Organisms need a variety of nutrients for maintenance, growth, and reproduction. When one nutrient influences the ability of primary producers to access or use a second nutrient it is called co-limitation. There are a variety of mechanisms for co-limitation, and in Nahant, the availability of nitrogen has been found to limit the uptake of phosphorus in an important intertidal foundation species, the seaweed Fucus vesiculosus.
Val Perini, a graduate student in Matthew Bracken’s lab, spent two years studying the natural fluctuations in nitrogen to phosphorus ratios at Canoe Beach in Nahant. Then, based on observed patterns, she developed manipulative experiments to measure how nutrient levels in the water and in seaweed tissue impact the ability of F. vesiculosus to take up nitrogen and phosphorus. 
The research, which appears in the journal Oecologia, suggests that F. vesiculosus is not able to take up phosphorus without an adequate supply of nitrogen. Therefore, due to seasonal changes in nitrogen levels in coastal waters, F. vesiculosus may be phosphorus limited during periods of low nitrogen availability, despite ample phosphorus levels in Nahant waters throughout the year.