A review of protocols for the experimental release of kelp (Laminariales) zoospores

Kelps (order Laminariales) are foundation species in temperate and arctic seas globally, but they are in decline in many places. Laminarian kelp have an alternation of generations and this poses challenges for experimental studies due to the difficulties in achieving zoospore release and gametophyte growth. Here we review and synthesize the protocols that have been used to induce zoospore release in kelps to identify commonalities and provide guidance on best practices. We found 171 papers, where zoospore release was induced in four kelp families from 35 different ecoregions. The most commonly treated family was Laminariaceae, followed by Lessoniaceae and the most studied ecoregion was Central Chile, followed by the Southern California Bight. Zoospore release generally involved three steps: a pre-treatment which included cleaning of the reproductive tissue to eliminate epiphytic organisms, followed by desiccation of the tissue, and finally a post-desiccation immersion of the reproductive material in a seawater medium for zoospore release. Despite these commonalities, there was a high degree of variation in the detail within each of these steps, even among studies within genera and from the same ecoregions. This suggests that zoospore release may be relatively insensitive across the Laminariales. Nevertheless, greater attention to standardisation of protocols would facilitate comparisons of kelp zoospore release across species and locations. Based on practicality and most common practices, we suggest zoospore release should be achieved through 1) wiping clean the reproductive material, 2) desiccating the reproductive material by wrapping in moist paper towels for 12 hours at room temperature in darkness, and 3) submerging the tissue in seawater medium for one hour at room temperature in darkness. The choice of seawater medium should depend on the actual experiment conducted. Standardized protocols will facilitate broad scale comparative studies across this key taxa.