Adaptation and equivalence in open-ocean phytoplankton

Two marine phytoplankton species of the North Atlantic Ocean have inherently differt growth responses to changing nutrient conditions. Yet they co-occur. Thus, they can be compared under the same conditions via equivalence, provided that their adaptedness is linked to their responsiveness as follows. If Species x is adapted to nutrient changes, then it is responsive to these conditions and, certainly, if it is responsive to these conditions, then it is adapted to them. There is another expression that is equivalent to this one (that says the same thing): either Species x is adapted and responsive to these conditions or it is neither adapted nor responsive to them. The option just mentioned is resolved so that Emiliania huxleyi as Species x is adapted and responsive and Cyclococcolithus leptoporus as Species x is not adapted and not responsive. All the frequently observed species in the winter half of the year, November to April, from 1961 to 1972 are like E. huxleyi in being adapted and responsive or like C. leptoporus in being unadapted and unresponsive.Contribution No. 5806 from the Woods Hole Oceanographic Institution