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Indian Journal of Marine Sciences Vol. 18, September 1989, pp. 151-154 Zooplankton composition of the Kalpeni and Agatti atolls, Lakshadweep archipelago C T Achuthankutty, S R Sreekumaran Nair, P Haridas* & M Madhupratap National Institute of Oceanography, Dona Paula, Goa 403 004, India Received 1 February 1989, revised 19 May 1989 Composition of zooplankton in the lagoons was quite different from that of the sea and to a large extent, was independent of oceanic influence. While copepods were dominant in the sea, meroplank• ton, particularly brachyuran zoeae constituted the largest group in the lagoons. Zooplankton stand• ing stock was lower in the lagoons as compared to the sea. Among copepods, calanoids showed higher abundance in the sea whereas harpacticoids and cyclopoids dominated the Kalpeni and Agatti lagoons respectively. Several striking similarities were observed in the zooplankton composition be• tween the coral and coastal lagoons. Ecology of zooplankton of the coral lagoons has . received considerable attention 1 - 6 mainly because II • A of its unique fauna and its role in the energy • transfer in coral ecosystem. Among the atoll la• • goons of the Lakshadweep archipelago, zooplank• ton composition of the Kavaratti lagoon has been fairly well studied 7 - ll. Other lagoons like Kalpeni and Agatti however, have received very little at• tention. Zooplankton composition in and ar:ound N these atolls was studied and is compared with si• milar studies from other areas. N. 50 t 10·1 Scale I' 300 000 Materials and Methods 72- E 6' 10' During the 153rd cruise of R V Gaveshani (20 •B ;,. April - 4 May 1985), studies were undertaken in and around some atolls of the Lakshadweep ar• • chipelago in order to understand the biological productivity. Zooplankton samples were collected • from 6 stations each outside the Kalpeni and Agatti atolls, 4 stations in Kalpeni lagoon and 3 stations in Agatti lagoon (Fig.1). All samples were collected by making surface tows using a HT net (mouth area 0.25 m2, mesh width 0.3 rom) equipped with a calibrated flowmeter. As var• iations in zooplankton composition and abun• dance between the stations were not found to be significant (P> 0.05) within each study area, aver• age value for each area is presented. 7 "!('30' E 3"' 40' *Regional Centre of National Institute of Oceanography, Fig. I-Station poslt1ons inside and outside the Agatti (A) Cochin 682 018, India and Kalpeni (B) atolls 151 INDIAN J MAR SCI, VOL. 18, SEPTEMBER 1989 Results capod crustaceans dominated in the lagoons Zooplankton biomass and composition- A (96.3% at Kalpeni and 91.4% at Agatti). Brachy• comparison of the mean biomass showed that the uran zoeae were the most abundant among them sea outside Kalpeni and Agatti atolls was 3 to 10 (> 90%). Larval stages of sergestids, palaemonids, times richer [1.3 and 3.3 ml (100 m3tl] than the alpheids pagurids and callianassids constituted the respective lagoon [0.13 and 1.03 ml (100 m3tI]. remaining. Corresponding numerical abundances were 1363, Among the holoplankton, Copepoda was, by 3828,305 and 5776 (100 m3tI. far, the biggest group both in the sea and the la• Various taxonomical groups of holo- and mero• goons. Its contribution was 98.4% in Agatti la• plankton identified from the 4 areas are given in goon, but was reduced to 48.9% in Kalpeni la• Table 1. Copepods formed the dominant compo• goon where amphipods and cumaceans also oc• nent outside Kalpeni (75.5%) and Agatti (74.6%) curred in considerable numbers (22.1 and 18.7%). atolls. On the contrary, larval decapod crusta• Carnivores such as chaetognaths (14%) and si• ceans dominated (71.1 and 68.2% respectively) in phonophores (8.5%) respectively formed the sec• the lagoons. Here copepods were only the second ond largest group in the sea outside the Agatti abundant group (12.8 and 25%). and Kalpeni atolls. An important feature noticed in the zooplank• Composition and distribution of copepods• ton composition was the dominance of mero• Among copepods, calanoids were dominant in the plankton in the lagoons. This formed as much as sea (82.7 and 93.2% outside the .Kalpeni and 73.8 and 74.6% of the total zooplankton counts Agatti atolls) whereas harpacticoids formed in the Kalpeni and Agatti lagoons whereas it was 75.5% in the Kalpeni lagoon and cyclopoids only 2.8 and 6.2% respectively in the sea outside formed 78% in the Agatti lagoon. Calanoids were the lagoons. Among the meroplankton, larval de- repre~ented by 6 families