Papers by Ranju Radhakrishnan
Benthic foraminifera, predominantly marine unicellular organisms, are abundant and diverse. Their... more Benthic foraminifera, predominantly marine unicellular organisms, are abundant and diverse. Their tests with intricate and varied surface ornamentation make them unique and fascinating organisms. Among them, Unilocular calcareous benthic foraminifera have always been the least explored group due to their less frequent occurrence and small, fragile tests. Hence, a study on the unilocular foraminifera was conducted by collecting a core (4.15 m long deep-sea core of 12.7 cm diameter) sample from the deep-sea environment (3083 m depth) of the Bay of Bengal on the Research Vessel MGS Sagar. This study describes the vertical distribution of unilocular foraminifera, assesses their community structure, provides illustrated taxonomic descriptions and reports new records from the Indian waters. Twenty-five species belonging to seven genera, two families and one suborder were recorded, of which eight species are new reports from the Indian waters. The total abundance of the Unilocular foraminifera was 219 number/gram (9% of the total foraminifera abundance) Fissurina (77), Oolina (46) Parafissurina (28) and Lagena (28) were the most abundant genera. Vertical distribution of the unilocular species showed a decreasing trend with 19 species in the 0-100 cm to three species in the 301-415 cm of the core sample. Shannon Weiner diversity index (H') values ranged between 0 and 3.75, with the highest of 3.75 recorded at the 138-140 cm layer. Pielou's species evenness (J') values ranged from 0.82 to 1, and species dominance ranged from 0 to 0.5. Results of the analysis of similarity proved a significant variation in the species composition of unilocular benthic foraminifera between various depth layers of the core. Systematic descriptions of this taxa have also been included in the present study. This study is thus expected to fill the gap in knowledge of this lesser-known group of benthic foraminifera from the Indian waters.
The use of the free living protozoan communities has benefited in perfectly characterizing and mo... more The use of the free living protozoan communities has benefited in perfectly characterizing and monitoring the prevailing environmental conditions of aquatic habitats that are typically found at marginal freshwater regions. A particular community of organism may be useful as an environmental indicator due to many reasons. Some may have sensitivity to low levels of anthropogenic contaminants, yet some others may tolerate and survive in the hardy and extreme conditions, and others also may react quickly to change in environment. Thus they tend to become a unique biotic tool to understand the ecological status of an aquatic habitat. Vembanad Lake and its adjacent kol lands has acclaimed international recognition as a Ramsar site. This lake is a biological niche of a multitude of organisms and it is intricately woven with the lives of the resident communities of its banks. The lake has also been facing severe environmental crisis during the last 3 decades due to anthropogenic influences. Presently, 19 species of free-living protozoans have been identified and characterized from this lake. A total of 15 testacid rhizopods belonging to 2 orders, 6 families and 9 genera were recorded. And the ciliates of 3 orders, 3 families were recorded. Among the testaceous rhizopods 1species from Arcellidae family, 5 from Centropyxidae, 1 species from Nebelidae, 6 from Difflugidae belonging to the Class Lobosea and 2 species from the Class Filosea belonging to Cyphoderiidae and Euglyphidae families were identified. Some of these freeliving forms have given certain insights of the prevailing ecological conditions of this lake thus acting as perfect Bioindicators. Euglypha tuberculata reported in the present study is a species of wide tolerance and survives in diverse habitats. Similarly Cryptodifflugia oviformis which was reported for the first time in India in this study prefers dryer environments. Due to its small size, this species mainly feeds on bacteria and yeasts, their high abundance explains active decomposition process in the area. The diversity of the free-living ciliates in the study area included species belonging to 3 genera namely Euplotes, Tachysoma and Coleps and they were pollution indicators possessing the property of heavy metal uptake. The water quality analysis and heavy metal analysis also proved the waters of the lake polluted with heavy metal concentrations. Thus the present study draws our attention to the possibility of using these dominant ciliate species for bioremediation of aquatic pollutants in this lake. Thus these freshwater free living protozoans serve as good bioindicators reflecting the natural ecological conditions prevailing in the Vembanad Lake. They can also be effective bioremediation tools that can be applied to solve the heavy metal pollution crisis of the lake.
Reports on Some Benthic Foraminifera from the Agatti Island Lakshadweep India
Journal of Environment and Sociobiology, Jun 30, 2021
This communication gives an account of 18 species of benthic foraminifera collected from the Agat... more This communication gives an account of 18 species of benthic foraminifera collected from the Agatti Island, Lakshadweep. Out of the 18 species, 12 species belong to the calcareous imperforate group and 6 species of calcareous perforate group. Three species, viz., Quinqueloculina reticulata, Lachlanella cooki, Amphistegina lobifera are recorded for the first time from Indian waters. Six species, viz., Adelosina reticulata, Amphistegina lessonii, Neorotalia calcar, Pyrgo murrhina, Quinqueloculina auberiana and Sorites orbiculus are numerically abundant, with usual higher abundance at lower depth. Tests of the benthic foraminifera were found to have larger size possibly due to the higher availability of sunlight in the much shallower coast which preserve typical tropical oceanic conditions.
