Rec. zool. Surv. India: Vol. 122(4)/425-431, 2022
DOI: 10.26515/rzsi/v122/i4/2022/168786
ISSN (Online) : 2581-8686
ISSN (Print) : 0375-1511
Amphibians of Anjudiva Archipelago West Coast,
Arabian Sea, India
Amit Hegde and Girish Kadadevaru*
Breeding Behaviour and Bioacoustics Lab, Department of Zoology, Karnatak University, Pavate Nagar,
Dharwad – 580003, Karnataka, India; Email: kadadevarug@gmail.com
Abstract
Anjudiva archipelago in the Arabian Sea is close to the mainland on the west coast of India. It constitutes eight small island
patches seen parallel and close to the central Western Ghats. Islands have rocky, laterite, open grasslands and forests. As
there are no previous studies on the faunal diversities of these islands, the present study is undertaken to record amphibian
species availability within the islands. The present study records two species of dicroglossid frogs through primary
surveys and questionnaire methods. Since saltwater is considered a barrier for amphibian dispersal, we hypothesize that
these species might have lived in these islands for a long period when all of the islands were connected to the mainland
historically, as the wild flora species display a similar pattern to Western Ghats diversity. On the other end, introductions of
these two species of frogs could be human-mediated in the process of getting fresh water to the islands.
Keywords:: Anthropocene, Climate Change, Dicroglossidae, Dispersal, Small Island
Keywords
Introduction
Islands
are
nonrandom
subsets,
microcosm
environments of emerging biodiversity treasures having
unique evolutionary, phylogenetic, functional, and
biogeographical patterns (Russell & Kueffer, 2019).
Islands show a greater difference in diversity, density,
and divergence based on the size, space, time, and
degree of isolation. “Islands are laboratories of evolution”
due to their uniqueness in ecological and phenotypic
diversity. They bring about microevolutionary changes
in population and within the species (Losos & Ricklefs,
2009). Because of the microclimatic niches and isolation,
islands are considered to be of greater importance as
they reveal the evolution in action, adaptation, endemic
radiation, colonialization and speciation. Islands may
be of different sizes, which may range from continent to
small landmass. Small island studies are essential because
of their simplified abundance that helps in understanding
the patterns of evolution and geographical isolation.
Archipelagos having more isolation and less rate of
colonization have shown more diversified organisms.
These are the ideal spots to study character displacement,
where they offer unique signatures in an ideal setting.
Small landmasses or islands which are connected to
larger ones are known to have more species (Rand, 1969).
If these islands are natural and ancient, their flora and
faunal species are either endangered, rare or invasive
(Losos & Ricklefs, 2009).
Globally and even in the Indian context, only the
islands with large landmasses or large groups of islands/
archipelagos are well-studied (Harikrishnan & Vasudevan,
2018; Hidayathulla et al., 2012; Rao, 1991). India comprises
more than 1380 islands out of which only 21 islands and
3 groups are studied (Pandey et al., 2013). However, the
majority of them are unnamed and biodiversity studies
are neglected, hence requiring great attention. Only two
archipelagos are considered significant in comparison to
other islands: The Andaman and Nicobar archipelagos
on the east coast and Lakshadweep on the west coast.
There has been no comprehensive information about
the biodiversity of several smaller islands close to the
coastline of the mainland or peninsular India.
Many of the islands, in India, are wildlife and bird
sanctuaries, protected areas, biosphere reserves and
harbour coral reefs, historical wealth and support human
habitation. Endangered species such as the Dugong, Sea
turtles and several endemic species of mangrove and
seagrass species are found in smaller islands close to the
coastline.
* Author for correspondence
Article Received on: 08.03.2022
Accepted on: 07.06.2022
Amphibians of Anjudiva Archipelago West Coast, Arabian Sea, India
Amphibians are one of the most diverse vertebrates
adapted to different ecosystems and habitats. They
show a cosmopolitan distribution to point endemism.
They are considered as an ideal model to understand
biogeography and dispersal patterns (Harikrishnan &
Vasudevan, 2018). As they are sensitive to osmotic stress
and salinity, they are thought to be good model systems of
biogeography/zoogeography to understand archipelago,
islands, landmass connections and their patterns (Vences
et al., 2003).
Anjudiva archipelago in the Arabian Sea is close to
the mainland on the west coast of India. It has a historic
record of human habitation for long period, dating back
to pre-colonial times, the Sondha kingdom ruled these
islands (Naik, 2014). In 1498 AD, Ships of Portuguese –
sailor Vasco da Gama accidentally landed for the first time
on Anjudiva Island, and the Portuguese conquered these
islands. Earlier these islands had a wide scope for trade
and commerce between the Western world and India
(Naik, 2014). Later, Marathas tried a failed attempt of
acquiring islands from the Portuguese. These islands are
also of historical significance, as they have forts, cannons,
lighthouses, temples, and church ruins (Campbell, 1833;
Naik, 2014). These islands have had various names in
different timelines by different rulers and conquerors.
