Many marine invertebrate larvae must feed to fuel development through metamorphosis to the juvenile stage. These feeding larvae capture suspended food particles in diverse ways. Laboratory evidence suggests that different larval feeding mechanisms may affect performance depending on particle types. For example, larvae of echinoderms feed by ciliary reversal, a mechanism that apparently limits clearance rates on small particles (<10 um diameter). In contrast, mollusk larvae feed using opposed bands of cilia, which limits clearance rates on larger particles (>10 um). Because the concentration of suspended food particles can constrain larval growth in natural waters, and because the size distribution of natural particles varies over space and time, maximum clearance rates imposed by a particular feeding mechanism may restrict larval growth rates and development. As a result, the planktonic period of suspension-feeding larvae would be extended and larval mortality (due to predation, or advection from suitable adult habitat) increased, leading to lower recruitment. In this way, performance constraints associated with particular larval feeding mechanisms could strongly affect population dynamics. Such effects are missing from population-dynamic models of benthic invertebrates, largely because they are not well understood. Toward this end, controlled comparisons are needed of the feeding capabilities of ciliated larvae that differ in feeding mechanism.
The present study will examine the feeding capabilities of larvae that gather food using one of three particle capture mechanisms (ciliary reversal, opposed band, or a "mixed" strategy of opposed band feeding and encounter feeding on large particles), and for larvae with distinct body forms (e.g., within opposed band feeding, trochophores vs. veligers). Three main hypotheses will be tested. (1) Larvae that differ in particle capture mechanisms/body form will also differ in either maximum clearance rates, or in the size spectrum of particles cleared at high rates. Laboratory experiments will involve artificial particles, varying only in size. (2) Hypothesized differences in (1) also hold for natural particles. Experiments will test semi-natural prey communities. (3) Larvae with different feeding mechanisms will perform best in specific feeding environments (e.g., those dominated by small particles versus large particles). Larval growth rates will be tested in experimentally manipulated, semi-natural food regimes.
Intellectual merit: Yielding explicit, planned comparisons of larval performance as a function of feeding mechanism, larval body form, and particle type, this research would improve understanding of the importance of larval feeding mechanism in the population dynamics of marine invertebrates. This study is relevant to many compelling questions in reproductive biology, ecology and evolution, such as: how do seasonal changes in the types of particulate food affect the performance of larvae with particular feeding mechanisms; how might such linkages be related to the evolution of seasonal reproductive patterns in various taxa of marine invertebrates; and how might human-mediated shifts in ocean temperature and chemistry (predicted to alter the size spectrum of potential food particles) affect performance of larvae with particular feeding mechanisms?
Broader impacts: This project will have significant broader impacts in integrating research and education, and in increasing the participation of underrepresented groups in science. Substantial research has shown that intense undergraduate research experiences are correlated with subsequent engagement and success in STEM careers like biology. This project will provide such experiences for 8-10 undergraduates and one graduate student, who will be supported by this project. Additional student researchers will be supported using existing programs at CSU Long Beach and the Friday Harbor Laboratories (UW) that focus on enhancing cultural diversity in biology. Research assistants will be trained in larval biology and experimental methods, and will design and carry out projects that contribute directly to addressing the proposal's goals. They will present their results at scientific meetings, and as coauthors of peer-reviewed papers. Equipment purchased as part of this project also will be used to redesign labs in several CSU Long Beach undergraduate courses. Moreover, as part of this project, the PI and students will create a freely available web site compiling data on the reproductive and larval biology of California marine invertebrates, a unique and valuable resource for biologists in the region.
