Ecological reference conditions and quality states of marine macroalgae sensu Water Framework Directive: An example from the intertidal rocky shores of the Portuguese coastal waters

Under the scope of the Water Framework Directive (WFD, 2000/60/EC), ecological reference conditions and quality states were established for the biological quality element of macroalgae. The work combined both historical and current monitoring data from northern Portuguese coastal waters (Portuguese ‘A5 typology’, matching the European ‘NEA1 typology’). Representative intertidal rocky shore sites were selected to: (1) have a robust variability in macroalgal communities within the water body type and (2) cover a gradient of anthropogenic pressure to understand the communities’ changes due to disturbance. First, a ‘reduced taxa list’ (RTL) was developed by selecting and grouping macroalgal taxa common in the study area, in proportion to the naturally occurring macroalgal taxonomic groups (Chlorophyta, Phaeophyceae – Heterokontophyta and Rhodophyta) and comprising taxa that require a moderate level of taxonomical identification expertise. Second, based on the RTL, the metrics of composition, i.e., species richness; the number and proportion of Chlorophyta, Phaeophyceae and Rhodophyta; the number and proportion of opportunists; ecological status groups (ESG) I, and ESG II; the ratios ESG I/ESG II, the number of opportunists/ESG I and the number of opportunists/ESG II; plus an abundance metric coverage of opportunists were studied to understand their behaviour under different levels of disturbance. The thresholds between the five quality conditions (‘high’, ‘good’, ‘moderate’, ‘poor’ and ‘bad’, similar to those required by the WFD to calculate the ecological quality status) were defined for the above macroalgal metrics in compliance with the WFD. Hence, reference conditions – pristine situations that exist or would exist with no or very minor disturbances from anthropogenic pressures – were established together, since this class of excellent quality is included in the ‘high’ quality condition.