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

Abstract

Abstract: 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 pretreatment which included cleaning of the reproductive tissue to eliminate epiphytic organisms, followed by desiccation of the tissue, and finally a postdesiccation 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 either that zoospore release may be relatively insensitive across the Laminariales or that little methods optimization has been undertaken. We suggest that greater attention to standardization of protocols and reporting of methodology and optimization would improve comparisons of kelp zoospore release across species and locations and facilitate a broader understanding of this key, but understudied life history stage.

Open research badges: This article has earned an Open Data Badge for making publicly available the digitally-shareable data necessary to reproduce the reported results. The data is available at https://doi.org/10.5061/dryad.0kh1f8j.

Keywords: Laminariales; desiccation; gametophytes; kelp forests; zoospore release; zoospores.

Figure 1

Characteristics of artificial zoospore extraction studies (171 papers, 421 studies). Classification of studies according to (a) the research question addressed; (b) the family studied; and (c) the genera studied. All papers and their classifications can be found in the raw data table provided on Dryad; see data availability statement

Figure 2

Global distribution of zoospore extraction based experiments. Ecoregions are colored based on the number of studies conducted and gray shading indicates ecoregions where kelps are present but for which no data were available. Black dots show the exact geographical location of the sites used for the collection of kelp tissue

Figure 3

Zoospore release protocol: (a) pretreatment method where W, wiped clean and dried; SW/R, seawater rinse; FW/R, fresh water rinse; FW/SW R, fresh water and seawater rinse; R/W, rinsed and wiped; No, no pretreatment; N/A, no data available; (b) desiccation environments where No, no desiccation treatment; N/A, no data available; (c) postdesiccation immersion media where FSS, filtered‐sterilized seawater; PES, Provasoli‐enriched seawater; US, unfiltered seawater; UAS, unenriched artificial seawater; TS, Tyndallized seawater. Colors refer to the families studied

Figure 4

Zoospore release desiccation treatment: (a) temperature; (b) period (hr); (c) light conditions. Colors refer to the families studied

Figure 5

Zoospore release postdesiccation immersion: (a) temperature; (b) period (hr). Colors refer to the families studied