A monothalamous saccaminid, Ovammina opaca Dahlgren, 1962, is being reported for the first time f... more A monothalamous saccaminid, Ovammina opaca Dahlgren, 1962, is being reported for the first time from the recent sediments of Arabian Sea. The species was found abundant in the shelf sediments along the southwest coast of India. Generally this group of foraminifera has been recorded earlier from the cold water environments, but has always been overlooked in shallower marginal regions. In the present study, the occurrence of the species has been presented in shallower water shelf
Observations on some symbiont bearing Foraminifera from the shelf and slope sediments of Eastern Arabian Sea
Journal of the Marine Biological Association of India, 2018
The present study records small and large benthic foraminifera with endosymbionts distributed in ... more The present study records small and large benthic foraminifera with endosymbionts distributed in the shelf sediments of the western continental shelf and continental slope (5-1333 m) of eastern Arabian Sea, with reference to climate change and coral reef monitoring. The larger benthic foraminifera (LBF) include Alveolinella quoyii, Amphistegina lessonii, Amphistegina gibbosa, Operculina granulosa, Heterostegina depressa and Amphisorus hemprichii which have symbiotic associations with diatoms, dinoflagellates, green algae, red algae and chrysophytes. The symbionts make these very efficient in utilising a wide range of the light spectrum and water depths. The size of species Alveolinella quoyii and Amphistegina lessonii recorded from water depths of 30 m to 1333 m showed intraspecific variations in size, those collected from deeper waters were larger than those found in shallow waters. It is evident that the presence of endosymbionts probably attributed to the intraspecific variations in size. The species belonging to these genera have evolved strategies like phenotypic plasticity and local adaptation of the concerned photosymbionts which have helped them tolerate thermal variations. The finding that the number of tests of LBFs decreased from shelf to slope areas may be indicative of the relation between oxidative stress, reduced light levels that affect the growth rate of these species. It is confirmed that LBFs have longer lifespan than the smaller forms.
This communication gives an account of 18 species of benthic foraminifera collected from the Agat... more This communication gives an account of 18 species of benthic foraminifera collected from the Agatti Island, Lakshadweep. Out of the 18 species, 12 species belong to the calcareous imperforate group and 6 species of calcareous perforate group. Three species, viz., Quinqueloculina reticulata, Lachlanella cooki, Amphistegina lobifera are recorded for the first time from Indian waters. Six species, viz., Adelosina reticulata, Amphistegina lessonii, Neorotalia calcar, Pyrgo murrhina, Quinqueloculina auberiana and Sorites orbiculus are numerically abundant, with usual higher abundance at lower depth. Tests of the benthic foraminifera were found to have larger size possibly due to the higher availability of sunlight in the much shallower coast which preserve typical tropical oceanic conditions.
The use of the free living protozoan communities has benefited in perfectly characterizing and mo... more The use of the free living protozoan communities has benefited in perfectly characterizing and monitoring the prevailing environmental conditions of aquatic habitats that are typically found at marginal freshwater regions. A particular community of organism may be useful as an environmental indicator due to many reasons. Some may have sensitivity to low levels of anthropogenic contaminants, yet some others may tolerate and survive in the hardy and extreme conditions, and others also may react quickly to change in environment. Thus they tend to become a unique biotic tool to understand the ecological status of an aquatic habitat. Vembanad Lake and its adjacent kol lands has acclaimed international recognition as a Ramsar site. This lake is a biological niche of a multitude of organisms and it is intricately woven with the lives of the resident communities of its banks. The lake has also beenrnfacing severe environmental crisis during the last 3 decades due to anthropogenic influences...
The present study records small and large benthic foraminifera with endosymbionts distributed in ... more The present study records small and large benthic foraminifera with endosymbionts distributed in the shelf sediments of the western continental shelf and continental slope (5-1333 m) of eastern Arabian Sea, with reference to climate change and coral reef monitoring. The larger benthic foraminifera (LBF) include Alveolinella quoyii, Amphistegina lessonii, Amphistegina gibbosa, Operculina granulosa, Heterostegina depressa and Amphisorus hemprichii which have symbiotic associations with diatoms, dinoflagellates, green algae, red algae and chrysophytes. The symbionts make these very efficient in utilising a wide range of the light spectrum and water depths. The size of species Alveolinella quoyii and Amphistegina lessonii recorded from water depths of 30 m to 1333 m showed intraspecific variations in size, those collected from deeper waters were larger than those found in shallow waters. It is evident that the presence of endosymbionts probably attributed to the intraspecific variations in size. The species belonging to these genera have evolved strategies like phenotypic plasticity and local adaptation of the concerned photosymbionts which have helped them tolerate thermal variations. The finding that the number of tests of LBFs decreased from shelf to slope areas may be indicative of the relation between oxidative stress, reduced light levels that affect the growth rate of these species. It is confirmed that LBFs have longer lifespan than the smaller forms.
