Indian Journal of Marine SciencesVol. 13, June 1984, pp. 75-79

Diurnal Variation of Zooplankton in Malad Creek, Bombay

S N GAJBHIYE, VIJA YALAKSHMI R NAIR & B N DESAI

National Institute of Oceanography, Regional Centre, Versova, Bombay 400061

Received 17 October 1983; revised receiued 5 March 1984

Variation in zooplankton biomass and composition in relation to the prevailing hydrographical conditions was studied for24 h in Malad creek, which was highly polluted by sewage. The adverse effect of pollution was more during the ebb tide withrelatively low values of salinity and zero values of dissolved oxygen. Zooplankton biomass varied from 0.01 to 13.2 ml. (100m ') ··1 [avo 3.4 ml. (100 m ') -1] during different tidal conditions. Zooplankton standing stock and total population were higherin night than in day collections. A bundance and diversity of zooplankton were directly correlated to the prevailing tide andpollution load. Copepods formed the predominant group followed by decapods, gastropods, chaetognaths and mysids.Variations in the incidence of different groups/species of zooplankton were discussed in detail.

In a tidal creek, environmental parameters andzooplankton population may change in magnitudeover very short periods. Diurnal variation ofzooplankton in such an environment is chieflyinfluenced by changes in physico-chemical parametersinduced by tide/fresh water influx and verticalmigration of zooplankton associated with lightintensity. Information regarding diurnal variation ofzooplankton from Indian seas particularly from thecoastal waters of India is limited 1-5. Hence the presentstudy was taken up to evaluate short term variations inzooplankton at the mouth of a tidal creek, in Bombay.

Materials and MethodsMalad creek is a prominent narrow inlet located

towards north of Bombay city (lat. 19°8' N and long.72°48' E). It receives approximately 200 mid ofeffluents", mainly from Versova a~d Malad pumpingstations. The collective effluents from the creek flowdownstream into the tidal water and affect the waterquality of the area.

The station selected for the study is located towardsthe mouth of the creek at a depth range of 12-15 m.Samples from surface and bottom were collected on18/19 Feb. 1981 at hourly intervals during day andonce in 2 h during night. Water samples were collectedfor salinity, dissolved oxygen (DO), pH, and nutrientsand estimations were made as per Strickland andParsons 7. Zooplankton samples were collected byoblique hauls using a Heron Tranter net (mouth areaof 0.25 m2 and mesh size of 0.3 mm) fitted with acalibrated TSK flow meter. The net was towed for 5min. The samples were preserved in 5% seawaterformalin for biomass, taxonomical and numericalstudies.

Results and DiscussionPhysico-chemical characteristics-At 0830 hrs when

sampling started ebb to flood tide was in progress. Itattained the slack period around 1230 hrs, then ebbtide started which continued up to 1830 hrs. Thesecond flood was recorded during 0030 to 0130 hrs.

Variations in physico-chemical parameters studiedare given in Fig. 1. Fluctuation in water temperaturewas not much and the maximum difference was 2.3°Cfor the surface and 1.7°C for the bottom. The pHvalues were relatively lower thai"! that can normally beexpected for nearshore waters. In general, the recordedpH values for the ebb period was relatively low.Diurnal variations of salinity, dissolved oxygen, BOD,and nutrients were considerable. Salinity decreasedduring flood to ebb period and well definedstratifications of this parameter was also observed. Itappears that the influx of sewage into the creeklowered the salinity to a great extent resulting in themovement of less dense water of low salinity to thesurface and dense water of high salinity to the bottomlayer of the creek. The occurrence of zero values of DOat Versova creek was a common feature during the ebbperiod. This trend in the variation of DO and salinity isin agreement with the earlier reports'':". The amount ofBOD was very often high during ebb tide amounting to80 mg.l -\. The distribution of reactive phosphate,nitrite, nitrate and ammonia were also directly relatedto the tide and discharge of effluents. Consequently,nutrient values were relatively high during the ebb thanthe flood period. In general, the hydrographicalfeatures of the area indicated the prevailing pollutionload.

