2) limited integration of multiple types of technologies, (3) limitations in the experimental design for in situ studies, and (4) potential unpredicted bias in monitoring outcomes due to the infrastructure's presence and functioning footprint\" [29]. The results presented here demonstrate that gliders can be effectively used as noninvasive ocean observatories for ecosystem monitoring and as research platforms expanding spatial coverage over a wide spatiotemporal scale while integrating multiple types of sensors able to record environmental and biological variables. Gliders thus add to the toolkit of long-term remote noninvasive devices tested in the Norwegian Arctic (e.g., [12; 14; 68]). Traditionally, autonomous vehicles have mainly been used for collecting physical and chemical data from the oceans. Direct observations of multiple trophic levels have been lacking partly due to the size and power consumption of older scientific echo sounders hampering the deployment onboard autonomous vehicles. The small echo sounders deployed in this project, however, allowed for data collection of zooplankton densities and distribution over the whole deployment period, ensuring detection of the organisms in an undisturbed state. The Sailbuoy survey reliably recorded data over a large spatiotemporal scale and thus provided new insights into plankton distribution patterns and behavior that would not have been possible to observe using traditional ship-based instrumentation alone due to among other issues, the duration and costs of research cruises collecting data daily, over a period of months. Furthermore, while hull-mounted echo sounders generally fail to provide data from the upper 5-20 m of the water column due to strong acoustic reflections from the surface and the ship's draft that obscures the near-surface region [69], the echo sounder on the Sailbuoy recorded zooplankton densities at shallow depths (2-10 m depth) with little to no negative effects due to mechanical noise [49]. This is because transducers were mounted at a deeper water depth on a surface vessel as compared to gliders. Nevertheless,  
Figure 9: Temperature–salinity diagrams (T-S) comparing observations collected by the gliders (**left panel**), the NorShelf-2.4 km model (DA, **central panel**), and the NorKyst-800m model (**right panel**). the quality of the acoustic records in the upper layers did vary with weather conditions as bubble entrainment during periods of strong wind and high wave action disturbed the signal mainly in the upper four meters, but on occasions even down to 25 m. In addition, the acoustic data provided by the Sailbuoy were recorded without introducing light pollution. Recently, it was shown that biological surveys performed in the dark by illuminated ships, may introduce biases on biological sampling, bioacoustic surveys, and possibly stock assessments of commercial and non-commercial species, due to among others, disruption of species diel vertical migration and strong light-escape responses [70; 71; 72]. This becomes especially problematic in the Arctic polar night, characterized by low irradiance levels day and night. The glider echo sounder survey aimed at mapping zooplankton densities in the uppermost 50 m of the water column by employing 70 kHz (ES70-18 CD) and 333 kHz (ES333-7 CDK) center frequency transducers.