ABSTRACT: A unique flow-through mesocosm system powered by solar energy was developed for examining growth rates of marine invertebrate larvae in the field. The planktotrophic veligers of queen conch Strombus gigas were used as a test species. The mesocosmsystem was moored in a remote location in the oligotrophic waters of the Bahamas. Natural assemblages of phytoplankton (mean 160 ng chl a l^-1) were filtered with 5 um and 50 um filters to determine the growth rates of larvae fed 2different assemblages. Initial stocking in each mesocosm was 20 veligers l^-1; and prior to metamorphosis, density was gradually reduced to 0.7 veligers l^-1. Growth rates from 0 to 9 d were identical for larvae fed 5 and 50 umphytoplankton assemblages. The 5 um treatment was discontinued on Day 9; the 50 um treatment was continued through Day 16 when 95% of the veligers were competent for metamorphosis. The mesocosms provided good replication; growth rates for veligers fed 50um filtered phytoplankton were identical in Mesocosms 1 and 2. Routine sampling for chlorophyll a inside and outside the mesocosms showed no indication of phytoplankton biomass accumulation inside the mesocosm after 48 or 96 h of operation. Thismesocosm system is an ideal apparatus for conducting ecological research with marine invertebrate larvae. Determination of larval growth and survival under field conditions can provide more accurate information on dispersal potential, and length of timeand survival to metamorphosis compared to results achieved in the laboratory.