Nature of Phosphorus Limitation in the Ultraoligotrophic Eastern Mediterranean
by T. F. Thingstad et al in Science 12 August 2005 vol. 309 pg. 1063-1071

Journal abstract: Phosphate addition to surface waters of the ultraoligotrophic, phosphorus-starved eastern Mediterranean in a Lagrangian experiment caused unexpected ecosystem responses. The system exhibited a decline in chlorophyll and an increase in bacterial production and copepod egg abundance. Although nitrogen and phosphorus colimitation hindered phytoplankton growth, phosphorous may have been transferred through the microbial food web to copepods via two, not mutually exclusive, pathways: (i) bypass of the phytoplankton compartment by phosphorus uptake in heterotrophic bacteria and (ii) tunnelling, whereby phosphate luxury consumption rapidly shifts the stoichiometric composition of copepod prey. Copepods may thus be coupled to lower trophic levels through interactions not usually considered.

My commentary: Ultra-oligo-tropic means extremely-sparce-nutrient, i.e. this part of the Meteriterranean Sea, about 100 km South of Cyprus, has few nutrients. In this case this means low total nitrogen and phosphorus. The experiment consisted of releasing, i.e. dumping, a large amount of phosphate (compared to what was already present) in a 16 square km area of sea and following the growth of several classes of organisms for about 10 days. The somewhat surprizing finding was that the chlorophyl concentration (an index of phytoplankton) decreased, while the concentration of bacteria and the amount of eggs carried by copepods increased.
My diagram on the left is an illustrated (and perhaps idiosyncratic) version of Fig. 4 in this paper; first some definitions:

phagotrope- eats other organisms
osmotroph- adsorbs nutrients through cell wall
heterotroph- requires complex organic compounds to live, e.g. amino acids.
phytoplankton- small (just a few microns in diameter) organisms that can use inorganic minerals and sunlight to grow.

P- inorganic phosphorous, e.g. the phosphoric acid that was dumped into the sea by the experimenters (the "P" is large because the concentration is large).
N- inorganic nitrogen, e.g. ammonia, nitrate (the "N" is small because the concentration is very low.
DOC- dissolved organic carbon, e.g. amino acids, fats, carbohydrates.
DON- dissolved organic nitrogen, e.g. amino acids

The knee jerk guess of what would happen to the added phosphate was that the phytoplankton would absorb most of it and grow like crazy; they in turn would be eaten by those higher on the food chain. However, the phytoplankton can't use organic nitrogen, thus they are starving in the midst of the phosphate feast. However, bacteria can use both phosphate and organic nitrogen, so they grow and pass the phosphate up the food chain.

In addition to this "bypass" theory, both bacteria and phytoplankton may accumulate phosphate quickly even before they start to multiply (phytoplankton never do). This increase in quality of the prey may trigger increased egg production by copepods before the mass of food increases; a kind of trophic "tunneling".