Germplasm cryopreservation of macroalgae for aquaculture breeding and natural resource conservation: A review

The expansion of the global macroalgal aquaculture and climate change creates the need for germplasm preservation of valuable aquaculture strains and maintenance of natural biodiversity. Compared to the large number of studies in fish and shellfish species, relative few studies have been conducted on the macroalgal germplasm cryopreservation. The first cryopreservation of macroalgae to 75 degrees C was reported on Neopyropia tenera (formerly called Porphyra tenera) in 1964. To date, a total of 34 studies reported germplasm cryopreservation in 33 species, including Chlorophyta (7 species), Ochrophyta (14 species), and Rhodophyta (12 species). The goal of this review was to summarize the published studies on macroalgal germplasm cryopreservation, compare the reported protocols for the cryopreservation process, and identify the factors affecting post-thaw viability. Overall, macroalgal germplasm cryopreservation included haploid or diploid thalli, spores, and gametes. Cryotubes (1.5-ml or 2-ml) have been widely used to package germplasm samples for cooling and storage in most studies, and the 0.5-ml straws and 5-ml cryotubes have been used in several studies. Two approaches (programmable controlled cooling and vitrification) were employed for macroalgal germplasm cryopreservation. A two-step programmable controlled cooling (e.g., from initial culture temperature to a frozen temperature, such as 40 degrees C, and then directly plunging into liquid nitrogen at 196 degrees C) was determined to be an effective cooling strategy. Vitrification, a super rapid cooling for a sample to form non-crystalline amorphous solid, was applied on macroalgal germplasm cryopreservation with sample encapsulation and dehydration. Survival of post-thaw samples varied significantly in different studies. Based on research updates, recommendations are made for future research. It is expected that this review can serve as a foundation for future germplasm banking of macroalgae for aquaculture and biodiversity preservation.

Automated summary

The expansion of global macroalgal aquaculture and climate change have highlighted the importance of germplasm preservation in the context of aquaculture strains and natural biodiversity. While there have been limited studies on macroalgal germplasm cryopreservation compared to fish and shellfish species, various approaches such as programmed controlled cooling and vitrification have shown effectiveness in preserving macroalgal samples. The variability in post-thaw viability in different studies underscores the need for continued research and improvement in the field of macroalgal germplasm cryopreservation.