HYDROBIOLOGICAL STUDIES WITHIN THE TEA GARDENS AT SRIMANGAL , BANGLADESH . VI . DESMIDS ( XANTHIDIUM , ARTHRODESMUS , STAURODESMUS AND STAURASTRUM )

In this last instalment of the series, 78 desmid taxa belonging to four genera, namely Xanthidium (8 taxa), Arthrodesmus (3 taxa), Staurodesmus (11 taxa) and Staurastrum (56 taxa) have been recorded from different aquatic habitats located within the tea gardens at Srimangal, Maulvi Bazar. Of these, nine are described as new records for Bangladesh. An overall assessment of the algal flora of the study area reveals desmids as the single largest group consisting of 230 taxa out of 421 recorded algal taxa. The paper comments on the conservation potentials of the studied aquatic habitats as monitoring tools of land use pattern like tea-gardening. Introduction In a series of hydrobiological papers, Islam and Irfanullah have recently described the aquatic macrophytes (Islam and Irfanullah 2000) and the major proportion of the algal flora (Islam and Irfanullah 2005a, b, c, 2006) of some selected habitats within the tea gardens at Srimangal, Maulvi Bazar District. The present paper is the concluding instalment of this series dealing with four desmid genera, namely, Xanthidium, Arthrodesmus, Staurodesmus and Staurastrum, from these aquatic habitats. Materials and Methods The studied water bodies (described in Islam and Irfanullah 2000), namely, Baraoora Lake, the Burburia River, ditches and paddy fields were mainly acidic (Islam and Irfanullah 2005a). A total of 120 algal samples were collected in different seasons of 1996 and 1997: winter (9 January 1996 and 6 January 1997), spring (18 March 1997), rainy season (20 July 1997) and autumn (20 October 1997). The methods of sample collection, preservation and subsequent examination were described by Islam and Irfanullah (2005a). Taxonomic enumeration This study revealed 78 desmid taxa belonging to four genera, of which nine are new records for Bangladesh. The new records are marked with asterisks. Eighteen desmid taxa belonging to the mentioned four genera have already been reported from this area by the Corresponding author. Present address: The World Conservation Union (IUCN), Bangladesh Country Office, House 11, Road 138, Gulshan 1, Dhaka-1212, Bangladesh. E-mail: hmirfanullah@yahoo.co.uk 112 ISLAM AND IRFANULLAH same authors as new records for Bangladesh (Islam and Irfanullah 1998, 1999), thus are not marked in this account. Remaining other taxa are briefly described along with their spatial and temporal occurrence, and abundance. Class: Chlorophyceae; Order: Zygnematales; Family: Desmidiaceae Genus: Xanthidium Ehrenberg 1. X. acanthophorum Nordst. (Pl. 1, Fig. 4) (Islam 1970, 928, 14: 4) L. csp. 59.4 μm, L. ssp. 44.5 μm, W. csp. 46 μm, W. ssp. 37.8 μm, I. 12 μm. Lake (autumn 1997) and river (spring 1997); rare. 2. X. burkillii W. & W. fa. (Pl. 1, Fig. 5) L. csp. 74.2-78.3 μm, L. ssp. 52.6-54 μm, W. csp. 87.7; W. ssp. 59.4-61.4 μm. I. 23 μm. Differs from Islam and Haroon (1980, 582, 16: 232) in the ornamentations at front view. Lake; winter 1996; few. 3. X. hastiferum Turner var. javanicum (Nordst.) Turner (Islam and Irfanullah 1999, 103, 3: 31) Lake; autumn 1997; rare. 4. X. hastiferum var. javanicum fa. planum Turner (Islam and Irfanullah 1999, 103, 3: 30) Lake; autumn 1997; few. 5. X. spinosum (Josh.) W. & W. fa. (Pl. 1, Fig. 2) L. ssp. 50 μm, W. ssp. 48.6 μm, W. csp. 54 μm, I. 25.6 μm. Ten pairs of spine not regularly arranged as described by Islam and Haroon (1980, 584, 16: 226-227). Lake (winter 1996 and spring 1997; few) and river (winter 1997; rare). 