Western Indian Ocean journal of marine science最新文献

{"title":"Assessment of tropical cyclone-induced shoreline and riverbank changes at the Rufiji Delta using satellite remote sensing methods","authors":"K. H. Kai, J. Francis, Y. Shaghude","doi":"10.4314/wiojms.v21i1.4","DOIUrl":"https://doi.org/10.4314/wiojms.v21i1.4","url":null,"abstract":"The study aimed at quantifying changes in shoreline and riverbanks caused by tropical cyclones (TCs) and associated rainfall in the Rufiji Delta, southern Tanzania. Long term changes of the shoreline and riverbanks were analysed using medium resolution (Landsat TM and ETM) satellite imagery (1991, 1997 and 2007), while short-term changes (2013 to 2014) were analysed using high resolution (Pleiades) satellite imagery. Delineation of the shoreline and riverbank changes were accomplished through the analysis of appropriate coloured image composites, Sobel filtering and maximum likelihood classification of land cover. Analysis of Landsat data showed a relatively higher magnitude of erosion between 1991 and 2007, followed by minor changes between 1997 and 2007. Simbauranga was the most severely eroding site, with an estimated magnitude of erosion of 83 to 100 m during the study period. The maximum magnitude of short-term changes of the riverbanks were estimated at about 31 m2. Apart from the erosion of the riverbanks, other changes were the conversion of water to vegetation covered areas (amounting to approximately 200 m2). Short-term shoreline changes were up to 206 m with higher magnitude of accretion (142 m) than erosion (-4 m). The study conclusively calls for further detailed research on shoreline and riverbank changes based on the impacts of TCs on land cover.","PeriodicalId":200681,"journal":{"name":"Western Indian Ocean journal of marine science","volume":"2 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122660778","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Phytoplankton distribution along a salinity gradient in two Kenyan saltworks (Tana and Kurawa)","authors":"Sheban M. Hinzano, Francis A. Okalo, M. M. Ngarari, M. Opiyo, E. Ogello, Alexander M. Fulanda, Dan O. Odiwour, B. Nyonje","doi":"10.4314/wiojms.v21i1.9","DOIUrl":"https://doi.org/10.4314/wiojms.v21i1.9","url":null,"abstract":"The current study assessed the diversity and abundance of phytoplankton genera in two Kenyan saltworks (Tana and Kurawa) in March and September 2021. Water samples were obtained from ponds with salinities ranging from 30 to 200 ppt by filtering 40 l of water using a 20-μm phytoplankton net. Seventy-six genera of phytoplankton were identified. Genera richness, evenness and diversity decreased with increasing salinity while phytoplankton abundance increased with increasing salinity. Higher phytoplankton densities were observed in the Tana than in the Kurawa saltworks. Ponds of <100 ppt were dominated by Dinophyceae and Bacillariophyceae which accounted for >90 % of the phytoplankton community. Ponds of salinities >100 ppt were dominated by Cyanophyceae which accounted for >90 % of the phytoplankton community. From the results it was concluded that Kenyan saltworks host diverse phytoplankton genera whose richness decreases with increasing salinity and varies with seasons. The present data describes variation of phytoplankton assemblages in salt ponds between two selected seasons, but several samplings throughout the year would be more appropriate to describe variations of phytoplankton with season in these salt ponds.","PeriodicalId":200681,"journal":{"name":"Western Indian Ocean journal of marine science","volume":"31 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122605498","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Review of fisheries and management of sea cucumbers in the Indian Ocean","authors":"C. Conand, M. Claereboudt, Chamari Dissayanake, A. Ebrahim, Stella Fernando, Rodney Godvinden, T. Lavitra, M. Léopold, T. K. Mmbaga, T. Mulochau, Shafiya Naaem, S. Shea, Devarajen Vaitilingon, S. Yahya, K. Friedman","doi":"10.4314/wiojms.v21i1.10","DOIUrl":"https://doi.org/10.4314/wiojms.v21i1.10","url":null,"abstract":"Several sea cucumber species (Echinodermata: Holothuroidea) are fished, mostly for export of the dried product for Oriental consumers. Previous studies had analysed the historical trends at the world-scale until 2014. In the Western Indian Ocean (WIO) holothurian fisheries have a long history and several programmes have tried to ameliorate their management. Information has been recently gathered through a questionnaire and access to the most recent, yet unpublished available data (2015 to 2021) from different countries, through the evaluation of catches and/or processed product, present management systems, the imports of beche de mer and other products from Indian Ocean (IO) countries into the major market hub of Hong Kong SAR, and the Food and Agricuture