Res . Agric . Livest . Fish . Vol . 2 , No . 1 , April 2015 : 151-160 ABUNDANCE AND COMPOSITION OF ZOOPLANKTON AT SITAKUNDA COAST OF CHITTAGONG , BANGLADESH

Correction: Table 1 and Table 2 were omitted in from the PDF of this article. On 29th April 2015 the two tables were included in the PDF and the page numbers were changed from 151-158 to 151-160. Eight groups of zooplankton were found at Sitakunda coast, Chittagong, northeastern part of the Bay of Bengal during January to June 2007. The identified groups were Appendicularia (2.46%), Chaetognatha (2.45%), Cladocera (2.31%), Copepoda (26.05%), Ctenophora (5.86%), Crustacean zooplankton (21.64%), Ichthyoplankton (17.77%) and Meroplankton (21.45%). Abundance of zooplankton varied from 413 to 7730 individuals/m3.Mangrove vegetate area (station- VI) has the highest abundant possibly due to the organic and inorganic matters dissolved in the water while ship breaking area (station- IV) has the lowest abundant. Zooplankton population was significantly (p>0.05) higher in the mangrove vegetate area than the fishermen community area and ship breaking area. The mangrove vegetate area has the highest composition (57.06%) of zooplankton than the fishers community area and ship breaking area (29.77% and 13.16%, respectively). Calanus sp. (12.29%) belonging to Copepods and fish eggs (9.25%) belonging to Ichthyoplankton were the most abundant and Oikopleura albicans (0.66%) from Appendicularia, Metapenaeus brevicornis (0.71%) and Metapenaeus monoceros (0.90%) belonging to Crustacean larvae were the lowest abundant species found at three major investigated area. Res. Agric., Livest. Fish.2(1): 151-160, April 2015


INTRODUCTION
Zooplankton is an aquatic animal community that has limited swimming capacity against the ambient currents.Even with their quite limited swimming capacity, they carry out day-night periodic movements of hundreds of meters.They prefer to feed at night on the water surface and effectively graze the phytoplankton, and hence they referred to as living machines.They habitually represent a vital link between the microbial portion and the large grazers (Laval-Peuto et al., 1986;Pierce and Turner, 1994).The zooplankton, secondary consumer plays a key role in the food chain of aquatic ecosystem by transferring energy from phytoplankton to higher tropic levels leading to the production of fisheries to human exploitation.The health of marine ecosystems inherently linked to the abundance of zooplankton and their biodiversity.The potentiality of marine pelagic fishes directly or indirectly depends on the availability of zooplankton.In the aquatic ecosystem zooplankton are being used as the indicator species for the physical, chemical and biological processes due to their universal distribution, small size, and rapid metabolic and growth rates (Heinbokel, 1978;Fenchel, 1987), huge density, tinier life span, drifting nature, great species diversity and diverse tolerance to the stress (Gajbhiye, 2002).
A survey report of FAO (1985) stated that the tidal areas of Bangladesh are relatively rich in zooplankton.The abundance of zooplankton and their ecology in the coastal and estuarine environment of Bangladesh is little studied.Islam and Aziz (1975) studied on zooplankton of the northeastern part of the Bangladesh coastal area and identified a total of 18 genera and 18 species.Bhuyain et al. (1982) made an observation on the macro-zooplankter of the continental shelf of the Bay of Bengal and reported the occurrence and distribution of 18 calanoid copepods.Ali et al. (1985) recorded a periodic variation of zooplankton in the coastal estuarine water in the southeastern part of Bangladesh.The major groups of zooplankton are copepoda, decapoda, chaetognatha, cladocera and fish and shellfish larvae.Zooplankton diversity of salt marsh habitat in the Bakkhali river estuary, Cox's Bazar, Bangladesh has also studied by Ali (2006).
Coastal zone contains critical terrestrial and aquatic habitats, such as mangrove forests, wetlands and tidal flats.Sitakunda coast under the Chittagong district, northeastern part of the Bay of Bengal is adjacent to the Sandwip Chanel, having tidal mangrove, ship breaking yard and fishermen community area and an important source of fisheries resources.The purpose of this study is to provide more information on the abundance and composition of the zooplankton community on the Sitakunda Upazila coastal water, north of the Chittagong city, which is currently affected by ship-breaking activity on the shore.

MATERIALS AND METHODS
Sitakunda coast, which is the northeastern part of the Bay of Bengal, located in between 22°22´ and 22°42´ northern latitudes and in between 91°34´ and 91°48´ east longitudes.For the present investigation this coastal area was divided into three pre define activities community with six sampling stations (Fig. 1).Station-I (Salimpur) and station-II (Saidpur) was considered as a fishermen community area, station-III (Grisubedar Ship yard) and station-IV (PHP Ship yard) located in Bhatiari area was considered as ship breaking yard and station-V (Barabkunda) and station-VI (Muradpur) was considered as a tidal mangrove vegetate area.

