ABSTRACT
The plankton community was studied twice a week from September 2006 to August 2007,
in a green mussel raft-cultured area, Si Racha Bay, in the Gulf of Thailand. Phytoplankton was
collected by filtering with a 20 μm plankton net and zooplankton was collected by vertical
hauling with a plankton net of 330 μm mesh size. Several hydrographical conditions were
measured in situ but nutrient analyses of water samples were carried out in the laboratory. Fifty
seven genera of phytoplankton and 34 groups of zooplankton were recorded. The mean abundance
of phytoplankton was 38,777 ± 27,453 units l-1 while that of zooplankton was 3,368 ± 1,183 ind. m-3.
The dominant group of phytoplankton was diatoms; while copepods, cirripede nauplii, Lucifer sp.,
and Sagitta spp. were the major contributors to zooplankton abundance. Noticeable variation in
composition of phytoplankton was demonstrated by an algal bloom of dinoflagellates (Ceratium
furca (Ehrenberg) Claparède & Lachmann) in July 2007. The plankton community showed no
significant differences in abundance between months in the annual cycle but the high value was
during the Southwest monsoon. Moreover, the average value of primary production (3.85 ± 2.79 mg
m-3) during the Southwest monsoon was higher than that of the Northeast monsoon season (1.11
± 0.36 mg m-3). Composition variation was also influenced by water temperature, salinity, ammonia
and dissolved oxygen. Hydrographical conditions and nutrients showed temporal fluctuations. In
this regard, the maximum values of nutrients and dissolved oxygen agreed with Thai standard levels
of seawater suitable for an aquaculture area.
ABSTRACT
The plankton community was studied twice a week from September 2006 to August 2007,
in a green mussel raft-cultured area, Si Racha Bay, in the Gulf of Thailand. Phytoplankton was
collected by filtering with a 20 μm plankton net and zooplankton was collected by vertical
hauling with a plankton net of 330 μm mesh size. Several hydrographical conditions were
measured in situ but nutrient analyses of water samples were carried out in the laboratory. Fifty
seven genera of phytoplankton and 34 groups of zooplankton were recorded. The mean abundance
of phytoplankton was 38,777 ± 27,453 units l-1 while that of zooplankton was 3,368 ± 1,183 ind. m-3.
The dominant group of phytoplankton was diatoms; while copepods, cirripede nauplii, Lucifer sp.,
and Sagitta spp. were the major contributors to zooplankton abundance. Noticeable variation in
composition of phytoplankton was demonstrated by an algal bloom of dinoflagellates (Ceratium
furca (Ehrenberg) Claparède & Lachmann) in July 2007. The plankton community showed no
significant differences in abundance between months in the annual cycle but the high value was
during the Southwest monsoon. Moreover, the average value of primary production (3.85 ± 2.79 mg
m-3) during the Southwest monsoon was higher than that of the Northeast monsoon season (1.11
± 0.36 mg m-3). Composition variation was also influenced by water temperature, salinity, ammonia
and dissolved oxygen. Hydrographical conditions and nutrients showed temporal fluctuations. In
this regard, the maximum values of nutrients and dissolved oxygen agreed with Thai standard levels
of seawater suitable for an aquaculture area.
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