Further Investigations on Larval Nutrition and its Influence on Juvenile Performance of Benthic Invertebrates: Competition, Thermal Stress, and Natural Populations

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The nutritional condition of benthic invertebrate larvae and its potential influence on juvenile performance (growth and survival in the days and weeks after settlement) is an almost unstudied area of marine ecology. Further understanding of the connections between oceanic (planktonic) and benthic components of the complex life-cycles of many marine invertebrates will require exploration of how the nutritional environment of the planktonic larva affects the performance of the post-metamorphic, benthic juvenile. In the first 3 years of work on this topic, we have shown that larval diet, manipulated in the laboratory, resulted in changes in larval organic content and size. Furthermore manipulations of larval diet had significant influences on growth and survival of newly metamorphosed/batched benthic juveniles under field conditions. This research joined lab experiments and field studies on juveniles from three different invertebrate phyla (barnacles, sea urchins and snails) and should help focus attention on early juvenile biology of marine invertebrates. Increased understanding of early juveniles should help clarify the importance of larval supply and post-settlement processes in population dynamics such as structuring populations and marine communities. It may also reveal whether larval nutritional status affects survival of juveniles to adulthood.In the proposed research, investigations will determine how variations in larval nutritional history may affect intraspecific and interspecific competitive interactions among young juveniles. A number of different barnacle species that occur in intertidal and subtidal habitats in coastal and estuarine environments will be studied, thereby exploring influences of larval nutrition in habitats that vary in types and degrees of stresses (temperature, desiccation, and salinity, and types of food). Competitive interactions among juvenile and adult barnacles are well documented, but whether larval nutritional history has an influence on competitive outcome is unknown. By placing juveniles in interactive situations, this work will explore the influence of larval nutrition in field conditions that reflect settlement conditions in natural populations of many species.A second part of the work will examine how larval nutritional history effects other features of juveniles besides their growth and survival. Measurements will be made on the effects of larval nutritional on the size of the juvenile feeding apparatus and molt rate and on the biochemical response of juveniles to thermal stress. This data will show morphological and physiological consequences of larval diet and contribute to our understanding of why growth and survival are affected. For the physiological responses to thermal stress, the induction of heat shock proteins (lisp 70's & 90's) and ubiquitin-conjugates will be quantified, (proteins that reflect reversible and irreversible damage to proteins, respectively).Lastly, examinations of natural variation will be made for larval size and energy content and its affects on juvenile performance of the same barnacles for which we have conducted experimental manipulations, competition studies and physiological studies. By measuring size at metamorphosis and following performance of naturally settling barnacles we can determine whether the manipulations created in the laboratory are reflected among natural populations. Additional measures of larval size, organic content, and expression of thermal stress proteins will help join the laboratory and field-based studies. Natural settlement will be monitored throughout the year to look for seasonal patterns in larval quality and whether larval quality consistently influences juvenile performance.This project should provide much needed empirical data on juvenile growth and survival, a broader context for understanding the role of larval nutrition, and new methodologies for further experimental investigations of juvenile ecology of marine invertebrates.