by Rohan Nath
The Meghalayan plateau region adjacent to the Indo-Burma biodiversity hotspot is known for Cherrapunjee and Mawsynram. With the second-highest annual average rainfall of 11,820 to 11,872 mm, these regions are hosting a bountiful of perennial water bodies (Fig 1).
Fig. 1. Overview map of Mawsynram and Cherrapunji. Image Source: qGIS.
The algal diversity of these water bodies remains unexplored. Algae belonging to Cyanophyta (Cyanoprokaryota/Cyanobacteria) have been reported on the moist soil surfaces and rice fields of the region. Several other species of algae have been reported from these locations:
i. Two species of Lyngbya and one species each of Schizothrix, Spirulina, Stigonema and Scytonema have been reported by Biswas (1934) from moist soils of the Khasi and Jaintia hills of the location.
ii. Oscillatoria variabilis C.B. Rao has been reported from the field soil surface.
iii. One species of Cylindrospermum and two species of Nostoc from the rice cultivation fields and Stigonema dendroideum Frémy have been reported from the moist soils of Cherrapunjee.
iv. Oinam et al. (2010) and Devi et al. (2010) reported five cyanophytes, namely, Phormidium tenue (Menegh.) Gomont, Anabaena doliolum Bharadwaja, Plectonema nostocorum Bornet ex Gomont, Oscillatoria laevittae Buell and Calothrix marchica Lemmerm. from the soil surfaces of the area
The small town of Cherrapunjee is located in the East Khasi Hills district of Meghalaya at a distance of 59 km from Shillong and an altitude of 1484 m above mean sea level. It is known as the wettest place on earth since it receives an average annual rainfall of 11,820 mm along with the neighbouring village Mawsynram with an average annual rainfall of 11,872 mm.
Severe deforestation has led to the loss of subtropical forest canopy resulting in soil erosion due to the heavy rainfall. Grasslands now dominate this area with large trees only present in protected sacred forests.
Algal samples were collected from five different fresh waterbodies study sites (Fig 2).
a. Seven Sister waterfall in Cherrapunjee
b. Stream in Mawsynram
c. Fish pond in Cherrapunjee
d. Nohkalikai waterfall in Cherrapunjee
e. Mawsynram waterfall
Forty-eight algal taxa were reported in total from the five different freshwater bodies of Cherrapunjee and Mawsynram belonging to Chlorophyta (26), Cyanophyta (6), Euglenophyta (1) and class Bacillariophyceae under Heterokontophyta (15) (Table 1). Most of these algae occur as planktonic or inside the water as epilithic of the submerged stones.
|Cyanobacteria||Phormidium chlorinum||No sheath, filaments solitary, cells almost isodiametric and trichomes straight.|
|Oscillatoria jenensis||Trichomes without sheath, thallus dark bluish-green, filament not constricted and trichomes shortly attenuated at the ends.|
|Oscillatoria limosa||Filamentous, thallus bluish-green, unsheathed, unbranched.|
|Scytonema ocellatum||Short false branches present and thallus blackish to blackish-green in colour.|
|Calothrix marchica||The sheath is very thin, almost invisible and filaments yellowish in colour.|
|Stigonema minutum||Yellowish-brown in colour, filaments with 2 – 3 rows of cells and sheath thick.|
|Chlorophyta||Spirogyra sp.||Chloroplasts spirally arranged and filaments are straight.|
|Cylindrocystis subpyramidata||Cell apices sub pyramidal with rounded ends and cells cylindrical.|
|Closterium calosporum||Cells gradually attenuated to subacute apices and cells small.|
|Closterium kuetzingii||Cell median part fusiform, single and attenuated towards each extremity into long processes.|
|Closterium libellula||Cells much longer than broad, single, large and gradually attenuated from the middle towards the apices.|
|Closterium navicula||Cells are straight, solitary and gradually narrowed towards both ends.|
|Euastrum ansatum||Cells are deeply constricted, small and sinus narrowly linear with dilated extremity.|
|Euastrum dubium||Cell green, solitary, basal angles broadly rounded, upper and lower lateral margins equally rounded.|
|Cosmarium awadhense||Cells slightly longer than broad, small and sinus narrowly linear towards the apex and slightly open outwards.|
|Cosmarium decoratum||Cells deeply constricted, slightly longer than broad, semi cells semi-elliptic and sinus narrowly linear.|
|Euglenophyta||Phacus pleuronectes||Cells posteriorly a stout caudus which is obliquely turned to the right anterior end and ovoid to suborbicular in outline.|
|Aulacoseira granulata||Frustules attached continuously to form chain-like structures and cylindrical structures.|
|Cyclotella meneghiniana||Frustules rectangular and undulated in girdle view and discoid in valve view.|
|Synedra cyclopum||Frustules slightly bent, linear, the apical area is attenuated to an obtuse end and the middle portion is slightly wide.|
|Navicula tripunctata||Frustules slightly constricted to form rostrate apices and are elliptical – lanceolate in shape.|
The low algal diversity can be attributed to the temperature at the study site which was congenial with a range of 20 to 25°C and the pH which was acidic from 5.5 to 6.5. The surrounding water bodies showed excessive algal growth due to the loading of anthropogenic wastes. The habitat wise distribution pattern of algal diversity is as follows: waterfall> streams> ponds.
Reference 1. Das, S. K., & Adhikary, S. P. (2012). Freshwater algae of Cherrapunjee and Mawsynram, the wettest places on earth. Phykos, 44(2), 29-43.