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Western Indian Ocean Journal of Marine Science
Number of Followers: 1

This is an Open Access Journal

Open Access journal
ISSN (Print) 0856-860X
Published by African Journals Online

[261 journals]

Supplementation of probiotics in Nile tilapia fingerling cultivation
subjected to microbial challenge
- Authors: Angélica A. Jossefa, Ivan C. Nerantzoulis, Aidate Mussagy
  Pages: 1 - 9
  Abstract: The intensification of aquaculture has brought about the need to find alternative feed supplement sources to reduce production costs. One of the alternative sources of feed in fish farming is animal manure. However, the use of animal manure may cause health problems in fish cultures. The objective of this study was to determine the effects of probiotics on Nile tilapia fingerlings subjected to microbial challenge using swine manure. Three hundred (300) fingerlings weighing 2±0.05g and measuring 5±0.06 cm, were distributed among four treatments with three replications each. Swine manure was inoculated in water in the proportion of 10 % of fingerlings live weight. Probiotics Saccharomyces cerevisiae and Lactobacillus plantarum were used as ration supplements in the proportions of 0.5 % per 100 g of ration. The results showed no significant differences (P>0.05) in terms of growth between treatments. The inclusion of S. cerevisiae reduced the number of pathogenic bacteria in the intestine of fingerlings and resulted in better production performance. Feed supplementation with L. plantarum had no effect, neither on production, nor on intestinal microbial population. The fingerlings under study showed typical signs of yersiniosis, edwardiellosis and mycobacteriosis. From the experiment it was concluded that the supplementation of the probiotic S. cerevisiae on the Nile tilapia fingerlings treated with swine manure showed a positive effect in the sense that this probiotic avoided the intestinal colonization of fingerlings by pathogenic bacteria. Additionally, the presence of the probiotic seems to promote better grow performance and hence reinforce the results of previous studies on the role of probiotics in aquaculture. More experimental studies are required, particularly in situ experiments, with the addition of other performance analyses linked to the immune response of the fingerlings.
  PubDate: 2023-02-27
  DOI: 10.4314/wiojms.v21i2.
  Issue No: Vol. 21, No. 2 (2023)
Retained fish catches of artisanal fishers is dependent on fishing area,
season and fishing gear type: A case study from the south coast of Kenya
- Authors: Athman Mwakaribu, Cosmas Munga, Mumini Dzoga, Paul Njihia, Danny Mulala
  Pages: 11 - 23
  Abstract: The artisanal fishery is one of the sources of livelihood along the Kenya coast. Catches of retained fish of artisanal fishers between two fishing areas on the south coast of Kenya were compared. Artisanal fishers usually retain a portion of their daily catch which is reserved for family consumption while the rest is traded for cash to meet other family needs. This study hypothesized that retained fish catches were influenced by fishing area, fishing gear type and season. Daily fish landings and retained fish catches among artisanal fishers were monitored between August 2020 to July 2021 covering the South East Monsoon (SEM) and North East Monsoon (NEM) in Msambweni and Vanga fishing areas. A total of 60 fishers (30 for each area) were randomly selected and their retained catch monitored on a daily basis. The overall total fish landings were 23.3 tons and 210 tons in Msambweni and Vanga, respectively. The mean catch rate at Msambweni was 3.3 ± 0.12 kg.fisher-1day-1 in the NEM season and 2.2 ± 0.09 kg.fisher-1day-1 in the SEM season. Fish catch rates in Vanga was 8.5 ± 0.28 kg.fisher-1day-1 in the NEM season and 7.9 ± 0.29 kg.fisher-1day-1 in the SEM season. A total of 0.98 tons (only 4.2 %) of fish was retained versus 22.32 tons (95.8 %) not retained by the artisanal fishers in Msambweni, while in Vanga a total of 1.64 tons (only 0.78 %) was retained versus 208.36 tons (99.22 %) not retained. Retained fish catch varied significantly with season and type of fishing gear used (p < 0.05). Among the retained species in Msambweni, Siganus sutor made the highest contribution (53 %), followed by Lethrinus mahsena, (5.08 %). The species Euthynnus affinis and Sphyraena obtusata were mostly retained in Vanga with a contribution of 10.4 % and 10.2 %, respectively. The same retained fish species represented the most abundant species in the overall fish landings, however sizes were significantly smaller than those not retained by fishers (p < 0.05). Results of non-Metric Multidimensional Scaling (nMDS) ordination showed differences in species composition between fishing areas, seasons and fishing gear types with implication on fishers’ retained catches.