Zooplankton biomass, total population andcomposition- The zooplankton biomass in the areavaried from 0.01 to 13.2 ml. (100 m') -\ (Fig ..2). Thebiomass decreased drastically with the advent of theebb tide and again increased when flood tide had set in.In general, biomass values were higher for the night

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INDIAN J MAR SCI, VOL. 13, JUNE 1984

'1·3 35·6- - -- Bottom pH 25 -NH48-0 -- Surface

15~ 7·5

57-0

;1/ I

2·5 -N02DO

8

.-. ?_ 1·5I -. cu- t;E

0

36 12-N03

MI

a~ J2 6x

---...0 AirTemperature

u 2So

1830 2330

2'·~20

10

0730HRS

O~~~~~~~~-L-L~~~~~~~I~I0830 1330 183~ 2330 0738

HRS

Fig. 1-Variation in physico-chemical parameters at Malad creek

collections and average values for night and daysamples were respectively 5.1 and 2.32 ml. (100 m ') ~I.

Total zooplankton population fluctuated duringdifferent tidal conditions (Fig. 2). The maximumdensity [37570.(100 m3)~I] was recorded at 1030 hrsduring ebb to flood tide, while the density decreaseddrastically during flood to ebb cycle and attained a

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minimum [70.(100 m3)~I] at 1730 hrs. The recordedpopulation was relatively more during the night [avo18846.(100 m ') ~I] than during the day [avo 11649.(100m 3) ~I]. The highest population density wasrepresented by 14 faunal groups and the mostabundant group was copepods (92.9%). The restincludes gastropods, decapods, chaetognaths, mysids,

GAJBHIYE et al.: DIURNAL VARiATION OF ZOOPLANKTON

Vl 25o,:J )00 Z0:::<..:> 0

.....J 20 ~<l: .....JZ :J:J c,<t 0u, o,.....J 15 20 .....J

~ g0l- I-

olJ

10Vl AVl<t \

10z \

0 \\

CD 5 '0'/

)0

0----0 Total Population()..---() Total faunal groupst.---tJ.. Biomass

1830 HRS

Fig.2-Variation in biomass [m!. (100m3) IJ. population (x 103) and faunal groups (No.) of zooplankton at Malad creek

0530

siphonophores, fish larvae, Aceles sp., medusae, fisheggs, stomatopods and polychaetes. Maximum groupdiversity was also noticed at 2330 and 0130 hrs. Ingeneral, there were more groups found during floodtide than during ebb tide. The lowest populationdensity was represented by 5 faunal groups, viz.copepods (81.43%), gastropods. amphipods, ostracodsand isopods.

Copepods: In all the zooplankton samples, thedensity of copepods varied from 38.22-97.26/~ (Fig. 3).Their abundance was relatively low during the peakebb period. Copepods were represented by 19 species.The maximum number of copepods species (8) wasobtained at '1130, 0130 and 0330 hrs. The mostcommon species were Acartia spinicauda, Acrocalanussimilis, A. gracilis, Euchaeta concinna, Eucalanussubcrassus and Paracalanus crassirostris and P.aculeatus. The other species found were Canthocalanuspauper, Paraea/anus parous, Acrocalanus inermis, A.monaehus, Labidoeera pectinata, Acartia pacifica, A.plumosa, A. centrura, Acartia sp., Cyclops buxtoni,Laophonte sp. and /dyaea sp.

Chaetognaths: The frequency of occurrence of thisgroup was 94.4% and the percentage compositionvaried from 0.12-3.83% of the total zooplanktoncount. The occurrence of chaetognaths was closelyrelated to the phase of the tide. The highest [502.(100

m ') -IJ and lowest [6.(100 m ') -IJ population wererecorded respectively at 2130 and 1830 hrs. Meandensity of chaetognaths was 2.2 times more duringnight than the day collections. Sagitta bedoti was thedominant species in the collection contributing to thebulk of the population (95%). The other species, S.enflata and S. pulchra, were restricated to the floodperiod. However, the lowest density was representedentirely by S. bedoti.

