*Correspondence author: Bam Deo Pandey, Udai Pratap College, Varanasi, India
How to cite this article:Bam Deo P, S G Yeragi. Habitat Ecology and Biological Characteristics of a Hypersaline Ciliate, Fabrea salina from Solar Salterns of Mumbai Coast, India. Oceanogr Fish Open Access J. 2020; 12(2): 555833. DOI: 10.19080/OFOAJ.2020.12.555833
The ecology of a hypersaline ciliate, Fabrea salina was studied in two saltpans along the Mumbai coast, India. There was an apparent trend of its seasonal abundance being maximum (up to 58 x 103 cells L-1 in May) during late post- monsoon to summer months and complete disappearance during monsoon period. Being the most dominant species in microzooplankton community, it had an average annual density of 18 x 103 cells L-1. It flourishes well under higher temperature (30-39ºC) and salinity (40-150 ‰) conditions. Among phytoplankton, Dunaliella was the dominant one with a highest density of 58 x 103 cells mL-1 in April, followed by Chlorella with up to 42 x 103 cells mL-1, in March. The ANOVA test for physical and chemical variables has revealed significant difference (P=0.05) in their values in different months. Except in water temperature and NO2-N, no significant difference was observed at various stations as the case with phytoplankton and zooplankton. There was strong positive correlation of Fabrea with water temperature (r=0.866, 0.801), salinity (r=0.966, 0.957), total alkalinity (r=0.717, 0.729) and PO4-P (r=0.750, 0.897) while negative correlation with water depth (r=-0.767, -0.757) and pH (r=-0.086, -0.411). Fabrea varies widely in its total length (60-600 μm) and cyst diameter (70-180 μm). The average length of body cilia is 12 μm and the width of each adoral zone of membranelle (AZM) is 10 μm
Keywords: Fabrea salina; Hypersaline ciliate; Solar salterns; Ciliate ecology
Ciliates are the most specialized and perhaps most widely distributed and diverse group of protozoa having representatives in virtually all kinds of freshwater to marine environments, often in extremely high densities . They form an important component of estuarine as well as coastal marine ecosystems as they feed upon bacteria and in turn serve as food for metazoans [2,3]. However, the ecology and biology combined with factors controlling the distribution of protists in tropics have received very little attention . Many hypersaline environments are inimical to macroscopic life but are the preferred habitats of a variety of microorganisms. The heterotrichous ciliate, F. salina , reported from several diverse environments such as salt marshes, hypersaline lakes and solar salterns [5-7], has received much attention in the recent years primarily due to its potentiality as live food source for maricultural purposes [8-11] and also as an experimental animal in basic research of applied value in eukaryotic microbiology [12-16]. Though fairly a good amount of literature is available on the hydrobiology of estuaries and backwaters in India, the information on the plankton ecology in inland saline lakes and solar salterns is
very scanty. The present study deals with the ecology of F. salina in two saltpans near Mumbai, West Coast of peninsular India, for a period of one year, January 1998 to December 1998.
The study areas, Mira Road and Bhayandar saltpans, the parts of Thane District, Maharashtra, India, are located at 19º16’N Lat & 72º51’E Long and 19º19’ Lat & 72º51’E Long, respectively. The former relates to Manori creek while the later with Bassein creek, along the Mumbai coastline. Two sampling stations in each saltpan, denoted as MR1 & MR2 at Mira Road and BH1 & BH2 at Bhayandar were selected in the present study. The region has typical tropical climate.
For phytoplankton analysis, one-liter water was directly collected whereas zooplankton
samples were taken by filtering 50 L of water through plankton net of 40 μm mesh size. The
samples were preserved with Lugol’s solution. After three days
of stagnation, the phytoplankton samples were concentrated to
100 mL volume by decanting the supernatant. Except Dunaliella
that was counted by haemocytometer, all the plankton were
enumerated using Sedgwick-Rafter cell counter (50mm x 20mm
x 1mm). For each month, the average density of Fabrea, Dunaliella
and Chlorella were taken for statistical purposes.
Hydrological and Soil-Quality Parameters
Both ambient and water temperatures were measured using
thermometer with 0.1ºC accuracy while water depth by a meter
scale. Salinity and pH were recorded at the site using Salinity
Refractometer (S/Mill- E, Atago) and portable pH meter (Model
No. E Merck 325). Other water quality parameters such as
dissolved oxygen, dissolved free carbon dioxide, total alkalinity,
ammonium- nitrogen (NH4+-N), nitrite-nitrogen (NO2-N), nitratenitrogen
(NO3-N) and phosphorus (PO4-P) were analyzed
following Standard Methods (APHA, 1992) monthly. The values of
various parameters obtained at both the stations of each saltpan
were summed up and average values are used in data analysis.
The soil-quality parameters viz. percentage of sand, silt, clay,
organic carbon, organic matter and total nitrogen and phosphorus
(mg/100 g of soil sample) were analyzed following Ghosh et al.
 during pre- monsoon, monsoon, and post-monsoon periods.
Encystment and Excystation
To validate the existence of F. salina in encysted form during
the periods of non- availability of its free-swimming trophozoites
in nature, the sun-dried scum- mat with some soil of salt-pans was
immersed at 5 g L-1 in saline water (2 L) of six different salinities
i.e. 30, 40, 50, 60, 80 and 100 ‰ provided with mild aeration.
For encystment, the salinity of culture medium (5 L) was raised
gradually from 65 to 110 ‰. After harvesting, the cysts were
subjected to hatching under different salinities as indicated
above. These experiments were carried out at ambient and water
temperature of 34±1ºC and 31±1ºC, respectively.
