Feeding of Calanus finmarchicus on the microplankton assembalge in the Trondheimsfjord

• Main Author: Striberny, Anja
• Format: Thesis
• Language: English
• Published: 2011
• Subjects: Calanus finmarchicus
• Online Access: https://oceanrep.geomar.de/id/eprint/10965/; https://oceanrep.geomar.de/id/eprint/10965/1/Dipl.%202011%20Striberny,A.pdf; https://oceanrep.geomar.de/id/eprint/10965/2/Dipl.%202011%20Striberny,A_Anhang.7z

With the onset of the phytoplankton spring bloom, individuals of Calanus finmarchicus ascent from the deep layers of the oceans and fjords to the surface layers to face good nutritional conditions for molting and reproduction. During spring 2010 the feeding behavior of Calanus finmarchicus was studied in incubation experiments with natural sea water sampled during spring bloom and at post-bloom conditions from the Trondheimsfjord. A gradient of the ciliate concentration was created to investigate the potential for selective feeding behavior of Calanus finmarchicus. Results of microplankton counts showed that Calanus finmarchicus behaved generally omnivorous. During spring bloom conditions, with 200 μg C L-1, the diet consisted mainly of diatoms. However, ciliates were ingested when offered at concentrations >6 μg C L-1. Non-linear regression analysis showed that ingestion rates followed a Holling’s functional response type 3. The selectivity index D indicated that C. finmarchicus positively selected large conic ciliates such as Laboea sp. and Strombidium ´conicum`. Biomass was 20 μg C L-1 during post-bloom conditions. Ingestion rate of ´conic ciliates >35 μm` showed a linear relation to the abundance of ´conic ciliates >35 μm` in the environment. This corresponds to a functional response type 1. However, due to the low total biomass a satiation of the ingestion rate was not reached. During post-bloom conditions ciliates were positively selected, selectivity indices indicated a negative selection of diatoms though. Ingestion rates were correlated with both relative environmental contribution, and absolute values for the biomass of the prey offered. It was shown that feeding behavior of C. finmarchicus is influenced by the biomass of ciliates. The relative fraction of ciliates in the available food seems to be irrelevant for the feeding behavior.