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International Journal of Marine Science 2014, Vol.4, No.23, 210-218
http://ijms.biopublisher.ca
216
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
S
colelepis 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 b
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.75
0
27’ 23” E, Lat.11
0
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