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THE ZOOPLANKTON FROM THE EUTROPHIC AND OLIGORROPHIC (COASTAL AND DEEPER WATERS) MARINE ENVIRONMENT OF THE NORTH ARABIAN SEA WITH RELATION TO THE MONSOONAL REGIMES AND A SPECIAL REFERENCE TO THE PLANKTONIC LARVAE OF COMMERCIALLY IMPORTANT SPECIES

Kidwai, Samina (2004) THE ZOOPLANKTON FROM THE EUTROPHIC AND OLIGORROPHIC (COASTAL AND DEEPER WATERS) MARINE ENVIRONMENT OF THE NORTH ARABIAN SEA WITH RELATION TO THE MONSOONAL REGIMES AND A SPECIAL REFERENCE TO THE PLANKTONIC LARVAE OF COMMERCIALLY IMPORTANT SPECIES. PhD thesis, University of Karachi, Karachi.

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Abstract

Zooplankton biomass, taxonomic composition, numeric abundance and behavioral trends have been investigated with relation to oceanographic changes during different annual monsoon periods, in the eutrophic and oligotrophic marine environments of the northwest Arabain Sea. The study area covers the northwest Arabian Sea between 20º to 26º N and 59º to 68º E. Reference to some of the economically important groups with a commercial fishery potential of the area was also taken into account The Arabian Sea zooplankton biomass generally remains consistently high all year round. Some seasonal variation in the biomass was observed in the oceanic waters (F=7.60, p<0.05). The zooplankton production was observed to be higher in the eutrophic (near shore) waters than in the oligotrophic (offshore) environment. In the coastal waters although no statistically significant difference was observed in the overall zooplankton biomass. The distribution patterns reflected temporal (seasonal) as well as spatial variations (mouth and upcreek) at different times of the year It was generally observed that in both the coastal eutrophic and oligotrophic offshore area, the zooplankton biomass was patchy and spatially variable. Zooplankton biomass was significantly different (F=12.67, p<0.05) between the low and high productive areas in the oceanic environment. No fixed “high” or “low” overall zooplankton productive zones geographically, suggesting uneven distribution of high zooplankton patches. Monsoon reversals influenced zooplankton distribution both in the coastal as well as the oceanic environment. In the oceanic environment, the distribution followed the surface wind circulation patterns during the northeast and southwest monsoon periods. In the shallow eutrophic coastal creeks, the major contributor to the overall zooplankton distribution was tides and currents, in addition to the monsoonal influence Diel vertical migration in night and day zooplankton biomass was not evident in the surface layers at the macro-level (zooplankton biomass). However, at a micro-level, several groups show differences in concentrations in the surface layers from night and day. This was observed to be more common in the larger and coloured crustacean species (mysids 1:3.6, ostracod 1:32, amphipods 1:6.6), compared to others. Reverse migration was also observed in copepods and fish eggs and larvae The zooplankton community structure of the coastal as well as offshore environment showed some similarity. Some groups (copepods, chaetognaths, fish eggs and larvae etc.) were common in both the eutrophic and oligotrophic conditions, but a few were specific to either. Some oceanic groups such as Lucifer sp. in the deeper waters, and the coastal species move out into the open ocean environment in the same way. This is also a confirmation index to seawater ingression into the estuarine creeks of the Indus delta The study also examines the distribution and abundance of economically important ichthyoplankton, cephalopod and crustaceans and identifies spawning seasons, penaeid shrimp (mainly Metapenaeus spp.), were present in the creeks throughout the year, indicating that they spawn all the year round. However, the peak season was during October, when their numbers were the highest in the creeks. The cephalopod larvae in samples from different monsoon periods (fewer in the southwest monsoon period), were indicative that also spawned through out the year. Family Ommasterphidae, was the most dominant, the smallest sized individuals of family appeared during both the northeast, the smallest sized individuals of family appeared during both the northeast monsoon, suggesting that the peak spawning time was the northeast monsoon period. The lobster phyllosoma larvae were observed in the coastal waters off Indus delta. Their presence in this area is speculated to be due to parallel coastal currents (also with seasonal reversal) that carry the larval froms form the west coast to the east of Pakistan and bock The study extended further to investigate the bio-physical relationship of zooplankton in different monsoon periods. No direct relationship was observed between the biotic factors (overall zooplankton biomass, fish and cephalopod para-larvae) and abiotic (physical) parameters such as temperature, salinity dissolved oxygen and wind speed in eutrophic and oligotrophic conditions. A weak relationship was observed between the penaeid shrimp and temperature in the eutropic environment No active upwelling phenomenon was observed during the sampling period in eigher the coastal or the shelf waters of Pakistan. Very velar differences in the physical parameters were observed both in the coastal as well as oceanic waters. The vertical structure of the water column was clearer in the oligotrophic conditions The present study was part of the North Arabian Sea Environment and Ecosystem Research founded by the US ONR and project funded by the WWF- Pakistan. The results obtained from this study fills in the lacunae in information on zooplankton production, distribution and community structures in northwest Arabian Sea (coastal and offshore waters of Pakistan), supported with statistical analysis. It addresses issues of bio-physcial relations, eutrophic-oligotrophic interface. On the whole, it also sets the scene for future research initiatives in zooplankton and fishery oceanography, by generating key and fundamental information for concept formulation

Item Type:Thesis (PhD)
Uncontrolled Keywords:zooplankton, eutrophic marine environment, oligorrophic marine environment, north arabian sea, monsoonal regimes, planktonic larvae, ichthyoplnakton cephalopod, mollusk, crustacean larvae
Subjects:Biological & Medical Sciences (c) > Biological Sciences(c1) > Biology (c13)
ID Code:1309
Deposited By:Mr. Muhammad Asif
Deposited On:27 Jan 2007
Last Modified:04 Oct 2007 21:05

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