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1. General introduction
Gelatinous zooplankton are fragile animals that live in the water column of the
ocean. They have very delicate often transparent bodies that are easily damaged or
destroyed (Lalli & Parsons, 2001). All jellyfish are gelatinous zooplankton, but not all
gelatinous zooplankton are jellyfish. The most commonly encountered organisms
include ctenophores, medusae, salps and chaetognaths in coastal waters. However,
almost all marine phyla, including Annelida, Mollusca and Arthropoda, contain
gelatinous species, but many of those odd species live in the open ocean and the deep
sea and are less available to the casual ocean observer (Nouvian, 2007).
The gelatinous zooplankton has also been called "Gelata". The carnivorous
gelatinous zooplankton is defined as scyphomedusae, cubomedusae, siphonophores
and ctenophores are important representatives of coastal and marine ecosystems.
Some early records on the occurrence of jellyfishes in Indian waters date from the
beginning of the last century (Annandale, 1915; Menon, 1930; Daniel and Daniel,
1963.) In recent years, various authors have suggested that they are heading towards a
more gelatinous future (Mills, 2001; Purcell et al., 2007). Some authors, however,
claim that gelatinous zooplankton blooms have ancient origins and are not a new
phenomenon (Condon et al., 2012). Others argued that due to lack of sufficient long
term jellyfish data sets, trends in population increase are not yet clear (Purcell, 2012).
Hydromedusae, in both their hydroid and medusa stages, occur commonly in
all oceans and seas but a synthesis of their world distribution has never been
attempted (Kramp, 1959, 1961, 1968 for the medusa stage only). They are important
carnivorous predators and they are structurally inconspicuous to understand taxonomy
and their main structure is umbrella (Buillon et al., 2004).
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The marine and coastal ecosystems are considered as physical environment
and interaction between species and their environment are correlated in complex food
webs. So, density and number of gelatinous zooplankton are most important to know
the distributional range, status of the ecosystem and their community structure.
However, the apparent simple body plan of jellyfish often disguises sophisticated
interactions with their biological, chemical and physical environment that contribute
to patchy distribution of jellyfish throughout the marine environment (Hamner, 1985).
Salps are common gelatinous holoplankters in shelf and oceanic waters. Like
other tunicates, salps are fine mucous filter to remove a wide range of particles,
including bacteria and phytoplankton, from the water column. About 20% of the
known species are benthic, that is belonging to the lowest zone of the ocean, or
benthic zone, and can attach to algae and rocks. They are found in all marine waters,
from surface tropical waters and shallow tide pools to the deep sea and Polar Regions.
The salps therefore play a key part in pelagic ecosystem, particularly when they form
dense swarm (Alldredge and Madin, 1982). They swim by jet propulsion, drawing
water through in current siphons at opposite end of the body. Due to their efficient
removal of small particles from surface waters, salps are capable of packaging and
exporting primary production to deeper waters, thus influencing biogeochemical
cycling (Madin et al., 2006).
The Phylum Chaetognatha commonly called “arrow worm”, exclusively
marine organisms and majority of them are planktonic. Chaetognatha, meaning hairjaws, which belongs to phylum of Predatory marine worms that are a major
component of plankton worldwide. They can be found in all oceans from the surface
to great depths and are often second or third in abundance after copepods.
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Chaetognaths are also known as excellent indicator of water masses because
of their close relationships with certain environmental variables (e.g. salinity,
temperature and dissolved oxygen) as well as their species-specific horizontal and
vertical distribution. The impact of chaetognaths predation on fish larvae may be
exaggerated due to the relative scarcity of fish larvae in the plankton. They
nevertheless contribute to the reduction of larval abundance during periods of fish
production (Casanova, 1999). They also prey on other small crustaceans, larval fish
and other chaetognaths and play an important role in the transfer of energy from
copepods to higher tropic levels (Bone et al., 1991).
The gelatinous zooplankton which in turn may change predation on or
competition with other components of the food web (Mills, 2001; Parsons and Lalli,
2002). Recent research shows that increase in biomass, shifts in distribution and
unusually dense aggregations of large medusa in
various coastal environments.
Because of the paucity of data, highly productive fisheries and the adjective nature of
the ecosystem, it is sometimes assumed that gelatinous zooplankton have not
historically formed a major component of the food web in coastal upwelling areas
(Mills, 2001; Parsons and Lalli, 2002).
There is intense interest in how the biological structure of the oceans may be
changing as a result of climate change, eutrophication and overfishing (Halpern et al.,
2008). It has been suggested that targeted removal of the larger fish remaining in
ecosystems may cause a progressive pattern of fishing down the food chain until
systems are dominated by invertebrates, such as jellyfish (Hay 2006; Daskalov et al.,
2007). The distribution of jellyfish populations is sporadic and seemingly
unpredictable in nature. Meteorological conditions, currents, water temperature,
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pressure, salinity and predation may play a significant role in determining the
population size.
The most abundant and important species in the Asian jellyfish fishery which
represents a multimillion dollar seafood business in Asia (Omori & Nakano, 2001).
China is the first country to process jellyfish for human consumption (Morikawa,
1984). Although the Chinese have been eating jellyfish for more than a thousand
years, the jellyfish industry only recently has become a commercial fishery. Other
jellyfish producing countries learned the traditional processing techniques from the
northern China with slight modification. Processing jellyfish in Asia is a low-cost
operation that requires little capital but is labour intensive.
