Browsing by Author "Chandrasekera, L.W.H.U."

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Abundance and diversity of freshwater molluscs in some selected reservoirs of the Kala Oya river basin, Sri Lanka
(Sri Lanka Association for Fisheries and Aquatic Resources, 2015) Weerakoon, S.N.; Chandrasekera, L.W.H.U.; Amarasinghe, U.S.
Benthic macroinvertebrates such as molluscs are known to be possible bioindicators of aquatic ecosystems. We carried out a study to investigate how the abiotic factors affect the abundance and diversity of molluscan fauna at 10 irrigation reservoirs in the Kala Oya river basin during the dry season from August to November 2014. In each reservoir, three sampling sites were selected where at each site, a 50 m long perpendicular line transect was established running from its maximum water supply level towards the center of the reservoir. Three soil samples were collected at 10 m intervals each along each transect using a 0.5 dm3 soil corer. These samples were sieved in situ through a 1 mm sieve and the remains were preserved in 10% formalin solution containing Rose Bengal. Later the molluscs and other associated macrofauna were identified to the nearest possible taxonomic category using standard taxonomic keys and the fauna belonging to each taxon were enumerated separately. In addition, data related to vegetation cover, intensity of human disturbances, intensity of pollution, agrochemical inputs, soil texture and human settlements based on a modified scoring system were also collected. Altogether 4328 molluscs belonging to 11 genera were recorded. Molluscan genera such as Bellamya (45.9%), Melanoides (26.7 %) and Thiara (16.9 %) dominated the samples while the remainder (10.5%) belonged to less dominant genera consisting of Planorbis, Gyraulus, Indoplanorbis, Lamellidans, Planorbella, Lymnaea and Pila. The abundance of the molluscan genera varied significantly between the reservoirs (MANOVA; F (99, 899) = 4.300, P = 0.000; Wilk’s λ = 0.06515) and along the transect distances (MANOVA; F (44, 483) = 0.901, P = 0.654; Wilk’s λ = 0.73988). High diversity measures of molluscs were observed at Angamuwa wewa, Katiyawa wewa, Rajanganaya reservoir and Usgala-siyambalangamuwa wewa. Principal Component Analysis (PCA) for the mollusc abundance and the relationship between PC1 scores and Shannon–Wiener diversity index endorsed that Bellamya, Melanoides and Thiara were the highly contributing genera to the high diversity of the molluscs in the above reservoirs. Results of the PCA for abiotic factors revealed that both the abundance and species diversities were high at moderately sandy bottoms with high vegetation cover and agrochemical inputs. In contrast, the intensity of human disturbances, pollution, human settlement and shadiness showed a negative effect on the abundance and diversity of these molluscs. This study was carried out as part of a comprehensive study which investigates how the aspects related to biotic integrity and multiple uses of reservoirs could be used to develop effective management options for reservoir fisheries in Sri Lanka.
Accidental introduction of alien plankton into the Sri Lankan coastal zone through ballast water of cargo ships
(Sri Lanka Association for Fisheries and Aquatic Resources, 2009) Chandrasekera, L.W.H.U.; Fernando, M.A.S.T.
Accidental introduction of alien plankton through ballast water is a major ecological issue in many countries in the world. As there are no local studies addressing this problem, the present study was carried out to see whether alien plankton are introduced into Sri Lankan coastal zone through ballast water. Marine plankton occurring within ballast water holds of five cargo ships arrived at Colombo harbour and three local sites including Colombo inner harbour and two neighboring coastal sites were sampled. The physico-chemical parameters of water samples were also measured. Data on species abundance and physico-chemical parameters were analyzed using multivariate and univariate statistical tests as appropriate. Altogether 159 taxa of plankton were found in the samples. In the ballast water samples alone, there were 56 different taxa of which 50% of them were totally alien to the local coastal zone. The physico-chemical parameters of water samples between the four sites were not significantly different. However, multivariate statistical tests confirmed that the plankton community of the ballast water samples was significantly different from that of the three local sites. Considering the large number of ships calling annually at Colombo harbour, the great potential of accidental introduction of alien plankton into the Sri Lankan coastal zone should never be underestimated.
