Food Size Dependent Feeding and Egg Production of Acartia pacifica from a Tropical Strait

Abstract

A study was carried out to observe the effect of food size spectra and food concentration on the ingestion rate and egg production rate (EPR) of Acartia pacifica (Steuer, 1915), a small calanoid copepod (total length 1.0-1.3 mm), from the Strait of Malacca. Food particles were divided into four size fractions (10-20, 20-35, 35-50, and 50-140 ?m) and quantified in terms of chlorophyll a concentration and carbon biomass with the C:N values used as an indication of food quality. Acartia pacifica showed significantly higher carbon ingestion rates for the 50-140 ?m food size fraction, reflecting the species' affinity for larger food particles; however, mean EPR was significantly higher for the 35-50 ?m food size fraction where the mean C:N value was 14.7. Similarly, gross egg production efficiency (Ep) was the highest for this food size fraction. In general, Ep was comparable to other acartia species from tropical areas, but lower than those from temperate regions. This probably is due to a higher metabolic carbon demand and a lower quality of food in the tropical environment. Acartia pacifica effectively utilized food from the broad size spectrum used in our study with an affinity for larger particles with higher (though not highest) C:N content.