Absorption of dissolved and dispersed nutrients from sea-water by Panulirus japonicus phyllosoma larvae

This study examined the capacity of Japanese spiny lobster Panulirus japonicus phyllosoma larvae to absorb nutrients directly from the surrounding water. For this purpose, 48-, 81-, 124-, 160-, and 264-day-old intermoult larvae were starved for 48 h, held for 30 min to 4 h in 0.05 g L^–1 solutions or dispersions of cholesterol, peanut oil, saccharose and horseradish peroxidase in seawater, and subsequently examined by histological and ultrastructural methods. Lipids, carbohydrate, and protein were detected in either the lumen of the midgut gland tubules, the midgut gland cells, the haemolymph or in the cells of the epidermis of all larvae examined after each experimental period, with general improvement of the cell and tissue characteristics over unfed controls. The lipids were also found in the cuticle. Thus, the results provide evidence of nutrient absorption via the digestive tract, and possibly also via the integument. Structural adaptations that may be involved in the process of absorption were tentatively identified. Our observations suggest the possibility that particulate organic matter (POM) and dissolved organic matter (DOM) can be utilized by the P. japonicus phyllosoma larvae, perhaps as supplementary sources of nutrients to macroscopic diets.