Organisation (FAO) yearly statistics. The results are first presented for WIO countries, highlighting recent improvements in management. Imports from 16 WIO countries into the Hong Kong market (2017-2020 data) indicate the importance of the hub. The FAO world statistics are used to present the changes for the last few years, concentrating on the WIO countries. The recent trends show that demand for holothurians is still very high. Inconsistencies in the unit used in the reported statistics (fresh or dry weight) exist, and this needs to be addressed. The national data should be collected at the species level, to be able to follow the changes and the stock status. A regional approach is needed to encourage use of comparable management tools and follow future trends.","PeriodicalId":200681,"journal":{"name":"Western Indian Ocean journal of marine science","volume":"8 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123733643","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Sightings of sea stars (Echinodermata, Asteroidea) and a first record of crown-of-thorns starfish Acanthaster at Saya de Malha Bank, Mascarene Plateau","authors":"S. Ramah, D. Kaullysing, R. Bhagooli","doi":"10.4314/wiojms.si2021.2.17","DOIUrl":"https://doi.org/10.4314/wiojms.si2021.2.17","url":null,"abstract":"Field note - N/A","PeriodicalId":200681,"journal":{"name":"Western Indian Ocean journal of marine science","volume":"20 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-07-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117186565","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Marine mollusc (Mollusca: Gastropoda and Bivalvia) diversity of the Saya de Malha and Nazareth Banks, Mascarene Plateau","authors":"S. Ramah, D. Kaullysing, R. Bhagooli","doi":"10.4314/wiojms.si2021.2.9","DOIUrl":"https://doi.org/10.4314/wiojms.si2021.2.9","url":null,"abstract":"Marine molluscs are among the largest assemblages of the animal kingdom and inhabit the marine environment from the intertidal zone to the deep sea. This study reports the diversity of marine molluscs (Gastropoda and Bivalvia) collected from sediments at 19 stations (SS) at the Saya de Malha and Nazareth Banks during the EAFNansen expedition in May 2018. Sampling was carried out using the five hydraulic Van Veen grabs mounted on a Video-Assisted Multi-Sampler (VAMS). The mollusc shells were morphologically identified using established procedures and published guides. Shannon-Wiener diversity (H’) and Pielou’s evenness (J) indices were used to assess the diversity of the molluscs at each station. A total of 56 genera of marine gastropods belonging to 34 families, and 40 genera of bivalves from 16 families were recorded. The SS8 station at the Saya de Malha Bank had the highest diversity at a depth of 79 m for Gastropoda and Bivalvia, while SS1 harbored the highest overall molluscan diversity. At the Nazareth Bank, highest gastropod diversity was recorded at SS44, while SS43 had the highest bivalve and overall molluscan diversity. This study provides new information on the molluscan diversity at the Saya de Malha and Nazareth Banks.","PeriodicalId":200681,"journal":{"name":"Western Indian Ocean journal of marine science","volume":"19 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-07-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122661143","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Grain size analysis and total organic matter and carbonate contents of sediments on Saya de Malha and Nazareth Banks","authors":"Arnaud Nicolas, Rohinee Bhiwajee","doi":"10.4314/wiojms.si2021.2.6","DOIUrl":"https://doi.org/10.4314/wiojms.si2021.2.6","url":null,"abstract":"The Mascarene Plateau is one of the least studied regions of the Western Indian Ocean. The aim of this paper is to describe the qualitative grain size characteristics and the total organic matter and carbonate contents of sediments on the two underwater banks known as the Saya de Malha and Nazareth Banks. Sediment samples were collected during the R/V Dr Fridtjof Nansen expedition in 2018, using a Video-Assisted Multi-Sampler (VAMS). Sieving techniques and GRADISTAT software were used for granulometric analysis and grain size statistics, respectively. Total organic matter and carbonate contents were determined with the sequential weight loss on ignition method. Grain size parameters from 15 stations (depths ranging from 37 to 381 m) are reported in this study. The results showed that sand was the dominant grain size on both banks. Eleven of the 15 stations had a mean grain size of coarse sand, three stations had a mean size of medium sand and one station had fine sand. The average total organic matter and carbonate contents on the Banks ranged from 2.1 to 7.7 % and from 53.9 to 58.3 %, respectively. This study provides baseline information that will help to classify benthic habitats and better