Award: OCE-1060801

The larvae of many marine inverterbrates – e.g., sea urchins, sea stars, segmented worms, and snails – spend weeks or months drifting in the plankton. During that time they must capture food particles (mostly single-celled algae) in order to fuel their growth. Different types of larvae use different methods to capture food particles. For example, larvae of sea urchins and sea stars capture particles using a mechanism called "ciliary reversal"; larvae of worms and snails capture particles using "opposed bands" of cilia. These different capture methods seem likely to influence how well larvae feed on particles of different sizes. There is some evidence, for example, that larvae that feed with ciliary reversal capture large particles more efficiently than they capture small particles; the opposite is true for larvae that feed using opposed bands. Such differences in feeding performance can have important consequences. Some larvae may only perform well (that is, grow rapidly) in certain habitats. For example, larvae that feed using ciliary reversal may perform better during times or in places where large algal cells are common. This can affect larval survival and dispersal, both of which have important effects on the ecology and evolution of larvae. Further, climate change is predicted to alter the size distributions of algal cells in seawater. Detailed knowledge of how larvae feed can help us to predict how different types of larvae will be affected by such changes. In this project we carried out detailed lab studies on the feeding performance of larvae feeding with ciliary reversal and opposed bands of cilia, addressing the question: how do larvae with these two feeding mechanisms perform on food cells of different sizes? We carefully controlled food size and flavor by using artificial spherical particles. We found a clear pattern of ciliary reversal feeders feeding more effectively on larger particles, and opposed band feeders feeding more effectively on smaller particles. We thus predict that these two types of larvae will perform differently in field habitats with different particle size distributions; we plan to test this prediction directly in subsequent experiments. We also found that opposed band feeders had higher feeding rates per unit of ciliary band, which has important implications for the evolution of larval form. We also discovered something unexpected in this project. Studies of the feeding abilities of larvae usually involve assessing their feeding when offered particles of a single type – either a single species of alga, or artificial particles of a single size class. Such studies have been very useful in understanding feeding mechanisms of various types of larvae, and have also been used to make inferences about larval performance in the field, and about how larvae might impact phytoplankton populations in the field. However, in nature larvae are immersed in a suspension of many different types of particles, varying in size, shape, flavor, density, surface properties, and nutritional quality. How might the presence of large, non-ingestible particles (e.g., many diatoms and dinoflagellates) affect feeding on small, ingestible particles? As part of a graduate-student led project, we designed studies to address this question. We carried out these experiments using larvae of six species of echinoderms, and the results were striking – for all species tested, the presence of even low concentrations of large, non-ingestible particles dramatically reduced feeding rates on small, ingestible particles. This work is important for interpreting both how larvae perform in the field, and how larvae affect populations of their prey organisms. Because feeding performance is strongly tied to planktonic larval duration in feeding marine invertebrate larvae, it also has implications for larval mortality (and thus recruitment to adult populations), as well as dispersal (and thus such topics as optimal spacing of marine reserves). During this work, two graduate students and eight undergraduates were trained in experimental design, analysis, and presentation of results, as well as many methods (e.g., larval culture, flow cytometry, microscopy). We presented results of this work at five scientific conferences; one student poster won the best student poster award at one of these conferences. Additional conference presentations will occur in the next two years. Some of this work has already been published in peer-reviewed scientific papers, and more will be submitted in the next two years. We also designed and published a website aimed at informing the general public and other scientists about the reroductive biology of marine invertebrates in southern California (http://web.csulb.edu/colleges/cnsm/depts/biology/invertebrate_reproduction/). Two datasets (the data underlying Pernet et al. 2016 and Jones et al. 2016) have been submitted to BCO-DMO (http://www.bco-dmo.org/project/528891) for data sharing. We will submit at least two more datasets to BCO-DMO in the next year, one concerning the effects of large particles on clearance rate in echinoderm larvae, and one including data on clearance rates as a function of particle size in larvae that feed with opposed bands vs. ciliary reversal. Last Modified: 01/03/2017 Submitted by: Bruno Pernet