First evaluation of coral recruitment in Madagascar

The distribution of larvae and recruitment of scleractinians in the southwest region of Madagascar were evaluated for the first time between October 2013 and September 2014 at 3 sites. The presence of coral larvae (planulae) was monitored through weekly sampling using a plankton net and the recruitment rate evaluated by monthly sampling of the newly settled corals (<1 year stage) on recruitment tiles and by a monitoring of the recruitment of juveniles (1< Juveniles < 2 years) using the quadrat method. Planulae were present in the plankton for 9 months during the survey. The recorded mean annual density of planula varied from 0.43 ± 0.41 larvae m-3 to 3.23 ± 5.72 larvae m-3 depending on site, with a peak in larval density towards the end of November and the beginning of December. The variability in the occurrence of planula is very high and implied that the density observed in the year does not present a significant difference between the sites (pKW=0.33). The average density of total recruits was 620.13 ± 621.30 recruits m-2, 40.28 ± 50.97 recruits m-2 and 36.34 ± 33.82 recruits m-2, respectively at the sites of Nosy Tafara, Grande Vasque and Rose Garden. Seasonal distribution of coral recruitment was different between the sites. The mean annual density of newly settled recruits (< 1 month stage) was significantly higher at Nosy Tafara with 94.91±101.08 recruits m-2 compared to Grande Vasque and Rose Garden with 18.75±34.32 recruits m-2 and 11.57±18.47 recruits m-2 (pKW<0.001), respectively. The highest density of newly settled recruits was observed between October to December. Higher density of recruits was also observed in March at Nosy Tafara and in May at all three sites. Results of juvenile monitoring showed high rates (> 10 juveniles m-2) compared to other regions and the threshold, but it revealed high mortality among recruits. Coral recruitment in the southwest region of Madagascar was found to be high and could result in increased resilience of the coral reef assemblages.

Impact of a ring net fishery in the inshore marine waters of Kilifi on the reproductive biology of six pelagic fish species

Ring nets are modified purse seines used for pelagic fishing along the Kenya coast. This method is however associated with potential negative environmental implications in inshore and shallow fishing grounds. Biological impacts on selected pelagic species caught in the marine waters of Kilifi were investigated during the Southeast Monsoon season (SEM) in April, May and September 2014, and the Northeast Monsoon season (NEM) in October and November 2014, and March 2015. Amblygaster sirm, Rastrelliger brachysoma, Sardinella gibbosa, Rastrelliger kanagurta, Hemiramphus far and Sphyraena obtusata were the most abundant species caught by the ring nets and comprised 68.9 % of fish catch composition. Analysis of ring net impacts on the fish sizes and maturity status were conducted for the NEM and SEM seasons. The catch composition for A. sirm in October comprised of 53.3 % juveniles and 53.4 % juveniles for S. obtusata in November. High percentages of H. far (78.3%) and S. obtusata (58.9 %) were captured in September. Incidences of undersize fish for A. sirm, S. gibbosa, R. kanagurta and R. brachysoma were observed across the seasons. Sex ratios for A. sirm, R. brachysoma, R. kanagurta and S. obtusata in the NEM season deviated from a normal ratio of 1:1 with more males observed. Females were dominant in the catch for H. far (1: 1.28) but the ratio was not different for S. gibbosa (χ² = 5.564, df = 1, p = 0.21). Males were dominant for A. sirm (1: 0.8) and S. gibbosa (1: 0.7) in the SEM season but the ratios were not different for H. far, S. obtusata, R. brachysoma and R. kanagurta. Differences in sex ratios were attributed to fish migrations and reproductive processes. Ring nets fished relatively offshore during the NEM season and targeted mainly spawning aggregations in stage IV. Immature fish in stage I and II which comprised of juveniles were harvested within sheltered inshore waters in the SEM season. Use of ring nets to target juveniles and spawning aggregations may disrupt recruitment processes. To enhance sustainable management of the ring net fishery, there is a need to develop harvesting strategies based on the information on stock status of the target fish.