  PubDate: 2023-02-27
  DOI: 10.4314/wiojms.v21i2.
  Issue No: Vol. 21, No. 2 (2023)
Zoonotic helminths and protozoa infesting commercially important marine
crustaceans along the Kenyan coast
- Authors: Valarie N. Silali, Fredrick C. Maloba, Thomas K. Mkare
  Pages: 25 - 32
  Abstract: Marine crustaceans support important small-scale fisheries along the Kenyan coast. Annual catches have been declining, with climate change, pollution, overfishing and parasites proposed as causes. It is unknown whether parasite intensity and diversity change between locations, sea - sons and host species. The current study aimed to address this by analysing gastro-intestinal (GIT) parasites of two prawn species, Penaeus indicus and Metapenaeus monoceros, and two lobster species, Panulirus ornatus and P. homarus. A total of 240 prawns and 240 lobsters were collected from Malindi, Kilifi and Gazi, and intestinal contents microscopically examined for the presence of parasites. Observed parasites included Schistosoma mansoni (mean egg per gram (EPG) of 112.33), Strongyloides spp. (mean EPG of 94.80), Hymenolepis diminuta (mean EPG of 104.55), and Hymenolepis nana (mean EPG of 104.85). The Protozoa Entamoeba coli (mean EPG of 75.76) was observed. There was a significant difference in parasite intensity among host species (p < 0.00) as well as intensity between seasons. There was no significant difference in intensity among landing sites, except in E. coli (p = 0.05). Parasite diversity was not dependent on sites or seasons but varied with host species. The current study found that all the GIT parasites identified are zoonotic and could present a human health threat.
  PubDate: 2023-02-27
  DOI: 10.4314/wiojms.v21i2.
  Issue No: Vol. 21, No. 2 (2023)
Free-living marine nematode communities in Rhizophora mucronata Lam.
(Rhizophoraceae) forest at Mida Creek, Kenya
- Authors: Beth W. Waweru, Agnes W.N. Muthumbi, Ann Vanreusel, Virginia Wangondu, Amos Mutua
  Pages: 33 - 43
  Abstract: Nematodes are among the most abundant organisms in marine ecosystems where they play a critical role in nutrient cycling, provision of nourishment to the higher organisms in the food web, pest control, and act as disease-causing vectors. This study determined the abundance and community structure of nematodes in three plots of Rhizophora mucronata forest stand at Kirepwe Macho and Dabaso sites at Mida Creek, Kenya. Replicated sediment samples were randomly collected from one forest plot in Kirepwe Macho and two plots in Dabaso during the months of January and April 2011. Total organic matter, sand and silt proportions were not significantly different across the study sites and between January and April. A total of 90 and 81 nematode genera were encountered in the month of January and April, respectively. At both sampling times, the nematode community was dominated by Terschellingia (20.5 % - 15.3 %) and Paracomesoma (10.6 % - 6.6 %). The Shannon-Weiner diversity index was relatively high in the three forest plots both in January and April ranging from 2.76 to 3.40. There was no significant difference in nematode community assemblage within sites (p > 0.05, 0.901) but there were differences between sampling time (p > 0.05, 0.001). The results showed that the three sites had similar nematode community structure suggesting that the three Rhizophora mucronata mangrove forest plots did not differ in terms of nematode generic composition even though the plots were not all close to each other.
  PubDate: 2023-02-27
  DOI: 10.4314/wiojms.v21i2.
  Issue No: Vol. 21, No. 2 (2023)
Seasonality of Fish Juvenile Community Structure and Diversity in a
Tropical Seagrass Meadow of Watamu, Kenya
- Authors: Alphine Mboga, James Mwaluma, Rose Kigathi, Bernards Okeyo, Noah Ngisiange, Jibril Olunga, Monika Winder, Margareth Kyewalyanga
  Pages: 45 - 56
  Abstract: Seagrass are important marine habitats that function as nursery grounds for juvenile fish. Human activities and other natural factors have contributed to their decline, and this has compromised their role as nurseries, specifically in non-continuous patchy seagrass beds. In this study, juvenile fish abundance from tropical seagrass beds of Watamu were examined, while testing the hypothesis that seagrass cover and seasonality influenced juvenile fish abundance
  and diversity. Two sampling stations were identified, Watamu Blue Lagoon (WBL) and Watamu Beach (WB), based on seagrass cover, and were sampled for a period of 10 months that included two south-east monsoon (SEM) and two north-east monsoon (NEM) seasons. Monthly samples were collected by seining within the shallow seagrass habitats of WBL and WB. A total of 31 juvenile fish families were obtained, the dominant taxa being Lutjanidae and Siganidae. Seasonal and interannual variability in juvenile abundance was observed over the two years (p<0.05); year 1 recorded higher abundance than year 2, specifically during the SEM. In year 2 a higher mean abundance was recorded during the NEM when compared to the SEM. Chlorophyll a (p<0.05) and salinity (p<0.05) were found to significantly influence juvenile fish abundance.
