Monitoring of seagrass by lightweight AUV: A Posidonia oceanica case study surrounding Murter island of Croatia

Abstract

Posidonia oceanica (Neptune Grass) is an endemic species to the Mediterranean Sea. It forms dense and extensive green underwater meadows which provide important ecological functions and services and harbour highly diverse communities; as such it is identified as a priority habitat type for conservation under the EU Habitats Directive (Dir 92/43/CEE). Over the last decades many Posidonia oceanica meadows have disappeared or have been altered. Efficient monitoring is the key of the ecosystem conservation. Monitoring of vast areas covered by Posidonia oceanica is extremely difficult, costly and time consuming and generates pronounced need for new methods and tools. This case study presents potential and promote use of lightweight autonomous underwater vehicles (AUV) with the remote sensing payload as the environmentally non-destructive monitoring method. The study was performed from 2011 to 2013 on the Croatian island Murter during the ”Breaking the Surface” - international interdisciplinary field training of marine robotics and applications. Four AUVs equipped with different payloads were performing the missions in the study area. This paper presents results and analysis of different aspects important for the monitoring such as compliance with the existing monitoring indicators and descriptors used to assess the conservation status of P. oceanica, performance of the AUVs and their sensor sets, cost and time efficiency of the monitoring and geographical-localisation accuracy of the data collected.