“…Nitrate is often considered to be the major form of nitrogen that fuels this high productivity, yet its availability in many temperate reef systems varies greatly among seasons and years (Brzezinksi et al, ; Chapman & Craigie, ; Jackson, ; van Tussenbroek, ). Despite this high variability and the limited capacity for some kelps to store nitrogen for less than a few weeks (Gerard, ), measurable growth occurs year‐round in many kelp systems (Hepburn, Holborow, Wing, Frew, & Hurd, ; Kirkman, ; Pessarrodona, Foggo, & Smale, ; Reed, Rassweiler, & Arkema, ; Vadas, Beal, Wright, Nickl, & Emerson, ; van Tussenbroek, ). Such observations have prompted suggestions that recycled forms of nitrogen (e.g., ammonium and urea) are important in sustaining kelp growth during extended periods of low nitrate availability (Brzezinksi et al, ; Hepburn & Hurd, ; Smith, Brzezinski, Melack, Miller, & Reed, ; Wheeler & Druehl, ).…”