Acetylcholinesterase inhibition in Nile tilapia, Oreochromis niloticus following exposure to low concentrations of Chlorpyrifos and Carbosulfan: exposure– response relationships in fry, fingerlings and sub-adults
(Sri Lanka Association for Fisheries and Aquatic Resources, 2004) Chandrasekera, L.W.H.U.; Pathiratne, A.
Acetylcholinesterase (AChE) inhibition is considered as a specific biomarker of exposure and effect for organophosphorous and carbamate pesticides. Oreochromis niloticus, which is an abundant food fish in inland water bodies is a potential sentinel species in monitoring biological effects of pollutants in aquatic environments in Sri Lanka. In the present study, pesticide exposure and AChE inhibition relationships in different size groups of O. niloticus were assessed under laboratory conditions following exposure to an organophosphate, Chlorpyrifos and a carbamate, Carbosulfan, to evaluate the influence of body size on exposure-response relationships. Fry (0.9-2.0 g, 3.2-4.8 cm), fingerlings (3.0-9.7 g, 5.9-8.5 cm) and sub-adults (11-40 g, 9.2-15.0 cm) of fish were continuously exposed to a series of environmentally relevant concentrations of Chlorpyrifos (0.5 –12 g l-1) or Carbosulfan (1 –10 g l-1) for 14 days in a static system and brain AChE activities on 2, 6, 10, 14 days post exposure were determined using the standard spectrophotometeric method. Comparable size groups of fish maintained in aged tap water under similar laboratory conditions served as controls. Results showed that AChE activities in all groups of fish were inhibited following exposure to the insecticides tested in a concentration dependent manner. Exposure-response relationships indicated that fry stages were more sensitive to the pesticide exposure in comparison to the fingerlings and sub-adults. AChE activity of fingerlings and sub-adults exposed to 1 g l-1 Chlorpyrifos or Carbosulfan restored to near normal levels in 14 days post exposure whereas the activities of the fish exposed to other concentrations remained significantly inhibited even after 14 days. The results suggest that brain AChE activity in O. niloticus could be used as a sensitive molecular biomarker in monitoring organophosphorus and carbamate pollution in aquatic environments. However, the size groups of the fish should be taken into consideration when this fish is used in environmental monitoring
Alaboratoryassessment of the survival and verticalmovement of twoepibenthicgastropodspecies, Hydrobia ulvae (Pennant) and Littorina littorea (Linnaeus), afterburial in sediment
(Journal of Experimental Marine Biology and Ecology, 1998) Chandrasekera, L.W.H.U.; Frid, C.L.J.
Physical disturbance may result in the burial of the epibenthic fauna in sediment. The patches thus created undergo a `recovery' which may include the buried fauna migrating through the sediment to regain their original position in the sediment. A series of laboratory experiments were carried out to investigate the effects of prolonged burial on twoepibenthicgastropodspecies, Hydrobia ulvae and Littorina littorea, under various sediment temperature regimes. Their ability to regain the sediment surface under simulated winter (i.e. 7.5�C) and summer (i.e. 20.3�C) temperature conditions was studied in relation to the depth and the duration of burial. The effects of sediment silt and water content was also examined in a separate experiment. The proportion of H. ulvae surviving burial in natural sediment to 5 cm depth decreased with increasing duration of burial and sediment temperature. Burial to 5 cm was fatal to L. littorea within 24 h at all the temperatures examined. In sediment mixtures which had, by dint of large interstitial spaces, a good supply of oxygen or which were very fluid (i.e. `high silt-high water' sediment) a large proportion of H. ulvae and L. littorea regained the surface within 1 day of burial. No individuals of either species regained the surface in sediment mixtures with high silt and low water contents, this included the unaltered natural sediment treatment. In all cases, the depth of burial significantly reduced the surface regaining ability of L. littorea while it had no effect on H. ulvae. The survival and the escape behaviour of buried H. ulvae and L. littorea is discussed in relation to their respiratory metabolism and the oxygen stress in the sediment. The potential contribution of the buried fauna to the recovery of soft-bottom patches is assessed.
