Fróðskaparrit - 01.01.2005, Page 84

The relative importance of
protozooplankton and copepods as
grazers on phytoplankton during the
1999 spring bloom on the Faroe Shelf
Lutfalsliga ávirkanin av protozooplankton og kopepodum á
várblóming av plantuplankton á landgrunninum í 1999
Høgni H. Debes1, Benni Winding Hansen2 and Per Juel Hansen3
1 Faroese Fisheries Laboratory, Box 3051, FO-IIO Tórshavn, Faroe Islands. Email: hoegnid@frs.fo
2 Roskilde University, Dep. Life Sciences and Chemistry, Box 260, DK-4000 Roskilde, Denmark.
Email: bhansen@virgil.ruc.dk
1 Marine Biological Laboratory, University of Copenhagen, Strandpromenaden 5, DK-3000 Helsingør,
Denmark. Email: PJHansen@zi.ku.dk
Úrtak
Kanningarnar vórðu gjørdar undan várblómingini og í
várblómingini. í tíðarskeiðinum undan várblómingini
var lítið til av plantuplankton (<3 mgC m"3 í miðal),
men í várblómingini vóru nøgdirnar í miðal 201 mg
Cm'3. Nøgdimar av protozooplankton vóru sum heild
lágar, men vístu somu gongd sum plantuplankton.
Tann stóri kopepodurin Calanus finmarchicus mynd-
aði í stóran mun nøgdirnar av djóraplankton alt tíð-
arskeiðið. Av teimum smærri kopepodunum var
Pseudocalanus spp. at finna í lutfalsliga stórum nøgdum
í tíðarskeiðinum undan várblómingini, meðan Acartia
longirenús og Temora longicornis vóru at finna í størri
nøgdum undir várblómingini. Orsakað av gýtingini
hjá djóraplankton sæst ein broyting frá samansetingini
av djóraplankton frá vaksnum kopepodum undan
várblómingini til smærri kopepodittar í várblómingini.
Ávirkanin av protozooplankton á plantuplankton varð
mett til at vera sera lítil alt tíðarskeiðið. Hinvegin,
varð mett, at møguleiki var fyri stórari ávirkan frá
kopepodum á plantuplankton í tíðarskeiðinum undan
várblómingini.
Abstract
The research period was split up in two different
productive periods: a pre-bloom and a mid-bloom
separated by a transition period of 2 weeks. In the
pre-bloom period the biomass of phytoplankton was
low (<3 mgC m'3 on average), but during mid-
bloom the biomass was 201 mgC m'3 on average. The
protozooplankton biomass was only slightly higher
during mid-bloom (3.5 mgC m'3) than during pre-
bloom (1.4 mgC m'3). The large oceanic copepod
Calanus finmarchicus dominated the copepod biomass
with more than 3A during both periods. Pseudocalanus
spp. dominated small neritic copepods during pre-
bloom while Acartia longiremis and Temora longicornis
were more numerous during mid-bloom. As a result of
spawning success a clear shift in development stage
composition towards younger stages was observed from
pre- to mid-bloom. The estimated grazing impact on
the phytoplankton by the protozooplankton and the
copepods was negligible during mid-bloom. However,
during pre-bloom the copepod grazing impact on the
phytoplankton standing stock was potentially liigh. Our
results suggested that grazing by the protozooplankton
during pre-bloom was negligible.
Fróðskaparrit 53. bók 2005: 82-99