The architecture of the lower parts of submarine canyons on the western Nigerian continental margin

Multi-beam,sub-bottom and multichannel seismic data acquired from the western Nigerian continental margin are analysed and interpreted to examine the architectural characteristics of the lower parts of the submarine canyons on the margin.The presence of four canyons： Avon,Mahin,Benin,and Escravos,are confirmed from the multi-beam data map and identified as cutting across the shelf and slope areas,with morphological features ranging from axial channels,moderate to high sinuosity indices,scarps,terraces and nickpoints which are interpreted as resulting from erosional and depositional activities within and around the canyons.The Avon Canyon,in particular,is characterised by various branches and sub-branches with complex morphologies.The canyons are mostly U-shaped in these lower parts with occasional V-shapes down their courses.Their typical orientation is NE–SW.Sedimentary processes are proposed as being a major controlling factor in these canyons.Sediments appear to have been discharged directly into the canyons by rivers during the late Quaternary low sea level which allows river mouths to extend as far as the shelf edge.The current sediment supply is still primarily sourced from these rivers in the case of the Benin and Escravos Canyons,but indirectly in the case of the Avon and Mahin Canyons where the rivers discharge sediments into the lagoons and the lagoons bring the sediments on to the continental shelf before they are dispersed into the canyon heads.Ancient canyons that have long been buried underneath the Avon Canyon are identified in the multichannel seismic profile across the head of the Avon Canyon,while a number of normal faults around the walls of the Avon and Mahin Canyons are observed in the selected sub-bottom profiles.The occurrence of these faults,especially in the irregular portions of the canyon walls,suggests that they also have some effect on the canyon architecture.The formation of the canyons is attributed to the exposure of the upper marginal area to incisions from erosion during the sea level lowstand of the glacial period.The incisions are widened and lengthened by contouric currents,turbidity currents and slope failures resulting in the canyons.

The Salient Issues of Coastal Hazards and Disasters in Nigeria

The Nigerian coastline which stretches about 853 km has four distinct morphological zones namely, Barrier Lagoon, Mahin Mud coast, Niger Delta and Strand coast. Nigeria’s coastal zone is richly blessed with various natural resources like oil, gas, fish, sand etc., which are presently being exploited for economic development. Coastal populations have increased erratically from about 20% of the National population in 1993 to approximately 51,037,122 m (30% of the national population) in 2011. Development of coastal areas in Nigeria is accelerating and user conflicts are increasing. Both natural and anthropogenic activities in the coastal zone are leading to coastal hazards and eventual rapid degradation of the area. Significant coastal hazards include coastal erosion, storm surges, floods, land subsidence, pollution, especially oil spills and possibly seismicity, which could lead to earthquakes and tsunamis. These hazards are leading to disasters and effecting the socio-economic sustainability of the coastal area.

Antibiotics Resistance Pattern and Plasmid Profiling of <i>Edwardsiella tarda</i>Isolated from <i>Heterobranchus longifilis</i>

A study was carried out to investigate antibiotic resistance patterns and plasmid profiling of Edwardsiella tarda isolated from farmed-cultured Heterobranchus longifilis in Lagos State, Southwest of Nigeria. A total of 44 Edwardsiella isolates were recovered from 80 fish samples collected from the 10 fish farms using selective random stratification. It was observed that Edwardsiella tarda isolates were 100% resistant to Amoxicillin, Chloranphenicol, Levofloxacin, Streptomycin and 90% resistant to Nalidixic Acid respectively. All the isolates were 100% susceptible to Spectinomycin and Ciprofloxacin, while Ofloxacin, Gentamycin, and Pefloxacin vary in their level of susceptibility with 90%, 80% and 70% sensitivity respectively. Conversely, 8 out of 10 fish farm locations studied were observed to have antibiotic-resistant strains, and 5 out of 8 drug-resistant strains were found to carry plasmid and the sizes of the plasmid ranges between 20.027 kb to 23.130 kb. The plasmid after treatment with mitomycin C and ethidium bromide were lost during the process of plasmid curing confirming that the multiple drug resistant exhibited by the isolates was plasmid mediated. There are fewer studies on antibiotic resistance in Edwardsiella tarda from aquaculture enterprises and this study provides further support to the view that there is a potential risk of transfer of resistant bacteria and their genes to human pathogen through the food chain. Although, in Nigeria there is no antibiotic product registered for aquaculture usage, yet fish farmers use them off-label for bacterial diseases prevention.

