{"refrec":{"BRefID":111036,"RR":"Reubens, J. (2007). Het verschil in gebruik van natuurlijke, heraangeplante en gedegradeerde mangroves door de ichtyofauna in Gazi Baai, Kenia = The difference in use of natural, replanted and degraded mangroves by the ichthyofauna in Gazi Bay, Kenya. MSc Thesis. Universiteit Gent. Faculteit Wetenschappen: Ghent. 77 + 2 appendices pp.","BEntID":105685,"PublicFlag":1,"CheckedFlag":0,"wosflag":null,"vabbflag":null,"RefStringPartII":". MSc Thesis. Universiteit Gent. Faculteit Wetenschappen: Ghent. 77 + 2 appendices pp.","DocTypID":5,"DocType":"Book/Monograph","MarineFlag":1,"FreshFlag":0,"BrackishFlag":0,"TerrestrialFlag":0,"Authorstring":"Reubens, J.","OrigTitleTranslFlag":1,"Authorstringtrunc":"Reubens, J.","Englishabstract":"This study handles about the importance of mangal as a feeding ground for fish. The impact of degradation and reforestation of mangal on the associated ichthyofauna is also investigated. Mangrove forests fulfil numerous important socio-ecological functions and provide a diversity (of economically important) products, with a direct or indirect human value. In many places in the world the surface of mangal decreases much faster than natural regeneration can take place. More than 50% of the global surface of mangal is lost due to anthropogenic influences (Spalding et al .1997). The environmental consciousness about the importance of mangrove forests made a spectacular rise in the past 30 years (Field 1999). Many initiatives to prevent further loss of the ecosystem have been undertaken, of which Gazi Bay, Kenya is an example. This thesis fits within the follow-up of a reforestation project carried out in 1994 in Gazi Bay.The purpose of this essay is to find out if there are differences in use of the mangal, in different stages of degradation or reforestation, by the ichthyofauna.The samples were taken at the south coast of Kenya, in Gazi Bay, in September 2006. Five sites were selected: a natural Sonneratia alba site (NAT), a 12 year reforested S. alba site (RFOR), a degraded site (DEG), a fragmented S. alba site (FRAG) and the sandy beach (SB). The different sites were sampled with fyke nets and a seine net.In the first part of this research the community structure was investigated. Clear differences were found in density, species richness and biomass between the different habitat types, caused by the environmental factors. Each habitat is characterised by biotic and abiotic factors, of which each fish species has it’s preference and a certain tolerance. Small-scale habitat differences play an important role here. Each estuary has quite some microhabitats. Each microhabitat houses its own community, influenced by the biotic and abiotic environmental factors.The ichthyofauna observed in the reforested site can serve as an indicator for (partly) recovery in function and provision of the mangrove forest in the site. This however, does not mean that the reforested site is the equivalent of a fully recovered ecosystem. The time needed for functional equivalence at the natural site is much longer than the time needed for visual recovery of the habitat itself.The fragmented site is the transitional situation from natural to degraded. Relative small changes in the structure of the mangrove forests can lead to significant changes in abundance and diversity of macrobenthic organisms. These changes, at their time, can lead to a whole cascade of effects on higher tropic levels. As a result, the quality of these habitats as nursery and feeding grounds firmlydecreases. In the second part of this research the feeding ecology was investigated.The possibility of differences in feeding activity in different habitat types depends on the species.In general we can say that there are few differences in fullness index between the sites. This has two possible causes: or the species does not feed in the mangal, or the species does feed in the different habitats and possibly changes the diet between sites. For most species the feeding hypothesis was not confirmed. Three diet types were defined: a detrivorous, a carnivorous and a piscivorous diet. Besides four trophic classes were defined: an omnivorous, detrivorous, carnivorous and piscivorous class. If smaller trophic classes are a must, prey-items should be classified in smaller groups by determination till genus- or species level.There exists a serious dearth in scientific knowledge on distribution patterns of the vagile fauna in mangrove forests, due to the time consuming and often difficult sampling methods. Rönnbäck et al. 1999 gave some suggestions and remarks about the sampling methods to form a platform forfuture studies. Via some remarks from the present research this platform is extended and some suggestions are made.
The ichthyofauna is vagile and can enter and leave the mangal at any place, so the selected sites need to be large enough and distributed over different locations. In this manner fishes that fed in one site do not become part of the analysis in another site.
The different sites need to be sampled simultaneously, because temporal variations in tide amplitude, currents and weather conditions may influence the catches (Rönnbäck et al .1999). However, the number of sites that can be sampled simultaneously is limited by manpower, time and available materials.
