Distribution and Diversity of Intertidal Macrofauna of Dharmadam Beach, South West Coast of India  

V. Anu Pavithran , S. Bijoy Nandan
Department of Marine Biology, Microbiology and Biochemistry, School of Marine Sciences, Cochin University of Science and Technology, Kochi - 682 016, Kerala, India
Author    Correspondence author
International Journal of Marine Science, 2014, Vol. 4, No. 23   doi: 10.5376/ijms.2014.04.0023
Received: 07 Feb., 2014    Accepted: 09 Mar., 2014    Published: 24 Apr., 2014
© 2014 BioPublisher Publishing Platform
This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Preferred citation for this article:

Pavithran and Nandan, 2014, Distribution and Diversity of Intertidal Macrofauna of Dharmadam Beach, South West Coast of India, International Journal of Marine Science, Vol.4, No.23 210-218 (doi: 10.5376/ijms.2014.04.0023)

Abstract
This contribution presents the abundance and diversity of macrofauna in the pristine intertidal regions of Dharmadam beach along the Kerala coast (South West coast of India) during August 2009 to January 2011.The width of the beach is 15-30m, which alternates according to the tidal height. Environmental parameters like salinity, nutrients, conductivity and total dissolved salts analyzed exhibited significant correlation with macrofauna that dwells in the habitat. Gastropods (45.54%), polychaetes (10%), tanaids (43.4%) dominated in the present study. The monthly variations in abundance were displayed by dominant faunal species in various stations but did not show any seasonal variations except that of Emerita holthuisi, which was observed only in pre monsoon (Feb-May) and monsoon (Jun-Sep) months. Analysis of community indices showed monthly variations in species diversity. The peak mean species diversity was observed in station 1 in May, 2009 and Station 2 in December, 2009 and January, 2010.The spatial distribution of some organisms were not even in the study area. The sparse distribution, low richness and higher dominance of organisms were the characteristic feature of community structure. The dissimilarity trend of organisms like polychaetes, gastropods and total groups were discernible by MDS plotting. It best explained the dominance of polychaetes and gastropods on the beach. Assessing the correlation of water quality parameters to the fauna residing in study area BEST (Bio-Env + Stepwise) analysis was done and salinity showed more significance towards fauna. Draftsman plot were also done to observe the interactions of organisms. The highest correlation has been showed by barnacles and gastropods (0.825).The present study discussed the interaction of organisms in the selected habitat with environmental factors prevailing there along with the diversity and abundance.
Keywords
Dharmadam Beach; Intertidal macrofauna; Environmental parameters; Diversity