Biological factors affecting brain and muscle acetylcholinesterases in Oreochromis niloticus (Nile tilapia): Implications in biological monitoring of aquatic pollution
(Sri Lanka Association for the Advancement of Science, 2005) Chandrasekera, L.W.H.U.; Pathiratne, A.
Body size related differences in the inhibition of brain acetylcholinesterase activity in juvenile Nile tilapia Oreochromisniloticus by chlorpyrifos and carbosulfan
(Ecotoxicology and Environmental Safety, 2007) Chandrasekera, L.W.H.U.; Pathiratne, A.
Effect of biological and technical factors on brain and muscle cholinesterases in Nile Tilapia(Oreochromisniloticus): Implications for biomonitoring neurotoxic contaminations
(Archives of Environmental Contamination and Toxicology, 2008) Pathiratne, A.; Chandrasekera, L.W.H.U.; de Seram, P.K.C.
Influence of body length, body weight, gender, sexual maturity, and tissue storage on brain and muscle cholinesterases (ChE) in Nile tilapia was evaluated considering its potential use in biomonitoring neurotoxic contaminations in tropical environments. Results show that ChE activities in both tissues decreased significantly with increased total length (4?24.5 cm) or body weight (1?186 g) of the fish and the relationships were curvilinear. Comparisons of the slopes and elevations of the regression lines of the logarithmic ChE and body size relationships of males with those of females indicated that gender had no significant effect on the body size-specific ChE activities. Response of the ChE of sexually mature males to chlorpyrifos exposure was similar to that of females. Gonadal maturity stage of this fish does not seem to influence ChE activities. Storage of tissues at ?80?C for 28 days had no significant effect on ChE activities in the control fish and the fish exposed to carbofuran. However, a partial reactivation of brain ChE activities was observed in the fish exposed to carbosulfan after 28 days of storage. The results emphasize the importance of consideration of body size of the fish and storage time of the tissues in order to formulate accurate conclusions about the neurotoxic chemical exposure when ChE of the fish is used in biomonitoring programs.
Effect of crowding, food quality and body size on food utilization of the exotic snail, Pomacea canaliculata (Lamarck), a potential pest of rice in Sri Lanka
(Sri Lanka Association for Fisheries and Aquatic Resources, 1999) Kumara, P.A.D.A.; Chandrasekera, L.W.H.U.; Costa, H.H.
Effects of biological and technical factors on brain and muscle cholinesterases in Nile tilapia, Oreochromis niloticus: implications for biomonitoring neurotoxic contaminations
(Springer-Verlag., 2008) Pathiratne, A.; Chandrasekera, L.W.H.U.; De Seram, P.K.C.
Influence of body length, body weight, gender, sexual maturity, and tissue storage on brain and muscle cholinesterases (ChE) in Nile tilapia was evaluated considering its potential use in biomonitoring neurotoxic contaminations in tropical environments. Results show that ChE activities in both tissues decreased significantly with increased total length (4–24.5 cm) or body weight (1–186 g) of the fish and the relationships were curvilinear. Comparisons of the slopes and elevations of the regression lines of the logarithmic ChE and body size relationships of males with those of females indicated that gender had no significant effect on the body size-specific ChE activities. Response of the ChE of sexually mature males to chlorpyrifos exposure was similar to that of females. Gonadal maturity stage of this fish does not seem to influence ChE activities. Storage of tissues at –80°C for 28 days had no significant effect on ChE activities in the control fish and the fish exposed to carbofuran. However, a partial reactivation of brain ChE activities was observed in the fish exposed to carbosulfan after 28 days of storage. The results emphasize the importance of consideration of body size of the fish and storage time of the tissues in order to formulate accurate conclusions about the neurotoxic chemical exposure when ChE of the fish is used in biomonitoring programs.