short communication
A monothalamous saccaminid, Ovammina opaca Dahlgren, 1962, is being reported for the first time f... more A monothalamous saccaminid, Ovammina opaca Dahlgren, 1962, is being reported for the first time from the recent sediments of Arabian Sea. The species was found abundant in the shelf sediments along the southwest coast of India. Generally this group of foraminifera has been recorded earlier from the cold water environments, but has always been overlooked in shallower marginal regions. In the present study, the occurrence of the species has been presented in shallower water shelf sediments.
India is a country well known for its Biodiversity rich ecosystems. The coral reef ecosystems are... more India is a country well known for its Biodiversity rich ecosystems. The coral reef ecosystems are indeed very unique and are home to a multitude of organisms. Currently there are 5 major reefs in India that include Gulf of Kutchch, Gulf of Mannar, Palk Bay, Lakshadweep Islands and Andaman and Nicobar islands and minor reefs are distributed along the intertidal regions of Ratnagiri, Malvan and Redi, South of Bombay, west of Mangalore and the Hermatypic corals along the shore are reported from Quilon in the Kerala Coast to Enayem in Tamil Nadu. But these rich abodes are facing a number of anthropogenic threats and the current status of the Indian reefs is also discussed in this review. BEST Journals 26 V. Jayaprakas & Ranju Radhakrishnan
This communication gives an account of 14 species of testate amoebae (Rhizopoda : Protozoa) and t... more This communication gives an account of 14 species of testate amoebae (Rhizopoda : Protozoa) and three species of ciliates, collected from the Karaparambil near Vaikom Road (Kottayam district) in the estuarine sector of the Vembanad Lake, which is an important Ramsar site covering 3 districts of Kerala, namely, Alapuzha, Kottayam and Ernakulam. This communication appears to be the first report of the freeliving protozoans from this lake.
Vembanad Lake, an important Ramsar site has been subjected to a number of serious stresses from a... more Vembanad Lake, an important Ramsar site has been subjected to a number of serious stresses from anthropogenic influences. Pollution stress in an aquatic environment is often observed by abrupt changes associated with discharges from industries and sewage. This lake thus requires an active bioremediation programme using a fast, efficient and cost effective biotic system. Ciliates are excellent water qualifiers as they call attention to a system, overload, indicate cause and gravity of the situation in their own way. With this in view a study was conducted in Karaparambil site located in the southern part of Vembanad Lake. The diversity of the free-living ciliates in the site was observed for a period of three months.
Two species of testate amoebae viz., Cryptodifflugia oviformis Penard, 1890 and Difflugia binucle... more Two species of testate amoebae viz., Cryptodifflugia oviformis Penard, 1890 and Difflugia binucleata Penard 1902 are reported herewith from Vembanad lake, one of the Ramsar sites of Kerala which are new records from India.
Conference Presentations by Ranju Radhakrishnan
Foraminifera are the most dominant and diverse group of the shelled unicellular protozoans.Benthi... more Foraminifera are the most dominant and diverse group of the shelled unicellular protozoans.Benthic foraminifera form an important link in the trophic food chains of the marine realm. These meiofauna play the role of both the active predators as well as prey adopting a number of feeding strategies like suspension feeding, detritivory, parasitism, chemosymbiosis etc. Distribution of benthic foraminifera in ocean bottom provides a variety of valuable paleoenvironmental information. And no detailed studies on the taxonomy and systematics of benthic foraminifera have been carried out from the southwest coast of India.22 surface grab samples were collected from the depth ranges of 5 to 50 meters. A total of 98 species of benthic foraminifera belonging to 37 families and 65 genera were identified from the samples.The suprafamilial classification of these foraminifera was done where in 21 suprafamilial groups were recorded. These were further grouped into epifauna and infauna on the basis of their habitat preferences. Highest diversity was recorded from the Miliolid groups followed by Spiroloculinids. Least species diversity was recorded by the Nubeculariids and Nummulitinids.Based on the Composition of test, three groups namely Calcareous imperforate, calcareous perforate and agglutinated foraminifera were recorded.Cochin region showed the maximum species diversity as compared to other regions.
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Papers by Ranju Radhakrishnan
Conference Presentations by Ranju Radhakrishnan