Browsing by Author "Nehemia, Alex"

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Ecological impact of salt farming in mangroves on the habitat and food sources of austruca occidentalis and littoraria subvittata
(Elservier, 2019) Nehemia, Alex; Chen, Margaret; Kochzius, Marc; Dehairs, Frank; Brion, Natacha
The impact of salt farming on the habitats and food sources of Austruca occidentalis and Littoraria subvittata was studied in mangroves along the coast of Tanzania using stable isotopes ( 13 C and 15 N) and sediment particle size analysis. The 13 C and 15 N stable isotope composition in mangrove leaves, sediments and invertebrate tissues, were used to evaluate whether there are differences in feeding ecology of the crab Austruca occidentalis and the snail Littoraria subvittata collected from natural mangroves and mangroves around the salt ponds. Organic C, total N content and particle size distribution in sediments were used to assess if there are differences in habitat characteristics of mangroves around the salt ponds. Mangrove leaves and sediments were found to be 13 C en- riched around salt ponds compared to those from natural mangroves. Likewise the macroinvertebrates collected from mangroves around salt ponds were found be enriched in 13 C relative to undisturbed mangroves. In addition, mangrove sediments around salt ponds were poorer in organic carbon and nitrogen and had more sand content compared to sediments from natural mangroves. These results indicate that salt pond activities have contributed to the modification of the habitats of macroinvertebrates by causing δ 13 C stable isotopes enrichment and al- teration of sediment characteristics in the ecosystem.
Genetic erosion in the snail littoraria subvittata (reid, 1986) due to mangrove deforestation
(Journal of molluscan studies, 2016) Nehemia, Alex; Huyghe, Filip; Kochzius, Marc
In tropical coastal ecosystems mangrove forests are important as feeding, spawning, breeding and nursery grounds for many marine species. High human population pressure in coastal areas has led to the loss and deterioration of mangrove habitats. Solar salt production can affect these habitats along the East African coast. Littorinid snails live on mangrove trees, forming an important component of the mangrove ecosys- tem and have been used as bioindicators of environmental health and community stress. Littoraria subvittata is the most abundant littorinid species in mangroves along the East African coast. Partial mitochondrial cytochrome oxidase subunit 1 (COI) gene sequences of 298 individuals were used to assess the impact of mangrove deforestation at salt ponds on the genetic diversity and structuring of L. subvittata populations, as well as to infer the demographic history of the species. Nucleotide and haplotype diversities were found to be lower in samples from mangroves at salt ponds than in samples from natural mangroves. The mean nucleotide diversity was 0.049 ± 0.036% and 0.115 ± 0.068% in mangroves at salt ponds and natural mangroves, respectively. The mean haplotype diversity was 0.23 ± 0.14 and 0.50 ± 0.14 in mangroves at salt ponds and natural mangroves, respectively. Analysis of molecular variance (AMOVA) detected a sig- nificant population structure (Ф st = 0.049; P < 0.0001) for the combined populations. Hierarchical AMOVA detected a significant population genetic structure only between populations from mangroves at salt ponds and natural mangroves (Φ ct = 0.022; P < 0.05), but not between any other groupings. Populations from natural mangrove sites showed a significant genetic structure (Ф st = 0.054, P < 0.0001), while populations from sites at salt ponds could not be differentiated (Ф st = −0.0026, P = 0.64). Reduced effective population size was observed in most samples from mangrove sites at salt ponds compared with natural mangrove. The direction of migrants was mostly from salt ponds to natural mangroves. These results show that salt ponds have a negative impact on the genetic diversity of L. subvittata populations and modify the population’s genetic structure.
Length-Weight relationship and condition factor of tilapia species grown in marine and fresh water ponds
(Agriculture and Biology Journal of North America, 2012) Nehemia, Alex; Maganira, Justin D.; Rumisha, Cyrus
The aim of this study was to describe the differences in Length-Weight relationship and condition factor of Tilapia zillii and Oreochromis urolepis urolepis reared in full strength sea water (FSSW) and fresh water (FW) ponds. The environmental condition in FSSW and FW ponds were also analyzed to determine their impacts on Length-Weight relationship and condition factor on both species. The regression coefficient "b" exhibit negative allometric growth in FW and positive allometric growth in FSSW for both species. The value of exponent "b" and condition factor (K) for T. zillii in FW and FSSW (in the bracket) were found to be 2.94 (3.3) and 2.07 (0.74) respectively. On the other hand the value of exponent "b" and condition factor (K) for O. urolepis urolepis in FW and FSSW (in the bracket) were found to be 2.81 (3.46) and 0.86 (0.53) respectively. Though both species performed well in FW, the study also revelead that farming of these tilapia species in FSSW can be feasible if water quality parameters are properly monitored.
Reduced genetic diversity and alteration of gene flow in a fiddler crab due to mangrove degradation
(PLOS, 2017) Nehemia, Alex; Kochzius, Marc
The fiddler crab Austruca occidentalis is a dominant species in mangrove forests along the East African coast. It enhances soil aeration and, through its engineering activities, makes oth- erwise-inaccessible food available for other marine organisms. Despite its importance, the hab- itat of A. occidentalis is threatened by human activities. Clearing the mangroves for salt farming and selective logging of mangroves trees continue to jeopardise mangrove ecosystems in the Western Indian Ocean. This study aims to use partial mitochondrial COI gene sequences and nuclear microsatellites to determine whether salt farming activities in mangroves have a nega- tive impact on the genetic diversity and gene flow of A. occidentalis collected along the Tanza- nia coast. The level of genetic diversity for both mitochondrial DNA and nuclear microsatellites are relatively lower in samples from salt ponds compared to natural mangrove sites. Analysis of molecular variance (AMOVA) among all populations showed low but significant differentia- tion (COI: F st = 0.022, P < 0.05; microsatellites: F st = 0.022, P < 0.001). A hierarchical AMOVA indicates lower but significant genetic differentiation among populations from salt ponds and natural mangroves sites (COI: F ct = 0.033, P < 0.05; microsatellites: F ct = 0.018, P = < 0.01). These results indicate that salt farming has a significant negative impact on the genetic diver- sity of A. occidentalis. Since higher genetic diversity contributes to a stable population, restoring the cleared habitats might be the most effective measures for the conservation of genetic diver- sity and hence adaptive potential to environmental change in this species.
Survival and growth of tilapia zillii and oreochromis urolepis urolepis (Order perciformes; Family cichlidae) in seawater
(Western Indian Ocean J. Mar. Sci, 2014) Nehemia, Alex; Mmochi, Aviti; Mtolera, Matern
The potential for Tilapia zillii and Oreochromis urolepis urolepis culture in seawater was evaluated by determining their survival and growth in seawater at 35‰. Fingerlings were collected from Pangani River using seine nets and reared in 1 m 3 concrete ponds after acclimatization from salinity of 2‰ to 35‰. Fingerlings were also reared in freshwater as controls. Fingerlings were fed twice daily using commercial fish feeds (White Rose floating pellets), initially at a rate of 5% of their total body weight (TBW) and 10% of their TBW after two weeks. Their growth rate (length and weight) was recorded weekly except controls for handling, their growth being recorded at the beginning and end of the experiment. The average weight gain (g.week -1 ), percentage weights gain (week -1 ) and specific growth rate (SGR, %.day -1 ) were determined in freshwater and seawater. There was no significance difference (p >0.05) in the SGR between the two species in seawater. The survival rates of O. urolepis urolepis were 100% in freshwater and seawater and 89% and 96% respectively for T. zillii. This study showed that T. zillii and O. urolepis urolepis can survive and grow in seawater but the former is a better candidate for mariculture.