731

15(1): Cryptogams: Algae

Dictyosphaeria cavernosa (Forssk.) Børgesen

Revis. Forssk. alg.: 2, pl. 1, fig. 1 (1932).

SIPHONOCLADACEAE

2n = unknown

Ulva cavernosa Forssk. (1775), Valonia favulosa C. Agardh (1822), Dictyosphaeria favulosa (C. Agardh) Decne. ex Endl. (1843).

Australia: Green bubble weed (En).

Dictyosphaeria cavernosa is widely spread in tropical and subtropical seas all over the world. In South-East Asia this alga is recorded in all countries except Cambodia, Vietnam and Brunei Darussalam.

Dictyosphaeria cavernosa is used as human food and as an antimicrobial medicine. No toxic effects to eukaryotes are known.

Thalli sessile, dark green, hollow, 2—5(—12) cm in diameter, nearly spherical, irregularly lobed or partly collapsed, occasionally concrescent; sometimes rupturing, irregularly saucer-shaped, and in deep water reaching a diameter of 30 cm, attached by irregularly elongated (rhizoidal) cells; thallus surface consisting of a single layer of large angular vegetative cells, 0.1—1(—4.5) mm in diameter; connecting tenacular cells numerous, 35-50 µm x 60—65 µm, lenticular, with simple or bifurcate haptera, often with fimbriate distal margins. Life cycle diplo-haplontic and isomorphic. Sporophytes with quadriflagellate zoospores; male and female gametophytes producing biflagellate isogametes.

Isogametes of Dictyosphaeria cavernosa can also develop parthenogenetically and then form new gametophytic thalli. When young, thalli form hollow spheres which rupture when mature. Isogametes fuse soon after release and the resulting zygotes settle on the substrate, germinating without any delay. Quadriflagellate zoospores, zygotes, and even unfused parthenogametes germinate in a fundamentally identical way after shedding their flagella. They first round up, forming a cell wall within 24 hours, then increase their volume and develop into spherical bodies, which produce some rhizoidal filaments. About three months after germination, segregative cell divisions take place within the unicellular germlings, which are by then 3—5 mm in diameter. First many spherical protoplasmic bodies are formed, which then develop into a layer of polygonal daughter cells that together form the monostromatic mature thalli. These are attached by rhizoidal cells formed by elongation of basal cells.

Dictyosphaeria cavernosa is commonly found on rocks and reefs in the intertidal zone, where it is however often poorly developed. A little lower down on the shore it reaches full size, and it has also been recorded at depths of up to 55 m. The composition and texture of the rocky substrate greatly influence communities of this alga. It often grows on white, porous shell remains, which reflect light and have a high waterholding capacity. The alga can penetrate this substrate and then grow in semiprotected niches.

Phycoculture of Dictyosphaeria cavernosa is not known.

Dictyosphaeria cavernosa is harvested only by hand-collecting.

Dictyosphaeria cavernosa is mainly used fresh.

The use of Dictyosphaeria cavernosa as human food is likely to remain limited. Its antimicrobial capacity might be developed in the future.

Enomoto, S., Hori, T. & Okuda, K., 1982. Culture studies of Dictyosphaeria (Chlorophyceae, Siphonocladales) II. Morphological analysis of segregative cell division in Dictyosphaeria cavernosa. Japanese Journal of Phycology (Sôrui) 30: 103—112.
Enomoto, S. & Okuda, K., 1981. Culture studies of Dictyosphaeria (Chlorophyceae, Siphonocladales) I. Life history and morphogenesis of Dictyosphaeria cavernosa. Japanese Journal of Phycology (Sôrui) 29: 225—236.

P.Y. van Aalderen-Zen

van Aalderen-Zen, P.Y., 2001. Dictyosphaeria cavernosa (Forssk.) Børgesen. In: Prud'homme van Reine, W.F. and Trono Jr, G.C. (Editors): Plant Resources of South-East Asia No 15(1): Cryptogams: Algae. PROSEA Foundation, Bogor, Indonesia. Database record: prota4u.org/prosea