Koggala Lagoon Research Articles (Page 1)

Comparative analysis of the microbiota in wild mud crab (Scylla serrata) intestine, sediment, and water in Koggala Lagoon, Sri Lanka

Fish is one of the best organisms in many scientific studies to evaluate heavy metal pollution and human health hazards as they are well-understood organisms in the aquatic environment. The present study was carried out to examine the level of heavy metals in different tissues of Etroplus suratensis (Green chromide) in Koggala lagoon, Sri Lanka. Atomic absorption spectrophotometer (AAS) was used to determine the levels of copper (Cu2+), cadmium (Cd+3), lead (Pb+2) and Chromium (Cr+3) ions in the different tissues (skin, liver, gill, and flesh) of fish belonging to three different sizes; small (7.8-10.2) cm, medium (14.1-16.6) cm, and large (19.8-25.2) cm. The number of thirty-six fish were collected from the lagoon randomly. According to available sizes, 12 fish for each size class were used for the analysis. Furthermore, the histological analysis was carried out to identify the changes at the tissue levelling the gill and liver of fish in three different size classes. Heavy metal concentration in fish samples were compared with the standard levels of heavy metals. Heavy metal concentrations in body tissues of three different body sizes of fish were found to be mainly in the order of Cu>Pb>Cr> Cd. The highest concentrations (P<0.05) of heavy metals were found in the fish flesh and skin, while the lowest concentrations were found in the gills. The range of heavy metal concentrations (g g-1 dry weight) in body tissue of small size, E. suratensis fish were, Cu: 0.0443-0.6210, Cd: 0.0110–0.0214, Pb: Below Detection Level (BDL)- 0.46 and Cr: BDL-39.633, Medium size fish were, Cu: 0.0713–0.6210, Cd: 0.0134-0.0170, Pb: BDL-40.906, Cr: 0.0014–0.0500 and large fish were, Cu: 0.0553–0.345, Cd: 0.0110–0.0256, Pb: 0.0204–0.2103 and Cr: 0.0194–0.0773. However, Cd, Cr and Pb concentrations of flesh tissues were under the standard recommended limits referred by the FAO. Through the Cu concentration in flesh, tissues exceeded the standard limits of FAO. It is not considered as a toxic heavy metal. Histological analysis revealed that the deviation of shape of hepatic cells in the liver may due to the exposure to heavy metals in the lagoon. According to the overall result, biomagnification nature of heavy metals, and the consumption of E. suratensis in the Koggala the bioaccumulation and lagoon may create health hazards to consumers. 
 Keywords: Green chromide, Koggala Lagoon, Heavy metals, Histology

Mangrove ecosystems, amongst the most productive and biologically complex on Earth, are being degraded worldwide, and their widespread decline during the past decades has affected vital ecosystem services. Mangroves at Koggala lagoon on the southern coast of Sri Lanka have been degraded at an alarming rate due to agricultural practices, coastal zone development, and tourism activities. Most of the banks are heavily eroded due to boat and sea plane activities, and the mangrove ecosystem has been significantly damaged. Implementation of a scientific rehabilitation project was needed to restore this degraded mangrove ecosystem, and research was carried out to enrich the mangrove community by re-establishing mangroves on the eroded banks using corrosion-resistant plastic barrels. The sustainability of replanted mangroves was monitored under phase one and the re-establishment of ecological functions in the mangrove community was monitored under phase two. The accumulated biomass carbon during the period of two and half years was calculated by an allometric equation suggested for calculating biomass carbon of mangroves using the girth and height of individuals. The highest rate of girth increment was observed by the 24th month from establishment, whilst the growth rate declined between the 18th and the 30th months. During the study period, the average above-ground and below-ground biomass per barrel showed a linear increment. Our case study showed that the new method used for restoration is successful in establishing mangroves in sites with high erosion. This restoration technique was successful in coping with the situation in Koggala lagoon where previous restoration attempts were failures. Thus, we recommend this restoration method for sites facing the threat of severe erosion.