Zooplankton sampling and isolation
The sampling was conducted during January to June 2007 by using a wooden boat.Zooplanktons were collected using a net (Hydrobios model 55 μm mesh size) ending with a cod end to retain the organisms which was towed horizontally.A flow meter (FMC 0.3) was attached within the aperture of the net to measure the amount of water displaced.At each station, the net was slanted three times for 45 minutes each while the boat was moving slowly.The sampling was taken place in the sub-surface layer (0.2m-0.5m) of the water column.Abundance of organisms was calculated from the volume of water displaced through the plankton net and expressed as numbers of individuals per cubic meter.Immediately after collection, the samples were preserved in 4% formalin (45% formaldehyde) in 250 ml plastic bottles and labeled.Then the samples brought to the laboratory of Institute of Marine Sciences and Fisheries, University of Chittagong for qualitative and quantitative analysis.For efficient sorting, a vital stain "Rose Bengal" was added and the sample left for overnight.Zooplanktons were sorted out with the help of fine brushes, needle, forceps and an inverted microscope (Model-Axiovert 25, CFL) and Sedgwick-Rafter chamber was used for counting.

Data analysis
The zooplankton abundance was calculated using the following formula: a.Total number of zooplankton specimens =Total counts of the specimens (say x)/ Volume of water filtered (V).
No. /m3 = x/v (No. can also be expressed/ 100 m -3 or 1000 m -3 ).b.Total number of specimens of a particular zooplankton taxon = Total counts (x)/Volume of water filtered (Y) No. /m3 = x / y.SAS ( 2003) was used to analyze the data for analysis of variance (ANOVA).

RESULTS
Eight groups of zooplankton were identified, i.e.Appendicularia, Chaetognatha, Cladocera, Copepoda, Ctenophora, Crustacean zooplankton, Ichthyoplankton and Meroplankton at six different stations on Sitakunda coast, Chittagong, Bangladesh.In total 10 known species of Crustacean, 7 known and unidentified species of Meroplankton, 6 species of Copepoda, each 2 species of Appendicularia, Ctenophora and Ichthyoplankton and each one species of Cladocera and Chaetognatha were identified during the investigation.Abundance of zooplankton varied from 413 to 7730 individuals/m 3 (Table 1).Figure 2 (A and B) shows the composition of the various zooplankton group on Sitakunda coast and the contribution of those groups in each station.

Appendicularia
This class includes Oikopleura albicans and O. dioica, comprising together 2.46 % of the total zooplankton population (Table 1).They live in the pelagic zone, especially in the upper sunlight portion of the ocean.These zooplanktons were found in all stations, but in low number (63 indi/m 3 ) was observed in the Bhatiyari area near the ship breaking yard and large number (1150 indi/m 3 ) were observed in the mangrove vegetate area.Among them, a few O. albicans (12 indi/m 3 ) was found in ship breaking area.

Cladocera
Cladocera the lowermost group made only 2.32 % of the total zooplankton population and Evadue sp. was the only identified zooplankton, which was very common in all stations.The abundance of Evadue sp. was 56 indi/m 3 to 503 indi/m 3 (Table 2).

Ctenophora
The ctenophores designed 5.86 % of the total zooplankton population.This group composed of Bolinopsis vitrea and Pleurobrachia sp. and the percentage occurred 2.81 % and 3.05 %, respectively.

Chaetognatha
Chaetognatha were the second lowermost group, forming 2.45 % of total zooplankton (Table 1).In mangrove vegetate and fishermen community area, they found great number compare to ship breaking area near Bhatiyari.The highest abundance was 507 indi/m 3 and the lowest was 64 indi/m 3 .

Copepoda
Copepods were the most abundant group encompassing 26.05 % of the total zooplankton population.This group consisted with Calanus sp., Microsetella sp., Oncaea sp., Calanopia sp., Coryeacus sp. and Oithona sp.During the study highest abundance 1,937 indi/m 3 was found in mangrove vegetate area (station VI) due to the high number of Calanus sp. while station-III & IV (Ship breaking area) was the lowest abundance 2 indi/m 3 and 7indi/m 3 , respectively owing to Oncaea sp.Calanus sp. was the most abundant and found at all stations, comprising 12.29 % of the total zooplankton population (Table 2).

Lucifer
Lucifer sp. was very common and made only 4.14 % of the total zooplankton population.The amount of Lucifer sp. was quite high in mangrove vegetate and fishermen community water while the number was lower in the ship breaking area.The average abundance showed substantial differences in those tables.
In all stations, Sergestes similis also found in worthy number.In mangrove vegetation (926 indi/m 3 ) and fishermen community area (395 indi/m 3 ) the number was high, but in the ship breaking area (74 indi/m 3 ) the number was very low.