understand the ecosystem functioning and dynamics on of the Saya de Malha and Nazareth Banks.","PeriodicalId":200681,"journal":{"name":"Western Indian Ocean journal of marine science","volume":"32 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-07-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114333205","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Diversity and distribution of the shallow water (23-50 m) benthic habitats on the Saya de Malha Bank, Mascarene Plateau","authors":"S. Ramah, Gilberte Gendron, R. Bhagooli, M. Soondur, Andrew Souffre, Rodney Melanie, Priscilla Coopen, L. Caussy, D. Bissessur, O. Bergstad","doi":"10.4314/wiojms.si2021.2.5","DOIUrl":"https://doi.org/10.4314/wiojms.si2021.2.5","url":null,"abstract":"The Saya de Malha Bank (SMB) is one of the largest and least studied marine banks on the Mascarene Plateau. This study aimed to examine the diversity and distribution of the main benthic habitats in the shallow waters of the SMB (23 to 50 m). The survey was carried out in May 2018 during the EAF-Nansen Indian Ocean Research Expedition using a Remotely Operated Vehicle (ROV) deployed at 15 stations. Four main benthic habitats were investigated and their relative abundance determined during the survey. The 143,110 m2 surveyed area revealed proportional benthic habitat cover of 43.6 ± 22.4, 24.5 ± 21.9, 21.2 ± 27.8, and 10.5 ± 12.6 % for seaweed, abiotic substrate, seagrasses and corals, respectively. The seaweed habitat (43.6 %) was mainly composed of Halimeda spp. It represented up to 77 % of the habitats observed at SS34 (4553 m2). Even though seaweeds are considered seasonal, their dominance at all stations creates an important habitat structure for many organisms. The seagrass habitat (21.2 %) was dominated by Thalassodendron ciliatum. This habitat covered up to 93 % of the area investigated at SS38 (5950 m2) and was found mainly on the eastern side of the bank. The live hard coral habitat (10.5 %) was the highest at SS36-2 (35% of 9819 m2) and was more homogenously spread within the shallow areas. The unstable and the stable bare bottom substrate habitat (24.7 %) characterized as abiotic habitat was mainly composed of bedrock, sand, and rubble. It dominated at SS42 where it constituted 72.5 % of the 5114 m2 investigated and was recorded at all stations. Further research is warranted to better understand the diversity and the distribution of benthic habitats within the shallow waters of the SMB, along with collection of targeted benthic organisms for identification at higher taxonomic levels, to better formulate conservation and management measures and strategies.","PeriodicalId":200681,"journal":{"name":"Western Indian Ocean journal of marine science","volume":"85 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-07-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116463999","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Inorganic nutrient distribution at Saya de Malha and the eastern slope of the Nazareth Banks","authors":"Anishta Audit‐Manna, R. K. Oogarah, Y. Neehaul","doi":"10.4314/wiojms.si2021.2.2","DOIUrl":"https://doi.org/10.4314/wiojms.si2021.2.2","url":null,"abstract":"The distribution of nutrients in the Mascarene Plateau is poorly studied due to limited data collected in the region. This study investigated the distribution of nutrients in the water column of the Saya de Malha and eastern slope of the Nazareth Banks. Water samples were collected at the Saya de Malha and eastern slope of Nazareth Banks during the scientific expedition on board the R/V Fridtjof Nansen in May 2018 and the vertical profiles of physical parameters were used to identify the different water masses. Phosphate, nitrate and silicate showed typical nutrient profiles along with the nutriclines. The dissolved oxygen and chlorophyll-a showed a correlation with nutrients. Most of the sampling stations on the Saya de Malha and Nazareth Banks showed high oxygen saturation above 92 % in the upper 75 m. Low chlorophyll-a values were recorded at both banks indicating an oligotrophic system. The nutrient results also reveal an increase in the concentration towards the northern part of the region due to the South Equatorial Current crossing the plateau.","PeriodicalId":200681,"journal":{"name":"Western Indian Ocean journal of marine science","volume":"15 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-07-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126111276","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Variable photo-physiological performance of macroalgae and seagrasses from Saya de Malha and Nazareth Banks, Mascarene Plateau","authors":"R. Bhagooli, M. Soondur, S. Ramah, Arvind Gopeechund, D. Kaullysing","doi":"10.4314/wiojms.si2021.2.7","DOIUrl":"https://doi.org/10.4314/wiojms.si2021.2.7","url":null,"abstract":"The photosynthetic performance of macroalgae and