MEPS 399:103-115 (2010)  -  DOI:

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

Morten Foldager Pedersen1,*, Jens Borum2, Frank Leck Fotel1

1Department of Environmental, Social & Spatial Change (ENSPAC), Roskilde University, Box 260, 4000 Roskilde, Denmark
2Freshwater Biological Laboratory, Biological Institute, University of Copenhagen, Helsingørsgade 51, 3400 Hillerød, Denmark

ABSTRACT: 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 (Ulva and Ceramium) took up dissolved inorganic P (DIP) much faster than thicker, slower growing species (belonging to Fucus, Ascophyllum and Laminaria) 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, Ceramium and Ulva were potentially P-limited during summer, whereas Ascophyllum and Laminaria were able to acquire sufficient external DIP to remain P-replete throughout the year. Storage of P prevented Fucus species 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.

KEY WORDS: Macroalgae · Seaweeds · Nutrient dynamics · Phosphorus · Eutrophication

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Cite this article as: Pedersen MF, Borum J, Leck Fotel F (2010) Phosphorus dynamics and limitation of fast- and slow-growing temperate seaweeds in Oslofjord, Norway. Mar Ecol Prog Ser 399:103-115.

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