Comparisons among the amino acid composition of females, eggs and food to determine the relative importance of food quantity and food quality to copepod reproduction

A field study was carried out to determine the relative importance of both food quantity and food quality to reproduction of the copepod Euterpina acu tifrons. The total protein concentration of the seston 3 to 20 mu m size fr action was used as the indicator of food available for copepods in the fiel d. Food quality was quantified by comparing the amino acid (AA) composition of females, eggs and the seston 3 to 20 mu m size fraction, and by conside ring the species composition of the phytoplankton community. Egg production rate was mainly determined by food concentration. However, for the same fo od concentration, a reduced egg production rate was observed when there wer e more differences between the AA composition of eggs and females. Hatching success was correlated only with food quality. A higher hatching success w as obtained when the similarity between the AA composition of eggs and fema les and between the AA composition of females and seston was higher. Howeve r, a reduced hatching success was observed when the proportion of diatoms i n the phytoplankton was higher than 70 %. Therefore, food quality limitatio n was due to an AA imbalance in the natural seston and, perhaps, due to the presence of inhibitory compounds. Copepods were food Limited for long peri ods of the year. Food quality mainly limited copepod reproduction in spring and early summer, whereas food quantity Limited reproduction at the end of autumn and early winter. In summer and early autumn the reproductive succe ss of copepods was higher.