A key life history stage of many bottom-dwelling marine invertebrates is a microscopic feeding larva that swims in the water column for days, weeks, or months before settling to the bottom to metamorphose into its adult form. The larval stage is risky, and the more rapidly larvae can feed and return to the bottom the greater their chance of survival. Feeding rate is determined in part by the amount of food particles available, but recent work on the larvae of echinoderms has also shown that it may be affected by the abundance of large inedible particles (e.g., large phytoplankton cells, zooplankton fecal pellets, or microplastics) in the water column. When abundant, large particles seem to interfere with larval feeding. This project aimed to determine if naturally occurring large particles affect feeding rate of sand dollar larvae; if large particles can affect not only feeding rate, but also the length of time sand dollar larvae must spend feeding in the water column; and if large particles also affect feeding rate in members of other phyla of animals. We found that naturally occurring large particles can indeed reduce feeding rates of sand dollar larvae. However, in lab experiments, the presence of large particles did not affect the length of time these larvae spent in the water column before becoming competent to metamorphose. Finally, our experiments did not detect any effect of large particles on the feeding rates of larvae of segmented worms, another phylum that includes many species with feeding larvae. In addition to this work, during this project we carried out numerous other studies on the ecology of marine invertebrate larvae, on e.g. food limitation in nature in the larvae of sand dollars, food-induced phenotypic plasticity in echinoderm larvae, the feeding mechanisms of annelid larvae, and effects of salinity on larvae and juveniles of an invasive brackish-water annelid. In total, the project has so far resulted in six published peer-reviewed papers, with four more in review or in preparation. The primary broader impact of this project has been in training undergraduate and graduate students in scientific research. Three graduate students and 16 undergraduates were involved in the project. Many of these students gave presentations on their work at scientific meetings (three of these presentations winning best student presentation awards), and many are coauthors of publications or manuscripts in review or in progress. Many of the students involved in the project have gone on to additional training and careers in STEM fields. Last Modified: 10/06/2024 Submitted by: BrunoPernet