Transintegumentary Uptake of Dissolved Amino Acids in the Sea Star Asterias rubens. A Reassessment of its Nutritional Role with Special Reference

Sea stars Asterias rubensof about 1.5 g body weight were exposed to different nutritional conditions. Experimentals received soft parts of mussels Mytilus edulis as particulate food; controls were starved. In order to determine the nutritive significance of epidermal amino-acid uptake in terms of body-weight changes, 3 concentrations (10, 30, 90 vM) of a natural amino-acid mixture were offered. The sea stars were kept at 15 "C in 1 1 of sea water, which was renewed daily. At an ambient concentration of 90 PM amino acids, body-weight increases were observed during 3 4 weeks, not differing greatly from weight increases of sea stars fed mussel meat. Subsequent weight losses in these two groups could be attributed mostly to poor water quality resulting from bacterial contamination. The experimentals offered 10 FM amino acids did not differ significantly from the starved controls; both groups steadily reduced their body weights. Weight decreases of sea stars maintained at an ambient concentration of 30 FM were less than those of starved controls. Microbial populations reacted to the dissolved amino acids offered within a few hours, exhibiting rapid absorption and increased multiplication. Maintenance of asteroids in sea water together with bacteria, which had been allowed to grow for some days on a 10 KM natural amino-acid mixture, and subsequent net influx analysis revealed that uptake of dissolved amino acids is primarily a bacterial process. The data obtained do not provide evidence that, in A. rubens, epidermal amino-acid uptake significantly contributes to metabolic energy demands.