Management of multi-species and multi-geared fisheries is challenging due to conflicts and competitions of fishers. However, such a complex fishery exists for the last 100 years in Koggala lagoon, which extends only for 727 ha area, in southern Sri Lanka. This study evaluated the fish catch and income sharing mechanisms which enable to survive these fisheries in highly dynamic biological and socio-economical environments. Eight landing sites at the lagoon body, lagoon mouth and adjacent coast were weekly visited from April to August 2015 in drawing random samples to determine gear-based catch per unit effort (CPUE), species diversity and income levels. Questionnaires and discussions among fishers were used to identify potentials and threats for the fishery. Dominant 25 fish species and 6 shrimp species were observed in the catches of 11 fishing methods including snares, a fish trap which was not recorded from Koggala lagoon. During the study period high variations of CPUE were observed within and among fishing methods. Hierarchical cluster analysis based on present-absent data showed two clearly separated clusters (P<0.05). Though the educational level and years of experience significantly differed between lagoon and coastal fishers (P<0.05), the respective income was not significantly different. Targeting different species and different life history stages by different types of gear seems to be the key in sustaining multi-geared fisheries in the lagoon for last 100 years. Though school education does not have any effect on selecting fishing location, fishing experience seems to be important in operating some specific gear. Species aggregation and their susceptibility for different gear reveled in this study must be important in developing fishery management strategies for the lagoon. Despite to the effective catch sharing mechanism, the sand bar formation, which is the most concerned issue by both lagoon and coastal fishers, will determine whether Koggala lagoon fisheries will survived for another 100 years due to its effects on altering species diversity. Keywords: Artisanal fisheries, Catch composition, Socio-economic status

This study was conducted to determine the present status of the Mud Crab (Scylla serrata Forskal) population in Koggala Lagoon, including details on size at maturity, sex ratio and carapace width - body weight relationship. This Crab is the most common edible Crab species found in the lagoon, comprising 93.10% of total catch from crab pots and 89.86% of total catch from crab nets. Sex ratios (male:female) were 1:0.86 and 1:0.82 in crab pots and nets, respectively. Female crabs of various sizes were randomly sampled to determine size at maturity. The results indicate that size at maturity of females was 12.17 cm carapace width. Size at maturity of males could not be determined using external characteristics. Population parameters were estimated from length-frequency data collected in 2009 and 2011. Asymptotic carapace length (L∞) and growth constant (K) were estimated to be 20.12 cm, 0.91 yr−1 in 2009 and 19.27 cm, 3.2 yr−1 in 2011, respectively. Exploitation rates were 0.32 in 2009 and 0.44 in 2011. There was a significant difference in Crab size between harvests by the crab nets versus traditional crab pots. Results indicate that S. serrata population is declining due to over-fishing as of increased fishing gear efficiency from traditional crab pots to modern crab nets. Commercial catches of crab net and crab pots comprised 85.7% and 72.0% of immature females, respectively, based on the size at first maturity revealed by this study. In order to maintain natural health of the Mud Crab population, immediate management action is needed to regulate fishing in Koggala Lagoon.

The Journal of the National Science Foundation of Sri Lanka publishes the results of research in all aspects of Science and Technology. The journal also has a website at http://www.nsf.gov.lk/. 2021 Impact Factor: 0.682The JNSF provides immediate open access to its content on the principle that making research freely available to the public supports a greater global exchange of knowledge.

Aquatic environments are usually represented by physicochemical properties, including flow regime on riverbed configurations, sediment size and stability, and water quality. This monograph focuses on the habitat of submerged macrophytes. Recent changes to the aforementioned physicochemical properties because of human activities have altered the aquatic habitats for submerged macrophytes, resulting in increases in the number of invasive species and extinction of native species. The expansion of invasive species into new environments often changes the physicochemical properties of these environments through accumulation of fine materials or changes in water quality. This is especially true in stable water areas— such as spring-fed rivers, rivers from lakes, lakes, and lagoons—where the submerged macrophytes are often found. In these locations, sufficient natural discharge and floods sizeable enough to renew the aquatic environment cannot be expected. In this case, increases in underwater invasive species tend to have further negative impacts on the natural environment, as they create conditions that are more suitable to themselves. These areas are considered to be among the most sensitive environments to human influences. In order to overcome this issue, it is necessary to understand the factors that limit the growth of both invasive and native endangered species. With this knowledge, it may be possible to predict future changes to physicochemical properties—focusing on limiting factors with and without the use of some countermeasures—in order to find effective management strategies. Thus, the cooperation of ecologists and civil engineers is essential in order to integrate their knowledge. To that end, all studies introduced here were presented and discussed at the annual meeting of the Ecology and Civil Engineering Society held in Saitama Prefecture, Japan, in 2009. The essential contributions made by several researchers to this issue are summarized here. Shinohara et al. (2013) point out the importance of carbon dioxide (CO2) and light availability to the distribution of submerged macrophytes. Takahashi and Asaeda (2012) clarify that low pH spring water increases the growth rate of Egeria densa by affecting free CO2 concentration in water. It is known that submerged macrophytes play an important role in the ecosystems of shallow lakes and stable streams by changing water quality, creating a refuge for other creatures, reducing bottom shear stress by stabilizing the substrate, and reducing the presence of suspended particles. Submerged macrophytes, however, have been disappearing, and the cause is purported to be a limited supply of photosynthetically active radiation (PAR) because of phytoplankton blooms. Therefore, studies showing the importance of free CO2 are of interest to those who seek to develop the above-mentioned management strategies. Matsui (2012) presents his study on the distribution and habitat of submerged macrophytes in the Seta River as it flows out of Lake Biwa, Shiga Prefecture, Japan. He introduces the clear relationship between sediment type and submerged macrophytes. The study by Gunaratne et al. (2012). addresses changes in lagoon morphology, specifically inlet morphology and flushing properties of Koggala Lagoon, Sri Lanka. According to this study, the flushing half-life, which is the time needed to replace half T. Chibana (&) Department of Civil Engineering, The University of Tokyo, Hongo 7-3-1 Bunkyo-ku, Tokyo 113-8656, Japan e-mail: chibana@hydra.t.u-tokyo.ac.jp