Quick and cost-effective mapping of subsistence and artisanal fishing areas within and adjacent to a marine protected area

Spatial information on artisanal fisheries is largely lacking, making subsequent management and threat or impact assessments difficult. Local knowledge, current and readily available mapping software and Global Positioning System (GPS) techniques were used to map small-scale (subsistence and artisanal) fishing areas within and adjacent to the western boundary of the Ponta do Ouro Partial Marine Reserve in southern Mozambique. Data on habitat types were collected in the field and combined with available literature. Thirty-one fishing areas were identified and mapped resulting in a total area of 293.1 km2 with a perimeter of 396.7 km, from the Inhaca Island lighthouse in the north to the Maputo River mouth in the south. Habitats within the fishing areas included isolated intertidal sand banks, seagrass beds, estuarine channels, as well as intertidal muddy areas adjacent to the coast. The fishing areas covered on average 9.5 km2 (SD=12.0) and varied immensely in size (0.3–50.1 km2). Overall, 58.4 % (171.2 km2) of the total fishing area mapped was located inside the reserve. Costs associated with data collection equated to an average of U$D 3.61 per mapped km2 or U$D 2.63 per km tracked. The method was found to be quick, cost-effective and easily replicable elsewhere.

Presence of microplastics in jellyfish (Crambionella orsini) along the Kenyan coast

Microplastics are plastic particles less than 5 mm in diameter. These plastics mostly result from degradation of larger plastics. Due to their small size, they are often accidentally ingested by sea faunas, particularly the deposit and filter feeders. However, information on the ingestion of microplastics by sea fauna such as jellyfish is rare. This paper provides evidence of ingestion of microplastics by jelly fishes (Crambionella orsini) along the Kenyan Coast. Samples were taken from three stations (Mikindani and Makupa in Mombasa, and Dabaso in Mida Creek) between 31st January 2018 and 3rd February 2018 using tow nets. Samples were digested using 10 % KOH at 60 °C for 24 hrs and sieved through a 38 µm sieve. Products below 38 µm were filtered using a 0.8 µm Whatman filters, then dried in an oven and viewed under a dissecting microscope for microplastics. Suspected microplastics were confirmed using a hot needle test. Microplastics obtained were mainly fibres of different colours: black, blue, green, colourless, purple, red and yellow. Colourless fibres were the majority accounting for 53 % of the total number of fibres while purple fibres were the least at only 1 %. Mean concentration of microplastics was highest in Dabaso (0.05 mp/g of tissue), whereas in Mikindani and Makupa were almost equal (i.e., 0.03 ± 0.003 mp/g in Mikindani, and 0.03 ± 0.01 mp/g in Makupa). Statistically, the means were not significantly different between the stations (F1, 2 = 1.34; P = 0.43). This study presents evidence of contamination of the Kenyan coastal waters by microplastics and their ingestion by sea fauna such as jellyfish. Results of this study will help reinforce the plastic ban in the country to prevent further accumulation in the environment.

Fibropapillomatosis infection in a population of green turtles at Watamu Bay, Kenya

Anthropogenic stressors from onshore and offshore activities can act as driving factors of disease for a wide range of marine organisms. Green turtles (Chelonia mydas) are prominently afflicted with a tumour-causing disease known as fibropapillomatosis (FP) caused by the chelonid alphaherpesvirus ChHV5. Previous studies indicate that pathways of FP transmission may be genetic (vertical transmission) or linked to causal factors in a turtle’s environment (horizontal transmission). In this paper patterns of FP prevalence were examined in 10,896 records of green turtles caught or found stranded around Watamu Bay, Kenya, between 2003 – 2020. Findings were focused on locational and seasonal factors that may potentially influence infection. The findings show that FP prevalence varies significantly on an annual basis. Location significantly influenced infection prevalence, with prevalence higher in open ocean sites than sites located within the creek. Infection prevalence was highest at sites around the creek mouth and north of the creek mouth, with both regions exhibiting disparate annual patterns of infection. This paper is the first to examine long-term trends of FP prevalence in-depth in this region and has implications for the health of turtles and marine biota found along the Kenyan coast, and potentially within the wider Western Indian Ocean region. The findings emphasize the need to distinguish the infection pathways of causative agents via: i) further examination of the links between infection and environmental and/or biont community factors; and ii) the collection of data pertinent to the genetic diversity of green turtles and associated ChHV5 viral strains occurring in the Western Indian Ocean.

