Macroalgae and phytoplankton as indicators of ... - Naturstyrelsen

Figure 3.6 Modelled levels of algal variables as a function of water depth: A: total cover. B: cumulated cover, cumulated cover
of late-successional species and cumulated cover of opportunistic algae, C. fraction of opportunists, D: number of latesuccessional
algal species. Data are from 2001, 2003 and 2005.
Variation along depth gradients
Modelled levels of all tested algal variables differed significantly between
water depths (Table 3.5). As data from the most exposed shallow
depth intervals, having low algal cover were excluded in the data analyses,
the modelled levels of all algal cover variables declined with water
depth. Levels of total cover showed a sigmoid decline with depth (Figure
3.6A), whereas cumulated cover declined exponentially with depth (Figure
3.6B). The fraction of opportunists showed a relative minimum in shallow
water and a maximum at 3-7 m depth (Figure 3.6C). The number of
late-successional species at 1-3 m depth was about twice as high as in
deeper water (Figure 3.6D).
Temporal variation
Differences between years were significant for all algal variables except
for the cumulated cover and the cumulated cover of late successionals.
The average total algal cover was lowest in 2001 and highest in 2003
while 2003 levels were intermediate. Cumulated cover of opportunists
increased from 2001 to 2003 and then remained at the same level in 2005
34