Macroalgae and phytoplankton as indicators of ... - Naturstyrelsen

We assumed that mean values from the various algal sites would represent
the algae of a given coastal area and that the centrally located water
chemistry site would represent the physical conditions and water chemistry
of the same coastal area in spite of some distance between macroalgal
and water chemistry sites.
Water chemistry data were collected by the Danish counties and stored
in NERI's database. Sampling and chemical analysis were performed according
to common guidelines (Andersen et al. 2004) and typically represented
a sampling frequency between weekly and monthly sampling.
3.3.4 Statistical analyses of algal variables
Algal model
We focused the analysis exclusively on algae from the depth range
where disturbance was no longer a major controlling factor for cover (see
Figure 3.2). The coastward end of this depth range was estimated as the
water depth with highest algal cover using non-parametric adjustment
(LOESS, Cleveland 1979). This adjustment was made separately for each
area and showed that the areas could be categorised in weakly exposed
areas where maximum cover was located at water depths of ~1 m, moderately
exposed areas with maximum cover at water depths of ~3 m and
highly exposed areas with maximum cover at water depths of ~5 m (Carstensen
et al. 2005). As a consequence, we restricted the analysis to water
depths >1 m in weakly exposed areas, >3 m in moderately exposed areas
and >5 m in highly exposed areas. Only few (122) observations represented
water depths >13 m at 6 specific localities (Bornholm West and
East, North of Zealand, Hesselø and Little Belt, Northern Belt Sea) and
we therefore restricted the analysis to water depths