An investigation was undertaken to observe whether soft-bodied surface zooplankton of nutrient-depleted ocean waters, such as the Sargasso Sea, can take up and retain dissolved nutrients in a manner similar to that previously shown for many benthic forms living in richer environments. Freshly collected samples of 15 species (five phyla) were incubated for 2 h in sea water to which a small quantity of 14 C-labeled amino acid mixture had been added. They were then prepared as histological sections and examined with stripping film autoradiography. All of the forms showed strong uptake and retention of the tracer in parts of their epidermis, and various specific internal structures. Greatest uptake was seen in tentacles, parapodial paddles, gills and restricted parts of the guts or gastrovascular cavities. It is concluded that many animals living in depleted ocean waters still can obtain benefits from dissolved nutrients, either directly or by symbiotic relationships with microorganisms. These can supplement the more obvious forms of nutrition and perhaps play important roles in sustaining more isolated body parts. Some additional benefit also may be drived through fluid ingestion as well as ingestion of microorganisms that have taken up dissolved materials.

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