Macroalgal biomass
For the quantitative diving campaign, a main transect was installed in
the sublittoral off Hansneset, marking the vertical gradient between 2.5
and 15m depth below chart datum. Proceeding laterally ±15m from this
main transect, complete
destructive sampling was performed by scientific diving at 2.5, 5, 10
and 15m depth. At each depth horizon the attached macroalgal biomass of
all kelps and understory seaweeds was collected within randomly chosen 1
x 1m quadrats (n = 3). Additional sampling was performed in the
infralittoral fringe level (0m) using 50 x 50cm quadrats (n = 3) and
data was extrapolated to 1m² before analysis. Algae were sampled in net
bags and kept in seawater filled barrels for transport. In the
laboratory, biomass samples were stored in flow through seawater tanks
before further processing.
Algal material was sorted to species level, blotted dry with cotton
towels and fresh weight (FW) as well as dry weight (DW) was determined
(Mettler Toledo PB3002_S/FACT Delta Range, Max 600g/3100g, d =
0.01g/0.1g, Germany). Adult kelps were separated into holdfast, stipe
and blade prior to weight measurements. Juvenile individuals with a
stipe length ≤5cm were weighed as whole individuals. Dry weight of
species was recorded after drying over night at 70°C in a drying oven
(Termaks, Series TS9000, Model TS9135). Due to logistical reasons, the
DW could not be documented for every adult kelp specimen. For adult kelp
DW representatives of each species and stipe length category were dried
depending on their occurrence to represent the properties of the local
kelps as realistic as possible (Alaria esculenta : n = 8 (5–15cm,
31–50cm, >80cm); n = 10 (16–30cm), n = 9 (51–80cm);
‘Digitate Kelps’: n = 9 (5–15cm), n = 10 (16–30cm, 51–80cm), n = 14
(31–50cm), n = 3 (>80cm); Saccharina latissima : n =
3 (5–15cm), n = 8 (51–80cm, >80cm)). The resulting
regression formulas between FW and DW expressed high determination
coefficients (majority R² > 0.9) and were used to calculate
the DW of the remaining specimens (Appendix 1). All adult kelp
individuals ≥ 2 years collected from 2.5m and 5m depth were analyzed for
holdfast, blade and stipe DW as well as blade:stipe DW ratio.
Biomass dominant species were organized in two categories as well as six
groups (Kelps: A. esculenta , ‘Digitate Kelps’, S.
latissima ; Understory seaweeds: ‘Other Phaeophyceae’, Rhodophyta,
Chlorophyta) and the historical datasets were reanalyzed accordingly for
comparison. The following species are classified in the group ‘Other
Phaeophyceae’ (brown algae): Battersia arctica , Chorda
filum , Chordaria flagelliformis , Desmarestia aculeata ,Desmarestia viridis , Dictyosiphon foeniculaceus ,Ectocarpus sp., Fucus distichus , Halosiphon
tomentosus , Haplospora globosa , Laminaria solidungula ,
young Laminaria spp., Pylaiella sp., Sacchorhiza
dermatodea , Scytosiphon sp., Sphacelaria plumosa . In the
group of Rhodophyta (red algae) the following species are pooled:Coccotylus truncatus , Cystoclonium purpureum ,Devaleraea ramentacea , Euthora cristata , Odonthalia
dentata , Palmaria palmata , Phycodrys rubens ,Plocamium cartilagineum , Porphyra sp./Pyropia sp.,Ptilota sp., Rhodomela sp., Turnerella penneyi .
Some specimens of Devaleraea ramentacea were densely covered by
brown Elachista fucicola epiphytes which could not be removed but
were considered negligible relative to host biomass. The group
Chlorophyta (green algae) contains the following species:Acrosiphonia spp., Chaetomorpha melagonium ,Kornmannia leptoderma , Spongomorpha spp., Ulva sp.
Calcified coralline algae were present along the depth transect but were
excluded from identification as in the previous studies.