The uptake of dissolved organic material by the sea cucumber Parastichopus californicus (Stimpson) and its potential role in visceral regeneration

• We examine the uptake of free amino acids by the tissues of a sea cucumber.
• Uptake of amino acids from the seawater varies depending on tissue type and season.
• The respiratory trees had the highest rates of free amino acid incorporation.
• The uptake of free amino acids may provide biosynthetic materials for regeneration.

The sea cucumber Parastichopus californicus atrophies and regenerates its internal organs on an annual cycle. Previous research has suggested that during the period of maximal regeneration (January–March) no movement or feeding occurs; however metabolic rate is doubled compared to non-regenerative periods (June–August). Uptake of dissolved organic material (DOM) from the aqueous environment could provide an external source of biosynthetic materials for regeneration of the internal organs. P. californicus were collected in the summer (actively moving and feeding, not degenerating or regenerating), winter (inactive, degenerating), and spring (inactive, regenerating). Animals were incubated in seawater containing a mixture of amino acids labeled with 15N and 13C. Incorporation of 15N (summer, winter, spring) and 13C (summer, spring) by the respiratory trees was significantly higher than incorporation by other types of tissues. Additionally, dorsal and ventral epidermis, oral tentacles, digestive tract, muscle, and tube feet incorporated 15N and/or 13C during at least one season. These results demonstrate that certain tissues, especially the respiratory trees, of P. californicus assimilate free amino acids from the sea water which could be used as biosynthetic materials for regeneration. These results also indicate that the respiratory trees may have a role in nutrition as well as respiration.