Physical Forcing Induced Coastal Vulnerability along the Gulf of Guinea

Coastal areas of the Gulf of Guinea experience accelerated degradation as a result of erosion and flooding associated with intensification of extreme marine-meteorological phenomena. The coastal erosion process, especially on the sandy or muddy littoral, constitutes one of the main factors of the degradation of the Gulf of the Guinean coast. These risks, which are still poorly studied, could increase over the coming decades because of climate change and the human activities that exacerbate them. Data related to ocean forcing (tide, wave, and sea level anomaly), to hydrologic parameter (rainfall) and to the state (geomorphology, coastal slope, and rate of coastal retreat) of the coast were analyzed by several statistical methods and a numerical vulnerability model to map the vulnerability of the different coastlines of this region. The results showed that the vulnerability of these coastal areas is influenced by geomorphology, tide, waves and rainfall intensity. 24.34% and 37% of the entire coast are of low and moderate vulnerability respectively. While 26.98% and 11.66% are of high and very high vulnerability respectively. This information could facilitate developing sustainable policies to effectively manage hazards in this coastal zone.

Impact of Sand Dredging Activities on Ecosystem and Community Survival in Ibeshe Area of Lagos Lagoon, Nigeria

This study investigates the impact of sand dredging activities on coastal ecosystem and community survival around Ibeshe area of the Lagos Lagoon, Nigeria. Surface water and bottom sediment samples were collected from locations partitioned into Dredged Area (DA) and Undredged Area (UA) in the lagoon for laboratory analyses. Questionnaires were administered to community dwellers and sand miners to further analyze perception of locals. Significant differences in water quality parameters and sediments properties from Dredged and Undredged areas, and highly significant relationship between sand dredging and unsustainable ecological practices in Ibeshe were observed. One way ANOVA test indicates that all water quality parameters measured with exception of turbidity and nitrate concentration were not significantly different (P > 0.05) between Dredged and Undredged area. With exception of moisture content other sediment parameters measured were not significantly different (P > 0.05) between Dredged and Undredged areas. The project also determined the impact of dredging activities on the fisheries and fishing business in the environment. Turbidity values revealed that fishes will be negatively affected due to dredging activities;moreover dwellers pay little or no attention to conservation of the area due to unawareness. Sand dredging operations negatively influence ecological resources and water composition of the area. This project is designed to randomly sample the opinion of sand mining operators and residents;and questionnaires were administered to obtain data. Strict regulation and enforcement will assist to control ecological destruction and solve problems facing the lagoon environment.

Analysis of Some Elements and Speciated Compounds in Fish Found in the New Calabar River of the Niger Delta Area,Nigeria

The flesh of guinean and blackchin tilapia,and mullet found in Choba river were collected for elemental studies of mercury,cadmium,lead,arsenic,nickel and speciated forms.Analytical method of X-ray fluorescence(XRF)was used for the elemental studies while Gas chromatographymass spectrometer(GC-MS)was used for the speciated forms.4.3 mg/kg was the highest concentration of cadmium observed in blackchin tilapia.The three fish species all contained about 0.5 mg/kg of arsenic and 1 mg/kg of mercury.1.7 mg/kg of lead was detected in mullet while 7.3 mg/kg of nickel was detected in blackchin tilapia.Organometallic compounds found were nickel tetracarbonyl,borane carbonyl in guinean tilapia,nickel tetracarbonyl,borane carbonyl and germanium(iv)pthalocyanine dichloride in blackchin tilapia and[μ-(ƞ6-benzene)]bis(ƞ5-2,4-cyclopentadien-yl)di-μ-hydrodi-vanadium.Borane carbonyl was found in mullet.

Effects of Different Combinations of Two Spices:Clove and Nutmeg Seed Extracts on Antioxidants Levels in African Catfish(Clarias gariepinus)

The effect of different combinations of botanical spices such as clove and nutmeg in different proportion on the antioxidants activities which include lipid peroxidation(LPO),superoxide dismutase(SOD),catalase(CAT),glutathione-S-transferase(GST)and glutathione peroxide(GPX)in juveniles and adults sizes of Clarias gariepinus was investigated using different combinations of clove(C),and nutmeg(C.N 0:0-Control 0%of Clove and Nutmeg;C.N 1:3-25%Clove and 75%Nutmeg;C.N 3:1-75%Clove and 25%Nutmeg;C.N 2:2-50%Clove and 50%Nutmeg;C.4-100%Clove;N4-100%)in triplicates.The results from the study indicated that the anaesthetic caused a substantial(p<0.05)modifications in the five antioxidants under examination.The highest deviations in the studied antioxidants were observed in the fish exposed to C4 combination of the anaesthetics and the lowest in the control.The results from this work therefore suggest that the anaesthetics can alter antioxidants levels in the fish which was more noticeable in the fish exposed to C.N 3:1-75%Clove and 25%Nutmeg;C.N 2:2-50%Clove and 50%Nutmeg;C.4-100%Clove;N4-100%.Hence fish farmers and scientists are advised to take caution when combining these plant extracts for use in aquaculture.

