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).