Life history and culture studies of Monostroma oxyspermum (Kutz.) Doty (Monostromataceae, Chlorophyceae) growing in estuarine conditions along the central west coast of India
Figures 15. 1, Macroscopic thallus of Monostroma oxyspermum in natural habitat. 2, Vegetative cells (scale bar = 10 m m). 3, Settling zoospores (scale bar = 5 m m). 4, 10-day-old culture spore germination (scale bar = 20 m m). 5, 20-day-old culture showing tube-like thallus (scale bar = 50 m m).
mats in muddy substrata, 2040 ´ 1520 cm in size (Figure 1), monostromatic with frill margins, 2024 m m thick, outer margin yellowish at maturity, thallus cells polygonal, 1015 ´ 1820 m m (Figure 2) in surface view with single parietal chloroplast and one pyrenoid. The zoospores (swarms) are liberated, biflagellate, 57 ´ 24 m m in size, flagella of the same length. In culture swarms become round, losing flagella and subsequently develop a germination tube (Figure 3). Fusion does not take place among the zoospores. Division of cell in swarms takes place after 45 days, the upper cell forming the uniseriate filament and the lower rhizoidal development (Figure 4). Cyst formation does not take place at any stage. Further divisions in the filament are in vertical and transverse plane, resulting in about 12 months, in a sachet-like thallus (Figure 5), which becomes monostromatic (Figure 6). On reaching a size of 34 cm in about 34 months, sporangia develop on the surface (Figure 7) and liberate the swarms. Cytological studies of the thallus and swarm cells revealed the chromosome number to be 810 (Figure 8). There is no alternation of generation. The species contain high level of carbohydrates and can be recommended for economic exploitation, as it can be easily cultivated on a large scale, the growth rate being 0.32 g per day.
The species has earlier been reported from swamps and brackish waters in subtropics by Boergessen1 and Abbott and Hollenberg2. Life history of different species of Monostroma has been described by Tatewaki3. Another species of Monostroma occurring in Okha coast,
Figures 68. 6, Opened up tube forming a monostromatic thallus (scale bar = 100 m m). 7, Formation of sporangia in culture (scale bar = 10 m m). 8, Chromosome of M. oxyspermum (scale bar = 2 m m).
Gujarat, differs in the formation of cyst, smaller thallus (210 ´ 12 cm) (ref. 4), presence of alternation of generation
and a seasonal growth. According to Tatewaki (personal communication) this may be M. latissimum.
ACKNOWLEDGEMENTS. We thank the Director, National Institute of Oceanography, Dona Paula, Goa for providing facilities. G. D. is grateful to CSIR for the Research Associate award. This is contribution no. 1191 from NIO, Goa.
V. K. DHARGALKAR
A. G. UNTAWALE
Biological Oceanography Division, National Institute of Oceanography, Dona Paula, Goa 403 004, India
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