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Vol. 52, 2013
Mesozooplankton community structure in the upper 1,000 m
along the western Bay of Bengal during the 2002 fall intermonsoon
Veronica
Fernandes and Nagappa Ramaiah*
National
Institute of Oceanography (CSIR), Dona Paula, Goa 403 004, India
Abstract
Background: Stratification, no
upwelling, sediment load, and heavy cloud cover are known to limit
primary production in the western Bay of Bengal. Studies on primary
consumers in this area are few. Recent studies in the Bay have shown
the role of cold-core eddies in enhancing the biological production.
This study was carried out to provide a detailed account of variation
in mesozooplankton biomass, abundance, and copepod assemblages between
cold-core eddy and non-eddy regions in the western Bay.
Results: In this study carried out in the western
Bay during fall 2002 intermonsoon, we observed a very high zooplankton
biovolume of 2.2 ml/m3 in the mixed layer at station WB3
located within a shallow cold-core eddy. Zooplankton from 29 groups
were observed during this study. Calanoid and poecilostomatoid copepods
substantially contributed to the total zooplankton abundance and carbon
biomass. Below the 200 m depth, there were fewer groups but higher
proportion of copepods. Copepodites of calanoids were more abundant
between 500 and 1,000 m at the WB3 eddy station. Invertebrate eggs made
up a staggering 65% of the total collection in the 200- to 300-m
stratum at WB1, a location in the other cold-core eddy. Copepod species
diversity (3.39 to 4.77) and richness (2.32 to 4.84) were lower at WB3.
Among 147 copepod species in 69 genera found, Oncaea venusta (17% of the total copepod
abundance), Paracalanus indicus (5.4%), Lucicutia flavicornis (5.1%), and Pleuromamma indica (4.5%) were the four most
dominant ones.
Conclusions: High copepod diversity
throughout upper 1,000 m of the western Bay is attributed to the
moderate oligotrophy. We reported 93 copepod species for the first time
from this region, from which 7 are first records for the Indian Ocean.
Cold-core eddies seem to play a pivotal role in sustaining zooplankton
in nutrient-limiting regions such as the western Bay of Bengal.
Key words: Zooplankton; Biomass; Vertical
distribution; Copepods; Cold-core eddies.
*Correspondence: E-mail: ramaiah@nio.org
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