Efficacy of Lactobacillus plantarum and Saccharomyces cerevisiae on growth improvement of hybrid Nile and Rufiji tilapia populations

An investigation of the role of Lactobacillus plantarum and Saccharomyces cerevisiae on growth performance of hybrids from Oreochromis niloticus and Oreochromis urolepis urolepis was carried out in plastic tanks at 10 fish/m3 density and a salinity of 25 units. The probiotic treatments were 2, 4 and 6 g/kg feed while the control feed did not include any probiotics. Growth parameters were measured fortnightly and water quality parameters monitored every day. Survival rate and water quality factors revealed non-significant variations (p > 0.05). Final weight differed significantly among the treatments (p < 0.05). Furthermore, Food Conversion Ratio (FCR), Specific Growth Rates (SGR), and weight gain did not differ significantly (p > 0.05) between the control and 2 g/kg treatments. However, the 4 and 6 g/ kg feed treatments showed significant differences (p < 0.05) from the control diet and 2 g/kg for both L. plantarum and S. cerevisiae. The condition factor did not show any significant difference (p > 0.05) among the treatments. Results of this study indicate that increasing the quantity of commercial probiotics in feeds improved growth rates. Condition factor observed in the treatments could be due to the role of the tested probiotics in improving the water quality of tanks. Therefore, probiotics could potentially be used to enhance coastal aquaculture development.

Local people and mangroves: Ecosystem perception and valuation on the south west coast of Mauritius

Mangrove ecosystem services are multi-dimensional (ecological, socio-cultural and economic), and their valuation is complex as not all of these dimensions are quantifiable in terms of monetary value. The main goal of this study was to determine the perception of local residents on the economic values of the mangrove ecosystem along the south west coast of Mauritius (Savanne and Black River Districts). A survey questionnaire (Savanne district, N=142; Black River district, N=126) was designed electronically in English and Mauritian Creole language using dichotomous, multiple choices and closed ended questions. The mean value for the awareness score was 52.3 and the standard deviation was 4.8 for the district of Savanne as compared to Black River district, where the mean value was 53.8 and the standard deviation was 9.0. The mangrove products harvested by locals from the surveyed sites were fish, crabs and oysters. The respondents were less willing to contribute to mangrove conservation activities both in terms of money (Savanne district, 4.2 %; Black River district, 3.9 %), and time (Savanne district, 7 %; Black River district, 4 %). Hence, campaigns and education programmes are critical to raise the awareness and concern of local residents to achieve Sustainable Development Goal (SDG) 14 in Small Island Developing States (SIDS) like Mauritius.

Effects of different types of manure on the culture of marine plankton as a potential source of food for mariculture hatcheries

