Distribution of Compsopogon caeruleus (Balbis ex C.Agardh) Montagne (Compsopogonales, Compsopogonophyceae) in West Bengal, India

Compsopogon caeruleus (Balbis ex C.Agardh) Montagne, is one of the highly cosmopolitan organisms among the freshwater red algae. This alga has been reported in different aquatic habitats and various environmental conditions. It is found worldwide, with a higher prevalence in tropical and subtropical regions. It can also occasionally be found in northern temperate areas, such as the northern United States, Europe, Japan, and Ukraine (Vis et al., 1992; Rintoul et al., 1999).

Historically, the family Compsopogonaceae comprised eleven species of Compsopogon and three species of Compsopogonopsis. Compsopogon species were distinguished by their rhizoids, which are confined to the thallus base, whereas Compsopogonopsis species have rhizoidal outgrowths throughout the plant. Key characteristics for species identification within the genus include the structure of the basal portion of the thallus, the branching pattern, the size of monosporangia, the number of cortical layers, and the size of cortical cells. The thallus is highly branched, saxicolous or epiphytic, filamentous, uniseriate in younger parts, and multiseriate in older parts. A variable number of cortical layers surrounds the axial cell, and the organism reproduces asexually, lacking a sexual life cycle.

However, these thallus characteristics exhibit significant variation between populations and also change with seasons. In a taxonomic revision of the family Compsopogonaceae, Necchi & Dip in 1992, classified all taxa into two clearly defined species: Compsopogon caeruleus (lacking rhizoidal filaments in the cortex) and Compsopogon leptocladus (possessing such filaments in the cortex). Using multivariate morphometrics and image analysis, Vis et al., (1992) grouped several taxa of Compsopogonaceae into three species: Compsopogonopsis leptocladus (Montagne) Krishnamurthy (characterized by rhizoidal cortication throughout the plant), Compsopogon prolificus Yadav & Kumano (with U-shaped lateral branches curling around the central axis), and Compsopogon coeruleus (Balbis) Montagne (featuring uncurled branches in the axis). Their study also highlighted that microsporangial clusters, the basal system of the thallus, and spine-like branches exhibit significant variability, rendering them unreliable as diagnostic taxonomic characters (Vis et al., 1992). Based on molecular studies by Necchi et al., (2013), all reported species of the Compsopogon genus were synonymized under a single species, Compsopogon caeruleus (Balbis ex C.Agardh) Montagne. In this article, all the species previously reported from West Bengal and currently collected specimens are considered as Compsopogon caeruleus (Balbis ex C.Agardh) Montagne.

The study was conducted after a detailed review of the literature, which showed no reports of Compsopogonaceae members from northern districts. Hence, the field survey to the northern districts of West Bengal (WB) was carried out in December 2023. All the collected samples were preserved and processed correctly (Elaya Perumal et al., 2015; Elaya Perumal & Sundararaj, 2019, 2020), and the specimens are housed at CAL (Central National Herbarium, Howrah, WB). Slides were prepared using methods described by Elaya Perumal & Sundararaj (2019, 2020). Microphotographic documentation, along with morphological and morphometric analyses, was conducted using a Nikon Advanced Research Microscope (Nikon Eclipse Ni Series: H600L) in conjunction with NIS-Elements software. Organisms were identified based on standard monographs and various research publications, including Elaya Perumal & Sundararaj (2023). The geographic distribution of the Compsopogon species in WB was mapped using ArcGIS software (ArcMap desktop version 10.2.2), providing a spatial representation of sampling locations (Map 1).

Freshwater red algal samples were collected from 34 locations across West Bengal during an extensive field survey conducted in December, 2023. Of these, 22 samples contained members of the family Compsopogonaceae, 10 samples included Batrachospermaceae, and 2 samples harboured species of Audouinellaceae. These collections were made from seven northern districts: Alipurduar, Cooch Behar, Dakshin Dinajpur, Darjeeling, Jalpaiguri, Malda, and Uttar Dinajpur (Table 1). Previous studies had reported the presence of Compsopogon caeruleus (Balbis ex C.Agardh) Montagne primarily in a few southern districts (Ganesan et al., 2018; Elaya Perumal & Palanisamy, 2025); however, the current investigation reveals significant species diversity in northern regions as well (Map. 1). This study effectively expands the known distribution range of Compsopogon caeruleus, documenting its presence in seven additional districts of West Bengal, marking the first recorded occurrence of this species in these seven districts. The collected Compsopogon specimens exhibited a diverse range of morphological characteristics, consistent with descriptions from previous studies. The thalli varied significantly in size, ranging from microscopic forms to those several meters in height, highlighting the species’ remarkable structural plasticity (Necchi et al., 2013).