Phytoplankton and zooplankton were in abundance during
pre- and post- monsoon months while their density was quite low
in monsoon periods (Table 1-4). Zooplankters were completely
absent during July and August months. Dunaliella, the most
abundant species noted, was with a maximum density of 57 x
103 cells mL-1 during April. Chlorella, the second largely available
plankton, had the highest density of 40 x 103 mL-1 in March. This
was followed by the occurrence of Nitzschia sp., Navicula sp.,
Anabaena, Oscillatoria and Rhizosolenia.
Physical and chemical variables
The highest water temperature (39.0ºC) was recorded at
Bhayandar saltpan in May. The water pH was alkaline throughout
the year, varying from 8.0 to 8.6. Salinity was very low during
monsoon months, varying from nil to 16 ‰ contrary to its higher
values (up to152 ‰) prevailing during late post- monsoon and
pre- monsoon months. The levels of total alkalinity were generally
low during monsoon months being 100 mg L-1 in July. The low
DO levels (1.4- 3.4 mg L-1) were recorded during pre- and postmonsoon
months. Generally, the dissolved free carbon dioxide
was nil throughout the year. The values of NH4
+-N, NO2-N, NO3-N and PO4-P were less during monsoon months and higher in postmonsoon
periods. There was no wide variation in soil quality
parameters at both the saltpans (Table 5,6). The ANOVA has
revealed significant difference (P=0.05) in the values of all the
12 physical and chemical variables studied in various months. In
addition, water temperature and NO2-N values showed significant
difference at various stations too. There was strong positive
correlation of Fabrea with water temperature, salinity, total
alkalinity, and PO4-P while negative correlation with water depth
and pH (Table 7,8).
Population of Fabrea salina
F. salina was the most dominant species in microzooplankton
community. Its density varied from zero in monsoon months to
55 x 103 cells L-1 in May. The population abundance was in strong
correlation with salinity, temperature, alkalinity, water-depth, DO
and NO2-N. Fabrea flourishes well under the higher temperature
(30-39ºC) and salinity (40-150 ‰) conditions. Dunaliella acts
as natural food for Fabrea. The bloom of Dunaliella was noticed
during March to May with the concurrent abundance of Fabrea.
It is evident that 40 to 50 ‰ salinities are suitable for cyst
hatching. No significant hatching occurred beyond 60 ‰ salinity.
Dunaliellasalina has best growth in 120 ‰ salinity with a
tolerance limit of 350‰ . Like Dunaliella, diatoms are also
ubiquitous inhabitants of hypersaline environments, but they
never appear to dominate. The present findings are in conformity
with the occurrence of diatoms in solar salterns having salinity up
to 129 ‰ in the Great Salt Lake . Nitzschia sp. and Navicula sp.
are represented in all these aquatic environments. The probable
factors restricting the eukaryotic algae from many hypersaline
environments include their inability to osmoregulation under
prevailing conditions and to assimilate nutrients that may be
scarce coupled with periodic habitat desiccation.
Physical and Chemical Variables
The saltpans are exposed typically to a wide range of
environmental stress and perturbations. On solar heating of
brines having halobacterial colouration, a maximum temperature
of 46ºC is attained by the densely colored brine, while the clear
brines could reach up to 39ºC . Not only do gases diffuse more
slowly as brine density increases, the capacity to hold them also
becomes poor. Further the low DO levels in the present study were
also probably due to bacterial consumption of oxygen that diffuses
from the atmosphere or produced by microalga Dunaliella. The
low pH levels indicate the high levels of CO2 and alkalinity in water
bodies as observed in the present study. The noteworthy trend in
salinity values were due to influx of freshwater during monsoon
while prevailing higher temperature, excessive evaporation, and
low water-depths in the summer months.
Population of F. salina
The present study reveals great ability of Fabrea to withstand
wide ranges of environmental variables. Its better growth has
been obtained at 6 x 106 and 8 x 106Dunaliella cells mL-1 . As
observed, in solar salterns, it feeds voraciously upon Dunaliella
cells (Figure 1). However, it appeared that Fabrea, in extremely
saline conditions (>240 ‰) when Dunaliella is not available,
survives on halobacterial and it subsists on bacteria during food
scarcity . In marine planktonic realm, nearly all phytoplankton
produced are consumed, primarily by microzooplankton .
Protists are capable of sensing the biochemical properties of their
prey cells [23,24], and both ciliates and flagellates have been seen
to feed preferentially on more nutritious phytoplankton species
[25,26] indicating why Dunaliella is preferred by Fabrea. Fabrea
disappears from saltpans in monsoon months as it does not thrive
well in brackish water. It forms cyst and resumes normal active
form and life activities on the return of suitable conditions
during mid of November .
The positive correlation with nitrogen and phosphate is an
indication of demand-supply of nutrients to sustain its higher
densities in the month of April and May. The optimal production
of solar salt requires a well-established balance between primary
and secondary producers, with Artemia grazing on phytoplankton
constitutes the major interaction . Artemia also tolerates
very high salinities . It is surmised, therefore, that Fabrea too
contributes to solar salt manufacture. Very sparse, heterogeneous
distribution and above all almost vanished populations of Artemia
from majority of saltpans along the Mumbai coastline make
Fabrea as a predominant inhabitant of these solar saltworks .
The present knowledge of the ecology of Fabrea in its natural
habitat and effective management practices can be applied for
its controlled production on commercial scale in solar salt- beds
. The euryplasticity, easy acceptability of a variety of live and
inert feeds, short generation period and biochemical composition
make F. salina as an appropriate animal for studying microbiology
of hypersaline environments.
Tackaert W and Sorgeloos P (1993) The use of brine shrimp Artemiain biological management of solar saltworks. In: Seventh Symposium on Salt. Elsevier Science Publishers BV, Amsterdam, NetherlandsPp: 617-622.