Trophic ecology of Calanoides acutus in Gerlache Strait and Bellingshausen Sea waters (Antarctica, December 2002)

We measured ingestion rates of Calanoides acutus on different microbial components of the Gerlache Strait (GE) and Bellingshausen Sea (BE) waters during December 2002. At the time of the study the abundance of both zooplankton (42–133 ind m⁻³) and phytoplankton (0.76–1.5 µg chlorophyll a l⁻¹) were low, indicating that the spring phytoplankton bloom was still not fully developed. C. acutus showed high clearance rates along the study (up to 432 ml ind⁻¹ day⁻¹), selecting for large motile organisms such as ciliates and the dinoflagellate Gyrodinium spp., although their feeding impact was always <0.1% of the standing stock of any of their prey. The total daily rations were low (∼2% body carbon per day), mostly the result of phytoplankton consumption (except for station GE3 in which heterotrophic flagellates contributed to 73% of the diet), and barely enough to cover metabolic demands. Based on the relationship between oxygen (carbon) consumption and ammonia excretion (considered as indicative of the metabolic substrate) it seems that standard metabolic demands were supplied, apart from the diet, by the use of their own non-structural proteins, whereas the remaining reserve-lipids were used to produce eggs.