Article

Marine Biology

, Volume 129, Issue 3, pp 417-424

First online:

Seasonal growth of the giant kelp Macrocystis pyrifera in New Zealand

  • M. T. BrownAffiliated withDepartment of Botany, University of Otago, P.O. Box 56, Dunedin, New Zealand
  • , M. A. NymanAffiliated withDepartment of Mathematics and Computer Science, Alma College, Alma, Michigan 48801-1599, USA
  • , J. A. KeoghAffiliated withDepartment of Botany, University of Otago, P.O. Box 56, Dunedin, New Zealand
  • , N. K. M. ChinAffiliated withDepartment of Botany, University of Otago, P.O. Box 56, Dunedin, New Zealand

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Abstract

The seasonal growth pattern of Macrocystis pyrifera (L.) C. Agardh in New Zealand was determined from measurements of blade-elongation rates between March 1986 and December 1987. Growth rates remained relatively constant throughout most of the year, but declined significantly during the summer months. Seawater nitrate levels had a marked seasonal cycle, with concentrations of 0.3 μM detected in summer. The timing of the decline in internal nitrogen concentrations varied for different-aged blades, but occurred ∼1 mo after the decrease in seawater nitrate concentrations. Sufficiently high irradiance levels and seawater nutrient concentrations support active growth for most of the year, but growth is nutrient-limited during summer. No carbon accumulation during summer was observed. Between March and August 1988, growth estimates were also derived from node-initiation rates and stipe-elongation rates to permit comparisons with previous studies from the northern and southern hemispheres. Direct comparisons of the three growth parameters determined for non-terminated canopy and sub-surface fronds were used to assess possible differential resource allocation in the two frond classes.