Dama an Sea Sameer Terdalkar and I
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J. mar, biol. Ass. India, 2001, 43 (1&2) : 57 - 64 Die1 vertical migration of zooplanktox dama an Sea Sameer Terdalkar and I. K. Pai Departm Goa Uni; Goa - 40 Zoopra~~nr~exhibit die1 vertical migration (DVMJ 111 wlucn, rrir rlvurs UI uamn-s are spent near the surface and the day light hours at deeper depths. DVM, though studied by m workers, is poorly understood. Hence an attempt has been made to study and understand I--.- DVM pattern in Andaman Sea, known not only for its olieotro~hicV nature. but also for rimary and secondary productivity. The zooplanlcton samp~les were collected ii ,om the u~ lost euphotic zone for 24 hrs at an interval of twoI hours bjr using a I30ng0 net,. The bion lass --A n A r3 -- -3. -----L--- 1-- PA-- .--I.. -7d wet weight" varied from 0.01 - 0.05 ml m3m ~IIUV.WL.L 1116111- T~S;~~CXIV~IY.Lvpepuus 3minated the samp:les, followred by chiietognaths, amphipods, siphonophores, crustacc?ans ld pelagic: tunicates .The present studies reveal that, not only the light intensity, but alsoI the edine hablrs..!I- rwruductive stare--- arw---I- age of organism alters DVM in zoo~lanl-'-- . ,ical migration in zooplanKton is sence of any light stunu~us.The zooplanl<- well documented but rather poorly un- ton again rise towards the surface just be- derstood (Boaden and Seed, 1985). Mem- fore dawn and this phenomenon is termed bers of zooplankton undertake DVM as "dawn rise". Further, some species through the water column of somewhat display (in some areas/at some times) re- less than 400m on average by smaller and versed migrations, being near the surface over 600m by larger species. These verti- during the day and move to deeper areas cal movements, which may involve sus- at night (Parsons and Takahashi, 1979). tained upward swimming speeds of 12- DVM of zooplankton with greater noc- 200 rnh-' dependent on the size and down- turnal feeding rates has been scrutinised ward speeds, some three time faster, may with respect to grazing impact on phy- be undertaken twice a day. During the toplankton and bacteria. With increased day time, the zooplankton are relatively densities of zooplankton in surface wa- deep in the water column, but by dusk, ters at night, a decline in the concentra- they ascend to the surface (Herring and tion of food particles occurs, which is Campbell, 1990). They then dispense inversely proportional to the length of time somewhat through the water column in the zooplankton remaining in the upper the middle of night, the ph enomerlon layers. Conclusions from other investiga- termed as "midnight sinking" a led tors suggest that DVM behaviour and by Raymont (1983), which is aue ro ran- feeding activity may not be strongly linked dom wanderings of the animals in ab- (Kennish, 1989). 58 Sameer Terdalkar and I. K. Pai There are several studies on DVM from dices give 1968) for species various parts of the world (Por, 1989, of zooplar ed in thc ? sample!. Checkley, 1992 and Chae and Nishida, 1995). However, such studies in the The 12 samples were subjected to Link- Andaman Sea are limited to the work of age clustering within a similarity matrix, Goswami and Rao (1981) and which is considered as convenient method Madhupratap et al. (1981). The present for illustrating relationships. The method study was conducted to understand more used was simple linkage method as de- about the Dy ribed by Omori and Ikeda (1984). Andam an Sea. esults Authors express tnelr slncere gratin: to Department of Occ ean Deq velopmc The samples collected during the entire (Gov. of India) and Ni ~tionalI[nstitute el cycle of 24 hrs. showed that the bio- ass fluctuating from 0.01-0.05 ml m-3, Oceanography,, Goa for pro.viding i ~riedfrc 3m 0.04- cruise facility. hile the wet weight v: 2mg m" (Figure 1).Furtl her, major zoop- ..-- I - Material and mernoas lanktonic groups encountered were cope- The data for the present study was pods, chaetognaths, amphipods, crush- collected on board ORV Sagarbnya dur- ceans.' si~honovhoresI and velagic tuni- ing the multidisciplinary cruise organised ca tes. by National Institute of Oceanography from 15th Oct. to 15th November 1996 ' the Andaman Sea (Lat 10°30.23'N a Long 93'15.25'E). The depth of the s tion was 2300 m. The zooplankton bi was det mined by displacement volume method and the collected samples were preserved in 4% formaldehyde. The wet weight was +- determined by f ollowin;g the method gi% by Omori and Ikeda (1984). Later, 1theTn 1g samples were brougnrI 1 . to the IaDorarory1~1 . and analysed for abc I of major zooplanktonic groups a tified upto m axa zm ---a available - -1""" I species level by using literature U mw (Daniel 1985, Zheng Zhong et. al., 1989, Santhanam and Srinivasan., 1994). The Fig. 1. Die1 jiuctuatzon OJ azomass ana wet weights diversity was calculate^ ing the in- of zooplankton in Andaman Sea Die1 vertical migration of zooplankton 59 I 0- I- 8smLmn-m maunoarm IL~U~YIUI wruum maximum abundance of various copep- n w ods during a particular time of die1 cycle, @ U was 24% at 000 hrs for C. pachydactyla, 3l s 12% at 2000 hrs for Copilia mirabilis, 24% at 2200 hrs for E. concinna, 22% at 1400 it - h..