Náttúrufræðingurinn - 2014, Side 16

Náttúrufræðingurinn
16
Þakkir
Við færum starfsmönnum Hafrannsóknastofnunar, til sjós og lands, bestu
þakkir fyrir mikilsvert framlag þeirra til þessa verkefnis við margvísleg
úrlausnarefni. Einnig þökkum við Ólafi S. Ástþórssyni og tveimur ónafn-
greindum ritrýnum sem lásu handritið yfir og bentu á margt sem betur
mátti fara.
Heimildir
1. Swift, J.H. & Aagaard, K. 1981. Seasonal transitions and water mass
formation in the Iceland and Greenland Seas. Deep-Sea Research 28.
1107–1129.
2. Buch, E., Svend-Aage Malmberg & Stefán S. Kristmannsson 1996. Arctic
Ocean deep water masses in the western Iceland Sea. Journal of Geo-
physical Research 101 (C5). 11965–11973.
3. Rudels, B., Fahrbach, E., Meincke, J., Budéus, G. & Eriksson, P. 2002. The
East Greenland Current and its contribution to the Denmark Strait over-
flow. ICES Journal of Marine Science 59. 133–1154.
4. Blindheim, J. & Østerhus, S. 2005. The Nordic Seas, main oceanographic
features. Bls. 11–38 í: The Nordic seas: an integrated perspective (ritstj.
Drange, H., Dokken, T., Furevik, T., Gerdes, R. & Berger, W.). American
Geophysical Union, Washington DC.
5. Jeansson, E., Jutterström, E.S., Rudels, B., Andersson, L.G., Olsson, K.A.,
Jones, E.P., Smethie, Jr. W.M. & Swift, J.H. 2008. Sources to the East
Greenland Current and its contribution to the Denmark Strait Overflow.
Progress in Oceanography 78. 12–28.
6. Våge, K., Pickart, R.S., Spall, M.A., Héðinn Valdimarsson, Steingrímur
Jónsson, Torres, D., Østerhus, S. & Eldevik, T. 2011. Significant role of the
North Icelandic jet in the formation of Denmark Strait overflow water.
Nature Geoscience 4. 723–727. doi:10.1038/ngeo1234
7. Jón Ólafsson 2003. Winter mixed layer nutrients in the Irminger and
Iceland Seas, 1990–2000. ICES Journal of Marine Science 219. 329–332.
8. Ólafur S. Ástþórsson & Ástþór Gíslason 1995. Long-term changes in zoo-
plankton biomass in Icelandic waters in spring. ICES Journal of Marine
Science 52. 657–668.
9. Ástþór Gíslason & Ólafur S. Ástþórsson 1998. Seasonal variations in bio-
mass, abundance and composition of zooplankton in the subarctic waters
north of Iceland. Polar Biology 20. 85–94.
10. Hjálmar Vilhjálmsson 1994. The Icelandic capelin stock. Capelin
(Mallotus villosus) in the Iceland-East Greenland-Jan Mayen ecosystem.
Rit Fiskideildar 13. 281 bls.
11. Ásta Guðmundsdóttir & Hjálmar Vilhjálmsson 2002. Predicting total
allowable catches for Icelandic capelin 1978–2001. ICES Journal of
Marine Science 59. 1105–1115.
12. Hjálmar Vilhjálmsson 2002. Capelin (Mallotus villosus) in the Iceland-
East Greenland-Jan Mayen ecosystem. ICES Journal of Marine Science
59. 870–883.
13. Anon 2011. Þættir úr vistfræði sjávar 2010. Hafrannsóknir nr. 158. 80 bls.
14. Ólafur K. Pálsson, Héðinn Valdimarsson, Sólveig R. Ólafsdóttir, Haf-
steinn G. Guðfinnsson, Ástþór Gíslason, Hildur Pétursdóttir, Konráð
Þórisson, Björn Gunnarsson, Sveinn Sveinbjörnsson, Agnar M. Sig-
urðsson, Agnes Eydal, Björn Sigurðarson, Friðrik Guðmundsson, Jón
Ingvar Jónsson, Kristín Valsdóttir, Magnús Danielsen, Ragnhildur
Guðmundsdóttir, Ragnhildur Ólafsdóttir, Stefán H. Brynjólfsson &
Teresa Silva 2012. Leiðangrar og gagnasöfnun í Íslandshafi 2006–2008.
