Grazing pressure of the calanoid copepod Temora longicornis on a Phaeocystis dominated spring bloom in a Dutch tidal inlet

Abstract

Between 30 March and 1 1 May 1990, total copepod abundance and the abundance. b ~o m a s s and gut fluorescence of Temora longlcornls were determined and related to the abundance and succession of phytoplankton development in a Dutch tidal inlet Gut plgment values were h ~g h e s t In females and lowest In young copepodites, but weight-spec~f~c pigment concentrations were about slrnilar Pigment levels measured In the guts were relatively high at the beginning and end of the penod of investigation when diatoms d o m ~n a t e d the phytoplankton community, dnd low d u n n g the Phaeocystls d o m ~n a t e d period, when ambient chlorophyll concentrations were h ~g h e s t For the latter period, calculated ingestion rates In T longlcornls were low and estimated dally consumption amounted to less than 1 % of the phytoplankton standing stock, s u g g e s w g a negl~gible grazlng Impact on the development of the Phaeoc)/stls bloom In splte of the low grazrng on phytoplankton. T long]corms biomass increased by one older of magnitude The discrepancy between low giazlng pressuie and copepod development is explained by assumlng that T long~cornls scvltched to heterotrophic food a bloom of ciliates present during the Phaeocystls dominated period