But after the volcano there's been a lot more iron falling in to the ocean, so we have a fantastic opportunity to check whether iron makes the bloom last longer.

CNN: Could volcanic eruptions signal boom time for ocean life?

So while the additional dissolved iron triggered an earlier-than-usual phytoplankton bloom, as the metal triggered growth in a greater number of phytoplankton cells, the bloom was only 15-20% larger than normal because the growth was limited by the amount of available nitrogen, another vital ingredient required for the organisms to develop.

BBC: Iceland volcano ash cloud triggers plankton bloom