They were once known as Ajadurga Islands and then
Anjudiva Islands (Anjudeeva Island, Anjadiv Island).
Figure 1. A
. Mogeragudda Island; B. Devagadgudda Island; C. Madhyalingad Island;
D. Kurmagadh Island; E. Flamingo Island; F. Kangigudda Island.
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Zoological Survey of India
Amit Hegde and Girish Kadadevaru
Anjudiva archipelago constitutes eight small island
patches (Figures 1 & 2) excluding the rocky outcrops seen
parallel to the central Western Ghats, with a majority of
rocky shores and very few sand beaches which makes
islands inaccessible (Marati et al., 2002). There are no
proper reports on faunal diversity in these islands. Hence,
we are presenting an assessment of amphibian diversity in
this archipelago.
Materials and Methods
The amphibian survey was undertaken during the premonsoon season in the year 2017-2018. Field observations
were done twenty days a month for four months. An
opportunistic visual encounter and acoustics survey was
used to locate the anurans (Crump & Scott, 1994) during
the dusk, dawn and night hours. Freshwater habitats,
moist habitats, fossorial, murky or mangrove habitats,
shrub, tree, litter, grass, canopy, rocky boulders, and other
microhabitat were screened for the presence of anurans.
Searches for caecilians were made by digging soil, lifting
stones and clearing leaf litter.
A social survey was carried out through a questionnaire
with locals, fishermen, and island officials on the presence
of amphibians (n=31). The questionnaire included the
island’s natural history, the presence of freshwater habitat
on the islands and information about the presence of
amphibians on the islands by showing the anuran and
caecilian images, and by playing the recorded calls of
anuran species. Identification up to the species level
was done based on the morphological characters using
available literature and no specimens were collected.
Results
These islands have rocky, laterite, open grasslands, and
mixed deciduous forests.
(i) Anjudiva Island: The total land area is approximately
1.92 km2. It is the longest human-inhabited island in this
archipelago, with small natural forest patches dominated
by cultivated trees. It has an elevation of 13 m and is
located at a distance of 1.7 km from the mainland. This
island has a rain-fed pond as the freshwater source. We
have recorded two frog species on this island belonging
to the family Dicroglossidae: Euphlyctis jaladhara and
Hoplobatrachus tigerinus.
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Figure 2. A
njudiva archipelago: 1*. Anjudiva Island;
2. Maharshi Agastya Temple Island;
3. Mogeragudda Island; 4*. Devagadgudda
Island; 5. Madhyalingad Island;
6*. Kurmagadh Island; 7. Flamingo Island;
8. Kangigudda Island (* indicates islands
with frog populations) (long lines are break
water bridges and barriers); Main Land:
Karnataka State.
(ii) Maharshi Agastya Temple Island: The total land
area is approximately 0.93 km2. This Island is very closely
associated with Anjudiva Island and is the smallest island
in this archipelago. It is situated at a distance of 0.47 km
from the mainland and 3.84 km from Anjudiva Island. It
is a rocky island with grassland patches. It is located at an
elevation of 15 m from sea level. There is no freshwater
source on this island. During the present study, no
amphibian species were recorded on this island.
Zoological Survey of India
427
Amphibians of Anjudiva Archipelago West Coast, Arabian Sea, India
(iii) Mogeragudda Island: The total land area is
approximately 1.8 km2. It is approximately 0.9 km from
the mainland and 3.84 km from Anjediva Island with
an elevation of 46 m. This island has a comparatively
dense mixed deciduous forest than Anjediva Island and
Maharshi Agastya Temple Island. There is no freshwater
source, and no amphibians were recorded from this
island.
(iv) Devagadhgudda Island/Oyster Rock Lighthouse
Island: The total land area is approximately 3.0 km2. It
has one large and two small interconnected island patches
with rocky outcrops with an elevation of 41 m. The larger
part of the island has human habitation, and a major part
of the landmass has a mixed forest with deciduous trees.
It has freshwater sources in the form of an open well. It is
the last island towards the west in this archipelago having
an aerial distance of 6.89 km from the mainland, 4.68 km
from Kurmagadh Island, and 2.31 km from Kangi Island.
During the present study, eight individuals of Euphlyctis
jaladhara and six individuals of Hoplobatrachus tigerinus
belonging to the family Dicroglossidae were spotted.
