Advancing the taxonomy of economically important red seaweeds (Rhodophyta)

Abstract

The cultivation of red seaweeds for food (nori), agar and carrageenans is the basis of a valuable industry. However, taxonomic knowledge of these cultivated seaweeds and their wild relatives has not kept pace with advances in molecular systematics despite the fundamental importance of being able to identify commercially important species and strains, discover cryptic and endemic taxa and recognize non-native species with potentially damaging diseases and epiphytes. This review focuses on molecular taxonomic advances in the cultivated red algae with the highest commercial value globally: Eucheuma, Kappaphycus, Porphyra sensu lato Porphyra/Pyropia and Gracilaria. All four genera are similarly taxonomically challenging. They are speciose, morphologically plastic, have poorly resolved species boundaries, and a stable taxonomy for each genus is yet to be achieved. Eucheuma and Kappaphycus are frequently misidentified and the molecular markers cox2-3 spacer, cox1 and RuBisCO spacer have helped to in understanding phylogenetic relationships, and identifying new species and haplotypes. In Porphyra sensu lato (Bangiales) species identification and phylogenetic relationships were highly problematic until a major taxonomic revision based on a two-gene phylogeny (18S and rbcL) resulted in nine genera of bladed species. Pyropia, with at least 89 species, three in nori cultivation, has potential for new commercial evaluation. The recently published Porphyra genome will aid the exploration of evolutionary relationships in this group. In Gracilaria sensu lato, earlier efforts to resolve species-level taxonomy and generic descriptions were superseded by application of molecular tools, including DNA sequences of the RuBisCO spacer, rbcL gene, 18S and the ITS region. Relationships between clades are now fairly well established, but much research on species and genera is still needed. Studies of these cultivated red algal genera highlight the need for a robust taxonomy, a more standardized approach to the molecular markers used and a comprehensive dataset for each representative species. RecentCurrent work on DNA-based species delimitation, the emergence of high throughput sequencing, multi-gene phylogenies and publication of whole genomes (e.g. Porphyra umbilicalis) and the large number of genomes in the pipeline (e.g. Gracilaria) is increasingly improving our understanding of phylogenomic relationships and hence a better understanding of species relationships. This knowledge, in turn, can then be applied to improving red seaweed aquaculture.

Exploring, harnessing and conserving marine genetic resources towards a sustainable seaweed aquaculture

“…Eucheumatoids are sought after for their rich content of kappa and iota carrageenans (Lim et al, 2017). Carrageen is used as an additive in manufactured food or as a stabiliser in cosmetics.…”

“…Studies aimed at underpinning breeding efforts, however, have only been initiated in recent years and knowledge is particularly limited for tropical species. In fact, cryptic diversities in many seaweed groups have only recently started to reveal their breadth, with the aid of molecular data, including groups of major economic interest, such as the eucheumatoids (Lim et al, 2017, see also Box 1) and foliose Bangiales (Yang et al, 2020).…”

Cultivar Development of Kelps for Commercial Cultivation—Past Lessons and Future Prospects

“…The use of this term is often restricted to genera in the order Laminariales (e.g., Alaria, Ecklonia, Laminaria, Macrocystis, Nereocystis, Saccharina, Undaria), although some species in the order Fucales are regarded as kelps by the general public, e.g., in the genera Durvillaea and Sargassum (Fraser, 2012). "Nori" includes several red algae used for human food, especially Porphyra sensu lato, a taxonomically complex group which includes the genera Porphyra and Pyropia (Lim et al, 2017). Other important groups of red algae are known by the main product obtained from their biomass, as goes for the main producers of agar, the so-called "agarophytes" (which include the genera Agarophyton, Gracilaria, Gracilariopsis, and Gelidium), and the main carrageenan producers or "carrageenophytes" (which include the genera Kappaphycus and Eucheuma) (Santelices and Doty, 1989;Hayashi et al, 2017).…”

Feasibility of farming the agarose-yielding red alga Gracilaria dura using tube-net cultivation in the open sea along the Gujarat coast of NW India

“…14,500 t of agar with a commercial value of over US$246 million. The genus Gracilaria alone constituted over 91% (114,100 dry t) of processed raw material for the agar industry (Lim, Yang, Tan, Maggs, & Brodie, 2017;Porse & Rudolph, 2017).…”