Temporal shift in biomass and production of macrozoobenthos in the macroalgal belt at Hansneset, Kongsfjorden, after 15 years
Résumé
In Arctic macroalgal belt ecosystems, macrozoobenthic
production is thought to be an important link
between primary production and higher trophic levels.
Macrozoobenthic biomass and secondary production were
studied along transects (2.5–15 m depth) in the macroalgal
belt at Hansneset in Kongsfjorden, Svalbard, from 2012 to
2013. At 2.5 m, the standing stock reached its maxima of
174.8 ± 54.4 g ash-free dry weight per 1 m2, while density
(4341 ind. m-2 ± 1127 95 % CI) and production
(7.0 g C m-2 y-1 ± 2.8 95 % CI) were highest at 5 m
water depth in 2012/13. Compared to a study from
1996/98, this re-sampling indicated a drastic change in the
depth distribution of macrozoobenthic biomass and secondary
production at Hansneset. While both biomass and
secondary production increased with water depth in
1996/98, this pattern was inversed in 2012/13 owing to a
tenfold increase in biomass and secondary production in
the upper most sublittoral (2.5–5 m). Variability of
macrozoobenthic biomass and secondary production corresponded
to differences in the physical environment and
macroalgal vegetation along the depth gradient. In the last
decade, the number of ice-free days per year increased
probably due to Arctic warming. As a result, shallow rocky
habitats (2.5–5 m) are less affected by ice scouring,
thereby opening new space for colonisation by benthic
fauna. However, faunal secondary production was low
compared to macroalgal primary production, indicating a
considerable export of most of the algal production from
the shallow habitats to the adjacent areas.