The potential nursery areas and recruitment seasons of Siganus sutor in Madagascar

editorial reviewedBackground Seagrass beds support the productivity of coastal fisheries by ensuring the survival of juvenile fishes and securing their recruitment in adult populations. This habitat is a preferred fishing area targeted by small-scale fishermen in developing countries, using Mosquito seine nets as observed in SW Madagascar. Previous studies revealed that seines nets caught large proportions of juveniles, especially dominated by Siganus sutor up to 42% of catches. In a conservation perspective, recruitment monitoring of this highly affected species is needed to provide key information related to their spatial and temporal distribution along the coastal habitats. This research aims at understanding recruitment patterns of S. sutor in critical habitats of SW Madagascar. The specific objectives are (a) to detect the recruitment seasons of S. sutor; (b) to identify their potential nursery areas; and (c) to understand why S. sutor select specific zones as a nursery area. Methods Catches from small scale fishers from mangroves, seagrass meadows, intermediate areas (i.e. sandy bottoms between seagrass patches and coral reefs) and seagrass associated to coral reefs were sampled with three stations per habitat and three days per month from July 2021 to June 2022. In meantime, ecological data related to surface temperature and salinity were recorded In the laboratory, all individuals were identified, photographed in order to automatically measure their size with ImageJ software. Another survey was carried out to address biological data (food availability) and habitat characteristics (depth, seagrass cover and diversity) in order to understand their influence on nursery areas selection for S. sutor. Results The catch of 5714 individuals shows that the abundance and size of rabbitfish exhibited a spatial and seasonal variability pattern. Rabbitfish size increased from habitats located near the coast compared to those near the reef. The smallest S. sutor size only occurred in the mangroves and seagrass meadows with 2.2 ±1.46 cm, against 4.2±1.48 for the intermediate areas and 5.1±1.47 seagrass associated with coral reefs. Considering abundance, juveniles of S. sutor is significantly more abundant in seagrass meadows (with 59.4%) while this species appeared to be rare in mangroves (<1%). This is indicated that this species did not colonize mangroves at an early stage. The small sized S. sutor were most abundant in seagrass meadow, suggesting this habitat could be the main nursery area for this species. Two recruitment seasons corresponding to the smallest mean size and the most abundant occurred in August 2021 and in January 2022 so far. This highlights the seasonality of S. sutor recruitment in SW Madagascar during warm and cool seasons. Conclusion To conclude, seagrass meadows constitutes the main nursery areas for S. sutor. Their massive settlement occurred in January (warm season) and August (cool season). Madagascar is characterized by two main recruitment season so far. As sampling will be completed in June 2022, results explaining why S. sutor choose seagrass meadows as a potential nursery will be available by August 2022 and will be presented. Such information will be useful for the decision making to develop management measures for the sustainable use of S. sutor resources and coastal habitats.Fish juvenile recruitment in coastal habitats of Western Indian Ocean14. Life below water11. Sustainable cities and communitie

Overview and progress of consortium research related to the biology, ecology and aquaculture of rabbitfish