Table 1: Field Location Data of Collection Sites

This study reveals the occurrence of Compsopogon caeruleus across a range of physicochemical conditions (Table 2). Atmospheric temperatures recorded at the collection sites ranged from 20.2°C to 28.6°C, while corresponding water temperatures varied between 19.0°C and 26.8°C during the winter season (December 2023). Incident light intensity during sampling spanned 105.34 to 2024 µmol photons m⁻² s⁻¹. Water physico-chemical parameters, such as pH, were in the range of 6.6 to 8.7, suggesting the species’ tolerance to slightly acidic to alkaline conditions. Electrical conductivity fluctuated between 64 and 398 µS/cm, and total dissolved solids (TDS) ranged from 32 to 172 ppm, reflecting moderate mineral content and low to mild levels of pollution. These observations are consistent with earlier findings (Wehr & Sheath, 2003; Liu & Wang, 2004; Liu et al., 2004), which reported the species’ affinity for clear, temperate waters with moderate nutrient loads and its resilience to slight anthropogenic disturbances. The current data further support the ecological plasticity of Compsopogon caeruleus, indicating its ability to inhabit clear to slightly turbid habitats and persist across a broad spectrum of environmental parameters.

Table 2. Ecological and Physico-chemical parameters of sampling sites

Recent studies have highlighted the potential of red algae as sustainable biofertilizers and plant growth promoters. Polysaccharides and bioactive compounds from red algae play a vital role in enhancing plant growth and resilience. Their multifunctional properties support nutrient uptake, stress tolerance, and sustainable agricultural productivity (Trivedi et al., 2023). Biostimulants derived from red algae enhance plant vitality by supplying essential nutrients and bioactive molecules. These natural compounds help plants to withstand abiotic stress through improved physiological and biochemical resilience (Banakar et al., 2022). These findings support the broader use of red algal biomass in promoting plant health and productivity through natural, eco-friendly means. In parallel, Compsopogon caeruleus, a freshwater red alga, has shown remarkable ecological tolerance, particularly its ability to thrive in slightly polluted or thermally impacted water bodies (Andrzej & Andrzej, 2022). This resilience makes it a promising candidate for integrated aquaculture-agriculture systems. Its cultivation along with rice plants could serve dual purposes: biomass production for biofertilizer use and phytoremediation of agricultural runoff. The species’ adaptability to variable water quality conditions and its capacity to colonize submerged surfaces further enhance its utility in such agroecological models. Together, these insights underscore the untapped potential of red algae in sustainable agriculture, particularly in regions where water quality and soil fertility are limiting factors.

SYSTEMATIC TREATMENT

 Compsopogonophyceae G.W.Saunders & Hommersand

 Compsopogonales Skuja

 Compsopogonaceae F.Schmitz

Compsopogon Montagne

Compsopogon caeruleus (Balbis ex C.Agardh) Montagne, Sciences physiques. Botanique. Cryptogamie. 1:154. 1846; Conferva caerulea Balbis ex Agardh, 1824; Compsopogon aeruginosus (J.Agardh) Kützing, 1849; Compsopogon aeruginosus (J. Agardh) Kützing var. catenatum Yadava, & Pandey, 1980; Compsopogon chalybeus Kützing, 1849; Compsopogon hookeri Montagne, 1846; Compsopogon lividus De Toni, 1897; Compsopogon indicus Das, 1963; Compsopogon iyengarii Krishnamurthy, 1958; Composopogon prolificus Yadava & Kumano, 1985; Compsopogonopsis japonica Chihara, 1976; Compsopogon corinaldii (Meneghini) Kutzing, 1857; Compsopogon sparsus S.L.Xie  & Y.J.Ling, 1998.