6. X. spinosum (Josh.) W. & W. var. (Pl. 1, Fig. 3) L. 47.2 μm, W. ssp. 44.5 μm, W. csp. 48.6 μm, I. 24.3 μm. Small spines are irregularly, sparsely distributed all over the cell surface. River; spring 1997; rare. 7. X. urniforme (W. & W.) Scott & Croasdale (Pl. 1, Fig. 1) (Islam and Haroon 1980, 586, 13: 177) L. csp. 44.5 μm, L. ssp. 41.8 μm, W. csp. 41.8-44.5 μm, W. ssp. 39 μm, t. csp. 25.6 μm, t. ssp. 23 μm, I. 17.5 μm. Paddy field and river; autumn 1997; few to rare. 8. Xanthidium sp. (Pl. 1, Fig. 6) L. csp. 61 μm, L. ssp. 47 μm, depth 23.5-24.7 μm. River; spring 1997; rare. HYDROBIOLOGICAL STUDIES WITHIN THE TEA GARDENS 113 Plate 1 (Figs. 1-6) 1. Xanthidium urniforme, 2. X. spinosum fa., 3. X. spinosum var., 4. X. acanthophorum, 5. X. burkillii fa., 6. Xanthidium sp. [Scales = 20 μm] Genus: Arthrodesmus Ehrenberg 9. A. asperies Scott & Croasdale fa. (Islam and Irfanullah 1999, 95, 2: 17-18) Lake; winter 1996; few. 10. *A. curvatus Turner var. latus Scott & Prescott (Pl. 2, Fig. 8) (Scott and Prescott 1961, 76, 33: 1-3) L. 36.4 μm, W. csp. 70.2-73 μm, W. ssp. 39-41.8 μm, I. 13.5 μm. Lake; winter 1996; common. 114 ISLAM AND IRFANULLAH 11. A. curvatus Turner fa. (Pl. 2, Fig. 7) L. 36.4 μm, W. csp. 64.8-66 μm, W. ssp. 35-37.8 μm, I. 8 μm. Our form differs from Hirano (1972, 142, 7: 3) in narrow isthmus and angular sides. Side’s angles are comparable with Corasdale and Scott’s Staurodesmus indentatus (W. & W.) Teil. (1976, 542, 12: 1). Lake; winter 1996; few. Genus: Staurodesmus Teiling 12. Std. dejectus (Bréb.) Teil. var. dejectus fa. (Islam and Irfanullah 1999, 96, 4: 45-46) Lake; winter 1996; rare. 13. Std. dickiei (Ralfs) Lillier var. circularis (Turner) Croasdale (Islam and Irfanullah 1999, 96, 4: 39-40) Lake; autumn 1997; common. 14. Std. dickiei var. circularis fa. (Islam and Irfanullah 1999, 97, 4: 41-42) Lake; winter 1996 and 1997; rare to common. 15. Std. dickiei var. maximus (W. West) Thom. (Islam and Irfanullah 1999, 97, 4: 37-38) Lake; winter 1996; common. 16. Std. hebridarus (W. & W.) Förster var. hebridarus (Islam and Irfanullah 1999, 98, 4: 43-44) Lake; winter 1997; few. 17. Std. megacanthus (Lund.) Thunk. (Pl. 2; Fig. 12) (Ling and Tyler 1986, 53, 26: 5-7) L. 46 μm, W. csp. 58.8-68.2 μm, W. ssp. 44.7-50.5 μm, I. 11.8 μm. Lake; winter 1996; few. 18. Std. pachyrhynchus (Nordst.) Teiling (Islam and Irfanullah 1998, 94, 2: 16) Lake; winter 1997; few. 19. Std. unicornis (Turner) Thomasson var. ceylanicum W. & W. fa. (Islam and Irfanullah 1999, 98, 3: 32-33) Lake; autumn 1997; few. 20. Std. unicornis (Turner) Thomass. var. gracilis (Iyenger & Vimala Bai) Teil. (Croasdale and Scott 1976, 543, 14: 3) (Pl. 2, Fig. 10) L. 30.3 μm, W. csp. 34.3-36.4 μm, W. ssp. 25.6-28.3 μm, I. 7.4 μm. Lake; winter 1996; few. HYDROBIOLOGICAL STUDIES WITHIN THE TEA GARDENS 115 Plate 2 (Figs. 7-15) 7. Arthrodesmus curvatus fa., 8. A. curvatus var. latus, 9 & 11. Staurastrum leptodermum var. ikapoae, 10. Staurodesmus unicornis var. gracilis, 12. Std. megacanthus, 13. Staurastrum sp., 14. St. leptacanthum var. brachyurum, 15. St. freemanii fa. [Scales = 20 μm] 116 ISLAM AND IRFANULLAH 21. Staurodesmus sp. (Pl. 