editorial reviewedCoastal habitats support global fisheries by ensuring the survival of juvenile fishes. These habitats constitute one of the fishing areas targeted by small-scale fishermen in the least developed countries, including Madagascar. The accessibility of these habitats at low tides makes it an ideal fishing area for mosquito seine nets as observed for instance in SW Madagascar and beach seining in Kenya. However, this practice negatively impacts fisheries production due to catches of high numbers of juveniles, in Madagascar and Kenya mostly composed of shoemaker spinefoot rabbitfish (Siganus sutor). Despite Malagasy laws that forbid the deployment of mosquito seine nets, fishermen continue with their use. In Kenya, the beach seines have been outlawed but enforcement remains a challenge. This context highlights the need for management measures and alternative sources of income for a sustainable use of marine resources and for improving the fishermen livelihood. The ongoing consortium research entitled “Fish juvenile recruitment in coastal habitats of western Indian Ocean” was funded by MASMA program administered by WIOMSA. It is an interdisciplinary research program intending to understand recruitment patterns of shoemaker spinefoot rabbitfish (Siganus sutor) in coastal habitats of Kenya and Madagascar. It explores evidence-based solutions for improving the welfare of coastal communities and sustainable use of marine resources. Research activities were divided into four work packages. In WP1, Siganus sutor recruitment patterns in coastal habitats were targeted to identify the nursery ground and recruitment periods. It is based on juvenile fish sampling at four coastal habitats (mangroves, seagrass meadows, intermediate areas and seagrass associated with the coral reef) in Madagascar during twelve months. In WP2, sampling for the analysis of the population connectivity of S. sutor for detecting the sources of juveniles in the coastal habitats at five sites along the western coast of Madagascar was completed. In WP3, ecological models for predicting the arrival of newly settled S. sutor will be based on historical and newly collected data (WP1) using the random forests algorithm. Predictors are composed of remotely sensed oceanic conditions and a post-larval supply index calculated from post-larval sampling in the coastal habitats using light-traps. Like juvenile sampling, post-larval sampling was performed three nights per month which will cover all the juvenile sampling periods. In WP4, fish feeding behavior is studied and experiments on capture-based juvenile fish grow-out are ongoing at the Belaza aquaculture facilities (Toliara, Madagascar). Eight fish grow-out treatments focusing on three stocking densities, three fish diets, and pond dimensions are being tested. In WP1, about 5,720 juvenile individuals were obtained from 120 juvenile fish samples. The standard length of each of these individuals were measured for analyzing the spatial distribution of S. sutor. The nursery ground and recruitment seasons for S. sutor emerged from our research. The findings will be presented orally by PhD student Helga Berjulie Ravelohasina during the symposium. In addition, about 360 epifaunal community samples were obtained between July 2021 and April 2022. The spatial distribution of abundance, diversity and richness of epifauna associated with seagrass will be presented in a poster by MSc student Mory Justino. In WP2, at each location, 45 individuals were sampled, for a total of 225 adults for Madagascar and 180 from Kenya. Genotyping is in progress. In WP3, monitoring of the newly settled fish, in parallel with post-larval sampling, is in progress and should be completed by June 2022. In meantime, the extraction of remotely sensed oceanic conditions covering the sampling periods is being processed with R programming for the period. In WP4, preliminary results on fish grow-out identified the best fish diet and the most optimal stocking density at the smallest size (about 2 cm of standard length). More details related to these findings will be presented in a poster by master student Nandrianina Maminantenaina. In addition, the gut content and stage isotopes of three ontogenetic stages (i.e. post-larvae, juvenile, and adult) of S. sutor were analysed the natural trophodynamics. The findings are based on 1160 gut contents and muscle tissue samples collected during the warm (October 2021 to February 2022) and cool season (May to August 2022). The potential nursery areas and the main recruitment seasons of Siganus sutor were identified. The oral presentation entitled “The potential nursery areas and recruitment season of S. sutor in Madagascar” by Helga Berjulie Ravelohasina will provide further details of our findings. The variability of food availability related to epifauna concentration will be known in the poster on Mory Justino. The most optimal fish diet as well as the optimal stocking density will be presented in a separate poster entitled “Density and fish diet effect on rabbitfish growth in controlled systems” presented by Nandrianina Maminantenaina.Biology, ecology and aquaculture of rabbitfish14. Life below water2. Zero hunger11. Sustainable cities and communitie

Managing emerging fisheries of the North Kenya Banks in the context of environmental change

