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International Journal of Marine Science 2015, Vol.5, No.3, 1-7
http://ijms.biopublisher.ca
2
. These organisms are
important in the form of diet for many fishes and
invertebrates
. Some
species commonly live in large numbers in the
intertidal zone of estuarine and brackish waters,
normally in sediments of medium to high organic
content
.
Nereididae species exhibit a wide range of
reproductive modes, including external brooding,
viviparity and hermaphroditism
. Most species undergo morphological
and physiological modifications when they become
sexually mature, suiting many of them for a brief
pelagic existence and improving the chances that
sexual partners will find each other
. All Nereididae polychaetes have a semelparous
life cycle; they reproduce once in a lifetime and die
soon after spawning
.
The reproductive swarming of the Nereididae to the
surface waters of marine and estuarine environments
is a well-known phenomenon
. A conspicuous breeding behaviour, swarming
(mass
aggregation
of sexually matured adults for
spawning in the surface water), with or without typical
metamorphosis to the pelagic epitokal (heteronereis)
form, is known in many Nereididae species
. Metamorphosis of the immature worm
into a special reproductive form is known as epitoky
. This is the formation of
pelagic, reproductive individuals, known as epitokes,
from benthic non-reproductive individuals, or atokes.
The production of epitokes usually occurs
synchronously in an entire population, correlated with
lunar and tidal cycles
.
Swarming epitokes can be very conspicuous due to
the sheer numbers of worms, especially if they are
bioluminescent
. These
types of reproductive strategies enabled them to build
up large populations over very short time periods
.
Polychaetes are commonly found in Indian estuaries,
among 152 species recorded, 119 species from east
coast, 10 species from west coast and 23 species were
recorded from both east and west coasts. Many
investigations were carried out on the abundance and
distribution of polychaetes in the estuarine environments
of the south west coast of India
. Among the 34
estuaries of the south west coast of India, the largest
number of polychaetes species (19) were recorded in
the Cochin estuary
. However, there were no previous reports on
reproductive swarming of
Dendronereis aestuarina
Southern, 1921 in the estuarine and riverine conditions of
the south west coast of India. The present study is the
first report on mass reproductive swarming of
D.
aestuarina
on purely freshwater environment and second
report on mass reproductive swarming.
1 Materials and Methods
The swarming of
Dendronereis aestuarina
occurred in
the riverbank (Aluva Manapuram) (Figure 1) of
Periyar River (10°6'N, 76°21'E), south west coast of
India. At this point, the river bifurcates into the
Marthandavarma and the Mangalapuzha branches.
The Mangalapuzha branch joins Chalakkudy river and
empties into the Lakshadweep sea at Munambam, and
the Marthandavarma branch flows southwards,
through the Udhyogamandal area and joins the Cochin
backwater system at Varapuzha
. The tidal cycle in these estuaries was
semidiurnal with microtidal range (0-2m); tidal
influence extended to approximately 25km landward.
The study area is located ~33 km landward from
mouth of Cochin estuary; not under tidal influence.
The average rainfall in the study area was 310 cm/year
and characterized by a totally freshwater environment
during the monsoon, post monsoon and summer season
Figure 1 Location (
O
) of
Dendronereis aestuarina
swarming
observed in the Periyar River (Aluva Manapuram)