Quantification of laminarialean zoospores in seawater by real‐time PCR

Abstract

Laminarialean plants undergo heteromorphic alternation of generations between the macroscopic diploid sporophyte and the microscopic haploid gametophyte. The generations change through the formation and release of asexual or sexual reproductive cells. It is difficult to monitor the release and diffusion of zoospores into the environment. Furthermore, even if zoospores can be detected, species identification remains difficult. This study attempted to develop a sensitive and fast identification method for laminarialean zoospores using quantitative PCR. In addition, we aimed to estimate the density of zoospores in natural seawater. Specific primers for Saccharina japonica and Undaria pinnatifida were designed and used to estimate the quantity of zoospores in seawater. DNA samples (environmental DNA) were collected from seawater once or twice each month for 2 years at the same area, and seasonal variations in the release of zoospores was monitored. The estimated maturation period based on the number of released zoospores in this study was comparable with those of the previously reported maturation periods of S. japonica and U. pinnatifida sporophytes. This supports the validity of our method in estimating zoospore release from laminarialean plants. The method will be a useful tool for ecological studies on these commercially relevant species.

The role of seasonality in reproduction of multiannual delayed gametophytes ofSaccharina latissima

“…Furthermore, Nagasato et al. (2019) successfully quantified in vivo Saccharina japonica zoospore releases for the first time and found that over a period of 2 years, clear peaks occurred in October/November with undulations and slight increases above baseline of zoospore concentrations during spring in both years, supporting the seasonal lag hypothesis. The possibility of biannual fertilization events is also supported by the fact that spores and the microscopic forms of many macroalgal species have strong tolerances to long periods of darkness (Santelices et al.…”

Development of a framework and toolbox for measuring and evaluating ecosystem interactions of seaweed aquaculture

“…The application of qPCR in ecological studies is well established and also used in seaweed cultivation. For instance qPCR can be used to detect and quantify reproductive material of seaweed (zoospores) in seawater (eDNA samples) (Nagasato et al, 2020). It can also be used as a tool to detect seaweed pathogens (Bernard et al, 2018).…”

(A)biotic lifecycle controls of mutliannual delayed gametophytes of Laminariales (brown seaweeds)

“…Druehl and Hsiao (1973) even described seasonal events that are consistent with our described seasonal lag hypothesis, with two peaks in new macroscopic sporophyte production closely matching the periods in which increased gametophyte reproduction is predicted by our hypothesis. Furthermore, Nagasato et al (2019) successfully quantified in vivo S. japonica zoospore releases for the first time, and found that over a period of two years, clear peaks occurred in October/ November with undulations and slight increases above baseline of zoospore concentrations during spring in both years, supporting the seasonal lag hypothesis. The possibility of biannual fertilization events is also supported by the fact that spores and the microscopic forms of many macroalgal species have strong tolerances to long periods of darkness (Santelices et al 2002), suitable to survive winter conditions.…”