The North Kenya Banks have long been considered an important emerging fishery with the potential to spur economic growth for local fishing communities. As a regionally important extension to the otherwise narrow East African continental shelf, the North Kenya Banks remain under studied with implications for efforts to develop a sustainable fisheries management strategy. The local marine ecosystem is known to be strongly influenced by wind driven upwelling processes with seasonal variability driven by the changing monsoon seasons being of particular importance. Nevertheless, the Western Indian Ocean is warming due to anthropogenic climate change with evidence indicating reduced ocean productivity in future. How the ecosystem of the North Kenya Banks will respond is currently uncertain but is of great importance due to the significance of coastal fishery resources to coastal communities, and growing Blue Economy initiatives to exploit the North Kenya Banks fisheries more widely. There is, however, limited knowledge of the processes influencing productivity over the North Kenya Banks regions and currently there is no management plan in place to sustainably manage the fishery resources. Here, information about the North Kenya Banks fisheries are examined in relation to environmental processes and threats from climate change impacts with suggestions for future research and management directions

Environmental Implications of the Proposed Materials Handling and Ship-Loading Facility for the Export of Titanium at the Port of Mombasa, Kenya

A proposal has been made by Tiomin, Kenya to construct a materials handling and ship loading facility at Likoni in the vicinity of the port of Mombasa, Kenya. The proposed ship-loading site is a “brown-fields site”, which has been exposed to industrial and shipping activities for many years. Mangroves form the only significant marine habitat in the bay and show stress from previous oil spills. This study evaluates if implementation of the project, which includes construction of a warehouse and a jetty, could significantly compound the pollution problem. To achieve this, the project document, describing the construction and operational activities was obtained and a specialist study to describe the physical and biological environment, the currents dynamics for the area all year round were undertaken to predict the risk of accidents related to bad weather, indicating how the currents may transport oil (in the case of oil spill) to affect the mangrove habitat. The methods used to accomplish this study included a desk-top study for published information on the area, field visits to observe and describe the environment, and use made of the method for impact identification and evaluation developed by the Coastal and Environment Services, South Africa. Potential impacts revealed by the study included changes to water quality arising from sediment loading into the marine environment due to excavation activities, changes to benthic environment due to propeller wash during manoeuvring/docking, tank cleaning etc, effects on the water column from spillage the export minerals, potential impacts from invasive species from ballast water discharges, etc. Construction impacts were evaluated to be severe but of short-term duration. Such impacts are judged to be insignificant. On the other hand, operation impacts will be routine and may have moderate to significant impacts, if mitigation measures are not put in place and sustained. On mitigation, most of these impacts reduce to low impact and significance. However, the discharge of ballast water should not be allowed. Having established that most impacts were insignificant, it was concluded that implementation of the project would not significantly compound the existing environment condition in the harbour, and as such, implementation of the project was recommended

Alongshore distribution and abundance of fish larvae off the coast of Kenya

Knowledge is limited on the fish larval assemblage in shallow lagoonal reefs along the Kenyan coast. Fish larvae from five lagoons, spanning 120 km on the Kenyan coast, were sampled in March 2007 and April 2008 to compare interannual spatial variations in species composition, abundance and diversity along the coast. In all, 2 644 fish larvae were sampled, comprising 26 families and 37 species in 2007 and 43 families and 73 species in 2008. The larval assemblage was dominated by Gobiidae, Blenniidae, Pomacentridae and Gerreidae during both years. Larvae hatched from non-pelagic mode of spawning constituting 92% of total numbers. Mean larval abundance (no. 100 m–3 ± SE) along the coast ranged from 5.0 ± 1.0 to 414 ± 226, with highest densities occurring on the northern sites of Watamu (414 ± 226) and Malindi (31 ± 10). Interannual variation in larval abundance between 2007 (2.17 ± 0.3) and 2008 (2.16 ± 0.1) was not significant (p > 0.05). Shannon-Wiener species diversities between sites ranged from 1.2 ± 0.4 to 2.3 ± 0.3, with highest diversities occurring in Mombasa (2.2 ± 0.5) and Nyali (2.3 ± 0.3). In 2007, the occurrence of preflexion larvae increased northwards from Mombasa (18.2%) to Watamu (86.4%), whereas in 2008, the reverse was the case with the incidence of preflexion larvae reducing northwards from Mombasa Marine Park (76%) to Watamu Marine Park (2%). These trends indicate interannual variation in larval source sites for fish species. Correspondence analysis revealed distinct larval assemblages at sites along the coast, which varied between years. Keywords: abundance, alongshore, diversity, fish larval assemblages, reef lagoonsAfrican Journal of Marine Science 2010, 32(3): 581–58

