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

Abstract

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. Nøgdirnar av protozooplankton vóru sum heild lágar, men vístu somu gongd sum plantuplankton. Tann stóri kopepodurin Calanus finmarchicus myndaði í stóran mun nøgdirnar av djóraplankton alt tíðarskeiðið. Av teimum smærri kopepodunum var Pseudocalanus spp. at finna í lutfalsliga stórum nøgdum í tíðarskeiðinum undan várblómingini, meðan Acartia longiremis 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 midbloom 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 prebloom (1.4 mgC m-3). The large oceanic copepod Calanus finmarchicus dominated the copepod biomass with more than ¾ during both periods. Pseudocalanus spp. dominated small neritic copepods during prebloom 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 high. Our results suggested that grazing by the protozooplankton during pre-bloom was negligible.