The study of abundance of life in each ecosystem is a cognizance to everyone that how an ecosystem is performing. Intertidal zone are such fascinating ecosystems which have been pulled towards scientific community since many years. The intertidal, sometimes called the littoral zone, is defined as the part of the seafloor that lies between the highest high and lowest low tides (Castro and Huber, 2005). Being out of water and exposed to air establishes a unique nature to this environment. Intertidal zones especially the South West coast of India are harbor of distinct and specific organisms. The subsistence of intertidal habitat is almost by definition due to tides (Carefoot and Simpson, 1977, Kenchington, 1990), which are the outcome of confounded gravitational effects of the sun and moon of the oceans. Both flora and fauna found in between the intertidal zones experiencing the tidal movements, which influences the life of inhabitants there. The intertidal organisms are more prone to climate changing like sea level rise and temperature fluctuations, rainfall etc. It affects the abundance and distribution of organisms.
The distributions of organisms in the intertidal zones usually occupy only specific zones. The upper limit (high tide zone to mid tide zone) of intertidal organisms seems to be set by abiotic environmental factors like extreme temperature, prolonged exposure to air, less feeding time. In general abiotic factors set the boundaries to the range of a species within an environmental gradient (Beukema and Flach, 1995). But generally the lower limit of intertidal zone is controlled by the biological factors especially predation and competition.
The shores of west coast of India, particularly Kerala coast are famous for its enthralling beauty and lustrous greenery. From north to south the topography of Kerala coast (abutted on the west by Arabian Sea) is distinctive and alters abruptly. The coastline of Kerala is 560km long and endures several alterations in the near shore processes. The coast of Kerala embraces a great variety of shores according to the coastal geography and form of the substrate.
Sandy beaches are very dynamic environment. Wave, wind action, grain size and tide amplitude is the most important factors in their physical characterization (Nybakken, 1993). The intertidal macrofaunal studies have been great interest to the researchers during the mid of the 20th century. Between 1920s and 1980s shore studies were at its peak. Studies on soft shores were made by Dahl, 1952, Morton and Miller, 1968, Stephenson and Stephenson, 1972, Dayton, 1971, Menge, 1976, Peterson, 1977. In 1983 two researchers McLachlan and Brown have studied about the patchiness of sandy beach macrofauna. By following this Thrush, 1991, Morrisey et al., 1992 have been studied about the distribution and abundance of organisms including soft sediment macrofaunal patchiness. In India Seshappa, 1953, Kurian, 1953 were the first to carry out detailed studies on the bottom fauna of Madras, Malabar and Travancore. The other significant works have been done by McIntyre, 1968, Govindan Kutti and Nair, 1966. Recent studies have been done on intertidal faunal, physical and climatic interactions by Quadros et al. 2001, Misra and Kundu, 2005, Vaghela et al.2010.
In recent times several studies have been fashioned by the researchers to investigate community structure and diversity of the intertidal zones of India (Dutta et al., 2010; Singh Gohil and Kundu, 2012). In Kerala as a coastal state of India an approach to the study on intertidal zones and their diversity has been exhibiting a declining trend. Limited studies have been accomplished in various beaches of Kerala, mainly in southern part (Travallion et al., 1970; Philip, 1970). It would be a point of interest to explore new intertidal zones along the coast of Kerala. This as a purpose in mind, a pioneer study was undertaken on a sandy beach situated in the northern part of Kerala along the South West coast of India.
1 Results
1.1 Environmental factors
The important environmental characteristics were as follows: Tides are semi diurnal type with maximum tidal amplitude of 1.3m and a minimum of 0.01m.The speed of the long shore current varied from 0.023m/s – 0.034m/s. Among water quality parameters temperature, pH, and salinity of sand varied from 25-340c, 25.5-320c, 7-8.31, 6.48-8.32 and 17.5-33ppt, 10-33ppt at station 1&2 respectively. The particle size showed dominance of sandy grains. The percentage of sand varied from 37.4-99.2%.
1.2 Distribution and abundance of macro fauna
Thirty four species of macro invertebrates were obtained from the stations during sampling. Among the identified samples, gastropods, tanaids, and polychaetes formed the dominant organisms in order of faunal composition. The number of tanaids (43.4%) was highest at all months at station1 when compared to other groups whereas in station 2, gastropods (45.54%) were dominant. The obtained species and their abundance from high to low water mark are given in Table 1. The distribution of organisms from high tide to low tide marks was almost consistent throughout the sampling. Around high tide zone of the studied sites were characterized with burrows of ocypode crabs. The amphipod (Pontocrates altamarinus) occurred in a zone around mean high water at the time of the collection and the sea star, Astropectan irregularis was spotted at about these tidal levels at both the stations.

 

Table 1 Counts of Macrofauna from high tide to low tide


On the rocky fragments of high tide zone, gastropods especially Littorina sp. was abundant at station 2. The mid region of the intertidal zone was characterized by several polychaete worms, commonly Scolelepis (Scolelepis) squamata at both the stations, whose distribution extends down into the surf zone. Mid tide region was blessed with different kinds of macrofauna, Donax sp., mole crab larvae, and other crustaceans, like mysids etc. Low tide region was dominated by echinoderms, polychaetes and some gastropods like Turricula and Nassarius sp.
1.3 Macrofaunal diversity based on diversity indices
Spatially community indices varied from month to month at any given station. Species diversity varied from month to month at both the stations. Highest species diversity was observed in May, 2009 at station 1. As shown in the Figure 1, October shows zero values in diversity indices. This clearly enlightens the interruption of sampling due to heavy rain in that month. None of the organisms were obtained except dead shells and broken pieces of organisms.

