An update on the seaweed resources of Japan

Abstract

Natural seaweed beds, which play an important role for coastal ecosystems and marine fisheries, have been changing drastically in Japan. Interventions, such as decreasing the over-grazing by sea urchins, are being undertaken to maintain natural seaweed beds. Japan has at least 15 seaweed genera of economic importance utilized either directly as human food, as ingredients in food, or as raw materials for extraction of chemical compounds for various applications. Most species are produced through various cultivation methods that usually start in a land-based facility and are completed when seaweeds are transferred for open-sea cultivation. Cultivation, as well as harvesting, from natural populations, has sustained the Japanese seaweed industry for many years, but recently a downfall in seaweed production has been experienced in some areas for certain species due to warming oceans. Efforts to improve production have led to the development of forced cultivation techniques to reduce the cultivation period for Saccharina japonica while hybridization of different morphological forms of Undaria pinnatifida has resulted in the production of so-called “southern” and “northern types” that have desirable shapes for harvesting and processing. The future of the seaweed industry in Japan is geared towards producing high-grade products from seaweeds grown in land-based tanks using deep-ocean water.

The underexplored potential of green macroalgae in aquaculture

“…Today, U . prolifera aquaculture production in Japan turns out unnoticed in FAO aquaculture statistics, although annual production metrics have been reported elsewhere, despite with inconsistent values (eg 200, 1500, 3000 tonnes dry weight; equivalent to approximately ten times as much in fresh weight) 63,89,90 . The species is also cultivated in the southern coast of Korea, where it is valued as an ingredient in salads, soup and cookies 62,91 and likely represents the bulk of ‘green laver’ production reported at 6800 tonnes in 2018 (as previously referred).…”

“…20,000 tonnes fresh weight annually 19 . The present review indicates this value is significantly underestimated, particularly considering the absence of production data from Japan, where commercial cultivation of Monostroma , Ulva and Caulerpa species is a long standing and ongoing activity 63 . In addition, emerging ulvophycean taxa in aquaculture remain unaccounted for in international databases (eg Codium tomentosum ), while taxonomic uncertainty of species and/or seaweed‐derived products creates additional challenges to the academic, public and industrial players.…”

“…19 Molecular studies suggest that cultivated 'green laver' is composed exclusively of Ulva prolifera. 62 In turn, 'green laver' associated genera (Ulva and Monostroma) are considered important components of the aquaculture industry in Japan, 61,63,64 despite not showing in FAO statistics. A thorough revision of the taxonomic affinity of green seaweed products originating from aquaculture is therefore required, particularly those labelled under common trade names.…”

“…19 The present review indicates this value is significantly underestimated, particularly considering the absence of production data from Japan, where commercial cultivation of Monostroma, Ulva and Caulerpa species is a long standing and ongoing activity. 63 In addition, emerging ulvophycean taxa in aquaculture remain unaccounted for in international databases (eg Codium tomentosum), while taxonomic uncertainty of species and/ or seaweed-derived products creates additional challenges to the academic, public and industrial players. These issues call for more detailed molecular surveys and transparent data communication of green macroalgae aquaculture goods to provide more standardised, higher quality, traceable products, important requisites to increase consumer and industrial confidence.…”

Phylogeography of a canopy‐forming kelp, Eisenia bicyclis (Laminariales, Phaeophyceae), based on a genome‐wide sequencing analysis

“…They also serve as a significant carbon sink to mitigate global warming (Chung et al 2013, Krause-Jensen andDuarte 2016). However, kelp forests have been declining in various parts of the world (Krumhansl et al 2016, Wernberg et al 2019, including Japan (Fujita 2010), due to the dominance of sea urchins (Filbee-Dexter and Scheibling 2014, Ling et al 2015), overgrazing by herbivores (Gianni et al 2017, Zarco-Perello et al 2017, and climate change (e.g., Wernberg et al 2016, Rogers-Bennett and Catton 2019, Tanaka et al 2020. Although effective reforestation techniques have been developed to restore kelp forests (e.g., Ling et al 2010, Westermeier et al 2014, Fredriksen et al 2020, their implementation should consider intraspecific genetic diversity and genetic structure (Moritz 2002, Hoban et al 2020.…”