International Journal of Marine Science 2016, Vol.6, No.30, 1-8
6
Studies on swarms of
Acartia
species have been reported from tropical to temperate latitudes;
A. spinata
and
A.
tonsa
from turtle grass beds, coral rubble and mangrove prop roots in Florida and Belize (Bainbridge 1952);
A.
australis
from the lagoon in Davies Reef (Great Barrier Reef),
A. bisponsa
in Palau lakes (Emery 1968) and
A.
hamate
in fringing coral reefs in Okinawa and
A.
plumosa, A. steueri, A. japonica
and
A. omorii
in temperate bays
of Japan (Hamner and Carleton 1979). Aggregation of Family Acartiidae is likely linked to the fact that some
Acartia
species have the ability to disperse by producing resting eggs, leading to their sudden appearance when
favorable conditions are encountered (Udea 1983, Uye and Fleminger 1976). They are likely adapted to high
concentrations of food in coastal waters where the copepods are a major food of fishes (Uye
et al
., 1979).
Swarming behavior can also be affected by the interactions of swarming animals with light cues, water current
and turbulence, behavior of predators and prey. Photo taxis maintains swarms of cyclopoid copepod
Dioithona
oculata
in shafts of light between mangrove roots (Yoo
et al.,
1991) and similar responses to light gradients are
known in several other species (Ambler 1991, Hamner and Carleton 1979, Hebert 1988). Attraction to food odours
and increased turn in food patches which aids foraging and increased forager density have also been reported in a
number of species (Udea
et al.,
1983, Williamson 1981, Poulet and Ouellet1982, Tiselius and Jonson 1990).
Swarming also occurs in turbid water when turbidity increases planktonic omnivorous copepods that can
encounter more prey. Dissolved oxygen could also potentially affect the spatio temporal variation of copepods in
an estuary. During the study, as a result of swarming comparatively low dissolved oxygen and higher carbon
dioxide concentrations were recorded. Copepods are unresponsive to oxygen-saturated water; they usually avoid
hypoxic water, when dissolved oxygen (DO) is naturally depleted. In most cases, hypoxic conditions are observed
in eutrophic or polluted areas and in waters dominated by high stratification and residence time in summer
(Soetaert and Rijswijk 1993, Park and Marshall 2000). However, hypoxic conditions may cause habitat shrinkage,
which was not seen in the
Acartia
populations during this study. The other factors influencing the distribution of
copepods might be determined by preferences to environmental factors or tolerance to other species (Uye
et al.,
2000).
Thus, the overall localized habitat shifts in zooplankton population, arising from marked changes in
environmental variables, such as temperature, salinity, nutrients, carbon dioxide and other climatic and
anthropogenic factors could result in swarming conditions occurring in such coastal water bodies.
Acknowledgements
The authors gratefully acknowledge the financial support provided by University Grants Commission to conduct this study and also
to the Head, Department of Marine Biology, Microbiology and Biochemistry, School of Marine Sciences, Cochin University of
Science and Technology for the facilities.
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