Feeding of Clausocalanids (Calanoida, Copepoda) on naturally occurring particles in the northern Gulf of Aqaba (Red Sea)

A total of 12 feeding experiments were conducted in the northern Gulf of Aqaba during spring (March/April) and autumn (September/October) 2002 at the Marine Science Station (MSS) in Aqaba. Females of three species of clausocalanids were selected: Clausocalanus farrani, C. furcatus and Ctenocalanus vanus. Natural occurring particle (NOP) larger than 5 mu m were investigated as food source. The ambient chlorophyll a concentration at sampling depth (similar to 70 m) ranged between 0.15 and 1.00 mu g chl a l(-1) and NOP concentrations ranged between 1.78 and 14.0 x 10(3) cells l(-1) during the sampling periods. The division of particles into five size classes (5-10, 10-20, 20-50, 50-100 and > 100 mu m) revealed that most of the particles were found in the size classes below 50 mu m (81-98%), while most of the natural occurring carbon (NOC) was concentrated in the size classes larger than 20 mu m (70-95%). Ingestion rates were food density dependent rather than size dependent ranging between 0.02 and 1.65 x 10(3) NOP ind(-1) day(-1) and 0.01 and 0.41 mu g NOC ind(-1) day(-1), respectively, equivalent to a body carbon (BC) uptake between 0.4 and 51.8% BC day(-1). The share of the size classes to the total ingestion resembled in most cases the size class composition of the natural particle community.