Water clarity and color were observed during the RV HEINCKE cruise HE431 (HABCYST, 18.08.2024 - 08.09.2014, Bremerhaven, Germany - Bremerhaven, Germany) using a white Secchi disc with a diameter of 40 cm and a Forel-Ule color scale. The Secchi depth (SD) was recorded as a relative measure of water clarity at each in situ station during day time. At half SD the apparent color of the water above the submerged Secchi disc was determined using the Forel-Ule color scale. A Forel-Ule color scale is a classic tools used to differentiate the percieved color of water based on a scale from 1 (indigo blue) to 21 (cola brown). The measurements were conducted as recommend in literature (Garaba and Zielinski, 2015; Wernand, 2011; Wernand and van der Woerd, 2010).

Chief Scientist of RV HEINCKE cruise HE431: Dr. Uwe John, Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschun, BremerhavenThe HAB research was conducted as part of the IOC/SCOR program on Global Ecology and Oceanography of Harmful Algal Blooms (GEOHAB) within the Core Research Project on HABs in Fjords and Coastal Embayments. The AWI contribution was provided by the HGF Program Earth and Environment under PACES Theme 2 (Coast) Workpackage 3.