Effects of human trampling on tidalflat infauna
(Aquatic Conservation: Marine and Freshwater Ecosystems, 1996) Chandrasekera, L.W.H.U.; Frid, C.L.J.
1.?Human trampling has been shown to be detrimental to the survival of fauna of terrestrial habitats and on rocky coastal areas. However, its effects on saltmarsh benthic infauna were not known. 2.?The abundance of macro-benthic fauna at five locations on a transect across a footpath on the emergent marsh and on the tidalflat at Lindisfarne NNR were sampled during the summer 1994 and winter 1995. 3.?The abundances of dominant taxa increased in summer in the intensely trampled path on the unvegetated tidalflat leading to a change in the community structure. These changes were not apparent when the trampling intensity was lower in winter. 4.?The abundances of dominant taxa at a less intensively trampled site in the vegetated emergent marsh did not change in either season. 5.?The susceptibility of the saltmarsh infauna to human trampling depends on the intensity of trampling disturbance and on the nature of the habitat. The possible effects of human trampling on the macrofauna in these intertidal habitats are discussed with reference to coastal management.
Effects of Pyrene exposure on Xenobiotic metabolizing enzymes in Nile Tilapia, Oreochromis niloticus
(Sri Lanka Association for Fisheries and Aquatic Resources, 2005) Chandrasekera, L.W.H.U.; Pathiratne, A.
Effects of waterborne cadmium on biomarker enzymes and metalothioneins in Nile tilapia, Oreochromis niloticus
(Journal of National Science Foundation of Sri Lanka, 2008) Chandrasekera, L.W.H.U.; Pathiratne, A.; Pathiratne, K.A.S.
Cadmium is widely used in modern industry and ranks among the most toxic metals in the aquatic ecosystems. In the present study, activities of several biomarker enzymes viz. ethoxyresorufin O-deethylase (EROD), glutathione S-transferase (GST) and cholinesterase (ChE) were determined in Nile tilapia (Oreochromis niloticus) at different waterborne Cd22+ exposure levels (0, 0.001, 0.005, 0.01, 0.1, and 1 mg/L for 28 days) to evaluate the potential influence of environmental cadmium on these enzymes. In addition, hepatic metallothionein (MT) levels in these fish at different waterborne Cd2+ exposure levels were also studied to evaluate their response to waterborne cadmium exposure. The results revealed that hepatic MT levels in the fish exposed to Cd2+ increased 2-26 fold depending on the exposure level and duration. Hence hepatic MT in Nile tilapia is a sensitive biomarker to indicate cadmium pollution in the natural environments. Continuous exposure of fish to ? 0.01 mg/L of Cd2+ had no significant effect on hepatic EROD, hepatic GST and brain and muscle ChE activities whereas exposure to ? 0.1 mg/L Cd2+ evoked time dependent significant depression of hepatic EROD (41-55%) activity. Brain and muscle ChE activities of the fish exposed to 1 mg/L Cd2+ were depressed to 24-32% and 33-35% respectively. Results revealed that high concentrations of Cd2+ in the natural environments could inhibit the basal activities of the hepatic EROD and brain and muscle ChE in Nile tilapia affecting the normal functioning of these biomarker enzymes and influencing the biomarker response to targeted organic pollutants in the environment.
Evaluation of selected biomarkers in Nile tilapia (Oreochromis niloticus) as tools in monitoring aquatic pollution in Sri Lanka
(2010) Chandrasekera, L.W.H.U.