  PubDate: 2023-02-27
  DOI: 10.4314/wiojms.v21i2.
  Issue No: Vol. 21, No. 2 (2023)
Simulation of spatiotemporal interannual variability of oceanic subsurface
temperature off East Africa
- Authors: Majuto C. Manyilizu
  Pages: 57 - 70
  Abstract: The oceanic subsurface variability off East Africa in the tropical western Indian Ocean plays a crucial role in ocean dynamics and living resources as well as weather and climate variability. A regional ocean model is applied to understand the oceanic subsurface interannual variability off East Africa. The region with the highest sea surface temperature (SST) variability in the offshore region lies adjacent to strong subsurface temperature variations located between 30 and 130 m corresponding with strong variations in the thermocline depth. The weakest SST variations in the Tanzanian shelf waters lie over the subsurface waters with the smallest temperature variations in the upper 200 m with weak variations in the thermocline depth. Such signals are associated with induced forcings from the Indian Ocean Dipole (IOD) and El Niño-Southern Oscillation (ENSO) in both regions with different intensity and peaking times. The IOD-induced forcings are weaker, evolving in October and November-December in the region with the weakest and strongest SST variations, respectively. However, relatively stronger ENSO-induced forcings occur in both regions with stronger signals in the region with the strongest SST variations throughout the years except in August, and it peaks in January. The ENSO-induced forcings occur in January to May peaking in March and April in the region with the weakest SST. Consequently, anomalous Rossby waves as well as local Ekman downwelling and upwelling associated with both large-scale modes occur in the region leading to the subsurface temperature variations.
  PubDate: 2023-02-27
  DOI: 10.4314/wiojms.v21i2.
  Issue No: Vol. 21, No. 2 (2023)
Caudal fin as a proxy for dorsal muscle for nutrient enrichment monitoring
using stable isotope analysis: the case of Gerres filamentosus and G.
oyena from mangrove creeks of Tanzania
- Authors: Blandina R. Lugendo, Mathias M. Igulu, Masumbuko L. Semba, Ismael A. Kimirei
  Pages: 71 - 81
  Abstract: The use of fish dorsal muscles in stable isotope studies, which is an invasive method that results in fish deaths, limits their applicability for rare and endangered fish species, as well as when large sample sizes and replicates are required, prompting research into feasible non-lethal sampling methods. The possibility of employing fin clippings (a non invasive approach) was investigated as a proxy for dorsal muscle in nutrient pollution monitoring studies using two common mangrove fish species, namely Gerres filamentosus and G. oyena, which are known to spend their early life stages primarily within mangroves. The dorsal muscles and caudal fin tissues of fish from the mangrove creeks of Kunduchi and Mbegani, Tanzania, were examined for 13C and 15N signatures. Dorsal muscles from Kunduchi (mean SD: 13C = -16.8 ± 2.86, 15N = 9.34±1.15) were more enriched than from Mbegani (mean SD: 13C = -18.60 ± 2.11, 15N = 7.27±1.09), and this enrichment was consistent across the two studied species. Caudal fins indicated similar enrichment trends. Fin tissue stable isotope values explained between 62 % and 87 % of dorsal muscle 13C and between 89 % and 98 % of dorsal muscle 15N variability. These findings support the use of fin-clipping as a non-lethal proxy for stable isotope analysis of the studied species for nutrient enrichment, and additional research into non-lethal sampling methods is recommended.
  PubDate: 2023-02-27
  DOI: 10.4314/wiojms.v21i2.
