Phosphorus dynamics and limitation of fast- and slow-growing temperate seaweeds in Oslofjord, Norway

• Published in: Marine ecology. Progress series (Halstenbek) 2010-01, Vol.399, p.103-115
• Main Authors: Pedersen, Morten Foldager, Borum, Jens, Fotel, Frank Leck
• Format: Article
• Language: English
• Subjects: Algae; Ascophyllum; Ceramium; Coastal water; Eutrophication; Fucus; Kinetics; Laminaria; Macroalgae; Marine; Nitrogen; Nutrient uptake; Phosphorus; Photosynthesis; Seaweeds; Ulva
• ISSN: 0171-8630; 1616-1599
• DOI: 10.3354/meps08350

During coastal eutrophication, fast-growing, ephemeral macroalgae bloom at the expense of slow-growing, perennial macroalgae. This change in community composition has been explained by a differential ability to exploit and utilize inorganic nitrogen among macroalgae with different growth strategies. However, some coastal areas are becoming phosphorus- rather than nitrogen-limited; we therefore compared phosphorus dynamics among 6 temperate species of macroalgae with different growth rates in order to test whether differences in algal P-dynamics may explain macroalgal community changes. Thin, fast-growing algae (UlvaandCeramium) took up dissolved inorganic P (DIP) much faster than thicker, slower growing species (belonging toFucus,AscophyllumandLaminaria) but also had much higher P-demands per unit biomass and time. DIP concentrations in the Oslofjord were low from April through August, and fast-growing species were unable to meet their P-demand from uptake for several months during summer. Hence,CeramiumandUlvawere potentially P-limited during summer, whereasAscophyllumandLaminariawere able to acquire sufficient external DIP to remain P-replete throughout the year. Storage of P preventedFucusspecies from suffering severe P-limitation for several weeks in summer. The absolute amount of P stored within the algae per unit biomass did not differ systematically among the 6 species, but the storage capacity (i.e. the period of time for which stored P could support growth) was much larger for slower growing species since this parameter depended heavily on realized growth rate. Our results show how differences in macroalgal P-dynamics may explain the changing balance among macroalgae with different growth strategies in P-deficient coastal areas.