Hydromedusae: Frequency of occurrence of thisgroup was 72.22%. However, the percentagecomposition of medusae was negligible (0.004-0.3100)

and they were often absent during the ebb period. Themaximum population density [78.(100 m 3) -1] wasrecorded at 2130 hrs during flood period, whereasstray individuals [1.(100 m ') -1J were observed at 1'430to 1630 and 0330 hrs, Mean population ofhydromedusae was 1.95 times more during the nightthan the day samples. Nine species of medusae wererecorded, of these. Euphysora sp., Solll11111dellabitentaculata and Streenstrupia bigelowi were relativelymore common.

Decapods: Percentage of prevalence of decapodlarvae was 88.89%. Their percentage compositionvaried from 0.74-61.15% of the total zooplankton (Fig.3). The common groups of decapods were zoea ofBrachyura and Porcellanidae, alphaeids and

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100

80z0~Vl0 60a..~0u

w~ 40~zwua::wo, 20

INDIAN J MAR SCI, VOL. 13, JUNE 1984

08)0 1030 1230 11.)0 1630 1830 2130 0130 OSJO HRS

r=J COPEPODS I·::··:::~·.J DECAPODS ~ CHAETOGNATHS nnmnGASTROPODS •• MISC.

Fig. 3- Variations in percentage composition of zooplankton at Malad creek

palemonids. The highest densi ty [18475.(100 m 3) -1]was noticed at 1530 hrs represented by the brachyuranzoea (95~J and larvae of Palaemonidae (5%). Thedensity was lowest [4.(100 m ') -1] at 1930 hrs solelyrepresented by palaemonids (100%). During the nighttheir density was usually very high and the averagepopulation for the night was 11.76 times more thanthat observed for the day.

Lucifers were represented by the single speciesLucifer hanseni contributing 11.11% of the total count.The percentage composition of this species varied from0.003 to 0.011.

The genus Acetes was represented by the singlespecies Acetes indicus contributing 0.04-0.5% of totalzooplankton. The frequency of occurrence of thisspecies was 16.57% and the highest density [125.( 100m3)-t] was recorded at 2130 hrs.

Mollusca: Molluscs were represented by larvalforms of gastropods and lamellibranchiates. Theirfrequency of occurrence was respectively 94.40% and16.67/~. Gastropods contributed 0.05-25% of the totalzooplankton. The highest [7115.(100 m ') -1] andlowest [4.(100 m3)-t] population densities wererecorded at 2330 and 1930 hrs respectively. Averagedensity of gastropods during night was 2.23 times morethan the day collections: The contribution oflamellibranchiates was 0.01-1.16% of the total

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zooplankton and their incidence was limited to thesamples collected during day.

Polychaetes: Polychaetes were represented by Nereissp. and Tomopteris sp. The frequency of occurrence ofthe group was 33.33% and the percentage compositionvaried from 0.003-0.86%.

Mysids: Mysids were dominated by Mesopodopsiszeylonica. The percentage composition of mysids was0.03-0.53% of the total zooplankton. Their frequencyof occurrence was 61.11%.

Siphonophores: The frequency of occurrence ofsiphonophores was 55.5%. The percentage com-position of this group varied from 0.01 to 2.28%. Theirhighest population density [62.(100 m ') -1] wasrecorded at 2330 hrs.

Ostracods: The ostracods were represented by thesingle species Cypridina dentata and higher density wasrecorded during night collection. The frequency ofoccurrence was 44.44%.

Fish eggs and larvae: The frequency of occurrencefor fish eggs and larvae were 44.44 and 61.11 %respectively. The density of fish eggs and larvae wasvery poor contributing 0.01-2.61% and 0.003-0.43%respectively of the total zooplankton. They wereusually absent during ebb tide.