Re-description of two species of the cardinalfish genus Archamia (Teleostei: Apogonidae) from the Red Sea and Western Indian Ocean

Gon, Ofer, Gouws, Gavin, Mwaluma, James, Mwale, Monica (2013): Re-description of two species of the cardinalfish genus Archamia (Teleostei: Apogonidae) from the Red Sea and Western Indian Ocean. Zootaxa 3608 (7): 587-594, DOI: 10.11646/zootaxa.3608.7.

Restricted dispersal of the reef fish Myripristis berndti at the scale of the SW Indian Ocean

The reef fish Myripristis berndti (Jordan & Everman 1903) is a pantropical species. A genetic analysis was conducted on 353 individuals from 10 localities distributed across the SW Indian Ocean (SWIO) in order to determine patterns of connectivity in the SWIO. Both the mtDNA sequences (711-bp cytochrome b sequences) and the microsatellites (8 newly developed loci) reveal spatial patterns of differentiation within the SWIO. There is, however, a discrepancy between the structure observed with each kind of marker. MtDNA revealed that 3 peripheral populations (NW Kenya, SE Reunion, and SW Europa) were isolated from the 7 more central populations, which form a more densely connected population network, while microsatellite data indicated a more restricted connectivity with significant differentiation between most pairs of localities. Higher genetic differences between Reunion and Europa were found, which might be explained by geography and isolation by distance pattern. In contrast, the genetic signature of Kenya-the most divergent locality identified by mtDNA basis but not with microsatellite-was probably the consequence of a particular colonisation history. These results indicate a much more restricted connectivity than previously thought for this species

Occurrence and ingestion of microplastics by zooplankton in Kenya’s marine environment: first documented evidence

Microplastics can be ingested by marine organisms and may lead to negative impacts at the base of marine food chains. This study investigated the occurrence and composition of microplastics in the sea-surface water and sought evidence of ingestion by zooplankton. Surface seawater was collected using a stainless-steel bucket and sieved directly through a stainless-steel sieve (250-μm mesh), while a 500-μm mesh net was towed horizontally to collect zooplankton, at 11 georeferenced stations off the Kenyan coast in February 2017, on board the national research vessel RV Mtafiti. Microplastic particles were sorted and characterised using an Optika dissecting microscope. Polymer types were identified using an ALPHA Platinum attenuated total reflection—Fourier-transform infrared (ATR-FTIR) spectrometer. A total of 149 microplastic particles, with an average abundance of 110 particles m–3, were found in the surface seawater. A total of 129 particles were found ingested by zooplankton groups, where Chaetognatha, Copepoda, Amphipoda and fish larvae ingested 0.46, 0.33, 0.22 and 0.16 particles ind.–1, respectively. Filaments dominated both the surface-water microplastics and the ingested microplastics, contributing 76% and 97% to those compositions, respectively. White particles were prevalent in the water (51%), whereas black was the colour found most commonly (42%) across the zooplankton groups. The sizes of particles that were in the water were in the range of 0.25–2.4 mm, and those ingested ranged between 0.01 and 1.6 mm. Polypropylene was predominant in the surface water, whereas low-density polyethylene was the most-ingested polymer type. The results provide the first documented evidence of the occurrence, composition and ingestion of microplastics by zooplankton in Kenya’s marine environment, indicating that microplastics have the potential to enter pelagic food webs and cause pollution in the study area.Keywords: georeferencing, infrared spectroscopy, Kenyan EEZ, low-density polyethylene, ocean pollution, polymer, polypropylene, sea surfac