Mangrove sediment core analysis of foraminiferal assemblages - a study
at two sites along the western coast of India
P. Vidya 1 & Rajashekhar K. Patil 2
1,2 Department of Applied Zoology, Mangalore
University, Mangalagangotri, Mangalore, Karnataka
574199, India
1 vidya_p31@yahoo.com, 2 patilsirmu@gmail.com (corresponding
author)
Abstract: Mangroves are anunique habitat and are largely influenced by sea level changes and wave
energy. Foraminifera (Protista)
preserved in mangrove sediments provide an excellent proxy for deducing past
conditions. One
meter deep mangrove core samples at two sites on the western coast of
India were collected. The foraminiferal assemblages
at various depths showed significant changes in the abundance and diversity
down the cores. A total of 59
species belonging to 32 genera, 24 families and five suborders were identified
from the cores of these two sites. The cores showed an abundance of genus Rotalidiumparticularly the species Rotalidium annectans. Other species identified include Ammonia, Elphidium,Nonion, Spiroloculina, Quinqueloculina, Globigerinoides etc. The pH, organic matter and
CaCO3 also showed variations down the cores. There was a lack of correlation between
sediment characteristics and the abundance of foraminifera in the cores. The low diversity and differences in
distribution of foraminifera compared to surface intertidal samples may be due
to intense post depositional changes or anthropogenic disturbances. The mangrove ecology thus appears
disturbed by various factors.
Keywords: Diversity, ecology, Foraminifera, mangroves, sediment cores, western
coast.
doi: http://dx.doi.org/10.11609/JoTT.o3653.5485-91 | ZooBank: urn:lsid:zoobank.org:pub:85FF3200-300A-4113-B815-1EC61E93A1D9
Editor: R. Ramanibai,
University of Madras, Chennai, India. Date
of publication: 26 February 2014 (online & print)
Manuscript details: Ms #
o3653 | Received 04 June 2013 | Final received 07 October 2013 | Finally
accepted 11 February 2014
Citation: Vidya, P. & R.K. Patil (2014). Mangrove sediment core analysis of foraminiferalassemblages - a study at two sites along the western coast of India. Journal
of Threatened Taxa 6(2): 5485–5491; http://dx.doi.org/10.11609/JoTT.o3653.5485-91
Copyright: © P. Vidya & Patil 2014. Creative Commons
Attribution 3.0 Unported License. JoTT allows unrestricted use of this article in any medium,
reproduction and distribution by providing adequate credit to the authors and
the source of publication.
Funding: UGC- Special Assistance Programme (SAP).
Competing Interest: The
authors declare no competing interests.
Acknowledgements: The present study was supported by UGC SAP
funds. The Research Fellowship to Vidya P., through an UGC-SAP grant is gratefully acknowledged. We would like
to thank people who assisted in the field during the collection of sediment
cores.
For figures, images, tables -- click here
Mangroves are specialized ecosystems consisting of diverse groups of
tropical trees and shrubs adapted to grow in intertidal regions. The ecological and economical importance
of this most productive and diverse ecosystem are well explored (Blasco et al. 1996; Oakes et al. 2010). Mangroves efficiently trap sediments and
the sedimentation process is influenced by various factors like sediment
supply, hydrodynamics of the area, geochemical parameters etc. (Alongi 2008; Sanders 2012). The high rates of accretion make the
mangrove sediments useful in palaeoclimatic studies (Kumaran et al. 2004). These sediments show presence of many
organisms including Foraminifera which are unicellularprotists (Lezine et al.
2002). They typically produce a
test, or shell, made up of calcium carbonate or agglutinated sediment particles which are well preserved following their
death. The evolutionary
significance of Foraminifera and the exceptional quality of fossil records make
them an excellent proxy for inferring past climatic conditions (Nigam 2005;
Murray 2006). Studies around the
world have shown that the shell deposits of Foraminifera in the sediments of
mangroves help in palaeoclimatic reconstructions
(Horton et al. 2003; Gehrels & Newman 2004; Woodroffe et al. 2005).
The diversity and distribution of foraminiferalassemblages in mangrove sediments are controlled by environmental factors
(Bradshaw 1968; Murray 2001), post depositional changes (White & Walker
2011) and anthropogenic activities (Sarkar &
Bhattacharya 2010). The present
study was designed to understand the diversity and distribution of foraminiferal assemblages in down core mangrove sediments
collected from two areas in the western coast of India.