3, Fig. 26) L. 27.5 μm, W. 22.5-25 μm, I. 11.7 μm. Granules are concentrically arranged on each arm as well as on the poles. Shape is similar to Std. pachyrhynchus (Nordst.) Teiling (Islam and Irfanullah 1998, 94, 2: 16). Lake; winter 1997; very rare. 22. Staurodesmus sp. (Pl. 7, Fig. 70) L. 27.5 μm, W. csp. 25.8-27.5 μm, I. 7.5 μm. Lake; winter 1997; rare. Genus: Staurastrum Meyen 23. St. alternans Bréb. (Islam and Irfanullah 1999, 94, 2: 11-13) Lake; autumn 1997; rare. 24. St. alternans Bréb. fa. (Pl. 4, Fig. 37) L. 27 μm, W. 25 μm, I. 8.5 μm. River; spring 1997; rare. 25. St. bifidum (Ehr.) Bréb. (Pl. 7, Figs. 59 & 60) (Ling and Tyler 1986, 38, 28: 17 & 18) L. 43.2 μm, W. csp. 63.4-68.8 μm, W. ssp. 40.5-43.2 μm, I. 14-16 μm, cell wall punctuate, divergent processes on each arm tip. Ours are larger than Ling and Tyler’s specimens. Lake; winter 1996; common. 26. St. bifidum (Ehr.) Bréb. fa. (Pl. 3, Fig. 28) L. 32.4-37.8 μm, W. csp. 32.4-46 μm, W. ssp. 28.3-32 μm, I. 13.5-14.8 μm; smooth wall, flat poles. The distance between the level of spines and the level of isthmus is twice as much the distance between the level of spines and the level of the pole of a semicell. Lake (winter 1997, common) and river (spring 1997, few). 27. St. brevispinum Bréb. fa. (Pl. 7, Fig. 68) L. 25 μm, W. csp. 29-30 μm, W. ssp. 26.7-28 μm, I. 5.8 μm. Semi-cells broader and length-wise compressed compare with Hirano’s (1959a, 289, 38: 7) material. Lake; winter 1996; rare. 28. St. ? cerastes Lund. (Pl. 6, Fig. 48) (Hirano 1959b, 371, 50: 1) L. 37.8 μm, W. cpr. 50.5 μm, I. 7.4 μm, t. 9.4 μm. Lake; autumn 1997; rare. 29. St. ceylanicum W. & W. Paddy field; autumn 1997; few. 30. St. coarctatum Bréb. var. subcurtum Nordst. (Pl. 3, Fig. 27) (Islam and Irfanullah 1999, 96, 2: 15 & 16) Lake; winter 1996; few. HYDROBIOLOGICAL STUDIES WITHIN THE TEA GARDENS 117 Plate 3 (Figs. 16-30) 16-18. Staurastrum orbiculare var. depressum, 19. St. retusum var. boreale, 20. St. disputatum var. sinense fa., 21 & 22. Staurastrum sp., 23. St. disputatum var. sinense, 24. St. disputatum var. extensum, 25. St. punctulatum, 26. Staurodesmus sp., 27. Staurastrum coarctatum var. subcurtum (after Islam and Irfanullah, 1999), 28. St. bifidum fa., 29. St. ensiferum, 30. Staurastrum sp. [Scales = 10 μm] 118 ISLAM AND IRFANULLAH 31. *St. ? crenulatum (Näg.) Delp. (Pl. 6, Fig. 53) (Scott and Prescott 1961, 88, 59: 10) L. 25 μm, W. csp. 37.5 μm, W. ssp. 30.8 μm, I. 8 μm. Lake; winter 1997; few. 32. *St. ? cyclacanthum W. & W. (Pl. 6, Fig. 54) W. csp. 48.6-52.6 μm, W. ssp. 40.5-43.2 μm, I. 8 μm. Top view is similar to St. cyclacanthum var. armigerum of Scott and Prescott (1961, 89, 57: 1-3). Lake; winter 1996; rare. 33. St. disputatum W. & W. var. extensum (Borge) W. & W. (Pl. 3, Fig. 24) (Islam and Haroon 1980, 588, 17: 238 & 239) L. 24.3 μm, W. 27.7 μm, I. 8 μm. River; spring 1997; few. 34. St. disputatum W. & W. var. sinense (Lütkm.) W. & W. (Pl. 3, Fig. 23) (Skuja 1949, 157, 36: 1 & 2) L. cpr. 27 μm, W. cpr. 27-28.3 μm. I. 10.8 μm. Lake (winter 1996) and river (spring 1997); few. 35. St. disputatum var. sinense fa. (Pl. 3, Fig. 20) L. 20.2 μm, W. 17.5 μm, I. 5.4 μm. Comparable with Hirano (1959b, 298, 39: 3). Paddy field; autumn 1997; rare. 36. St. ensiferum Turner (Pl. 3, Fig. 29) (Turner 1892, 109, 14: 22; Ling and Tyler 1986, 40, 39: 23-26) L. ssp. 48.6 μm, W. csp. 46-48 μm, W. 