The investigation of hydrographical parameters between the gelatinous
zooplankton population is a pattern to comprehend and even predicting the gelatinous
outbreaks. The changes in climatological factor are related to variety of processes viz:
air temperature, ocean temperature, air pressure, wind and currents and have a
potentially significant influence the pelagic environment. The temperature, salinity,
light availability and current strength have indirect effects on jellyfish by altering the
phytoplankton bloom leading to increased secondary production, or by increasing the
abundance of zooplankton and ichthyoplankton in the water column both factors
which lead to increased food availability for gelatinous zooplankton (Lynam et al.,
2004) also increases in primary productivity are indirectly related to gelatinous
zooplankton population (Loeb et al., 1997).
The long-term trend in global temperature is slowly increasing has also
highlighted the trend in the world oceans showing a substantial increase in sea
temperature (0-3000m depth). Temperature gradually increases with profound effects
on marine ecosystems and the changes directly affect metabolism, growth and
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development rates of many organism. It can also alter the seasonality and length of
the reproductive active period for a number of species in addition to have greater
effects on the characteristics and timing of gelatinous zooplankton blooms (Purcell,
2007).
The major change in abundance of gelatinous zooplankton in Indian waters is
very essential to assess the ecosystem approach. Indian seas have less documented
areas of gelatinous zooplankton in the world. In contrast, considerable amount of
work has been done to understand the zooplankton populations in Indian waters tend
to focus mainly on copepods, the major zooplankton component. Other groups of
gelatinous zooplankton were studied some time only quantitative analysis along with
zooplankton studies hence not treated in detail as distributional pattern and their
seasonal variation and influence of environmental parameters. As discussed above,
the ecologically importance of gelatinous zooplankton have been attracted
considerably by the scientists. The vast majority of studies, however, have been
carried out almost in all aspects of these groups in and around the world. In contrast,
the Southeast Asia has almost nothing is known about the ecology of gelatinous
zooplankton (Omori and Nakano, 2001).
Most of the gelatinous zooplankton are very difficult to identify. So, the
molecular are useful and identify at the species level. Molecular data continue to
enhance our understanding of the evolutionary history of life at all hierarchical levels.
Nevertheless, many questions about cnidarian phylogenetic relationships remain
unanswered (Daly et al., 2007). The considerable morphological disparity present
within cnidaria is evidenced by delicate siphonophores, massive medusae and corals,
feathery hydroids, interstitial polyps and box jellies possessing complex eyes. Despite
this diversity, these relatively simple metazoans are united in possessing nematocysts,
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most probably as a result of common ancestry. Agree with evidence that cnidarians
are monophyletic within Metazoa comes from molecular sequence data of the small
subunit (SSU) of the ribosome (Kim et al., 2011; Collins, 2000), as well as the large
subunit (LSU) of the ribosome (Medina et al., 2001).
Most phylogenetic analyses of Cnidaria have focused on determining the
relationships among the four main taxa that compose it – Anthozoa, Cubozoa,
Hydrozoa, and Scyphozoa
(Salvini-Plawen, 1987; Brusca & Brusca, 1990; Bridge et
al., 1995). From this work, a consensus has emerged that Anthozoa is the sister group
of the remaining cnidarians, which are collectively referred to as Medusozoa
(Petersen, 1979), or less often as Tesserazoa (Salvini- Plawen, 1987). Particularly
convincing evidence for the monophyly of medusozoans is their shared possession of
linear mitochondrial genomes and medusae. However, relationships among the major
medusozoan groups remain contentious (Collins, 2000).
Studies on the biochemical composition and energy content of zooplankton is
important to have a better understanding of organic production, productivity and
cycling of biogeochemical elements in the marine environment. Such information is
of much importance in estimating the energy available to higher trophic levels, which
in turn, can be used to estimate harvestable fishery resources. Much of the available
information pertaining to biochemical composition and nutritive value of zooplankton
is from estuarine, coastal, inshore and offshore waters of India (Goswamy et al.,
1981; Goswamy, 1993). Zooplankton constitutes the largest ecological group of
organisms in the sea and play an important role in marine food chain. They feed on
phytoplankton and in turn form the food for animals at higher trophic level
(Chandramohan et al., 1972). Information on biochemical composition of
zooplankton in general and gelatinous zooplankton in particular especially from
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Indian waters is meagre. Estimation of biochemical constituents of zooplankton is
important in understanding their physiological functions, metabolism and nutritive
value which are relevant to the marine ecosystem, in its energy transfer and secondary
production.
Although the distribution, molecular taxonomy and biochemical composition
of gelatinous zooplankton have been studied very little in various parts of the world
and particularly in India. Hence, the present study was intended to know the
distribution of gelatinous zooplankton along the Bay of Bengal and Arabian Sea and
its relationship with physical features.
From the above facts, present study was framed with the following goals.
 To understand status of hydrobiological parameters in Arabian Sea and
Bay of Bengal during the Cruises. To study the diversity and
taxonomical position of gelatinous zooplankton.
 To study the molecular taxonomy of the dominant gelatinous
zooplankton.
 To study the seasonal abundance of gelatinous zooplankton in
Parangipettai coastal waters.
 To study the biochemical composition of a dominant Anthomedusae,
Porpita porpita.
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