seagrasses related to their body parts, depth and colours from the poorly-studied Saya de Malha and Nazareth Banks on the Mascarene Plateau was investigated in this study. Two seagrass (Thalassodendron ciliatum and Halophila decipiens) and seven macroalgae species (Caulerpa cupressoides, Acrosorium ciliolatum, Dictyosphaeria cavernosa, Halimeda opuntia, Ulva sp., Udotea orientalis and Udotea palmetta) were collected using the five Van Veen grabs attached to the Video-Assisted Multi-Sampler (VAMS) from 29-79 m depths in May during the FAO EAF-Nansen Research Programme 2018. The photosynthetic performance was measured using a Diving-Pulse-Amplitude-Modulated (D-PAM) fluorometer and the parameters included effective quantum yield at photosystem II (PSII) (ΦPSII), relative maximum electron transport rate (rETRm), photosynthetic efficiency (α), photoinhibition (β), saturating light level (Ek), and maximum non-photochemical quenching (NPQmax). All photo-physiological parameters varied significantly in T. ciliatum and C. cupressoides across their body parts. However, variation with seawater depths was not significant for NPQmax and β in the seagrass, and ΦPSII, rETRm and β in the macroalgae. Photo-physiological functioning of the leaf of T. ciliatum was optimal at 40 m. The photosynthetic performance of the frond and stolon of C. cupressoides decreased and remained unchanged, respectively, at 79 m when compared to that at 29 m. The whitish lobes of H. opuntia at 31 m exhibited significantly lower photosynthetic performance, in terms of ΦPSII, rETRm,α and Ek, than the greenish lobes. These findings provide a first insight of seaplant body parts-, depth- and colour-related photo-physiological performance from the Mascarene Plateau.","PeriodicalId":200681,"journal":{"name":"Western Indian Ocean journal of marine science","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-07-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129802534","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Spatial distribution of surface chlorophyll a and micro-phytoplankton density and diversity around two islands and at two banks of the Mascarene region","authors":"M. Soondur, S. Ramah, R. Boojhawon, D. Kaullysing, R. Bhagooli","doi":"10.4314/wiojms.si2021.2.3","DOIUrl":"https://doi.org/10.4314/wiojms.si2021.2.3","url":null,"abstract":"The present study validated the use of AquaMODIS sea surface chlorophyll a (Chla) concentrations and investigated the spatial variation in density and diversity of micro-phytoplankton around two islands and two fishing banks of the Mascarene region. The study included areas around Mauritius (MRU) and Rodrigues (ROD) Islands, at Nazareth (NZ) Bank, and in the Joint Management Area (JMA) between the Republic of Mauritius and the Republic of Seychelles, more specifically at the Saya de Malha (SM) Bank. The AquaMODIS data were based on 67 match-up data points of in-situ against satellite Chla concentrations. The micro-phytoplankton community structure was investigated by determining the density variation and using the Shannon Wiener (H’) and Evenness (Evar) diversity indices. The satellite and in-situ Chla data were significantly and positively correlated when pooled for the four sites studied (R2 = 0.441; r = 0.642, P < 0.01), and when analysed separately for islands (R2 = 0.480; r = 0.694), and banks (R2 = 0.233; r = 0.483). However, the Chla satellite values tended to be lower than the in-situ Chla data. The highest densities of micro-phytoplankton were observed in the eastern and northern regions for MRU and ROD, respectively. The most dominant genera of micro-phytoplankton were Coscinodiscus, Navicula, Chaetoceros and Ceratium. The Shannon-Wiener diversity index values for diatoms were all above 2.5 with waters around the islands having higher diversity compared to the banks. Overall, the different micro-phytoplankton around the islands, except for the group of cyanobacteria at ROD Island, were more evenly distributed (Evar > 0.6) compared to the banks. This study indicated that AquaMODIS Chla satellite data is valid and may be potentially used as a proxy for in-situ Chla concentration on the Mascarene Plateau. The results of this study also provide detailed insight into the spatial variation in micro-phytoplankton density and diversity on the Mascarene Plateau in the Western Indian Ocean. Further long-term studies are warranted to thoroughly understand the temporal (including seasonal and inter-annual) variations in Chla and micro-phytoplankton distribution for adequate and appropriate management of these ocean territories.","PeriodicalId":200681,"journal":{"name":"Western Indian Ocean journal of marine science","volume":"249 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-07-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121881392","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}