Gut content analysis my give some unreliable results with respect to the diet compositionand the source of the food (Lugendo et al. 2006). It is the only method however that gives some detailed information about the prey-type and the number of individuals taken. Stable isotope analysis gives an average of the diet over a period of weeks to months. A combination of both techniques will give the most reliable results.
Some more remarks to take into account:
In mangal you find both diurnal and nocturnal fish. Nocturnal fish hide in the mangrove forests during the day. At night the move to their feeding grounds in the mangroves and the seagrass beds.
There is possibly a difference in activity of the ichthyofauna during spring- and neap tide.
It could be that the ichthyofauna moves along a certain path trough the estuary.When tide comes in they follow the creeks and channels before moving into theforest. When tide goes out, they leave the forests at a random place and re-enterthe creeks and channels.
If we want a durable forest management, it’s important to take into account the social aspects.The human population must be seen as an inherent part of the mangrove forests (Field 1999).Anthropogenic activities have large impacts on the forests. At the same time we depend on these forests to survive. The local communities and governments should be firmly involved in the conservation- and rehabilitation projects. They should be an active participant and have responsibilities regarding the project (Yap 2000)","AbstractOtherLang":"Deze studie betreft het belang van mangrovewouden als voedingsgrond voor vissen en de impact van degradatie en herbebossing van mangrovewouden op de geassocieerde ichtyofauna. Mangrovewouden vervullen talrijke belangrijke socio-ecologische functies en voorzien in heel wat (economisch belangrijke) grondstoffen, die van direct of indirect belang zijn voor de mens. Op veel plaatsen in de wereld neemt de oppervlakte aan mangrovewouden af tegen een snelheid die veel hoger is dan dat natuurlijke regeneratie plaats kan vinden. Antropogene invloeden hebben ervoor gezorgd dat de globale oppervlakte aan deze bossen gereduceerd is met meer dan 50% (Spalding et al. 1997). De afgelopen dertig jaar is het bewustzijn over het belang van mangrovewouden echter sterk gestegen bij de bevolking (Field 1999). Heel wat initiatieven waarbij men de teloorgang van het ecosysteem tegen wil gaan werden ondernomen. Zo ook in Gazi baai, Kenia. Deze thesis kadert in de follow-up van een herbebossing uitgevoerd in deze baai in 1994.Het doel van deze verhandeling bestaat er in om na te gaan of er een verschillend gebruik bestaatdoor de ichtyofauna in mangrovewouden die zich in een verschillend stadium van degradatie o fheraanplanting bevinden.Staalname vond plaats aan de zuidkust van Kenia, in Gazi baai in september 2006. Vier sites werden aangeduid: een natuurlijke Sonneratia alba site (NAT), een 12 jaar heraangeplante S. albasite (RFOR), een gedegradeerde site (DEG), een gefragmenteerde S. alba site (FRAG) en het zandstrand (SB). De verschillende sites werden bemonsterd met fuiknetten en een seinnet. Het eerste deel van het onderzoek bestond uit de gemeenschapsanalyse, waarbij werd aangetoond dat er duidelijke verschillen bestaan in densiteit, soortenrijkdom en biomassa tussen de verschillende habitattypes. De oorzaak hiervan moet gezocht worden bij de omgevingsfactoren. Elk habitat wordt namelijk gekenmerkt door bepaalde biotische en abiotische factoren, waarvoor elke vissoort een bepaalde tolerantie en preferentie heeft. Hierbij zijn de kleinschalige habitatverschillen van groot belang. Binnen een estuarium komen heel wat verschillende microhabitatten naast elkaar voor, waarbij elk microhabitat een eigen gemeenschap herbergt, die beïnvloed wordt door de biotische en abiotische omgevingsfactoren.De ichtyofauna waargenomen in de heraangeplante site kan dienen als indicatie voor een (gedeeltelijk) herstel in functies en voorzieningen van de mangrovewouden in deze site. Dit wil echter niet zeggen dat het ecosysteem op zijn geheel hersteld is. De tijd die nodig is