The plankton and benthic macrofauna in relation to the open sea cage culture of Lates calcarifer during the period from

October 2008 to March 2009 off Munambam near Cochin were studied. The cage site and a reference site were selected for

simultaneous sampling. During the study, the cage culture activity was not found to influence the plankton population but

there is an indication of its influence on the benthic macrofauna

Ignatius, Boby

Imelda, Joseph

Joseph, Shoji

Manisseri, Mary K

Rao, G Syda

Thomas, V J

Varghese, Molly

CMFRI Digital Repository

75NotePreliminary studies on the impact of open sea cage culture ofLates calcarifer (Bloch) on the planktonic and benthic faunaoff Cochin, KeralaMOLLY VARGHESE, SHOJI JOSEPH, IMELDA-JOSEPH, BOBY IGNATIUS,MARY K. MANISSERI, V. J. THOMAS AND G. SYDA RAOCentral Marine Fisheries Research Institute, Kochi - 682 018, Kerala, Indiae-mail:  mollykandathil@hotmail.comABSTRACTThe plankton and benthic macrofauna in relation to the open sea cage culture of Lates calcarifer during the period fromOctober 2008 to March 2009 off Munambam near Cochin were studied.  The cage site and a reference site were selected forsimultaneous sampling.  During the study, the cage culture activity was not found to influence the plankton population butthere is an indication of its influence on the benthic macrofauna.Keywords:  Benthos, Cage culture, Cochin, Phytoplankton, ZooplanktonThe open sea cage culture is an effective avenue toaugment fish production from the sea.  Countries like China,Malaysia, Thailand, Philippines, Japan and Australia havemade great strides in sea cage culture.  In India, open seacage culture was launched in the sea off Visakhapatnamfor the first time and successful harvesting of the fish wasdemonstrated in April, 2008.  In Kerala, for the first time, asea cage for rearing the Asian seabass Lates calcarifer waslaunched off Munambam, near Cochin.  The cage wascircular in shape with a diameter as well as depth of netportion equal to 6 m.  The cage frame was made up ofHDPE pipes fitted with Poly Urethene Foam (PUF).  Itwas assumed that there would be some changes in the faunalcomposition of plankters and benthos associated with cageculture, as the cage would be stationary and uneaten feedand faecal matter would be available around the cage.  Thecage was stocked with Lates calcarifer in December 2008and the fish were fed with trash fish along with growoutpelleted feed @10% of body weight. The fishes wereharvested in April 2009.  An attempt was made to monitorthe changing pattern of plankters and benthic fauna in andaround the cage culture site.Samples of phytoplankton, zooplankton andmacrobenthos were collected from the cage site as well asfrom a reference site before and during the culture period.Simultaneous samplings from both the sites were carriedout at monthly intervals prior to stocking and at fortnightlyintervals after stocking.  The fish cage site was located about2 km away from the shore having a depth of 10 m (N 10°08.162´; E 76° 08.901´) and the reference site was fixedIndian J. Fish., 57(3) : 75-77, 20102 km away from the cage site towards south (N 10° 07.189´;E 76° 09.210´), having the same depth of 10 m.  One litreof water sample was collected on each occasion for genuslevel identification of phytoplankton and their quantificationin cells per litre was carried out as per Gopinathanet al. (1974).  The zooplankton samples were collected usingthe method adopted by Rajagopalan et al. (1992) andgroupwise counts of zooplankton per 100 m3 of water wererecorded.  Benthos was collected using a 0.05 m2 van Veengrab and the macrobenthos were expressed as numberper m2 (Ambika and Pillai, 1990).  ANOVA tests werecarried out using SPSS 10 software, to understand thevariations of phytoplankton, zooplankton and macrobenthosbetween cage and reference sites.Twenty two genera of phytoplankters were recordedfrom the study sites, comprising both the cage and referencesites.  They were Asterionella, Chaetoceros, Rhizosolenia,Melosira, Thalassiothrix, Biddulphia, Coscinodiscus,Ditylum, Thalassiosira, Thalassionema, Ceratium,Nitzschia, Surirella, Skeletonema, Navicula, Pleurosigma,Cyclotella, Dictyocha, Oscillatoria, Fragilaria,Prorocentrum and Peridinium.  