(v) Madhyalingad Island/Shimis Gudda Island: The
total land area is approximately 1.8 km2. It is located at a
distance of 2.79 km from the mainland and 0.53 km from
Kurmagadh, 4.68 km from the Oyster Rock Lighthouse,
and 3.83 km from Mogergudda. It is surrounded by rocky
cliffs, with the dense mixed deciduous forest at the top
dominated by trees, climbers and lianas. Outside the
forest patch, there is a grassland habitat with Wild banana
(Ensete superbum) plants. There are no freshwater sources
and no amphibian species were recorded on this island
during the present study.
(vi) Kurmagadh Island: The total land area is
approximately 5.3 km2. A highly elevated island in this
archipelago (64 m) which is approximately 2.53 km from
the mainland surrounded by mixed deciduous forest,
lianas, climbers, and some cultivated trees. It has two
rainfed freshwater sources, and one of them dries out
in summer. During our survey, we observed fourteen
individuals of Euphlyctis jaladhara and nine individuals
of Hoplobatrachus tigerinus.
(vii) Kangi Island/Flamingo Island: The total land area
is approximately 1.1 km2. It is one of the smallest islands
in this archipelago and is very close to the mainland. It
is approximately 0.13 km from the mainland during the
high tides and is connected to the mainland during low
tides. This island is 1.75 km from Kangigudda Island with
an elevation of 18 m. It has deciduous trees, grass, and
thorny bushes. The outer part of this island is a rockycliff.
There are no freshwater habitats.
(viii) Kangigudda Island: The total land area is
approximately 1.9 km2. This island has rocky surroundings
with dense mixed deciduous forest on the upper part with
trees, lianas, and climbers. The elevation of the island is
46m. No amphibian species were spotted on this island. It
is approximately 0.38 km from the mainland.
Anjudiva archipelago has only two known species of
anurans belonging to the family Dicroglossidae, Euphlyctis
jaladhara and Hoplobatrachus tigerinus on three islands
(Figure 3). During the study period, only adult frogs were
observed and no caecilians were spotted.
Out of the eight islands, we carried out both primary
and questionnaire surveys on six islands.
Figure 3. A
nurans found in islands: A. Euphlyctis jaladhara (Dinesh et al., 2022);
B. Hoplobatrachus tigerinus (Daudin, 1802).
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Zoological Survey of India
Amit Hegde and Girish Kadadevaru
For the other two islands, i.e., Anjudiva Island and
Maharshi Agastya Temple Island, we relied on secondary
information such as photographs and questionnaire
surveys.
Out of the thirty-one individuals who participated
in the questionnaire survey, twelve individuals had no
idea about the freshwater sources, twelve individuals
were aware of freshwater sources in islands, and seven
individuals were aware of freshwater sources and the
amphibian presence. We have relied on the photographs
of two anuran species that were shown by two individuals
from Anjudiva Island and Kurmagadh Island.
Discussion
Out of eight islands, three islands, i.e., Anjudiva Island,
Devgadgudda Island and Kurmagadh Islands (Figure 2.
1, 4, 6), are inhabited by humans both in the past (Precolonial era and Colonial) and present. These are the only
islands that have freshwater resources like the pond, open
well. All of them are rainfed during the monsoon, and
open well is of groundwater. The salinity of the water is
comparatively normal and residents use it for drinking
and other purposes. However, there are no salinity
studies on fresh waters of islands. There are no lotic or
stream like fresh water systems, and all of them are lentic
or still freshwater, these might have been constructed
during pre-colonial times, where they have used water
for the livelihood. Currently, we report amphibian
presence only on these three islands Anjudiva Island
(E. jaladhara, H. tigerinus: numbers not determined),
Devgadgudda Island (E. jaladhara: eight individuals,
H. tigerinus: six individuals) and Kurmagadh Islands
(E. jaladhara: fourteen individuals, H. tigerinus: nine
individuals) (Figure 2. 1, 4, 6). Most of the islands show
some mangrove vegetation (Viswambharan et al., 2017),
but they lack large mangrove habitats.
On the east coast of India at the Andaman archipelago,
there are reports of slightly salt tolerant estuary/
mangrove species Fejervarya cancrivora (Harikrishnan
and Vasudevan, 2018). On the west coast, Phrynoderma
karaavali a slightly salt tolerant frog species was reported
(Priti et al., 2016; Dinesh et al., 2021). In the present study,
none of these salt tolerant species were found on surveyed
islands. For the majority of the amphibian, the dispersal
from the mainland to the island, saltwater might act as
the main barrier (Bossuyt & Milinkovitch, 2001; Inger
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& Voris, 2001; Brown & Guttman, 2002). In addition,
limited freshwater resources on the small island are also a
challenge for their survival during the dry spells.
On the islands during the pre-monsoon,
Hoplobatrachus tigerinus is seen under the moist rock
crevices and moist soil part. During the rainy season, they
are seen near freshwater resources like ponds.