 

Figure 1 Monthly variations of macrofaunal diversity at station 1, Dharmadam beach


The low species diversity in the month of June 2009 at station 1 was mainly due to the abundance of larvae of Emerita holthuisi (Figure 1). This may be due to high reproductive periodicity of organism during this month. At station 2, in Dharmadam beach the highest species diversity was observed in December, 2009 and January 2010 (Figure 2). Species diversity is interrelated with relative species abundance in a community (Whittaker, 1965; Hulbert, 1971). The abundance of tanaid and polychaete species in the study area clearly showed the probability of less species diversity of that area.

 

Figure 2 Monthly variations of macrofaunal diversity at station 2, Dharmadam beach


One or few species dominating a community shows low evenness while those that have more even distribution have a high evenness. The species evenness observed in the Dharmadam beach agrees with the statement (Figure 3 & 4). The distribution of organisms was not even in monthly observations. The overall community shows low species evenness.

 

Figure 3 Monthly variations of species evenness at station1


 

Figure 4 Monthly variations of species evenness at station 2


1.4 Faunal interactions based on statistical analysis
BEST analysis was carried out to check the influence of water quality parameters on total groups collected from the beach on monthly basis. The results showed that the BEST correlation coefficient (Rho) for total groups from Dharmadam beach was 0.139 (Figure 5, Table 2). The variables are environmental parameters and the selected variables for each parameter have been displayed according to their SI No. (Table 2).

 

Figure 5 Histogram showing the BEST results of total groups (Rho 0.139)


 

Table 2 BEST results for total groups


According to the BEST results, among the twelve water quality parameters were analyzed from the study area, six (salinity, nitrate, nitrite, conductivity, total dissolved salts) showed significant correlations with the fauna (Figure 6 & Table 2). The highest significance has been shown by salinity.

 

Figure 6 Draftsman plot showing correlations between faunal groups for all the stations

 
The dynamics of an ecosystem has been determined by the interactions between and within the communities. The significant correlation has been showed by some groups. Barnacles and gastropods showed high significance (0.825) followed by bivalves and gastropods (0.660), mysids and amphipods (0.599), tanaids and polychaetes (0.517).
1.5 Non-metric multidimensional scaling bubble plots
The Figures 7, 8 & 9 show the results of ordination of polychaetes, gastropods and total groups of the studied area. As polychaetes and gastropods form the dominant organisms on Dharmadam beach, they have picked for MDS and bubble plot scaling to show the presence and dominance of the same. In Figure 7 bubble plot of total group of Dharmadam beach has been disclosed. The bubbles are used to explore the relative sizes of variables assist in exploring the trends in variables between samples (Clarke and Warwick, 2001). In the figure bubbles were drawn based on relative abundance of dominant group of macro invertebrates. Here it clearly shows that the gastropod components are abundant during almost all seasons. According to the size of the bubble, monsoon season (at station 2) showed highest abundance of gastropods. Ordinations based on MDS bubble plot of polychaetes on monthly basis were also done (Figure 8) as the polychaetes formed one of the dominant organisms in the study area. The segregation of a bubble (Figure 8) clearly shows the abundance of Prionospio sp. in December, 2009. It reveals the reason of dissimilarity with other, while the others having an abundance of the species Scolelepis (Scolelepis) squamata. The bubble plots enlightens the fact on the dominance of gastropods and polychaetes in Dharmadam beach.