Induction of pollutant responsive biomarkers, ethoxyresorufin–Odeethylase, glutathione S-transferase and biliary fluorescent aromatic compounds in tilapia inhabiting Bolgoda North Lake, Sri Lanka.
(Proceedings of the Annual Research Symposium 2005-Faculty of Graduate Studies, University of Kelaniya, 2005) Chandrasekera, L.W.H.U.; Pathiratne, A.; Pathiratne, K.A.S.
The presence of organic contaminants in aquatic systems poses a serious threat to environmental health. Biomarkers are sub-lethal biological measures of the response to and effect of pollutants in living organisms. Use of biomarkers has been identified as a powerful and cost-effective approach to obtain information on the state of the environment and the effect of pollutants on living biological resources. This study presents results of a part of the research project which focuses on evaluation of the use of biomarkers in food fish tilapia as tools in monitoring pollution in inland waterbodies in Sri Lanka. In the present study, activities of two enzyme biomarkers, ethoxyresorufin-O-deethylase (EROD) & glutathione S-transferase (GST) and biliary fluorescent aromatic compounds (FACs) in Nile tilapia (Oreochromis niloticus) collected from Bolgoda North Lake were evaluated in comparison to the baseline levels of the control fish in order to assess the biomarker responses in this fish. The results revealed that EROD and GST activities of tilapia inhabiting Bolgoda North Lake were significantly elevated several folds in comparison to the baseline levels. Liver somatic index and microsomal and cytosolic protein levels in the gill and liver tissues of fish collected from the lake were also elevated significantly compared to the controls. Induction of EROD and GST enzymes indicate the exposure of fish residing in the lake to organic contaminants such as polycyclic aromatic hydrocarbons (PAH) and polychlorinated biphenyls (PCB). Analysis of biliary FACs in the fish showed recent uptake of naphthalene, pyrene and benzo(a)pyrene type PAHs. Occurrence of PAHs in the colloids and sediments of Bolgoda North Lake has been confirmed by chemical analysis. Results suggest that EROD and GST in liver and gill tissues and FACs in bile in this fish are promising biomarkers of organic contaminations especially PAHs in the aquatic environments.
A preliminary study on the invasion of plankton into the west coast off Sri Lanka through ballast water
(Sri Lanka Association for Fisheries and Aquatic Resources, 2009) Chandrasekera, L.W.H.U.; Fernando, M.A.S.T.
Response of Brain and Liver Cholinesterases of Nile Tilapia,Oreochromis niloticus, to Single and Multiple Exposures of Chlorpyrifos and Carbosulfan
(Environmental Contamination and Toxicology, 2005) Chandrasekera, L.W.H.U.; Pathiratne, A.
Role of the gastropod Terebralia palustris (Linnaeus, 1767) in Rhizophora apiculata leaf litter decomposition
(Sri Lanka Association for Fisheries and Aquatic Resources, 2004) Ponweera, N.I.; Chandrasekera, L.W.H.U.
Macro-invertebrates play an important role in the breakdown of leaf litter in the mangrove ecosystems. Among them, the gastropod Terebralia palustris L., is considered to be an important species that significantly contribute to this process. The role of T. palustris on the leaf litter breakdown of Rhizophora apiculata, one of the commonest mangrove species in Sri Lanka, is assessed by a laboratory experiment where the loss of dry weights of R. apiculata leaf litter, increase of particulate organic matter and changes of the total reactive phosphate concentration in water at varying densities of T. palustris were measured at varying period of exposure. The distribution juvenile and adult T. palustris along the margin of the estuary from where the specimens were collected was also investigated in-situ using the belt transect method. Results showed that the loss of dry weight of leaves decreased significantly as a result of shredding by T. palustis. The total suspended particles were increased significantly with the period of exposure and the density of T. palustris. The total reactive phosphate concentration in water increased with the period of exposure, but this was not related to the density of T. palustris. The adult T. palustris were more abundant near the mangrove root system, while the juveniles were abundant in the open areas of the estuary. This study showed that T. palustris helps shredding large leaves into small litter particles and contributes immensely to the decomposition mangrove leaf litter. However, this process did not enhance the mineralization of phosphorus as the fragmented litter particles were not in critical size and the leaves were not exposed to an adequate period of time for leacheate loss.