Hafrannsóknir nr. 164. 5–13.
15. Héðinn Valdimarsson & Steingrímur Jónsson 2012. Ástand sjávar og
straumar í Íslandshafi. Hafrannsóknir nr. 164. 14–29.
16. Sólveig R. Ólafsdóttir 2012. Svæðatengdur styrkur og nýting næringar-
efna í Íslandshafi. Hafrannsóknir nr. 164. 30–44.
17. Strickland, J.D.H. & Parsons, T.R. 1972. A practical handbook of seawater
analysis. Fisheries Research Board of Canada 167. 310 bls.
Í því efni koma einkum til greina
fyrstu mánuðirnir í lífsögu loðnu,
þ.e. tímaskeið hrygningar, klaks
og lirfureks á landgrunni Íslands,
með tengslum við hlýnun sjávar,
breytingar á straumum og inn-
streymi í Íslandshaf.
Summary
Ecosystem structure in the Iceland
Sea and recent changes to the capelin
(Mallotus villosus) population
The objective of the Iceland Sea
Ecosystem Project was to analyse princi-
pal ecosystem patterns, with an empha-
sis on the life history of capelin. Ten sur-
veys were conducted for this purpose
between 2006 and 2008, and hydro-
graphic data from 1970 to 2011 were an-
alysed. Long-term temporal patterns
indicate an increase in the temperature
of surface and intermediate waters dur-
ing recent years in the Iceland Sea. The
phytoplankton consisted mainly of dia-
toms in spring, whereas flagellates and
dinoflagellates prevailed during spring
until late summer. Zooplankton and fish
were dominated by a few species. In late
summer, the trophic position of animals
in the pelagic foodweb ranged from
trophic levels 2–2.4 (Calanus finmarchcius,
C. hyperboreus, Metridia longa) to 3.6
(capeling (Mallotus villosus) and blue
whiting (Micromesistius poutassou)), ex-
cluding birds and mammals. Calanus
spp. proved to be an important diet
component of most of the studied spe-
cies. Increased importance of the Arctic
amphipod Themisto libellula in the diet of
adult capelin in Iceland Sea in August
2007 and 2008 could be explained by the
westward displacement of capelin.
Trends in nutrients and primary produc-
tion showed a clear seasonal pattern
with a spring bloom in late May, fol-
lowed by a peak in secondary produc-
tion in July/August. The spatial struc-
ture of the lower ecosystem levels in
summer was stable across the three
years, determined mainly by the spatial
structure of the water masses, i.e. the
Atlantic, polar and Arctic water.
Relations between the mesozooplank-
ton community and environmental pa-
rameters in late summer were analysed
using redundancy analysis (RDA). In
total, 29% of mesozooplankton variabil-
ity could be explained by five variables
(salinity, year 2008, bottom depth, tem-
perature and chlorophyll a). Three main
zooplankton communities could be
identified, an Atlantic community in the
eastern part with Calanus finmarchicus as
most abundant, an Arctic community at
relatively high latitudes and longitudes
with relatively high numbers of C. hy-
perboreus, and a community with
coastal affinities at lower latitudes with
relatively high numbers of coastal spe-
cies. The pelagic fish fauna consisted
primarily of adult pelagic fish and tran-
sient numbers of larval species. The
spatial pattern of capelin indicated
northward and westward displacement
of 0-group capelin and westward dis-
placement of older capelin in recent
years. It is suggested that these changes
are brought about by a northward and
westward displacement of the polar
front due to a warming of the surface
waters. The annual biomass was esti-
mated at 5.3 million tonnes of phyto-
plankton, ~29 million tonnes of zoo-
plankton, and 1.0 million tonnes of fish.