 

Figure 7 Bubble plot showing seasonal variations in total groups from Dharmadam beach. (monst - monsoon season, postst - post monsoon season, prest - pre monsoon season)


 

Figure 8 Bubble plot showing monthly variations in polychaetes from Dharmadam beach. (Decst - December month)


The MDS plotting (based on Euclidean distance to find the distance/dissimilarity between samples) of gastropods (Figure 9) another dominant group of that area shows that majority of the samples grouped closely and can assume that almost similar in composition. But two stations in the post monsoon season formed two separate groups. These separated stations in post monsoon season have different composition of species when compared to closely related stations. Samples grouped within the red circles showing significantly separate groups at an Euclidean distance of 6.4.

 

Figure 9 MDS plot of gastropods from Dharmadam beach. (Normalise variables, Square root transformation). (monst - monsoon season, postst- post monsoon season, prest - premonsoon season)


2 Discussion
2.1 Abundance and Influence of environmental gradients on macrofauna
The life and living in these zones are big challenges to the animals here. They are persistently facing fluctuating salinity, drying out by wind and sunlight, predators, strong currents that carry them back to the sea and changing weather conditions. Sedimentation, light, moisture, and temperature variations are also common.
As a first study on that beach, this reveals that the beach system supports high abundance of two or three species which has led to less species richness as well as low species evenness. The abundance of tanaids found almost all the months. Other organisms observed to be polychaetes (Scolelepis (Scolelepis) squamata) and gastropods formed the dominant group of organisms. Communities with a large number of species that are evenly distributed are the most diverse and communities with less species that are dominated by one or few species are least diverse. Some studies revealed that sandy beach ecosystems wherein species evenness and diversity are influenced by the population dynamics of numerically abundant species. (Holland and Polgar, 1978; Dexter, 1984).The present study agrees with this statement. Among groups polycheates (14 species were observed from two stations) and gastropods (9 species) have shown high species richness but the overall community showed lesser species. Sandy beach macrofauna is controlled by interaction between different factors (Sivadas et al., 2012). They could be abiotic and biotic factors.
According to Bortone (2005), the salinity range of Scolelepis squamata was 17-35ppt. In this study also the range of salinity at station1 was 17.5-33ppt (the abundance of Scolelepis species is more in station1). S. squamata is known to tolerate oscillations in salinity (Rizzo and Amaral, 2001).This could be one of the reasons for the abundance of species in that area. The results of BEST analysis clearly illustrates that salinity has high significant correlation with fauna that resides there. Except for other fauna, only mole crabs have the direct correlation with tidal heights. Being tidal migrants as tide advances it goes up to the beach and as tide recedes it follows the tide towards lower depths. Variations of abundance of dominant faunal species were significantly different in various stations (polychaetes at station1 and gastropods at sation2) but they did not show any differences between seasons except larvae of mole carbs (E.holthuisi). The highest peak was observed in monsoon and pre monsoon seasons. It could apparently be related to recruitment periods. According to the study on two sandy beaches along South-West coast of India by Ansell et al. (1972), there were two main periods of recruitment, one in pre-monsoon period and the other in monsoon periods. This exactly complements with the present study data.
2.2 Fauna in relationship with environmental variables: a statistical approach
Different statistical analysis clearly showed the similarities and significance of organisms that live there. From the BEST (Bio-Env + Stepwise) analysis it was inferred that salinity, nitrate, nitrite, conductivity, phosphate and TDS were the best matching variables for total groups on monthly basis. The present study reveals that water temperature and dissolved oxygen are not at all a limiting factor for the organisms in the area. MDS plotting of total groups on seasonal basis showed that gastropods were present in almost all seasons, specifically with high abundance in monsoon months according to the relative size of the bubble. MDS plot of gastropods on seasonal basis clearly supports this by disclosing the similarity trend between all seasons. Some organisms showed inter dependence. The interactions between some organisms were shown in Draftsman plot (between barnacles and gastropods). In a harsh environment like intertidal zone the interaction between organisms and environment variables is a must for the healthy survival of the organisms. These may be for feeding, shelter, or to escape from predators.
Diversity values are influenced by the values of evenness and total number of species. The dominance of two or three species affected the diversity of the beach system. The observations on abiotic and biotic factors clearly show that they directly or indirectly influence the organisms that persist there. In a heterogeneous habitat such as intertidal region the abundance and diversity of organism changes continuously according to the abiotic, biotic and climatic conditions that persists there (Harkantra and Parulekar, 1985). Being a dynamic system the beach environment is changing continuously. Anthropogenic activities also fasten the habitat destruction. A proper assessment of composition of organisms and the environmental properties of the beach is necessary for future management and protection of whole beach ecosystem.
3 Materials & Methods
3.1 Study area
Dharmadam beach (Long.750 27’ 23” E, Lat.110 46’ 35” N) is an exposed beach with less intense wave action. It is situated in Kannur district, northern part of Kerala. Continuous stretch of straight beach with lesser steeper profiles offers the area a unique impression (Figure 10). In every year, this zone experiences a tropical climate characterized by South-West monsoon (Jun-Sep), post monsoon (Oct- Jan), and pre monsoon (Feb- May). South-West monsoon (seasonal reversal of winds and associated rainfall) is prominent and heavy beach erosion befalls during this period. Besides the precipitation the beach has fresh water influx through a river mouth (Anjarakkandi River). The arms of this river enter from two sides of the beach (North & South). Two stations were selected for the study. On both stations sandy characters are predominate. But at station 2 mixed type of sediment composition is persists. Fine sand adhering with scattered laterite rock formation gives the beach a unique appearance. The beach boards an array of macrofauna. Before assaying the abiding macrofauna, the reconnaissance of environmental factors were carried out.

