Use of Posidonia oceanica as a bioindicator of ecological status for Maltese coastal waters

Abstract

Data on Posidonia oceanica attributes from Maltese Coastal waters are available from a number of research studies and environmental monitoring programmes. As part of Malta’s obligations for implement- ing the European Union’s Water Framework Directive, the Malta Environment and Planning Authority participated in an intercalibration exercise, involving Mediterranean countries that are also EU member states, aimed at ensuring comparability of different methods for the classification of coastal waters using P. oceanica as bioindicator. Data on P. oceanica attributes (shoot area, shoot biomass and shoot density), collected during the period 1999 to 2004 from 19 sites in Malta and Gozo, were analysed using Analysis of Variance and Principal Component Analysis to identify differences in values of seagrass attributes between the different sites surveyed. The output from the statistical analyses was used to derive values of the Eco- logical Quality Ratio (EQR) for the five status classes (high, good, moderate, poor or bad). Of the 19 sites considered, 2 sites were classified as having ‘high’ status, 14 sites had ‘good’ status, 2 sites had ‘moder- ate’ status, and 1 site had ‘poor’ status. None of the sites were classified as having ‘bad’ status; however, this was attributed to the lack of P. oceanica data from localities that represented highly degraded coastal areas. The results obtained are discussed in the light of knowledge of the environmental characteristics of the sites surveyed, and recommendations for development of a national method for assessing and classifying the ecological status Maltese coastal water, based on a larger data set and inclusion of additional seagrass descriptors, are proposed.