Introduction
In a series of hydrobiological papers, Islam and Irfanullah have recently described the aquatic macrophytes (Islam and Irfanullah 2000) and the major proportion of the algal flora (Islam andIrfanullah 2005a, b, c, 2006) of some selected habitats within the tea gardens at Srimangal, Maulvi Bazar District.The present paper is the concluding instalment of this series dealing with four desmid genera, namely, Xanthidium, Arthrodesmus, Staurodesmus and Staurastrum, from these aquatic habitats.

Materials and Methods
The studied water bodies (described in Islam and Irfanullah 2000), namely, Baraoora Lake, the Burburia River, ditches and paddy fields were mainly acidic (Islam and Irfanullah 2005a).A total of 120 algal samples were collected in different seasons of 1996and 1997: winter (9 January 1996and 6 January 1997), spring (18 March 1997), rainy season (20 July 1997) and autumn (20 October 1997).The methods of sample collection, preservation and subsequent examination were described by Islam and Irfanullah (2005a).

Taxonomic enumeration
This study revealed 78 desmid taxa belonging to four genera, of which nine are new records for Bangladesh.The new records are marked with asterisks.Eighteen desmid taxa belonging to the mentioned four genera have already been reported from this area by the same authors as new records for Bangladesh (Islam andIrfanullah 1998, 1999), thus are not marked in this account.Remaining other taxa are briefly described along with their spatial and temporal occurrence, and abundance.
Habitat-wise, Baraoora Lake had more taxa (mean number about 75) than the Burburia River (mean number around 30).The lake showed highest number of species in winter (>140 taxa), whereas the river showed maximum in spring (>75 taxa).The lowest species number (around 40 taxa) in spring was quite unusual for a lentic water-body like Baraoora Lake.The river was highly dynamic in rainy season explaining the lowest species richness in monsoon (<10 taxa).

Discussion
Conservation of algal communities lies with their habitat conservation.But it is difficult to peruse the stakeholders for conservation without direct and immediate benefits, which is often monetary.In many cases it is hard to prove the direct benefits of 'a species'.In case of microscopic organisms, like algae, it is even tougher.If we argue that saving a species is essential for maintaining ecological integrity, many species will lose their importance as they might not be crucial in maintaining the functioning of their native ecosystems (Lawton 1991).
But we believe that habitats like Baraoora Lake are important just because of the species diversity they possess.It is just like a living laboratory for aquatic biologists.Deepening this habitat and trying something financially profitable, like aquaculture, should not be encouraged (Of course, given the acidic pH, fish-culture might not be practical, anyway).Instead we should leave these habitats in their present state without any major interventions.Because of high species diversity, these can be used as 'natural tools' for monitoring the ecological quality of the tea gardens as a whole.Islam and Irfanullah (2005a) also emphasised on more systematic sampling and quantitative estimation of species abundance to get a clearer and detailed picture of the algal flora of these interesting habitats.
Institute like the Bangladesh Tea Research Institute (BTRI) can take initiatives to run simple analyses of water chemistry and plankton community on a regular basis and share the information with the tea garden owners.This will assist the latter to assess the ecological impacts of current tea cultivation practices (e.g.nutrient-holding capacity of the soil, major changes in the soil chemistry, effects of chemical residues, etc.).Correlating the tea garden soil chemistry with lake water chemistry and biology will also help them to trace the viability of tea garden ecosystems.Baraoora Lake could be one of the first sites for the ecological monitoring of catchment-lake connectivity in Bangladesh.A full limnological investigation in these habitats will strengthen the justification of these habitats becoming monitoring tools.