The distribution ofphytoplankton at the cage and reference sites, prior to andduring the culture period is depicted in Fig. 1.The density of phytoplankton was higher at the cagesite than at the reference site before as well as during theculture period (Fig. 1).  The average density ofphytoplankton observed before and during the cultureperiod at the cage site were 0.86 x 104 and 0.45 x 104 cellsper litre and that at the reference site were 0.24 x 104 and760.34 x 104 cells per litre of seawater respectively.  Thisindicates that the phytoplankton density was always higherat the cage site which can be due to the naturalcharacteristics of the site.  Thus the cage culture activitywas not found to influence the phytoplankton populationin the study area during the present investigation.  InOctober, the concentration of phytoplankton was observedto be very high at the cage site which was due to a bloomof Chaetoceros sp.  Again, in January, an increase wasrecorded in the cell density at the reference site which wasdue to the abundance of Rhizosolenia sp.  But during theseblooms, there was not much difference in the compositionof phytoplankton between the two sites.  In the case ofnutrients (nitrate, phosphate and silicate) in water, nosignificant alterations as influenced by cage culture weredetected (D. Prema, personal communication).  Nosignificant variation (p>0.05) was observed in majority ofphytoplankton genera between the cage and reference sites,before or during the culture period.  Demir et al. (2001)while studying the influence of cage culture of trout onplankton in an Antolian dam lake, also observed nofundamental difference in the composition of phytoplanktonbetween the two stations studied.A total of twenty groups of zooplankters were recordedfrom the study area, i.e., from the cage and reference sitestogether.  They were copepods, chaetognaths, bivalvelarvae, cladocerans, siphonophores, zoea stage of crab,appendicularians, fish eggs, fish larvae, prawn larvae,Lucifer sp., medusae, amphipods, Creseis acicula,gastropod larvae, polychaete larvae, foraminiferans,tintinnids, ostracods and balanid nauplii.  The quantitativedistribution of zooplankton at the cage culture site and atthe reference site before and during the culture period aredepicted in Fig. 2.The zooplankton density was higher at the referencesite than that of the cage site before as well as during theculture period.  The overall mean values of zooplankton atthe cage site before and after stocking the cage were1.58 x 104 and 3.22 x 104 and the same at the reference sitewere 2.94 x 104 and 6.68 x 104 numbers per 100 m3respectively.  The variation in the abundance of zooplanktonin different stations might be attributed to the patchy natureof zooplankton distribution.  Again, the statistical analysesof the data showed that there was no significant variationin the zooplankton population between the cage andreference sites, before or during the culture period.  Therewas also not much variation in the composition ofzooplankton among the two sites.  This indicated that thezooplankton fauna in the study area was not influenced bythe cage culture activity.Six groups of benthic organisms, viz., foraminiferans,bivalves, gastropods, polychaetes, copepods and amphipodswere recorded from the two study sites together. Afterstocking fishes in the cage, the macrobenthos increasedconsiderably at the cage site as compared to that at thereference site, but before stocking the fishes, the populationwas more at the reference site compared to the cage site(Fig. 3).  This increase of macrobenthos at the cage culturesite after stocking fishes could probably be due to theaccumulation of wastes from the cage in the form of excretaof fishes and uneaten feed.  The organic carbon content ofthe mud, studied simultaneously was also found to be lessat the cage site than that of the reference site throughoutthe culture period, even though the reverse was true forone sampling before stocking the fish in cage (D. Prema,personal communication). It is significant to mention herethat the sedimented organic matter is effectively consumedby benthos (Govindan, 2002) and that might be the reasonfor lower organic carbon at the cage site after stocking.Variation of macrobenthos between cage and reference siteswas not significant before the cage culture period, but duringthe cage culture period the variation was found to besignificant (p<0.05) in the case of total macrobenthos.  