*sfor R,, nasutus and 12% at s s ID for S. nigromaculata (Figure 3). 9 P , ~~~~l~~ugnathswere revresenteu1 vy LC~ tm lao m I- mm mm t+w wm mo I~J 3- ~uo ~Muul species. They shovved their maximum (30% Fig. 2. Major zooplankton groups exhibiting diel amongst all majc or grou ps) presence at vertical migration in Andarnan Sea 0200 hrs (Figure 2). Among the group, Copepods formed the dominant group Pterosagitta draco, was dominant species; representing as many as 35 species. They followed bv Sagitta robusta and S. showedi their Inaximu !%) bipuncta ta f during 3., repre;senting Les. chaetogna ular timc 3 . P. .. After 16UU hrs., the percentage of cope- of the diel cycle wa3. ^+L%at 1200 - 1400 pods dropped down to 40-50% showing hrs for P. draco a: 1 hrs. fo:r an abrupt fall after 1800 hrs. (Figure 2). S. robusta (Figure Copepods like Candacia pachydactyla, Amphipods represented by ten species Coycaeus affinis, Euchaeta concinna, Oncaea showed their maximum (40% amongst all venusta, 0.media, Rhinocalanus nasutus and major groups) (Figure 2) presence during Sapphirina nigromaculata showed their 1800 hrs. Among the group, Lestrigonus presence continously between 2000 hrs to schizogeneios was dominant species fol- 1200 hrs. But the members,of the family Pontellidae such as Pontellopsis tenuicauda, and P. securifer appeared at 1600 hrs and again frbm 1000 hrs to 1200 hrs The 2Ma 22W TIME (HOURS) Fig. 4. Species composition of amphipods, exhibit- Fig. 3. Species composition of copepods, exhibiting ing diel vertical migration in Andaman Sea diel vertical migration in Andaman Sea Sameer Terdalkar and I. K. Pai larvae, copepodid stages II/III and meta- naupliar stages of Pontellidae family. The species diversity index (D) varied between 6.7 at 0200 hrs. and 11.6 at 0000 hrs. It was fairlv high- during- 1600 hrs too. E vennessI valuesi were quite h~igh and sf \owed a n inver!;e relatic onship Iwith bio- n..-. --..I..-. "l.-~..~.A .. -- maaa. II~Cvalura alruvvcu a 51dd~alin- crease after 0000 hrs reaching the lowest at 1400 hrs and highest by 2000 hrs Fig. 5. Species composition of cheatognaths, ex hib- (F Yigure 6: iting diel vertical migration in Andaman S ea The similarity matrix resulte,d into a .. ,, ,, /,:,. .,, ,,&l lowed by Brachyscelus crusculum, dendrogra~l~\slll~ple linkage IILCLL~O~)(Fig- Cranocephalus s;p andR habdoson na sp . re 7) showing the highest value of 0.91 urn abundance of amphipod s Ir the samples collected at 1200 hrs and . - - -. - cies during a particula: f die1 cycle 1000 hrs, and hence these two samples was, 37% at 00 hrs fc hizogeneios, are linked together at 0.91 level. The sec- 16% at 1800 hrs for B. cruscuium, 26% at ond highest similarity is 0.81 between the 00 hrs for Cronocephalus species and 27% samples collected at 0600 hrs and 0800 for Rhabdosoma specie!s (Figure 4). hrs, hence linked together. The third high- Crustaceans consisted of three species, est link at 0.78 is between the samples a sergestidae member - Lucifer typus and collected at 0800 hrs and 1000 hrs thus euphausids like Stylocherion carinatum and forming a group. The next new group is Thysanopoda tricuspidata, showing their formed at 0.66 level by the samples col- presence from 1800-0000 hrs (Figure 2) lected at 2000 hrs and 2200 hrs. Finally the least similarity value of 0.25 was re- Siphonophores collected belonged to four species - Chelophyes appendiculata, Lensia subtilis, Praya reticulata and Sulculeolaria biloba. They showed their maximum (14%amongst all major groups) vresence at 0400 hrs (Fig 2). Tunicates represented by a single pe- lagic species - Salpa fusiformis, showed its presence from 1600 - 2200 hrs showing a maximum abundance (6%) at 2200 hrs. The samples collected from 1600 to 0000 Fig. 6. Die1 fluctutation of species diversity and hrs also showed presence of echinoderm evenness of zooplankton in Andaman Sea Die1 vertical migration of zooplankton 6 1 day to a considerable different light inten- sity or the rate of change of light intensitY may trigger- off other behavioura~pat- - A ~ms,wh ~ichcau se the i~nirnals to mov 'e ito higl-ker lighi- ities dc1ring th .e Wter part of the day, as seen in case of mphipo~ds like Anchylctmera bl osseville 1, , cruscul,urn, Vibi Via gibbo Isa, L.