Spatial patterns in diversity and distribution of benthic molluscs in a weak tidal tropical lagoon in south-west Nigeria were investigated from samples collected in eight study stations distributed along the stretch of the lagoon for two consecutive years. The study also investigated selected environmental conditions of overlying water and sediment of the lagoon to establish the roles played by environmental variables. There was a significant variation (p < 0.05) in salinity values along the study stretch which was predicated on the existing gradient in salinity of the lagoon. Higher values of mud and Total organic content (TOC) of sediment occurred in upstream compared to values observed in downstream stations. Mollusc communities were significantly influenced by the spatial gradient in salinity and variability in sediment parameters. The downstream stations had brackish conditions, while the upstream stations were typically freshwater, leading to differences in the composition and abundance of molluscs. The downstream stations recorded higher density and diversity of mollusc compared to upstream stations. Our results suggest that benthic molluscs in Epe Lagoon show spatial patterns related to differences in environmental parameters.
Ologe and Badagry Lagoons are important tropical lagoons in Lagos, Nigeria. The water quality and heavy metal concentration were studied for a period of 2 years (Aug. 2016 to Jul. 2018) using standard methods. The least temperature obtained was 28.70±0.05 °C in Ologe Lagoon during the wet season and the maximum recorded was 29.41±0.08 in in Badagry Lagoon during the dry season. During the wet season (May- October) the temperature was steady and similar between the two connecting tropical lagoons. The salinity values vary at different stations in both Lagoon, 0.06 to 0.44 % in Ologe Lagoon and 0.08 to 0.28 % in Badagry Lagoon. Badagry Lagoon showed significant higher values in conductivity, total dissolved solid, chemical oxygen demand, biological oxygen demand, total suspended solid and total hardness across seasons. Heavy metal results showed that except for lead (0.25±0.10 mg/L), Ologe Lagoon had higher concentrations of all examined heavy metals (Zinc, copper, iron, chromium, lead, cadmium, manganese and cobalt) than Badagry Lagoon across season. Furthermore, cadmium, manganese and cobalt were not detected in Badagry Lagoon across season. The two studied connecting Lagoons especially Ologe Lagoon is exposed to dramatic deterioration in its water quality due to different wastes that discharge into the water body. These lagoons are clearly polluted by metals for various utilizations. As a result, the study suggests enforcing the controls on waste discharged into lagoons.
This paper reports an in-vivo account of the impact of thermal stress on the biomass and sizedistribution of estuarine populations of Pachymelania aurita in Epe Lagoon, Nigeria. Off all physicochemical variables investigated only water temperature was statistically different among study stations. A total of 7626 individuals of the organism comprising 2,371juveniles, 3586 immature adults and 2,034of spawning adults were collected from the study area. Highest populations of juveniles and immature adults occurred in station 3 where the highest water temperature occurred while, station 1 recorded lowest populations of the two size classes. Spawning adults occurred in highest number in station 2 while their lowest population was observed in station 3.Of the total biomass of 2491 g recorded, juvenile population recorded a total biomass of 143.401 g, immature adults contributed 874.424 g while spawning adults recorded 1473.19 g. Highest juvenile biomass (34.7 g) occurred in station 5 while, the least (17.7 g), was recorded in station 1. Station 3 accommodated the highest biomass (233.60 g) of immature adults and the least biomass for this group was observed in station 1.Biomass of the spawning adults was highest (475.08 g) in station 2 and the lowest biomass (162.03 g) for this class was observed in station 3. The elevated water temperature observed in station 3 affected the growth of the organism such that only few individuals developed to spawning adult. It is therefore important that, the regulatory agencies should carry out regular monitoring of cooling water discharge from Egbin Power Station to ensure compliance with stipulated laws. © JASEM https://dx.doi.org/10.4314/jasem.v21i5.1
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