The spatial variation of macrobenthic community in the Negombo estuary in relation to physic-chemical parameters
(Sri Lanka Association for Fisheries and Aquatic Resources, 2011) Chandrasekera, L.W.H.U.; Hettiarachchi, A.I.
The effects of Relic fauna on initial patch colonisation in a British saltmarsh
(Netherlands Journal of Aquatic Ecology, 1996) Chandrasekera, L.W.H.U.; Frid, C.L.J.
When a disturbance impacts an area it rarely leads to a complete defaunation, some individuals survive forming a relic fauna. Relic fauna in azoic patches in an intertidal soft-bottom habitat were simulated by the separate introduction of individuals ofNereis diversicolor, Hydrobia ulvae andLittorina littorea into defaunated cores. These were exposed in the field for 24 hours and the effects of relics on colonisation were assessed separately for colonisation via the sediment surface and colonisation via the surface and laterally through the sediment. After 24 hours all the species in the ambient community were recorded from at least some experimental cores. Densities of the most abundant infaunal taxa,Corophium volutator, Enchytraeus buchholzi, Manayunkia aestuarina, Tubificoides benedeni and nematodes, varied between 1% and 279% of ambient. MDS ordinations showed significant differences in the fauna of experimental cores, a result of the lack of full colonisation by some species and the presence of other species at densities in excess of ambient. Comparisons (ANOSIM and ANOVA) of the fauna of the relic addition cores vs. no-addition cores showed an influence ofN. diversicolor on colonisation. However, this relic effect appeared to be masked by the high degree of variation in colonisation. Densities ofL. littorina andH. ulvae were not maintained in all of the experimental cores and there was no significant difference in the fauna of cores in which the treatments were maintained. It therefore seems that initial colonisation of patches in the emergent saltmarsh is controlled by the (i) supply of colonists and (ii) attraction to under-exploited organic matter and that any relic fauna exerts little influence on the early stages of the colonisation process.
The restoration of mud flats invaded by common cord-grass (Spartina anglica, CE Hubbard) using mechanical disturbance and its effects on the macrobenthic fauna
(Aquatic Conservation: Marine and Freshwater Ecosystems, 1999) Frid, C.L.J.; Chandrasekera, L.W.H.U.; Davey, P.
1. The growth of the common cord-grass, Spartina anglica, across many temperate coastlines has resulted in a reduction in the extent of tidal flats. Its colonization has reduced the abundance of macrobenthic fauna and hence has had a direct effect on the feeding of shorebirds. Although the use of chemical methods has proven successful in controlling Spartina swards on tidal flats, factors such as environmental and human health concerns have stimulated a search for alternative control methods. However, any such control method must not impact the macrobenthic fauna. 2. The effectiveness of a physical disruption to control Spartina swards on tidal flats was investigated in the saltmarsh at Lindisfarne NNR, UK. The sediment was disturbed by a light-weight tracked vehicle until the Spartina swards were dislodged and buried within the sediment. The post-disturbance dynamics of the infauna in the disturbed area was investigated 1, 12, 31, 92 and 384 days after the disturbance. 3. In spite of the drastic change brought about in the flora, there was no evidence that the infauna were impacted by the disturbance at any sampling time. Two possible mechanisms to explain the absence of changes in the abundance of the infauna are discussed with special reference to the unconsolidated nature of the sediment and the high mobility of the adult infauna. The abundance of Spartina swards in the disturbed area was lower than that in the undisturbed area. Physical disturbance to Spartina swards by the tracked vehicle seems to be an appropriate method for its control in tidal flats which obviates the need, with associated financial costs and environmental risks, of chemical control.