Biomass, production and rhizome growth near the northern limit of seagrass (Zostera marina) distribution

The biomass, shoot density, community production, and rhizome growth of Zostera marina stands were studied in the Hopavagen lagoon, Norway (63°35′65″N, 9°32′80″E), the northern-most location where seagrass growth and production has been studied. The nordic Z. marina patches were dense (>2700 shoot m^-2), with relatively small shoots (33-54 mg DW), so that the aboveground biomass developed was relatively low (about 140 g DW m^-2). The stands were moderately productive, at about 2 g O₂ m^-2 per day, similar to the average community respiration rate. The sequence of internodal lengths in the rhizome fragments harvested showed a clear annual cycle, indicating that the populations are perennial (rhizomes >2-year-old) producing about 25 leaves per shoot and 30cm of rhizome annually. The leaf plastochrone interval, of about 15 days, was close to that reported for stands situated as much as 25°S.