in the Kalpeni lagoon, 8 families in the Agatti lagoon and 10 families in Table 1- Percentage composition of various taxonomical the open waters. Families Calanidae, Paracalani• groups of holo- and meroplankton to total zooplankton in the dae, Pontellidae and Acartiidae were generally atolls abundant in the sea outside both the atolls (Fig.2). Lagoon68.21.271.113.238283050.034.60.1574.625.012.80.00.250.80.020.340.120.620.120.00.020.020.00.080.680.10.230.00.030.00.90.00.860.020.90.135.80.00.00.181.71.30.240.10.010.01.50.015.00.1257760.160.64.90.00.04Sea Agatti75.50.010.280.00.150.030.020.130.248.32.52.03.13.61.31.51.051363Kalpeni Among these, Paracalanidae and Acartiidae were fairly common in both lagoons albeit in smaller Meroplankton[no.FishPolychaeteSiphonophoraTunicataEchinodermCirriIsopodaAmphipodaPteropodaMysidaceaEuphausiaceaHydromedusaeMolluscaCumaceaOstracodaTotalChaetognathaCladoceraStomatopod (100 eggspede zooplanktonm3)-IJ& (veligers) laryae larvaelarvae(%) larvae larvae HoloplanktonDecapodCopepoda larvae(%) Sea numbers. Most of the other calanoid families, ex• cept Calanidae at Agatti, were either poorly rep• resented or absent in the lagoons. IUOUUI \ ------- ------- w --- I ----I;'U~::Ir/////JV////Jl\I!:1;,:::11000---- : ::i+-ACARTIIOAEo~ \ CALANIOAE ==.=L 0.. o 1 :IE Z80 W//AV//.t1_PARACALANIOAEW//..-1 PONTELLIOAE •••••• 0 0 CI 0~0..crWZa:: 4020 L 1====1tI'/M \. ,.1 ~ 60 ==_-_j::en . ==== W ~mL11~ o SEA LAGOON SEA LAGOON KALPENI AGATTI Fig. 2 - Percentage composition of different families of cala• noid copepods inside and outside the Kalpeni and Agatti atons 152 ,I ACHUTHANKUTIY et at.: ZOOPLANKTON COMPOSmON Species composition of copepods is presented in Table 2. The calanids Canthocalanus pauper Table 2 - Distribution of copepod species [no. (100 m3 t•j in and Undinula vulgaris although absent in the the atolls Kalpeni lagoon, were abundant in the sea and Agatti lagoon. Species of Eucalanidae were not Copepod species Kalpeni Agatti Sea ~ommon in the present study. Paracalanids in gen• Lagoon Sea Lag?On eral, were more abundant in the sea particularly outside the Agatti atoll. Among the two species Total Copepoda 1029 39 2855 1443 belonging to the family Temoridae, Temora di~ Order. Calanoida Canthocalanus pauper 97,7• 0,0 309.5• 23.7• caudata was more abundant in the sea and Agatti Undinula vulgaris 96.0• 0,0 720,2• 59.7• lagoon, but did not occur in the Kalpeni lagoon. Subeucalanus crassus 3.0+ 0.3+ 1.2+ 0.0 Pontellidae were generally not very abundant in Pareucalanus attenuatus 1.2+ 0.0 2.8+ 1.0+ Acrocalanus gibber 7,7• 2,3• 126.2- 0.0 the lagoons and the surrounding sea. However, 11 A monachus 0,0 0,3+ 4.5+ 3.3- out of the total 12 species recorded were from Acrocalanus sp, 110.3• 0,0 404.5• 31.0• the sea and many of them were common. Their Bestiola similis 72.5• 0.3+ 453.3• 0,0 diversity and abundance however, dwindled in the Paracalanus sp, 87.2• 0.7+ 194.7- 27.7• Euchaeta rimana 0,2+ 0,0 9.0+ 4.0+ lagoons. Acartiidae was represented by 6 species Temora discaudata 25.3• 0,0 40.5• 5.7• in the collections of which Acartia amboinensis, T. turbinata 0.3+ 0,1 + 0.0 0.3+ A. danae and A. negligens were more common in Centropages gracilis 0,2+ 0.0 3.S+ 0.0 C calaninus 0.3+ 0.1 + S.5+ 0.0 the open waters of the Kalpeni atoll. A. dweepi Cturcatus 0,0 0.3+ 19.2+ 1.0+ was collected in fairly large numbers, but only Candacia truncata 8,1• 0,0 0.0 0.0 from the Agatti lagoon. Species belonging to the C. pachydactyla 0,2+ 0.0 0.0 0.0 C catula 0,0 0,0 14.0• 0.0 families Centropagidae, Candaciidae, Calocalani• Pontella diagonalis 3~S- 0.0 5.3+ 0.0 dae and Euchaetidae were either poorly repre• P.danae 0.8+ 0.0 0.0 0.0 sented or absent in the collections from the la• P. spinipes 61.2• 0,0 17.0+ 0.0 P. princeps 21.8• 0,0 3.3+ 0.0 goons as compared to the surrounding sea. pomella sp, 22.2• 0,5+ 13.3- 0.0 Cyclopoid copepods were virtually absent in Pontellina plumata 26.2- 0.3• 226.5• 5.3• the sea. However, Oithona nana registered a Pontellopsis villosa 0.2+ 0.0 6,Jl• 0.0 Labidocera pavo 0.0 0,1 + 0.0 7.3+ m3)-1 density of 1107 (100 in the Agatti lagoon L minuta 2,7+ 0.0 0.0 1.7+ which was the highest for any species in this L acuta 6.2+ 0,0 0.0 0.0 study. All three species of poecilostomatoids were L. detruncata 19.5• 0.0 20.3+ 1.3+ 3.0+ 0,0 11.7• 0.0 abundant in the sea of which Corycaeus sp. had Labidocera sp, Calanopia minor 3,0• 0,0 3.0+ 0.0 the highest density. Of the total of 5 species of Calocalanus pavo 7,0- 0,0 13.5- 0.0 harpacticoids recorded, 3 species viz.