Restoration of the bull kelp Nereocystis luetkeana in nearshore rocky habitats

Abstract

Anthropogenic disturbances such as shoreline development and sediment loading can reduce or eliminate Nereocystis luetkeana populations and commercially important species associated with N. luetkeana. Hence, kelp restoration will become increasingly important in urbanized nearshore areas. Techniques to establish N. luetkeana populations in the northwestern waters of Washington State, USA, were examined and compared: (1) out-planting recently settled zoospores and microscopic sporophytes (0.5 to 1.0 mm blade length) grown in laboratory culture, in the field onto natural substrate, and at elevated positions, and (2) transplanting juvenile sporophytes (<15 cm stipe length) from natural populations, bypassing the culturing phase. Juvenile transplants were found to be more successful than cultured out-plants. The restoration cost for juvenile transplants was 12 US dollars (USD) per installed plant with a maximum cost estimate of 200 USD m-2. These had a 10 to 30% higher survival rate than previously reported kelp transplant efforts using larger individuals. The collection of smaller individuals for transplanting imposes smaller ecological costs to natural populations than does the collection of larger, established plants. Stipe breakage caused by the grazing gastropod Lacuna vincta posed the largest limiting factor on transplant survival. Lack of survival among the out-planted zoospores and microscopic sporophytes indicates that other methods will be more successful. Restoration efforts in the nearshore marine environment will benefit from an adaptive management approach in which techniques can be tailored to the specific physical and biological conditions at the restoration site. © Inter-Research 2005.