PHILLIPS, N.E.: Effects of larval nutrition on juvenile performance: the relative importance of constant vs. variable food rations

For marine invertebrates, increasing evidence points to the important consequences larval history can have for subsequent early juvenile performance. In an earlier experiment on the marine mussel Mytilus galloprovincialis, I raised larvae at 3 constant food rations, high, medium and low, then monitored juvenile performance after settlement. Settling larvae from the high larval food level were larger and had higher lipid content, and juveniles had greater survival and growth than those from lower larval food treatments even after 2 weeks in the same juvenile environment. The results indicated that juvenile growth and survival were strongly influenced by larval quality at settlement, which in turn was mediated by larval nutrition. In nature, however, food is unlikely to ever be constant over the course of larval life. So, in the current experiment I examined the relative importance of high rations early vs. late in larval life on juvenile performance. I repeated the above experiment using the following 4 food treatments: constant high, constant low, initially high (first 20 days) switched to low for 9 days prior to settlement (high/low treatment), and initially low (first 20 days) switched to high for 15 days prior to settlement (low/high treatment). Preliminary results show that juvenile survival was most strongly influenced by initial rations: larvae in high or high/low treatments had much greater juvenile survival than those in constant low or low/high treatments. Juvenile growth was influenced by larval rations in a gradient such that mean juvenile size increased in the following order of larval rations: low, low/high, high/low and high. Implications of these results for recruitment of natural populations will be discussed.