The study examined different types of organic manure on the culture of marine plankton as a potential source of food for rabbitfish, Siganus stellatus, larvae. Cow dung showed significantly higher species abundance and diversity of cultured marine plankton followed by chicken and finally mixed media manure (p<0.05). A total of 36 genera of phytoplankton (21) and zooplankton (15) were identified in all culture media. Class Bacillariophyta was the most abundant and diverse group which accounted for 41.3 % of the total phytoplankton. Calanoida was the dominant group of the identified zooplankton, accounting for 51.7 %. It was observed that the organic manure used favoured the growth of commercially important species of phytoplankton such as Chaetoceros sp., Skeletonema sp., Chlorella sp., Isochrysis sp., Nannochloropsis sp. and Spirulina sp., and zooplankton such as Eurytemora sp., Calanus sp., Oithona sp., Branchionus sp., Moina sp. and ostracods. The growth performance and survival rate of early stage rabbitfish larvae fed with live marine zooplankton performed better compared to those fed with Artemia spp. and commercial dry feed. This indicates that zooplankton have the potential to enhance growth performance and survival rate, hence increasing productivity and the development of mariculture.

Diversity of mangrove fungal endophytes from selected mangrove species of coastal Kenya

Endophytes are bacteria or fungi living asymptomatically in the internal tissues of plants. They are symbiotic in nature and can be exploited for novel bioactive metabolites with applications in agriculture, medicine and industry. Mangrove fungal endophytes from the marine environment are abundant and have been recognized as sources of bioactive natural products. The study was designed to isolate, purify and identify mangrove fungal endophytes from selected common mangrove species of Gazi Bay, Tudor and Mida creek on the Kenya coast. The colonization rate and isolation rate of the mangrove fungal endophytes were determined. The studied mangrove species were Rhizophora mucronata (red mangrove), Sonneratia alba (mangrove apple), Avicennia marina (grey or white mangrove), and Ceriops tagal (spurred mangrove). Samples from twigs of these mangrove species were collected and analyzed using standard methods. Isolation of pure cultures of the endophytes was performed using Potato Dextrose Agar (PDA) incubated at 28 ± 1ºC for 5 days. The fungal isolates were identified under a light microscope based on colony morphology characteristics, type and presentation of conidiophores and conidia. A total of 18 different mangrove fungal endophytes were identified and these belonged to 5 genera. These were Aspergillus, Penicillium, Fusarium, Cephalosporium and Blastomyces, with Aspergillus being the most dominant genus. Tudor Creek recorded the highest fungal community diversity (H’ = 1.35) and Gazi Bay had the lowest diversity (H’ = 0.45). Fungal community similarity based on the identified genera was highest between Gazi Bay and Mida Creek (0.80) and lowest between Tudor Creek and Mida Creek (0.57). The selected mangrove species recorded a colonization rate of endophytic fungi of between 38.9 – 94.4 % with the highest habitation being associated with S. alba and C. tagal. There were differences and similarities in the colonization rate within mangrove species across study sites. Findings of this study have confirmed that the selected mangrove species exhibit high diversity of fungal endophytes with host recurrence and spatial heterogeneity.

Seasonal variability of vertical patterns in chlorophyll-a fluorescence in the coastal waters off Kimbiji, Tanzania

A study on the vertical pattern of chlorophyll-a (Chl-a) fluorescence was undertaken in the Mafia Channel offKimbiji, Tanzania. Data was collected during the Southeast Monsoon (SEM) and Northeast Monsoon (NEM) seasons. There was higher Chl-a concentration of 0.1 to 1.1 mgm-3 in the surface layer off Kimbiji to about 50 m depth due to the presence of mixed layer depth (MLD) which allowed water mixing in the layer. A deep Chl-a maximum was recorded at around 40 m depth during the NEM and between 40 and 70 m in the SEM. Surface water between longitude 39.9°E and 40.2°E had low Chl-a from the surface to about 50 m depth due to poor nutrient input. The NEM had an insignificantly higher Chl-a value than the SEM (p > 0.05) which differed from other studies in which Chl-a was higher during the SEM than the NEM, than, the Chl-a concentration was higher at the surface during the SEM than during the NEM. Satellite data showed higher Chl-a in the SEM than NEM, localized along the Mafia Channel. During the SEM season the wind pushes higher Chl-a water from the Mafia Channel towards the north and leads to a higher concentration at Kimbiji.