Tropical Agricultural Research and Extension is a peer-reviewed international scientific journal covering a wide range of subject areas in tropical and subtropical agriculture published quarterly by the Faculty of Agriculture, University of Ruhuna, Sri Lanka. The journal is also available on the Faculty of Agriculture, University of Ruhuna website https://www.agri.ruh.ac.lk/tare/index.htm .

The changes of natural sensitivity in terms of lagoon morphometry, particularly the inlet morphometry and flushing properties of the Koggala lagoon, Sri Lanka, are presented in this paper. The morphometric assessment is based on analysis and consideration of morphometric characteristics for three scenarios of the lagoon, namely: (1) before the construction of the old groyne system or time period before 1996 (Koggala Scenario 1—KS1); (2) existing situation or time period after 2007 (Koggala Scenario 2—KS2); and (3) future scenario with respect to proposed groyne interventions for the mouth width of 20 m, as proposed by Gunaratne et al. (J Environ Sci 22(6):813–819, 2010) (Koggala Scenario 3—KS3). The morphometric assessment provides a simple means of defining natural sensitivity or vulnerability of individual scenarios of Koggala lagoon to external loads and anthropogenic activities. We found that KS1 and KS3 scenarios are relatively more sensitive than KS2, whereas KS1 has the highest natural sensitivity, and KS2 has the lowest natural sensitivity or the most robust conditions. In quantifying the tidal flushing of Koggala lagoon, the concept of flushing half-life (T 50% h) was adapted as the optimum measure of flushing time. Flushing half-life was calculated for KS2 and KS3 scenarios. The flushing half-life ranges from 9 to 37 h (1.5 days) for KS2 and from 12 to 72 h (3 days) for KS3. Flushing half-life suggests that the exchange rate between the lagoon and the ocean is controlled by the balance between fresh water inflow and the seawater inflow. Applications of the morphometric classification and flushing half-life presented in this article can be used to help guide management and policy-making decisions for the coastal environment of Koggala lagoon and other coastal water bodies of Sri Lanka.

Saltwater intrusion is a major coastal management problem which leads to the destruction of fishery, breeding grounds and habitat. Several dykes and water regulatory systems have been implemented to prevent salt water intrusion and to regulate water level in the catchment area in the Koggala lagoon. The groyne built at the lagoon mouth helped to keep the outlet open throughout the year for better mixing and water exchange, but it has been a matter of concern for local resource users due to salinity increase in the lagoon. Therefore, the study was focused in salt water intrusion into lagoon and upstream areas and its impact on water quality and drinking water wells of surrounding areas. Monthly mean salinity of the lagoon varied strongly from 20 psu to 34.5 psu in relation to the monsoon rains. During the drought, due to the water level difference between lagoon and the canal created a salt water intrusion into upstream areas through the sluice gates, even the gates were closed. During the period of high salinity (February and March) of the lagoon, surface and bottom salinity levels of the upsteam area were 16 and 22 psu respectively due to saltwater intrusion through the anicut at Warabokka. Moreover, the water exchange and mixing of the lagoon is governed by the gravitational circulation. However during the dry season, tide plays a major role for salt water intrusion and mixing creating well mixed condition. Thus, the lagoons can be classified as a partially mixed estuary. The faunal and the floral compositions of the lagoon had changed markedly due to salt water intrusion. Present analysis indicated that the salinity, dissolved oxygen content and chlorophyll-a content mostly affected the abundance and diversity of zooplankton in the Koggala lagoon. Construction of barrier across the rockfill groyne may minimize the salt water intrusion.

