Quantifying macro-aggregate distributions using a new index (MAI)

During the last decades, field observations by means of underwater video camera have been carried out in the Northern Adriatic within the framework of several research programs (e.g. ALPE ADRIA, INTERREG I-II, MAT) focusing on mucilage. The typical interpretation of these dataʹs lacked of homogeneity was merely qualitative and moreover the discrete nature of representations failed to be effectively comparable with oceanographic properties. A new Index called the Mucilage Aggregate Index (MAI) is proposed in order to overcome these difficulties. A continuous variable is defined allowing to obtain a weighted sum of different aggregate types and subsequent calculation of a single value for a selected water depth. The feasibility of this new Index is explored within the framework of data acquired during a cruise conducted in September 1997 as part of the Alpe Adria Project (PAA). The vertical and horizontal distributions of this Index were drawn and correlated to oceanographic properties. The new proposed procedure allowed effective representation of cumulative aggregate presence, providing a clear outline of the magnitude of the phenomenon. In addition the maps are useful towards an easy comparison of aggregate patchiness with the evolution in space and time of water masses. Furthermore, a first rough estimate of the scale of the phenomenon suggested an intensification of sampling spatial frequencies and added some information regarding aggregate movement and modification over time.