Ichthyoplankton
Fish eggs and larvae were very common and high in number, creating 9.25 % and 8.52% of total zooplankton respectively.Fish eggs and larvae found available in all investigated areas.The average abundance showed no significant differences between mangroves vegetate area and ship breaking area.

DISCUSSION
A sensible variation was observed in the zooplankton abundance in all stations.Table 2 shows the abundance of zooplankton in all sampling areas.Mangrove vegetate area have the highest abundant 35,755 individuals/m 3 and fishermen community area and ship breaking yard has 18,825 individuals/m 3 and 8,321 individuals/m3, respectively around the sampling period.Statistical analysis showed that the abundance of zooplankton population in the mangrove vegetate area was significantly higher (p>0.05)than the fishers community area and ship breaking area.The mangrove vegetate area has the highest composition (57.06%) of zooplankton then the fishers community area and ship breaking area (29.77% and 13.16%, respectively).Large carnivorous zooplankters namely, the Ctenophora and Chaetognatha are planktonic predators of fish larvae.The correlation between fish larvae and their predators, i.e.Chaetognatha, and Ctenophora was 0.8611, 0.8083 respectively, at 95 % confidence.The correlation of fish larvae and Copepoda, which their prey species was 0.9100 at 95 % confidence.
At all stations, the dominant species in the Sitakunda coast were as Calanus sp., Microsetella sp.belonging to Copepods, fish eggs and fish larvae belonging to Ichthyoplankton, Polychaete larvae and Crab zoea belonging to Meroplankton and Lucifer sp.belonging to Crustacean larvae.All most all species were lower at station III and IV, which was denoted as the ship breaking area probably due to oil pollution and other human activities.Copepods were the main contributors in the present investigation.Wimpenny (1966) and Omori and Ikeda (1976) reported that copepods are the most abundant zooplankton communities sampled in the world ocean.Houde and Lovdal (1982) showed that copepods are important components of larval fish food.The present investigation on Crustacean zooplankton found five commercially important species such as Penaeus monodon, Penaeus merguiensis, Metapenaeus monoceros, Metapenaeus brevicornis and Penaeus indicus.Penaeus and Metapenaeus have worldwide commercial importance in fisheries and aquaculture, and the larvae of many species have been reared in the respected shrimp hatchery.
In general, particularly in coastal waters, the composition and abundance of zooplankton varied remarkably due to the seasonal variations and their sheltered systems like coastal and mangrove waters.On the Sitakunda coast, in the mangrove vegetate area, total abundance of zooplankton was higher than the fishermen community area and ship breaking area.This is because of organic and inorganic matters dissolved in the water, which is ultimately support directly or indirectly to the zooplankton growth.Similar results have also been reported in the coastal waters of Bangladesh by Bhuiyan et al. (1982), Ali et al. (1985) and Zafar (2000).Fraser (1969) and Suwanrunpha (1983) reported that big carnivorous zooplankters namely Ctenophora, Chaetognatha, Medusae and Siphonophora are planktonic predators of fish larvae.In this study, a high correlation between fish larvae and their predator, especially chaetognatha was observed.Thus, their presence in numbers of zooplankton could have a serious effect on the recruitment of larval fish and could be very significant for the fish stocks and for the fishing industry.Houde and Lovdal (1982), Balbontin et al. (1986) and Anderson (1994) presented that small zooplankton e.g.Copepods, Tintinnids, Cladocerans, larval molluscs etc. are important components of larval fish food.The present study found a high correlation between fish larvae and their prey, especially copepods.Positive correlations indicated that fish tend to aggregate where the standing stock of copepods is highest.However, Sameoto (1972) found no significant correlation between standing stock of copepods and the valued abundance of herring larvae.Manyauthors point out that zooplankton was influencing on fisheries.Krisshnapillai and Bhat (1981) found that the fishcatching rate was maximum in while the zooplankton productive rate was high.Jacob et al. (1981) reported that the peak times in the zooplankton biomass coincided with the peak periods of pelagic fisheries.
Unfortunately, information about the fisheries in the present studied areas was not available, so that correlation of fish catch and zooplankton abundance was not measured.

CONCLUSION
The zooplankton abundance in the three locations showed a much different from each other.The zooplankton abundance in mangrove vegetate area was higher than the fishermen community and ship breaking area.The abundance and composition of the zooplankton can be used as an indicator of marine productivity.

Figure 1 .
Figure 1.Map of study area (Sitakunda coast) with the location of sampling stations.

Figure 2 .
Figure 2. Percent composition of various zooplanktons (A) and their richness at different sampling station (B).

Table 1 .
List of major groups and species of zooplankton identified and their number and percentage at Sitakunda coast, Chittagong

Table 2 .
Zooplankton abundance (individual/m 3 ) and their averages in fishers community area (St.-I and II), ship breaking area (St.-III and IV) and mangrove vegetate area (St.-V and VI) at Sitakunda coast, Chittagong.