 

Figure 10 Map showing location of study area


3.2 Sampling methods
The intertidal zones of Dharmadam beach was monitored from 2009 August to January 2011. Low tide time has chosen to sample the area. Two localities at 500m apart were selected for intensive sampling. A 15-30m transect was established from above the drift line to below the swash line with four regularly marked stations. At the précised stations a metal quadrate of 25x25cm area were sited and the sediment within the quadrate were collected and sieved through 0.5mm mesh sieve (Anastasios Elftheriou and Alasdair McIntyre, 2005). The retained organisms in the sieve were preserved in 5% buffered formalin and conveyed to the lab for sorting. The organisms present in the sediment were sorted out, preserved and identified.
In addition to the faunal component the measurement of water and sediment samples from the picked zones were also collected to analyze different physico chemical parameters. Temperature of the sediment was measured by using a centigrade thermometer. Dissolved oxygen was estimated according to Winkler’s method (Grasshoff et al., 1983). Salinity was measured by using a Systronics water analyzer (Model No. 317; accuracy + 0.01) calibrated with std. seawater (APHA, 2005). Conductivity was recorded by Systronics digital potentiometer (Model No.318). Turbidity, pH, and TDS were measured by using Systronics water analyser (Model No.317) Tidal heights were estimated from predicted tide tables. Long shore currents were measured by releasing a plastic bottle top to the water and determined the time for it to travel one meter. Three consecutive readings were taken.
3.3 Analysis of data
Diversity indices were computed according to Shannon-Wiener diversity (H’) and Pielou’s evenness index (J’) by using PRIMER Vs. 6.0 (Clarke and Gorley, 2006). The ordination plot of samples was also performed by non-metric Multi-dimensional scaling (MDS) using Euclidean distance as a distance measure (PRIMER Vs. 6.0) to explore trends between samples. Statistical analysis like BEST (Bio-Env + Stepwise) analysis for finding out the combination patterns that best explains the biological data. The BEST analysis gives the ‘best’ match between the multivariate among-sample patterns of an assemblage and that from environmental variables associated with those samples (Clarke and Gorley, 2006). Draftsman scatter plot were also done to find out interaction between organisms.
Authors Contribution
SBN is the research supervisor. VAP made the experimental design, data analysis, manuscript preparation.
Acknowledgement
Authors are thankful to the Head, Dept. of Marine Biology, Microbiology and Biochemistry, Cochin University of Science and Technology for providing necessary facilities.
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