SEASONAL GROWTH OF THE GIANT-KELP MACROCYSTIS-PYRIFERA IN NEW-ZEALAND

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 relativel y constant throughout most of the year, but declined significantly dur ing the summer months. Seawater nitrate levels had a marked seasonal c ycle, with concentrations of 0.3 mu M detected in summer. The timing o f the decline in internal nitrogen concentrations varied for different -aged blades, but occurred similar to 1 mo after the decrease in seawa ter nitrate concentrations. Sufficiently high irradiance levels and se awater nutrient concentrations support active growth for most of the y ear, but growth is nutrient-limited during summer. No carbon accumulat ion during summer was observed. Between March and August 1988, growth estimates were also derived from node-initiation rates and stipe-elong ation rates to permit comparisons with previous studies from the north ern and southern hemispheres. Direct comparisons of the three growth p arameters determined for non-terminated canopy and sub-surface fronds were used to assess possible differential resource allocation in the t wo frond classes.