FEEDING DETERRENCE PROPERTIES OF APO-FUCOXANTHINOIDS FROM MARINE DIATOMS .2. PHYSIOLOGY OF PRODUCTION OF APO-FUCOXANTHINOIDS BY THE MARINE DIATOMS PHAEODACTYLUM-TRICORNUTUM AND THALASSIOSIRA-PSEUDONANA, AND THEIR FEEDING DETERRENT EFFECTS ON THE COPEPOD TIGRIOPUS-CALIFORNICUS

The marine diatoms Phaeodactylum tricornutum and Thalassiosira pseudon ana have been shown to produce apo-fucoxanthinoid compounds which act as feeding deterrents against the harpacticoid copepod Tigriopus calif ornicus. The amounts and types of apo-fucoxanthinoids produced were sp ecies specific. Th. pseudonana produced small quantities of apo-12'-fu coxanthinal and apo-13'-fucoxanthinone only during senescence, while P . tricornutum produced much greater quantities of these two compounds during both log and senescence phases, in addition to producing a thir d compound, apo-10-fucoxanthinal, only during senescence. For both spe cies, production of apo-fucoxanthinoids increased as the cells entered senescence phase due to phosphate limitation. The amounts of apo-fuco xanthinoids necessary to reduce feeding in T. californicus by 50% rang ed from 2.22 to 20.2 ppm. This range was approximately 1000 times lowe r than the total apo-fucoxanthinoid concentration in P. tricornutum. T he amounts of apo-fucoxanthinoids necessary to cause a 50% mortality i n a population of T. californicus ranged from 36.8 to 76.7 ppm, Thus, these compounds are present in concentrations which may have ecologica l significance in the control of bloom formation and grazing. The prod uction of apo-fucoxanthinoids may be a phenomenon common to many diato ms, particularly as they enter senescence due to nutrient limitation.