Miscellaneous groups: The' other groups rarelyencountered in the samples were ctenophores,stomatopods, appendicularians, isopods, amphipods,

GAJBHIYE'et al.: DIURNAL VARIATION OF ZOOPLANKTON

cirripede larvae, cumacae, salps, cladocerans andinsect larvae. Of these, percentage composition ofctenophores varied from 0.003-0.04% with themaximum population density [2 (100 m3)-I] recordedat 0330 hrs. Appendicularians were dominated by thegenus Oikopleura. Their frequency of occurrence was44.4%. Stomatopods were represented by Alimalarvae of squilla and the percentage of prevalence wasonly 16.67%. The percentage composition of isopods,amphipods, cirrepede larvae, cumacae, salps,cladocerans was very low.

Mean biomass of zooplankton during the period ofstudy was 3.4 ml. (l00 m3)-I and the value iscomparatively lower than that reported off Maladcreek 9. Biomass, total population and diversity ofvarious groups of zooplankton increased during theflood tide and decreased during ebb tide attaining theminimum values during the peak ebb period. In thenearshore waters off Thai, shoreward increase inzooplankton during the flood period and reverse trendduring the ebb period were observed 1 0 while nosignificant effect of tides was recorded in Cochinback waters 2 •

Zooplankton population was invariably high duringthe night collections (Fig. 2) and this was reflected onthe species composition. Acrocalanus inermis, A.gracilis, Labidocera pectinata, Canthocalanus pauper,Paracalanus parous, Acartia pacifica, A. plumosa,Oithona sp., /dyaea sp., Acetes sp., Cypridina dentataand Sagitta pulchra were recorded only in the nightcollections. Groupwise populations of most of thegroups were more during the night time showing anincrease of 2.2 to 43 times than that recorded for theday. Mature' individuals of S. bedoti were caught onlyduring the night samples.

Associated with the phase of the tide there wassignificant variation in the representation of variousspecies/groups. Euryhaline copepod species Acartiaspinicauda, Acrocalanus similis and A. gracilis weremore abundant during ebb tide whereas Acrocalanusinermis, Cyclops buxtoni, Laophonte sp. and /dyaea sp.

were obtained only during ebb tide. The chaetognathspecies S. bedoti alone could tolerate the ebbconditions of the creek mouth. Fish larvae andstomatopod larvae were obtained only during theflood period. Preference of appendicularians to thecreek water was quite significant.

The overall pattern of diel rhythm of zooplankton inthe Malad creek is directly linked to the tide and otherenvironmental parameters. In the nearshore watersvariations in the environmental parameters are greatlyinfluenced by the tide. However, in a pollutedenvironment the adverse conditions will affect thewater quality leading to significant variations in thedisposition of zooplankton.

AcknowledgementThe authors are thankful to Dr V V R Varadachari,

Director for providing facilities. Thanks are due toDr M 0 Zingde and Mr P V Narvekar for theirassistance.

References

1 Chandramohan P & Rao T S S, Proc Indian Acad Sci, 75 (1972)23.

2 Pillai P P & Pillai A M, } Mar Bioi Assoc India, 15 (1973) 411.3 Madhupratap M & Rao T S S, Indian} Mar Sci, 8 (1979) 9.4 Goswami S C, Selvakumar R A & Goswami U, Mahasagar-

Bull Natn Inst Oceanogr, 12 (1979) 247.5 Mathe K J, Gopinathan C P, Rao D S, Regunathan A & Murthy

A V S, Proc Symp Warm Wat Zooplankton,(SPI. Publ NIO/UNESCO), 1977,250.

6 Anonymous, Studies on waste water disposal and submarineoutfall around Bombay, Technical Report (Nat InstOceanogr, Bombay) 1978.

7 Strickland J D H & Parsons T R, A practical handbook ofseawater analysis (Fish Res Bo Can Bull No 167), 1968, pp311.

8 Zingde M D, Trivedi S K & Desai B N, Indian} Mar Sci, 8(1979)271.

9 Gajbhiye S N, The ecology ofzooplankton with special referenceto polluted environments off Bombay, Ph.D. thesis, BombayUniversity, 1982.

10 Gajbhiye S N, Nair V R, Krishnakumari L & Desai B N, Indian}Mar Sci, 12 (1983) 166.

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