  Issue No: Vol. 21, No. 2 (2023)
Artificial reef structures and coral transplantation as potential tools
for enhancing locally-managed inshore reefs: a case study from Wasini
Island, Kenya
- Authors: Jelvas M. Mwaura, Dishon Murage, Juliet F. Karisa, Levy M. Otwoma, Hashim O. Said
  Pages: 83 - 94
  Abstract: Many severely degraded reefs in the western Indian Ocean region show no signs of natural recovery and have remained for decades as barren, unconsolidated coral rubble fields with depleted commercially important fish groups. Consequently, several restoration techniques have been designed and developed to mitigate the localized impacts on coral reefs. Evaluating the efficacy of combined use of artificial reef structures and coral transplantation in enhancing habitat and recovery of key functions in severely degraded reefs is key to improved conservation of coral reefs. In this study, the survivorship rate of corals transplanted on reef structures is assessed, and changes in coral and fish abundance on artificial reef units and nearby natural reefs over time are compared. Coral cover on artificial reef structures increased from a mean of 17 % one year after initial attachment of fragments to 41 % after two years, with Acropora corals providing the highest cover. The artificial reef structures were also rapidly colonized by reef fish, with fish densities of 18±13 indiv./100 m2 showing an increase of about three fold higher than on natural reefs after two years. Greater numbers of commercially important fish groups (e.g., Lutjanids and Acanthurids) were observed on artificial reefs while natural reefs harboured more small sized fish (Pomacentrids and Labrids). These findings provide insights for artificial reef projects that are capable of restoring the regenerative capacity of the human-induced coral rubble beds.
  PubDate: 2023-02-27
  DOI: 10.4314/wiojms.v21i2.
  Issue No: Vol. 21, No. 2 (2023)
Local perceptions, opportunities, and challenges of community-based
ecotourism in Gazi Bay, Kenya
- Authors: Robert M. Runya, Nicholas J. Karani, Agnes Muriuki, Donald M. Maringa, Anne W. Kamau, Nelly Ndomasi, Ken Njagi, Cosmas Munga, Judith A. Okello
  Pages: 95 - 108
  Abstract: Community Based Ecotourism (CBET) has the potential to both improve the conservation status of mangrove ecosystems and stimulate local economies. However, these ecotourism initiatives often fail due to a lack of active local participation, poor management and a lack of an appropriate benefit sharing scheme. This paper explores perceptions, opportunities and challenges of community mangrove-based ecotourism in Gazi Bay, Kenya. Data collected from household surveys, key informant interviews and focus group discussions were used to examine local perceptions, challenges and opportunities with respect to their participation in ecotourism as a tool for mangrove conservation. The results obtained indicated that 81.4 % of the Gazi village community was aware of the ecotourism activities being undertaken in the area with 62.8 % acknowledging the socio-economic as well as the environmental impacts of the ecotourism activities. Also, 66.0 % of the local community identified cultural traditions and local skills possessed by the community as having the potential to promote sustainable ecotourism activities in the area. For the design and implementation of any ecotourism venture and the management of mangroves to be sustainable, including that undertaken by the Gazi community, this study recommends prioritising effective local participation and capacity building. In addition, private sector involvement is essential for the mobilisation of resources to further enhance the management and conservation of mangroves in the long-term. The results provide key insights needed not only to improve the design and management of community-led marine conservation initiatives but also for ensuring that optimal conservation benefits are achieved.
  PubDate: 2023-02-27
  DOI: 10.4314/wiojms.v21i2.
  Issue No: Vol. 21, No. 2 (2023)
A checklist of the southwestern Madagascar sponge fauna with taxonomic
updates based on the current systematics
- Authors: Aro Ny A. Razafinampoinarivo, Thierry Pérez, Nicole Boury-Esnault, Lantoasinoro Ranivoarivelo, Cécile Fauvelot
  Pages: 109 - 129
  Abstract: Sponges are important components of coral reefs with diverse ecological roles. They can be dominant in certain ecosystems of the western Indian Ocean (WIO) region, but their biodiversity remains poorly studied. Most of the knowledge from this region originates from studies conducted 50 years ago in the South Western (SW) region of Madagascar, near Toliara, prior to the degradation of coral reefs and associated ecosystems caused by large environmental disturbances. Here, a reference list is presented including all sponge species that were recorded at that time in different marine habitats of Toliara. This state-of-the-art work includes taxonomic updates. So far, the sponge fauna of Toliara accounts for 267 species, belonging to 3 classes, 23 orders and 68 families, a remarkable diversity when compared to other tropical locations. More than 50 % of the past taxonomic names needed to be updated and with this new baseline it will be possible to allow assessment of long-term changes in sponge biodiversity in relation to environmental stressor changes that have occurred in the SW of Madagascar during the last 50 years.
