Growth and reproductive phenology of the kelp Lessonia variegata in central New Zealand

Abstract

A field study of Lessonia variegata growing in depths of 8–10 m on the south coast of Wellington, New Zealand investigated morphometric and biomass indices measured on destructively harvested entire algae, rates of blade elongation measured in situ using a blade hole punch technique, and timing of fertility over a 2‐year period. Blade fertility was estimated using a fertility score based on the visual appearance of the reproductive tissue. Lessonia variegata attained a maximum length of 154 cm, a density of 0.8 to 2.1 individuals m^‐2, and developed an areal biomass ranging from 1700 to 6000 g fresh weight (FW) m^‐2. The highest proportion of fertile blades (up to 100% of sampled blades) occurred during winter and the end of the fertile period coincided with the onset of the longer days and warmer temperatures of summer. Blade elongation occurred more rapidly in summer months (0.117cm day^‐1, SE = 0.015) than winter months (0.041cm day^‐1, SE = 0.009). The slower winter blade elongation rate meant that growth could not overcome tip ablation and average blade length reduced from 51.5cm (SE = 1.9) to 30.8 cm (SE = 1.7) between March and September 2003. Average blade length increased again over the following summer months to 40.7cm (SE = 1.6). Blade biomass dominated total fresh weight biomass (average 64% of total). Two parameters that are relatively easily measured on live macroalgae in situ, holdfast diameter and girth of all stipes collectively, predicted total biomass with an r² = 0.91, suggesting these could be useful tools for assessment of this potentially harvestable resource on Wellington's south coast.

Key words:

• Phaeophyceae
• Laminariales
• morphometry
• subtidal
• harvest