ABSTRACTVariations in tissue nitrogen (N) and phosphorus (P) were examined over a complete seasonal cycle for five macroalgae common in Oregon coastal water. Tissue N ranged from 2.0 to 5.5% dry weight (dry wt) in leafy macroalgae (Enteromorpha intestinalis(Linnaeus) Link.Ulva fenestrataPostels et Ruprecht, andPorphyrasp.) and from 0.9 to 2.6% drt wt in branched macroalgae(Codium fragile(Suringar) Hariot andPelvetiopsis limitataSetchell). Tissue P ranged from 0.32 to 0.86% dry wt in leafy macroalgae and from 0.27 to 0.50% dry wt in branched macroalgae,Ulva fenestrata, C. fragile, andP. limitataappeared to be N limited during part of the year based on tissue N levels. Variations in N:P showed a more distinct seasonal pattern than either tissue N and tissue P. All macroalgae examined appeared to be N limited at least part of the year based on N:P composition, and P limitation occurred for all macroalgae examined exceptC. fragile.Our results suggest that tissue N:P ratio for macroalgae may be a good index for evaluatingin situnutrient status.