Physical processes of the lagoon are influenced by structural interventions. Understanding the complex reality of physical processes sometimes difficult with field observations thus a model provides a simplified abstract view. Two dimensional hydrodynamic model is used to describe, restoration efforts to Koggala lagoon, a combined freshwater and estuarine complex of rich ecosystem on the southern coast of Sri Lanka. The lagoon mouth was naturally closed by a sand bar which controlled the seawater intrusion. Due to large-scale sand removal at lagoon mouth, formation of the sandbar shifted towards the lagoon. After the removal of natural sand barrier, rubble mound groyne structures were built to avoid sand deposition in the lagoon and to protect the highway bridge from the sea wave attack. Construction of the groyne resulted in the lagoon mouth being permanently open which in turn led to many environmental problems with saline intrusion. The aim of this study is to evaluate the current situation of the lagoon and propose alternative structural interventions for minimization of seawater intrusion and subsequently improve lagoon ecosystem. Hydrological parameters were investigated and mathematical models for hydrodynamic behavior of the lagoon were applied in order to describe the lagoon physical processes and flow characteristics. Existing rubble mound structures were redesigned in order to minimize the seawater intrusion. Numerical simulations were carried out for two different mouth widths (40 m and 20 m) with appropriate structural interventions. Existing salting factor for the lagoon is 0.68 and numerical simulation results showed salting factor for 40 m and 20 m openings are 0.61 and 0.54 respectively. This shows the mouth width can be reduced up to 20 m in order to obtain a slating factor close to 0.5, which indicates the predominant influence of fresh water which in turn leads lagoon to a fresh water ecosystem.

Restoration of Koggala lagoon: Modelling approach in evaluating lagoon water budget and flow characteristics

Intra-specific morphological variation in the indigenous catfish Arius jella (Ariidae) was studied in five estuarine localities in Sri Lanka (Koggala lagoon, Walawe estuary, Garanduwa lagoon, Nilwala estuary and Chilaw lagoon) using morphometric analysis. Five morphometric characteristics describing the shape of the fish were significantly different among some of the locations. Significantly shorter pre-orbital length (8.3% SL vs 9.2-10.7% SL in the other populations) in specimens from Walawe estuary is a population-specific character. Significant differences in other characteristics were found indicating heterogeneity in morphology. The first two canonical variates (CV) explained 82.7% of the total variation in the data, yet the plot of the CV failed to display significant separation of the sample populations. Derived classification functions could correctly classify an average of less than 50% individuals into their a priori groups. There was no agreement on the isolation by distance model. The results indicate a small degree of spatial separation in morphology in A. jella among the studied estuarine localities. Key Words: Estuarine Fish, Morphometrics, Partial Isolation, Spatial Separation, Population Structure Doi: 10.4038/cjsbs.v36i2.484 Cey. J. Sci. (Bio. Sci.) 36 (2): 100-107, 2007

Selected hydrographic parameters of Koggala lagoon over a period of four months in 2002-2003 are reported together with the preliminary results on the distribution of a marine bivalve within lagoon. Such data prior to the December 2004 tsunami may provide back-ground information for comparison of post-tsunami conditions. Moderate yet significant variation in most physico-chemical parameters was found among selected sites. Mean salinity decreased from 34.0 ppt at the mouth to 11.4 ppt at 2150 m into the lagoon indicating pronounced seawater influx and mixing with freshwater. Monthly inter-site variation in salinity was statistically significant (p<0.05). The marine bivalve Saccostrea forskalli (Chemnitz) was the dominant benthic mollusk with numbers (per m2) ranging from 111.5±9.7 at lagoon mouth to 23.5±2.1 at 2150m inner lagoon. Density distribution of S. forskalli was significantly correlated (p<0.05) with the overall variation in salinity (r=0.889). Salinity-dependent colonization success of S. forskalli demonstrates the domi-nance of marine conditions in Koggala lagoon.

Gross and net primary production together with chlorophyll-a biomass were investigated with respect to depth and diurnal changes in three categories of inland waters (reservoirs, temporary ponds, brackish water lagoons) in Sri Lanka. Ten field sites, in both the dry and wet zones of the island, were investigated. Bimodal productivity profiles were recorded in two of the three reservoirs studied. The diel pattern of net photosynthetic rate varied between sites although peak photosynthetic efficiency occurred at solar noon. Surface photoinhibition was characteristic of the reservoirs and brackish water lagoons but not of the temporary ponds. Mean gross primary production was 3.02 g C m−2 d−1 but was higher in the temporary ponds than in the reservoirs. The gross primary production in the brackish water Koggala Lagoon at 0.08 g C m−2 d−1 is a record low for tropical lagoons and was 2.5 times less than the two other lagoons investigated. Variability in net primary production between sites was similar to the variation in gross production with a relatively low mean value for tropical inland waters of 0.495 C m−2 d−1. Mean maximum photosynthetic rate was 0.30 mg C m−3 h−1 but was lower in the reservoirs than in the temporary ponds and lagoons.