Assessment of Heavy Metals Pollution in Sediments from Ologe Lagoon, Agbara, Lagos, Nigeria

This study was carried out to assess the level of heavy metals pollution in Ologe Lagoon, Agbara, Lagos, Nigeria. The Lagoon receives effluents from industries in the Agbara Industrial Estate. Cored Soft sediments were retrieved from six random sampling points within the Lagoon and labeled (S1, S2, S3, S4, S5 and S6). Subsamples of the sediments were prepared and analyzed for heavy metal concentration. The result from the heavy metal analysis of the sediments shows that average concentration of Mn, Zn, Cr, Ni, Cr, Ni, Co, Cu and Pb in the samples was 278.1 ppm, 21.7 ppm, 14.2 ppm, 6.6 ppm, 6.4 ppm, 6.4 ppm and 4.4 ppm, respectively. The correlation between the heavy metals varies from 0.71 to 0.98 shows that they have a strongly positive degree of association which suggests that they are from the same source. The geo-accumulation values for Cu in all stations ranged between (1 - 2.8 ppm) and it can be deduced that the sediments are moderately to strongly polluted. Pb varies between 1 and 2.1 suggesting that the sediments are moderately polluted. Zn exhibits strong pollution levels with a range from 2.5 and 3.5 ppm. Co is moderately polluted with 1.5 - 2.4 while Mn shows the highest level of pollution in all stations with Igeo values ranging between 4.1 and 5.8. This study showed that the Lagoon accumulates heavy metals as a result of anthropogenic activities evident in the dumping of municipal, sewage, industrial waste in the environment and domestic activities such as auto mobile transportation and mechanic repair workshop. Based on sediment quality guidelines, the Ologe Lagoon level of pollution ranged from Cu > Pb > Zn > Ni > Co > Mn > Cr > Al with Mn having the highest level of pollution.

Toxicological Assessment of <em>Chromoleana odorata</em>on <em>Clarias gariepinus</em>Juveniles

A study was carried out to investigate the toxicity effects of exposure of aqueous extract of Chromolaena odorata leave on gill/liver (histological) of juveniles catfish Clarias gariepinus. The leaves were harvested fresh, air dried for 7 days under ambient room temperature. 200 healthy juveniles catfish Clarias gariepinus specimen with average initial weight of 12.40 ± 2.46 cm (mean total length) and 8.26 ± 1.25 g (mean body weight) were exposed to aqueous extract of Chromolaena odorata leave at the concentration of 50, 100, 150, 200, 250 mg/l respectively. The physical reactions observed in the fish were: erratic swimming, gasping for air, loss of reflex, hyperactivities and skin discolorations which were more pronounced at high concentration and exposure time. The pH and dissolved oxygen significantly (P < 0.05) de-creased as the concentrations of C. odorata leaves extract increased. However, the values of Ammonia in the exposed media significantly (P < 0.05) in-creased as the concentrations of C. odorata leaves extract increased, compared to the control test medium. A high mortality rate was recorded, the histologi-cal conditions on gill and liver includes the deformation of gill tissue with overlapping of secondary lamella and disintegration of epithelial tissue lead-ing to diffuse mass of the gill lamella due to rapid cell lysis, gill clogging and gill structure disruption. Deformed primary and secondary lamella with dis-integrated gill filament, increasing vasculation, total fusion of gill filament lamella and filament length variation. Damage became severe with increasing concentration in C. odorata leaves to fish and exposure, while liver of Clarias gariepinus shows liver hepatocellular alteration and increase in hepatocyte disintegration, rupture blood cells in the entire cell with hemorrhage of the vessels and blur nature with severe breakage due to rupture.

Consequences of Direct Transfer to Fresh Water on the Blood Variables of Sarotherodon melanotheron(Rüppell,1852)

Alterations in blood variables of Sarotherodon melanotheron transmitted immediately from brackish water(salinity 13.71‰)to fresh water(salinity 0.12‰)were examined to evaluate the consequence of abrupt alterations in the environment on fish blood parameters.The results acquired revealed that significant reduction(p<0.05)in mean values of Haemoglobin(Hb)from 7.37±1.22 to 4.30±0.82dl-1;Packed Cell Volume(PCV)23.48±3.22 to 15.08±2.97%;Red Blood Cell(RBC)5.99±0.72 to 3.31±0.77 Cells x106;Mean Corpuscular Haemoglobin Concentration(MCHC)31.68±3.66 to 28.48±2.03 pg;and Platelets(PLT)195.44±16.77 to 138.99±9.05103 uL-1.However,notable elevation was recorded in the values of Erythrocyte Sedimentation Rate(ESR)from 4.89±0.16 to 10.58±1.48 mm/hr;White Blood Cell(WBC)27.03±2.96 to 33.09±3.72 x 109 L-1;Mean Corpuscular Volume(MCV)39.33±3.07 to 45.88±7.03 fL Neutrophils(NEUT)41.71±3.08 to 48.30±7.99%;Lymphocytes(LYMP)54.60±3.99 to 46.36±9.87%and Monocytes(MON)3.80±1.04 to 5.97±1.99%.These variations in the blood parameters were more perceptible in adult than juvenile fish.Results from this study consequently imply that direct transfer of fish to a region of lower salinity may have damaging effect on the physiology of S.melanotheron as observed in this study.