Larvae of the tropical spider crab Libinia ferreirae were reared in the laboratory from hatching to metamorphosis, and their growth (dry weight, DW; ash-free dry weight, AFDW) and respiration rates were measured. Variations in the rates and patterns of growth were compared in 2 hatches (larvae from different females). Ash content increased significantly during and shortly after each ecdysis, then remained constant (zoeae) or decreased slightly (megalopa). In contrast, organic substance (AFDW), increased throughout most of the moult cycle. Weight-specific respiration rates were high near ecdysis and low during the intermoult stages of the moult cycle. Energy partitioning was compared among the different larval instars by calculating amounts of energy accumulation from AFDW and metabolic energy loss from respiration.