PHILLIPS, N.E.: The effects of larval nutritional history on larval condition and post-settlement juvenile growth of the mussel Mytilus galloprovincialis

For organisms with planktonic feeding larvae, variation in food availability during the larval stage influences the condition of larvae as they develop, and may also have effects on the performance of juveniles after they settle. To investigate this issue for the mussel Mytilus galloprovincialis, full sibling larvae were raised in the laboratory in three different food treatments. Each treatment was composed of equal amounts of two species of cultured phytoplankton, and differed only in the total amount of food available. The food treatments were 20,000, 2,000, and 500 cells/ml. Larval size, measured weekly, varied predictably with larval food treatment (i.e. larvae from the highest food level were always largest). After 3-4 weeks, larvae were competent and settled onto introduced substrates. The mean size and lipid content of settlers was largest for larvae from the 20,000 cells/ml treatment. A subset of substrates from each larval food treatment were kept in the lab and half fed a high and half fed a low juvenile food ration for 10 and 20 days. The remaining substrates were moved to ropes hanging from a pier and left for two weeks. Juveniles were then recovered and measured. In all cases, juveniles from the highest larval food treatment were significantly larger than those from the lowest larval food treatment. From the pier, high larval food juveniles were 43% larger than low larval food juveniles even though they had been growing in the same environment for two weeks post-settlement. Juvenile growth compared between laboratory and field settlers from each of the different larval food treatments had substantial interactions. This work demonstrates the important effects larval nutritional history may have on juvenile performance, and how those effects might vary with conditions at the site of settlement.