Citizens and satellites: Assessment of phytoplankton dynamics in a NW Mediterranean aquaculture zone

• The MERIS colour hue angle correlates very well with in-situ hyperspectral data.
• MERIS FR data give reliable coverage of the Alfacs bay waters in the Ebro Delta.
• Citizens measure hue colour by discrete colour scales on a smartphone app.
• MERIS images and citizen data complement each other in coverage of the bay.
• Future citizen data on colour can be used for aquaculture and management.

Ocean colour measurements from space are well suited to assess phytoplankton dynamics over broad spatial scales. Closer to the coast however, the quality of these data degrades as a result of the loading of sediments and dissolved matter from terrestrial runoff, the influences of land reflection on atmospheric correction and sea-bottom reflection, which compromise their use in coastal management actions. Recently, the enabling of citizens to provide environmental observations has gained recognition as a way for enhancing the spatio-temporal coverage of satellite observations. In the FP7 funded EU project “Citclops” (Citizens’ observatory for coast and ocean optical monitoring), a smart phone app for the classification of water colour, simplified to 21 hues of the Forel Ule (FU) scale, is developed.In this study we examine two bays in the Ebro Delta (NW Mediterranean) where satellite data, hyperspectral measurements, and observations with the citizen tool for colour comparison were available. FU values and their corresponding novel colorimetric parameter, the hue colour angle, were derived in the bay at 12 stations with the traditional FU scale and one automated in-situ radiometric system at the Alfacs Bay aquaculture site. Both methods complied well during the study course of May–June 2011. These measurements were further compared to data from Full Resolution MERIS (Medium Resolution Imaging Spectrometer) satellite images. The quality of the retrieved hue angle varies over the image. For high-quality sites, MERIS hue colour angles and FU values gave a good estimate of seasonal algal dynamics in the bays over the year 2011, while ground measurements revealed colour changes over short space- and time frames, which are indicative of the fast dynamics of phytoplankton in the area that could not be fully resolved with MERIS data.The use of FU values and hue colour angle of water will allow a simple integration of data from hyperspectral measurements, MERIS multispectral observations and citizens observations with the (Citclops/EyeOnWater) water colour app. Such observational data can be included to local monitoring efforts, and can also foster an increased interest of the general public to local environmental management and governance issues.