Abstract
Marine planktons being dominant in the Inland Sea of Seto, Gymnodinium sp. (Gym. sp.), Hemieutreptia antiqua HADA (H. antiqua), Chiamydomonas sp. (Chl. sp.), Skeletonema sp. (Ske. sp.) and Nayicula sp. (Nav. sp.) were studied to examine the nutritional requirements for the growth and an applicability of eutrophication assessment of the sea water from the Hiroshima Bay.
Nitrogen source as nitrate and phosphorus source as phosphate were essential nutrients for the growth, however, some overplus uptake of phosphorus at the beginning of the growth could further support the growth on phosphorus free media. Cell yields based on nitrogen, ×105cells/μg N and phosphorus, ×105 cells/μg P were measured to be 0.4 and 3.1 for Gym. sp., 3.0 and 28.0 for Chl. sp., and 7.0 and 28.6 for Ske. sp., respectively. The mixture of vitamin B1 and B12, and biotin enhanced the growths of Gym. sp., H. antiqua and Nav. sp. whereas Chl. sp. and Ske. sp. did not require the vitamins for their growths. Vitamin B12 was an essential growth factor for the growths of Gym. sp. and Nav. sp.
The growth activities of Chl. sp. and Ske. sp. when they were grown on the media based on sea water from St. 1 to 3 either with or without spiking N or P or N and P suggested that nitrogen concentration in the sea water might be a growth limiting nutrient for the planktons rather than phosphorus. Relatively low concentrations of nitrogen and phosphorus might be classified the sea water of the Hiroshima Bay as a mesotrophy. The increases of growth activities of Gym. sp., H, antiqua and Nav. sp. when vitamin B12 was spiked in the samples from St. 2 suggested that vitamin B12 or its related substance might be a growth limiting factor for vitamin B12-requiring plankton in St. 2.
