Does competition for nanomolar phosphate supply explain the predominance of the cyanobacterium <i>Synechococcus</i>?

Abstract

Experimental work during a cruise along a W‐E transect in the Mediterranean Sea suggests that (1) orthophosphate concentrations in the upper photic zone show a decreasing trend from the west to the east reaching levels well below 1 nM and (2) microorganisms in the 0.6–2ߝµm size fraction, probably Synechococcus , have, in addition to high affinity for orthophosphate, significantly higher maximum uptake rates than heterotrophic bacteria or eukaryotic algae. These specific advantages concerning orthophosphate uptake at low (&lt;5 nM) as well as at relatively high (5–25 nM) concentrations could explain both general Synechococcus abundance in P‐depleted environments and transient blooms of this species in the open ocean where episodic orthophosphate nanopulse events are likely to occur.