Those floating materials in the northern Adriatic Sea: Observations from satellites

In August 2024, surface aggregations of unknown materials were captured in NOAA's OCView quick look medium-resolution satellite images over the northern Adriatic Sea (NAS), posing the question of whether these images features are caused by surface accumulation of mucilage (also called “sea snot”), red Noctiluca scintillans (RNS), or marine litter. All have been reported before in the NAS, which have caused various issues to fisheries and tourism. While the current effort in monitoring of the region is through monthly in situ sampling, inspired by these quick look satellite images, this study aims to provide a synoptic view of the various floating materials using satellite imagery between 1972 and 2024 through spectral reflectance analysis. Large-scale mucilage features were found during summer in a total of 10 years, from 1988 to 2024. RNS features were detected during spring, with the earliest event captured in 1980 and subsequent events in 1989 and 1998. Since 1998, 12 RNS events have been observed, with surface areas ranging from a few km² (1998 and 2014) to most of the NAS (2001, 2012 and 2021). Similarly, durations of the RNS events ranged from one day to three months. Both mucilage and RNS were found in the western part of the NAS, near the River Po delta. In addition, pollen was also observed in the eastern NAS and near the Kvarner Islands, occurring during May and with a recent increasing trend. The co-occurring environmental factors have also been analyzed and explored to determine what could possibly lead to these large events, but without positive findings.