Asexual propagation of Asparagopsis armata gametophytes: fragmentation, regrowth and attachment mechanisms for sea-based cultivation

Abstract

The red algal genus Asparagopsis produces secondary metabolites that when fed to ruminants reduce methane production by up to 98%. However, cultivation methods for Asparagopsis are nascent and fundamental information on reproduction, which is essential for large-scale cultivation, is lacking. In this study we examined asexual propagation in Asparagopsis armata, the regrowth of fragments and mechanisms of attachment to assess the potential for fragments to be used in sea-based cultivation. Asparagopsis armata gametophytes grow specialised structures, barbs, that hook fragments onto substrata. Surveys revealed barbs were abundant occurring at ~ 1 barb every 3–4 cm on gametophyte branches. Barbs did not regrow, but fronds did, either when attached to a barb or on their own. In contrast, fronds doubled in size with most developing barbs within 4 weeks. Barbs were, however, critical for the reattachment of fragments: barbs attached to substrata at four times the rate of frond fragments without barbs and they also attached in higher proportions to mussel rope than polypropylene rope, and two types of net. Utilising fragmentation for the propagation of A. armata gametophytes in sea-based cultivation requires that fragments can attach to a substratum and regrow once attached. We have shown that A. armata fragments in Tasmania require barbs for attachment and frond tissue for growth, which has implications for cultivation. Optimising fragmentation, attachment and out-planting methods are important future steps in establishing fragmentation as a method for sea-based cultivation in A. armata.

Exploring the effects of temperature and light availability on the vegetative propagation processes of the non-native species Asparagopsis armata

“…These findings differ to those found for A. armata in New Zealand and Tasmania where regrowth from single hooks was not possible (Bonin and Hawkes, 1987;Wright et al, 2022), but are in close agreement to those found in France where regrowth occurred (Codomier et al, 1979;Haslin and Pellegrini, 2001). The lack of regrowth in New Zealand and South Australia has been suggested to be attributed to seasonal effects or the existence of genetically different strains (Wright et al, 2022). In fact, there are genetic evidences of different clades of A. armata clearly linked to its geographic distribution (Dijoux et al, 2014;Preuss et al, 2022) and differences among these strains have been previously reported for other phenological responses (e.g.…”

“…Study findings showed how the development of new fronds from single hooks collected in northern Spain (1-3cm length) is possible. These findings differ to those found for A. armata in New Zealand and Tasmania where regrowth from single hooks was not possible (Bonin and Hawkes, 1987;Wright et al, 2022), but are in close agreement to those found in France where regrowth occurred (Codomier et al, 1979;Haslin and Pellegrini, 2001). The lack of regrowth in New Zealand and South Australia has been suggested to be attributed to seasonal effects or the existence of genetically different strains (Wright et al, 2022).…”

“…For A. armata gametophytes, only the effects of medium composition (i.e. nutrients) (Codomier et al, 1981;Haslin and Pellegrini, 2001) and the type of substrata haven been explored (Wright et al, 2022). These studies showed how the production and growth of vegetative structures (plantlets) was promoted by substances such us iron sulfate and potassium bromide.…”

A strategic review and research roadmap for offshore seaweed aquaculture—A case study from southern Australia

“…Gametophytes of Asparagopsis have been cultivated on longlines in wave‐sheltered waters, 89,91 while tetrasporophytes have been cultivated on land in small tanks (~110 L) and using finfish effluent a source of nutrients and carbon dioxide to enhance production 88,93 . A. armata gametophytes can be asexually propagated and fragmented fronds that contain barbs are attached to substrate for new tissue to grow 94 . A. taxiformis lacks barbs, therefore, seeding of tetraspores produced by cultured tetrasprophytes onto suitable substrate in a nursery is proposed as an alternative strategy for growth of gametophytes at sea in this species 82 .…”

“…88,93 A. armata gametophytes can be asexually propagated and fragmented fronds that contain barbs are attached to substrate for new tissue to grow. 94 A. taxiformis lacks barbs, therefore, seeding of tetraspores produced by cultured tetrasprophytes onto suitable substrate in a nursery is proposed as an alternative strategy for growth of gametophytes at sea in this species. 82 Based on current published knowledge, the life cycle has not yet been closed (from gametophyte to gametophyte), and so biomass production remains reliant on harvest of wild stock and/or fragmentation of the various life stages.…”