om functionele equivalentie aan een natuurlijke site te bereiken duurt veel langer dan het visueleherstel van het habitat zelf. De gefragmenteerde site is een overgangssituatie van natuurlijk naar gedegradeerd. Relatief kleine veranderingen in de structuur van mangrovewouden kan leiden tot significante veranderingen inde abundantie en soortenrijkdom van macrobentische organismen. Deze veranderingen kunnenop hun beurt cascade-effecten veroorzaken op hogere trofische niveaus waarbij de kwaliteit van dit habitat als kraamkamer of voedingsgrond sterk achteruit gaat.In het tweede deel van het onderzoek werd de voedingsecologie onderzocht.Of er een verschil in voedingsactiviteit bestaat indien een soort in verschillende habitattypesvoorkomt, hangt af van soort tot soort. In het algemeen worden weinig verschillen gevonden in fullness index tussen de sites. Dit heeft twee mogelijke oorzaken: ofwel vindt er geen voeding plaats in de mangroves, ofwel kan de soort zich voeden in verschillende habitatten, waarbij hetdieet eventueel wordt aangepast. Voor de meeste soorten kon de voedingshypothese echter nietbevestigd worden. Er werden 3 dieettypes afgebakend: het detrivore, carnivore en piscivore dieet. Daarnaast werden vier trofische klassen afgebakend: de omnivore, detrivore, carnivore en piscivore klasse. Indienmen de trofische klassen verder wil opsplitsen, moeten de prooi-items opgedeeld worden in meer gedi","BibLvlCode":"M","StandardTitle":"Het verschil in gebruik van natuurlijke, heraangeplante en gedegradeerde mangroves door de ichtyofauna in Gazi Baai, Kenia = The difference in use of natural, replanted and degraded mangroves by the ichthyofauna in Gazi Bay, Kenya","OrigTitleLangCode":"nl","OrigTitleLangCodeExtended":"dut","OrigTitleLangID":41,"DateLastModified":{"date":"2025-07-02 08:33:14.980000","timezone_type":1,"timezone":"+00:00"},"UserAccessRight":null,"UserAccID":null,"AuthorKeywords":null,"OtherDescriptors":null,"Notes":null,"AnaPub":null,"MonPub":2007,"DateUpdate":"2014-09-03","DateCreate":"2007-06-14","SecASFANote":null,"ConfID":null,"PeerRev":null,"VlizCoreFlag":1,"WoScode":null,"VABBcode":null,"OpenAcc":0},"refs":null,"anarec":null,"monrec":{"MonID":111036,"ISBN":null,"PubliDate":2007,"IssueDate":null,"Volume":null,"Issue":null,"Pagination":"77 + 2 appendices","Place":"Ghent","Edition":null,"BRefXtra":null,"BRefXtraRR":null,"SerID":null,"SerRR":null,"Ser2BRefID":null,"Ser2RR":null,"StandardTitleSer":null,"ISSN":null,"AbbrevSer":null,"Degree":"MSc","ThesisID":111036,"InsID":13,"Acronym":"MARBIOL","FullStandardName":"Universiteit Gent; Faculteit Wetenschappen; Vakgroep Biologie; Onderzoeksgroep Mariene Biologie","ToPubliDate":null,"SerNotes":null,"eISBN":null,"Pages":77},"serrec":null,"relations":null,"relationsRev":null,"addrec":null,"othpubs":null,"ownerships":null,"authors":[{"AutName":"Reubens","Firstname":"Jan","Initials":"J.","Affiliation":null,"Discriminator":null,"CorporateFlag":0,"BEntID":105685,"AutID":73851,"OrderNr":1,"DegrID":null,"EditorFlag":0,"CorrespFlag":0,"IllustratorFlag":0,"ReviserFlag":0,"TranslatorFlag":0,"InsAcronym":null,"InsFSN":null,"ORCID":"0000-0002-9823-5670","PersID":14823,"InsID":null}],"mapdetails":null,"datasets":[{"DasID":1287,"Acronym":null,"Citation":null,"StandardTitle":"Difference in usage of natural, reforested and degraded mangroves by the icthyofauna in Gazi Bay, Kenya","RelationID":2,"DOI":null}],"monographs":null,"monparts":null,"serparts":null,"BEntOpen":null,"BEntPrivate":null,"availability":[{"BInstID":121446,"LibID":36,"BRefID":111036,"EmbargoDate":null,"FullEmbargoDate":null,"PhysMedID":16,"hasOCRd":1,"ShelfLocCode":"121446","RFID":null,"PaidValue":null,"Medium":"Server","Description":"Interne VLIZ documenten","Acronym":"VLIZ","Library":"Vlaams Instituut voor de Zee","DutchTerm":"Non-open access","URL":null,"ClassifID":228,"Classification":"Non-open access","ReqLink":1,"ClassifTypID":3,"URLLocation":"https://www.vliz.be/imisdocs/publications/","SubDir":1,"InternalReq":1,"LoggedInReq":1,"Disclaimer":"Disclaimer_VLIZ_Intern","DutchDisclaimer":"
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