Lower depth distribution of kelp and kelp-like species over
time
A comparison of semi-quantitative data on lower depth distribution and
abundances of biomass dominant brown algae species over time is
illustrated in Figure 5. An overall upward shift in lower depth
distribution limit and a noticeable decrease in species abundance since
1996/98 is evident for all investigated species (A. esculenta ,
‘Digitate Kelps’, S. latissima , Saccorhiza dermatodea ,Desmarestia spp.). This change is especially prominent in
‘Digitate Kelps’ and S. latissima . The lower distribution limit
of ‘Digitate Kelps’ decreased severely by 10m over time from 15m in
1996/98 over 10m in 2014 to 5m in 2021. Similarly, the recorded depth
for lowest occurring S. latissima specimens decreased by 7m over
time from 16m (1996/98) over 14m (2014) to 9m (2021). For both taxa the
shift in abundance which was already observed between the
1st and 2nd study continued in 2021
and these species were not classified as dominant or sub-dominant any
more.
In contrast to the other two kelp species, the lower depth distribution
limit of A. esculenta remained relatively unchanged and varied
between 15m (1996/98), 18m (2014) and 13m (2021). However, also A.
esculenta abundance decreased throughout the investigated time points
as the species was sub-dominant at 12m in 1996/98 while this abundance
class moved upwards to 8m and 9m in 2014 and 2021, respectively.
Similar to A. esculenta , the lowest distribution limits ofSaccorhiza dermatodea and Desmarestia spp. only changed
slightly over time. However, despite their stability in depth
distribution, these species exhibited a decrease in abundance, which was
especially strong in Desmarestia spp. While Desmarestiaspp. had been mostly dominant to sub-dominant in 1996/98 between 20m and
9m, these abundance classes were not recorded at any depth level in
2021.