Fig. 1-27.

Vernacular /Common Name:  Staghorn algae

The Compsopogon specimens exhibited diverse morphological characteristics, occurring either as free-floating or attached to various substrates, including aquatic plants (Vallisneria sp.), green algae (Cladophora sp., Pithophora sp.), submerged rocks, and lifeless materials (dead wood, plastics, cloths, etc.) in streams and rivers. The thallus colouration ranged from blue-green to olivaceous green, with heights varying from 0.1 cm to 120 cm and diameters between 0.1 mm to 2 mm. Basal discs facilitated attachment to the host surface, while the thallus was either distinctly constricted or unconstricted, with apex attenuation varying towards both the tip and base. Branching patterns were highly variable, with branches occurring alternately or irregularly. Some specimens exhibited abundant branching, while others showed minimal branching, with branch angles ranging between 10 º∆ and 90 °∆. The thallus gradually attenuated towards the tips, though some specimens displayed abrupt constriction at the apex. Axial cells measured between 20.00 to 522.50 µm in height and 60.00 to 550.75 µm in breadth, while apical cells were depressed spherical structures, approximately 12-14 µm in diameter. The thallus was corticated with 1-3 layers of cortical cells, and their size ranged from 10.50 to 65.50 µm in length and 15.00 to 30.50 µm in breadth. These cortical cells divided obconically and formed monosporangia, with diameters ranging from 8.50 to 32.80 µm. The liberated monospore adhered to a host, enlarged, and subsequently divided to initiate new thallus growth, establishing attachment on the host.

Distribution: India-Arunachal Pradesh, Assam, Bihar, Gujarat, Jammu & Kashmir, Jharkhand, Karnataka, Kerala, Maharashtra, Madhya Pradesh, New Delhi, Odisha, Rajasthan, Tamil Nadu, Uttarakhand, Uttar Pradesh, West Bengal- North 24 Parganas, South 24 Parganas, Hoogly, Howrah Districts (Ganesan et al., 2018; Elaya Perumal & Palanisamy 2025). Global - Austria, Britain, Ireland, Croatia, Czech Republic Czechia, France, Germany, Italy, Malta, Poland, Arkansas, Florida, Louisiana, Mexico, New Mexico, North Carolina, Cuba, Lesser Antilles, Martinique, W. Atlantic, Argentina, Brazil, Paraguay, Algeria, Mauritius, Egypt, Iraq, Bangladesh, India, Khandesh, Indonesia, Malaysia, Thailand, Viet Nam, China, Japan, Taiwan, Australia, New South Wales, New Zealand, Queensland, Australia, Hawaiian Islands, Vanuatu (Elaya Perumal & Palanisamy, 2025).