Euphlyctis jaladhara is commonly seen in slightly
shallow water tank or ponds. Current study is the first
report from the islands and this species is a slightly salt
tolerant species in the west coast.
Further south to Anjudiva Island, Basavarajadurga/
Basavaraj Gadde Island also show the same amphibian
species diversity, this data is based on the secondary
survey and further detailed studies are required to
understand the diversity of amphibians on these islands.
Currently, we have two hypotheses which explain
Amphibian diversity in the islands:
The first hypothesis is that, from geological and
floral studies, the Anjudiva archipelago was once part
of the mainland on the west coast, Karwar region. The
geological studies also show that the Anjudiva archipelago
has Basaltic dykes and Granitoid rocks, migmatitic gneiss
formations (Ravi et al., 1998). The mainland on the
west coast closer to these islands has similar geology of
rock formations (Nadaf, 2019, Valdiya, 2015). Several
reports suggest that these islands were formed by the
submergence of the west coast mainland (Choudhary et
al., 2013, Hashimi et al., 1995).
The wild flora on these Islands shows a similar pattern
and affinities as the Central Western Ghats endemic flora
(Marati et al., 2002), which suggests that this might be a
reminiscence of the Western Ghats biodiversity hotspot.
However, many of the shore islands on the west coast
might be a part of the mainland (Valdiya, 2015). Like
the floral diversity of the island that shows the close
resemblances with the mainland and the Western Ghats
flora, the frog species inhabiting these islands may also be
the reminiscence of the mainland that was separated due
to submergence.
The Second hypothesis is that, according to Campbell
(1883), during colonial times in India, the British
transported timber, using water as a transport route in
the Western Ghats, and the Kali River was one of the
main timber transport routes. During the same, they
might have transported timber from the mainland to
these islands, for the construction light house and other
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Amphibians of Anjudiva Archipelago West Coast, Arabian Sea, India
buildings. During which amphibians might have reached
these islands along with timber and survived. On the
other end, in the three human-inhabited islands, possibly
humans might have used the mainland water and other
resources (still they are using) through which tadpoles or
adults might have been transported from the mainland,
and they survived.
Compared to the other vertebrate diversity
(unpublished data) amphibian diversity and density are
very low on these islands. Based on the present study,
amphibian populations on these islands are very small
and this could be due to scanty freshwater habitats, less
genetic diversity, or exchange of gene pool. On these
Islands Caecilians are absent it may be due to scanty
freshwater habitat and non-availability food, Further
intensive surveys and long-term studies are required to
understand the reasons.
According to Hidayathulla et al. (2012), In
Lakshadweep two species of Amphibians: Duttaphrynus
melanostictus (Schneider, 1799), Hoplobatrachus
tigerinus (Daudin, 1802) are reported, which we suspect
could have been introduced. Members of the family
Dicroglossidae, Bufonidae, and Microhylidae are known
to occur or survive in island conditions easily when there
is an optimum habitat (Harikrishnan & Vasudevan, 2018,
Hidayathulla et al., 2012).
Unlike Lakshadweep and Andaman and Nicobar
archipelagos, the islands in the present study are
comparatively tiny, and there are few islands in an
archipelago that are very close to the mainland. Though
they are closely located they are inaccessible during
the monsoon because of extreme conditions. Further
explorations in the breeding seasons are required to
understand the species diversity and density in these
islands and other numerous islands along the coastal line.
Islands are the most sensitive zones, small disasters
or catastrophic events can completely wipe out the
population, or they can change the pace of islands forever,
and can affect and completely change the evolutionary
and geographical dynamics of island biotas.
Acknowledgements
AH is grateful to Vijay Prabhu, Meetha Prabhu, Suresh
Mathias, Raju AK, Shantanu, Roshana of Cintacor Island
and Little Earth group for their support including staff:
Shivanath, Subash, Mohan, Gajendra. Special thanks to
Dr. K. P. Dinesh from Zoological Survey of India (ZSI) for
critical comments and suggestions and Deepak P., Mount
Carmel College, Bengaluru for the map and comments,
Prof. G. V. Nayak from Goa University, Dr. G. V. Hegde,
Dept. of mines and geology, Scientist. S. V. Hegde from
Geological Survey of India (GSI) for the Geology and
geography inputs and suggestions, Tejaswini Harikantra
and family and to the course on “Tropical Marine
Biology and Ecology in the Andaman and Nicobar
Islands” sponsored by the Department of Biotechnology.
Additional support from Sunita Rao, Dinesh Kumar,
Batt Anderson, Amila-Lupé Ellena Aguilar, Tom. We
are thankful to the Coastal Guards, other Government
Officials and the Karnataka Forest Department (KFD).
Work is supported by University Research Studentship
(URS) and UGC SAP II grant provided to Department
Zoology, Karnataka University, Dharwad.
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