Seaweed LAI comparison between 2012 and 2021:
The LAI was compared between 2012 and 2021 and across the species and
groups at relevant depth levels. Figure 4 illustrates the change in mean
LAI between the two years and statistical results of the separate
two-factorial ANOVAs are given in Table 2. Overall there was no
significant interactive effect of time x depth in any of the
investigated species or groups and the factor time was only significant
for ‘Digitate Kelps’. However, all species and groups exhibited
significant differences between depth levels except for Saccharina
latissima (2.5 – 5m) and ‘Other Phaephyceae’(5 - 15m). Detailed LAI
data of species and groups in 2012 and 2021 are given in Appendix 5.
Data from 2012 were sampled in 0.25m² frames and extrapolated to 1m².
Overall seaweed LAI (2.5 – 15m) changed significantly along the depth
gradient (p < 0.0001) and time integrated overall
seaweed LAI was maximal at 2.5m (LAI=9) followed by a gradual decrease
of 60%, 82% and 85% at 5m (LAI=3.6), 10m (LAI=1.6) and 15m (LAI=1.4),
respectively (2.5m > (5m = 10m = 15m), p <
0.002, Tukey test).
Similar to the LAI of all seaweeds, LAI of all kelps (2.5 – 5m)
exhibited a significant change with depth (p = 0.009) and the
time integrated maximal kelp LAI of 9 at 2.5m and was significantly 2.6
fold higher compared to 5m (LAI=3.4) (p = 0.009, Tukey test).
Interestingly, LAI of ‘Digitate Kelps’ (2.5 – 5m) was the only group
which changed significantly over time (p = 0.018) as well as with
depth (p = 0.004). Depth integrated LAI of ‘Digitate Kelps’ was
significantly 3.4 fold higher in 2012 (LAI=5.3) compared to 2021
(LAI=1.6) (p = 0.018, Tukey test). Time integrated ‘Digitate
Kelps’ LAI was significantly 84% lower at 5m (LAI=0.9) compared to 2.5m
(LAI=5.9) (p < 0.004, Tukey test).
Understory seaweed LAI (5 – 15m) changed significantly along the depth
transect (p = 0.046), although Tukey test did not reveal
significant differences between depth levels.
As Rhodophyta (5 - 15m) contributed most to the understory LAI, this
group exhibited similar responses and changed significantly with depth
(p = 0.025). Time integrated Rhodophyta LAI had its maximum at
15m (LAI=1.3) which was 1.2 fold higher than at 10m (LAI=1.1) and
significantly 14.7 fold higher compared to 5m (LAI=0.9) ((15m = 10m)
> (10m = 5m), p = 0.03, Tukey test).