Themean numbers of macrobenthos at the cage site before andFig. 1. Distribution of phytoplankton during the study period Fig. 2. Distribution of zooplankton during the study periodMolly Varghese et al.77during culture were 6.12 x 104 and 226.66 x 104 and those atthe reference site were 316.18 x 104 and 3.92 x 104 numberper m2 respectively.  This indicates that the number ofmacrobenthos increased tremendously after stocking whileat the reference site the number of macrobenthos decreasedsignificantly during the same period, which may be due tothe influence of cage culture on the macrobenthos.  Whilestudying the influence of cage culture of trout on benthos inan Anatolian dam lake, Demir et al. (2001) also observedthat the abundance of benthos was the highest in the cagestation.  As the composition of macrobenthos at both thesites did not vary much throughout the period, it is assumedthat the cage culture has not influenced the composition ofmacrofauna in the area.  Demir et al. (2001) while studyingthe influence of fish cage culture on benthos also found thatthe composition of benthos did not differ among stations.But, while examining the impact of a seabass (Dicentrarchuslabrax) cage farm on macrobenthic communities in Croatia,Katavic and Antolic (1999) found that the benthic flora andfauna were quite rich and diverse, but with respect to itscomposition, structure and distribution, some benthiccomponents were found clearly affected by the fish farm.on macrobenthos.  As the distribution of phytoplankton andzooplankton are patchy in nature and the macrobenthosaffected by the water currents, long term studies with morefrequent samplings have to be attempted to arrive at reliableconclusions.AcknowledgementsThe authors thank National Fisheries DevelopmentBoard (NFDB) for providing support for this work.  Theyare also thankful to Dr. D. Prema, Sr. Scientist, Shri.K. M.Sreekumar, Skilled Support Staff and Smt.G. Shylaja,Technical Officer, CMFRI, Cochin for the help andco-operation rendered during the present study.ReferencesAmbika Devi, M. and Gopalakrishna Pillai, N. 1990. Effect ofpollution due to coconut husk retting on the species diversityof benthic communities of Cochin backwaters.Indian J. Fish., 37 (2): 145-149.Demir, N., Kirkagac, M. U., Pulatsue, S. and Bekcan, S. 2001.Influence of trout cage culture on water quality, planktonand benthos in an Anatolian dam lake. Isr. J. Aquacult.,Bamidgeh, 53(3-4):115-127.Gopinathan, C. P., Ramachandran Nair, P. V. and Kesavan Nair,A. K. 1974. Studies on the phytoplankton of the Cochinbackwater–a tropical estuary. Indian J. Fish. 21(2):501-513.Govindan, K. 2002. Marine benthos–a future perspective.In: Quadros, G. (Ed.), Proceedings of the National Seminaron creeks, estuaries and mangroves–pollution andconservation, 28 to 30 November 2002, Thane.Katavic, I. and Antolic, B. 1999. On the impact of a seabass(Dicentrarchus labrax L.) cage farm on water quality andmacrobenthic communities. Acta Adriat., 40(2): 19-32.Rajagopalan, M. S., Thomas, P.  A., Mathew, K. J., Selvaraj,G. S. D., Rani Mary George, Mathew, C.V., Naomi, T. S.,Kaladharan, P., Balachandran, V. K. and Geetha Antony1992. Productivity of the Arabian Sea along the south-westcoast of India. Bull. Cent. Mar. Fish. Res. Inst., 45 : 9-37.Fig. 3. Distribution of macrobenthos during the study periodThe present study revealed that the cage cultureactivity has not influenced the production of phytoplanktonand zooplankton but there is an indication of its influenceStudies on the impact of open sea cage culture of Lates calcarifer on plankton and benthosDate of Receipt : 15.07.2009Date of Acceptance : 02.09.2010

Preliminary studies on the impact of open sea cage culture of Lates calcarifer (Bloch) on the planktonic and benthic fauna

off Cochin, Kerala

http://eprints.cmfri.org.in/5896/1/2._Mol.pdf

Preliminary studies on the impact of open sea cage culture of Lates calcarifer (Bloch) on the planktonic and benthic fauna off Cochin, Kerala

Abstract

Similar works

Full text

Available Versions

CMFRI Digital Repository