Phytoplankton in a coastal ecosystem in France were studied to see what nutrients they needed to grow. The researchers found that from March to July, the phytoplankton mostly needed phosphorus to grow. Nitrogen was only limiting for a short time in early March. Adding phosphorus made the phytoplankton grow faster, showing they were mainly limited by phosphorus. Silicon was also important for growth during a couple of weeks in May and June. The ratio of carbon to phosphorus in the phytoplankton varied a lot, and adding all three nutrients together had the biggest effect on their growth. This study shows that just looking at nutrient levels in the water isn't enough to predict what nutrients the phytoplankton need, and that phosphorus is really important for managing coastal waters.