Gracilariopsis (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Gracilariopsis E.Y. Dawson

Protologue: Allan Hancock Found. Publ. Occas. Pap. 7: 40 (1949).

Family: Gracilariaceae

Chromosome number: 2n= most probably 64

Major species and synonyms

• Gracilariopsis heteroclada C.F. Zhang & B.M. Xia - see separate article.

• Gracilariopsis lemaneiformis (Bory) E.Y. Dawson, Acleto & Foldvik - see separate article.

• Gracilariopsis longissima (S.G. Gmelin) Steentoft, L.M. Irvine & Farnham - see under Gracilaria "verrucosa".

Vernacular names

• Philippines: gulaman, caocaoyan, gargararao, lagot.

Origin and geographic distribution

Gracilariopsis occurs in many locations but due to taxonomic and nomenclatural uncertainties, reliable general data are not yet available.

Uses

Most Gracilariopsis are used both for food and as raw material for the agar industry. Several of these algae are also used as feed for cultivated fish and invertebrates and as medicine (as a laxative and for pulmonary complaints). Several Gracilariopsis, especially G. lemaneiformis are sources of high quality sugar-reactive agar.

Production and international trade

Often no separate data for Gracilariopsis are available; usually these data are incorporated in information on Gracilaria spp.

Description

• Plants usually bushy, arising from a small discoid base.
• Fronds cylindrical; branching secund or alternate; branches basically constricted or not, fleshy to cartilaginous.
• Medulla parenchymatous, consisting of large cells; cortex narrow, small-celled, assimilative.
• Life cycle triphasic, diplo-haplontic, isomorphic and dioecious.
• Tetrasporangia formed in cortex.
• Spermatangia cut off from surface cells, arranged in continuous superficial layers.
• Cystocarps hemispherical, with small-celled broad-based placental tissue without nutritive filaments, with prominent superficial pericarp composed of several layers of radiating cells.
• Carpospores discharge through a pore.

Growth and development

Shedding of tetraspores or carpospores in Gracilariopsis results in a remarkable increase of biomass during the months that follow. Exposure of thalli to air seems to be favourable to gamete maturation. Tetraspore formation in laboratory cultures can be induced by manipulating environmental factors such as photoperiod, photoflux density, temperature, salinity and nutrients. Laboratory-generated carposporelings can be planted out for phycoculture.

Other botanical information

Because of the economic interest in its products, in particular phycocolloids, the study of Gracilarioid algae has spread rapidly throughout the world, resulting in numerous proposals for taxonomic and nomenclatural change. Names of genera that have been separated from Gracilaria Grev. include Gracilariopsis. In South-East Asia, however, most described differences between these genera are often considered to be too technical for general acceptance, resulting in proposals to retain all species in the single genus Gracilaria. Nevertheless, the separation of Gracilaria and Gracilariopsis is at present often followed, as is done in the present volume.

Ecology

It is impossible to differentiate the ecological information found in data provided for Gracilaria and for Gracilariopsis.

Propagation and planting

The usual method of propagation used in Gracilariopsis phycoculture is vegetative fragmentation, although methods for propagation by spores have been described. Gracilarioid algae usually regenerate easily when cut. Thalli are chopped or split and bunches of branches or individual branches are used for planting (bottom-stocking) or broadcasting or for cultivation on ropes, either in fixed off-bottom frames, on floating long lines or on rafts.

Phycoculture

The methods used for Gracilaria cultivation can be applied to Gracilariopsis as well. In South-East Asia phycoculture usually takes place by broadcasting vegetative fragments in semi-enclosed ponds.

Harvesting

Harvest techniques used for Gracilariopsis are the same as those for Gracilaria. Thus not more than 50-70% of the natural stock should be harvested, and also in cultivation ponds it is necessary to allow sufficient material for regeneration. Harvesting is usually done by hand.

Yield

Data on Gracilariopsis yields are mostly included in those on Gracilarioid algae.

Handling after harvest

Post-harvesting techniques are the same for both Gracilariopsis and Gracilaria. The harvested algae should be cleaned on site and transported to a drying area. Once dried, the seaweeds should be packed in bags, stored in a dry place, and sold and transported as soon as possible.

Prospects

The quality of Gracilariopsis agar is often better than that of several Gracilaria spp., but a general rule cannot yet be given.

Literature

• Abbott, I.A., 1995. A decade of species of Gracilaria (sensu latu). In: Abbott, I.A. (Editor): Taxonomy of economic seaweeds 5. pp. 185-195.
• Kapraun, D.F., Lopez-Bautista, J., Trono, G.C. & Bird, K.T., 1996. Quantification and characterization of nuclear genomes in commercial red seaweeds (Gracilariales) from the Philippines. Journal of Applied Phycology 8: 125-130.
• Tseng, C.K. & Xia, B.M., 1999. On the Gracilaria in the Western Pacific and Southeastern Asia region. Botanica Marina 42: 209-217.

Authors

• W.F. Prud'homme van Reine