Materials and Methods
Mangroves of Chithrapu (13004’34”N
& 74046’49’’E), Karnataka and Kumbla(12035’41’’N & 74056’19”E), Kerala along the western
coast of India were selected for the present study (Image. 1). The main species of mangroves present in
these areas were Sonneratia alba, Rhizophora mucronata, Avicennia officinalis, Bruguiera zymnorhiza, Acanthus ilicifoliusalong with some associated species. Parallel sediment cores of about 1m depth were collected from each of these mangroves during
periods of low tide (Image. 2). The
areas cored were not much disturbed by anthropogenic activities and were
minimally infused with fresh water. The cores were transported to lab, cut and sub-sampled at every inch
(2.5cm intervals). The sediment
samples for foraminiferal assemblage study were oven
dried at 600C. The foraminiferal tests in the cores were easily susceptible to
breakage and dissolution due to the long time deposition. Hence, chemical treatments were avoided
and samples were repeatedly washed through 63μm sieve under low water
pressure. The sand fractions were
collected over whatman filter paper and oven dried at
600C. 5–10 g of
dried sediment samples were used for foraminiferalassemblage studies and all the results were finally represented as per gram
weight of sediment samples. Foraminiferal tests were examined, picked on to micropalaeontological slides and identified with the help
of a stereo microscope. The species were identified according toLoeblich & Tappan (1987). Biodiversity indices were calculated by
using Past software version 2.17 b.pH of the sediment
samples down the core were measured in supernatant suspension of a 1:5 soil
liquid mixture potentiometrically using pH meter (Trivedi & Goel 1986). Modified WalkleyBlack method (Trivedi & Goel1986) was used for calculating the percentage organic matter present in the
sediment samples down the core. An
estimation of calcium carbonate was done by acid soluble weight loss method (Campillo et al. 1992) and the percentage was calculated.
Results and Discussion
A total of 59 species belonging to 32 genera, 24 families and five
suborders were identified collectively from mangrove cores of Chithrapu and Kumbla (Table
1). Chithrapucores showed the presence of 55 species of Foraminifera belonging to all the 32
genera 24 families and five suborders while in Kumblacores there were 33 species of 20 genera 12 families and three suborders (Fig.
1). The cores of both the sites
showed abundance of Rotalidium species mainly Rotalidium annectanswhich are the abundant species found in the western coast of India (Nigam &Chathurvedi 2000; Gadi& Rajashekhar 2009). 77% and 72% of the foraminiferaltests in Chithrapu and Kumblacores respectively were that of Rotalidium annectans. Ammoniabeccarii was the next abundant species (11% in Chithrapu and 9% in Kumbla) while
most of the other species were found in fewer numbers. The occurrence of many
species like Pseudononion japanicum, Donsissonia florae, Hastigerinella riedieli etc.,
were restricted to a single test per gram of sediment in the cores. The most predominant suborder in the
cores studied here were Rotalina followed by Miliolina, Globigerinina, Textularrina and Legenina. The foraminiferaldiversity and distribution (Shannon (H’), Evenness (J’)) was low in both Chithrapu cores (H’=1.056, J’=0.2634) and Kumbla cores (H’=1.205, J’=0.3445) (Table 2). There were considerably wide variations
in the diversity and distribution of tests at every depth down the core. The comparatively lower diversity in
mangrove cores might be due to the poor preservation of tests in the deposited sediments which resulted in the loss or change in the
relative abundance of particular species, or a loss in species diversity (Smith
1987). The distribution of the
tests in the down core samples could have been affected by the dominance of some
particular species which could resist the post depositional and other
destructive changes (Hayward et al. 2004; Husain et al. 2007). Both the cores showed a complete absence
of foraminiferal tests at some continuous depths
(40–57.5 cm depth in Chithrapu, 90–97.5
cm depth in Kumbla), which might be indications of
past climatic changes such as sea level regression, increased atmospheric CO2 etc or due to post depositional taphonomicchanges etc. (Fig. 2).
The pH, organic matter (%) and CaCO3 (%) down the cores
varied from 7.3–8.6, 0.1–2.7 %, 2–13 % respectively in Chithrapu cores and 7.7–8.0, 0.2–3.5 %,
1–14 % respectively in Kumbla cores (Fig.
3). Hydrogen ion concentration (pH)
significantly affects the existence of foraminiferaltests. Lower pH (<7.0)
accompanied by lower temperatures can cause dissolution of calcium carbonate in
sediments (Bradshaw 1968). In Chithrapu cores, the calcium carbonate showed a slightly
decreasing trend towards depth while there was a slight increase in bottom
segments. According to Sundararajan & Srinivasalu (2010),
high sedimentation might be the reason for the high value of calcium carbonate
in the bottom segments and active detritus dilution might have caused the lower
concentration in the middle depths. The lower values of organic matter at certain depths could be due to
higher decomposition rates. Studies
have shown that surface sediments from intertidal zones show a significant
correlation between these sediment characteristics and the abundance of
Foraminifera (Gadi & Rajashekhar2007; Gandhi et al. 2007). But in
core samples especially those from mangroves, such correlations may not be
found due to the interference of many other factors (Sanders et al. 2010; Sundararajan & Srinivasalu2010). In the present study also,
such correlations between sediment characteristics and foraminiferalassemblages were not significant. This may be due to intense post depositional changes including
post-mortem taphonomical changes (Berkeley et al.2007) or the past environmental conditions which the
mangroves experienced (Ellison & Zouh 2012). In addition to this, anthropogenic
activities can also disturb the post-sedimentation process and alter the physico-chemical and biotic components of core samples to a
greater extent (Qiu et al. 2011; Lezineet al. 2002).
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