Specimens Examined: India- West Bengal, Cooch Behar District, Cooch Behar, Torsa River Bank, 12.12.2023, Dr. U Elaya Perumal, CNH-BSI-97703 (CAL); Alipurduar District, Sonapur, Stream, 12.12.2023, Dr. U Elaya Perumal, CNH-BSI-97709 (CAL); Alipurduar District, Madhya Rangali, River Bank, 13.12.2023, Dr. U Elaya Perumal, CNH-BSI-97715 (CAL); Alipurduar District, Madhya Rangali Bazar, stream, 13.12.2023, Dr. U Elaya Perumal, CNH-BSI-097717 (CAL); Alipurduar District, Madhya Rangali Bazar, River, 13.12.2023, Dr. U Elaya Perumal, CNH-BSI-97718 (CAL); Alipurduar District, Uttar Sisubari, river, Dr. U Elaya Perumal, CNH-BSI-97719; Alipurduar District, Uttar Sisubari, stream, 13.12.2023, Dr. U Elaya Perumal, CNH-BSI-97720 (CAL); Alipurduar District, Uttar Sisubari, stream, 13.12.2023, Dr. U Elaya Perumal, CNH-BSI-97721 (CAL); Jalpaiguri District, Near Nagarakata Toll Plaza, Big stream, 14.12.2023, Dr. U Elaya Perumal, CNH-BSI-97727 (CAL); Jalpaiguri District, Near Nagarakata Toll Plaza, small stream, 14.12.2023, Dr. U Elaya Perumal, CNH-BSI-97728 (CAL); Jalpaiguri District, Near Nagarakata Toll Plaza, stream, 14.12.2023, Dr. U Elaya Perumal, CNH-BSI-97730; Jalpaiguri District, Jalpaiguri, Nokha ghat, River, 16.12.2023, Dr. U Elaya Perumal, CNH-BSI-97761 (CAL); Jalpaiguri District, Sukani, Chauli River, 17.12.2023, Dr. U Elaya Perumal, CNH-BSI-97763 (CAL); Jalpaiguri District, Bahadur, stream, 18.12.2023, Dr. U Elaya Perumal, CNH-BSI-97765 (CAL); Jalpaiguri District, Jhabera Vita, Talma river, 18.12.2023, Dr. U Elaya Perumal, CNH-BSI-97766 (CAL); Jalpaiguri District, Balai Gachh, Kartowa Bridge, 18.12.2023, Dr. U Elaya Perumal, CNH-BSI-97767 (CAL); Jalpaiguri District, Jugibhita, Sau Bridge, 18.12.2023, Dr. U Elaya Perumal, CNH-BSI-97769 (CAL); Darjeeling District, Rahamu, Stream, 18.12.2023, Dr. U Elaya Perumal, CNH-BSI- 97770 (CAL);  Darjeeling District, Kantibhita, Stream, 18.12.2023, Dr. U Elaya Perumal, CNH-BSI-97774; Uttar Dinajpur, Uttar Bhagalpur, River, 18.12.2023, Dr. U Elaya Perumal, CNH-BSI-97776 (CAL); Dakshin Dinajpur District, Bansihari, Tangaon River, 20.12.2023, Dr. U Elaya Perumal, CNH-BSI-97781 (CAL); Malda district, Ramchandrapur, River, 21.12.2023, Dr. U Elaya Perumal, CNH-BSI-97785 (CAL).

IUCN Conservation Status: Least Concern (LC)

Despite potential threats from increasing anthropogenic activities and habitat degradation, Compsopogon caeruleus exhibits a widespread global distribution and remarkable adaptability to extreme (polluted) climatic conditions, where many other red algae struggle to survive. The species is documented across most continents. In India, Compsopogon caeruleus is widely distributed, with extensive documentation across multiple states. The corresponding author has critically studied the alga in various states and documented its presence in a few previous publications (Elaya Perumal & Sundararaj, 2023; Elaya Perumal & Palanisamy, 2025). Based on these observations, the authors conclude that the species maintains a substantial population across many studied locations, with only a few sites exhibiting lower population densities. This alga commonly forms dense populations, where mature individuals are frequently abundant, often numbering over 100 within a single subpopulation. However, in a few populations, it is observed at lower densities, with fewer than 50 mature individuals. This alga is commonly found from the monsoon through mid-to-late summer in many locations. In certain areas, however, it appears predominantly in the post-monsoon season. Even though this alga shows adaptability to pollution, it is not found in waters with high pollution (domestic and industrial polluted water bodies). Therefore, increasing anthropogenic pressures and water pollution may pose a growing threat to its long-term persistence. Nonetheless, based on its broad distribution, ecological resilience, and stable populations across multiple regions, this study provisionally assesses Compsopogon caeruleus as Least Concern (LC) under IUCN criteria.

The present study significantly extends the known distribution of Compsopogon caeruleus in West Bengal, revealing its presence in seven additional northern districts. This finding highlights the broader ecological adaptability of the species, suggesting its potential resilience in varied aquatic environments. Furthermore, the observed morphological diversity among collected specimens underscores the species’ structural plasticity, aligning with previous taxonomic descriptions. Given that earlier studies primarily reported Compsopogon caeruleus in southern districts, these findings contribute valuable new insights into its geographical range and habitat preferences. Compsopogon caeruleus is provisionally assessed as Least Concern (LC) in this study, given its widespread distribution and ecological resilience, though localized threats from anthropogenic activities warrant continued monitoring. The authors propose co-cultivating Compsopogon caeruleus alongside rice plants, enabling its direct use as a biofertilizer within the same agricultural landscape, thereby enhancing soil fertility and reducing dependence on synthetic inputs.