  PubDate: 2023-02-27
  DOI: 10.4314/wiojms.v21i2.
  Issue No: Vol. 21, No. 2 (2023)
Comparative assessment of the impacts of artisanal trolling and industrial
longlining on yellowfin tuna exploited off the Kenyan coast
- Authors: Almubarak A. Abubakar, Gladys M. Okemwa, Edward N. Kimani
  Pages: 131 - 140
  Abstract: The Indian Ocean yellowfin tuna stock has been classified as overfished and remains subject to overfishing by industrial and artisanal fleets despite the implementation of catch reduction measures to rebuild the stocks. This study assessed the impacts of artisanal trolling and industrial pelagic longlining on the population structure of yellowfin tuna exploited in Kenyan waters. Catch data including fork length, sex and gonad maturity was examined for the two fisheries between April 2019 and April 2021. Selection patterns were then compared using eight length-based indicators and a suite of indicator ratios. Results showed that artisanal trolling caught smaller individuals ranging from 32−177 cm with a mean of 76 ± 0.5 cm and a mode of 71 cm. The industrial fishery caught significantly larger individuals (p > 0.05) ranging from 52 – 204 cm with a mean of 137 ± 0.7 cm and a mode of 160 cm. Length at first capture (Lc) for artisanal trolling was estimated at 36 cm and 80 cm for the industrial fishery. Statistical tests further revealed significant differences in length distribution and selectivity curves. It was clear that the fisheries consistently captured distinct components of the yellowfin tuna population structure. The industrial fishery was dominated by mature individuals above length at 50 % maturity (>100 cm, L50) constituting 90 % of the sampled catch of which 56 % were large mega-spawners above the optimum length (> Lopt + 10%). On the other hand, 92 % the artisanal trolling fishery constituted small individuals below L50 and no mega-spawners. Overall, the average monthly sex ratio was skewed to males (F:M ratio = 1: 1.14). Deviations from the expected 1:1 sex-ratio were not significant; however, industrial longline catches were skewed towards large males, and artisanal trolling catches towards small females. The study illustrates application of widely used lengthbased approaches to derive insights on fishery interactions in data limited scenarios.
  PubDate: 2023-02-27
  DOI: 10.4314/wiojms.v21i2.
  Issue No: Vol. 21, No. 2 (2023)
Tidal cycle and time of day control pH levels in coastal habitats of the
western Indian Ocean: the case of Mnazi and Chwaka Bays in Tanzania
- Authors: Rushingisha George, Blandina R. Lugendo
  Pages: 141 - 150
  Abstract: Ocean acidification, a progressive decrease in the pH and change in the carbonate chemistry of seawater caused by the uptake of carbon dioxide (CO2) from the atmosphere, is a growing crisis that threatens marine species. pH data relevant to a species’ natural habitat in the coastal waters of the western Indian Ocean (WIO) is still sparse, limiting the capacity to undertake manipulative studies to better understand the impacts of ocean acidification on marine species. This study investigated tidal and day-night pH variations in mangrove, seagrass, and coral reef habitats of the WIO by using Tanzania as a case study. The mean pH of the studied coastal habitats was highest in seagrass (8.49 ± 0.29), followed by coral reef (8.33 ± 0.06), and lowest in mangrove (8.20 ± 0.17). Seagrass habitats had the highest pH (9.06) during the day at low spring tides, mangrove habitats had the highest pH (8.45) during the day at high spring tides, and coral reef habitats had the highest pH (8.47) during the day at low tides. Seagrass habitats had the widest pH range (1.03), followed by mangrove habitats (0.54), while coral reef habitats had the narrowest range (0.23). The water with the highest pH during the day was transported to nearby mangrove habitats during incoming tides and to coral reef habitats during outgoing tides, resulting in the highest mean pH in mangrove and coral reef habitats during spring high and low tides, respectively. pH within the seagrass habitats correlated strongly and positively with changes in temperature (r=0.80), dissolved oxygen (r=0.84), and salinity (r=0.72), while pH in mangrove habitats correlated moderately and positively with dissolved oxygen (r=0.59). This study provides in-situ evidence on the pH fluctuations in the WIO’s coastal habitats over time and space, with water from seagrass habitats capable of raising the pH of water in nearby mangrove and coral reef habitats during the day, thereby potentially helping in the mitigation of the effects of ocean acidification on these habitats.
  PubDate: 2023-02-27
  DOI: 10.4314/wiojms.v21i2.
  Issue No: Vol. 21, No. 2 (2023)