{"projectrec":{"ProID":1753,"StandardTitle":"The quantitative importance of the Scheldt estuary for marine fish populations: an analysis for the goby species Pomatoschistus minutus using geochemical markers","OrigTitle":"Het kwantitatieve belang van het Schelde-estuarium voor mariene vispopulaties: een analyse voor de grondelsoort Pomatoschistus minutus aan de hand van geochemische merkers","Acronym":null,"AbstractEnglish":"Estuaries perform a crucial role in the population dynamics of several fish species. They provide a migratory route for anadromous and catadromous fish and an environment for truly estuarine teleosts. Freshwater fish involved colonize the upper region of estuaries, while marine species use the estuarine mouth. Above all, these marine fish enter and remain in estuaries for a short period, mostly in very large numbers, particularly during early stages of their life cycle. A number of mechanisms have been suggested to explain this feature, including avoidance or attraction by abiotic factors or gradients, the reduction in predation levels and the increased food availability. \r\nThis proposal aims to clarify the spatial and functional role of estuaries for juvenile marine fish. The question is raised which proportion of estuarine migrants contributes to the next cohort, compared with their conspecific marine residents. Hereto fish have to be assigned to their respective habitats and exchange rates have to be determined. The Scheldt estuary–Southern Bight of the North Sea gradient is used as a model system and the target fish species is the marine demersal sand goby (Pomatoschistus minutus; Gobiidae).\r\nThe objectives of this proposal are\r\n1.\tidentification of estuarine migrants and marine residents in a spawning population of Pomatoschistus minutus using geochemical trace elements in otoliths (ear stones).\r\n2.\tReconstruction of the individual life history of these spawners using geochemical tracers in otoliths (coupled with aging).\r\n3.\tAssessment of migrations between the marine spawning and the estuarine nursery grounds using population dynamics and stable isotopes of fish tissue and stomach contents. \r\n\r\nSampling is organized in function of the life-history pattern of the target species Pomatoschistus minutus. Sand gobies usually live for one year, at most for two years. They spawn in early summer on shallow sand banks. Larvae are pelagic at first; young fish only start to live at the bottom when they reach 17-18 mm. Juveniles occur along the coast and in estuaries; before winter, they migrate to deeper waters. Sampling will be conducted during the spawning period (March-June) at different inshore locations between Dunkirk (France), the Westerscheldt (The Netherlands and Belgium) and Goeree (The Netherlands). To quantify migrations along the estuarine gradient, samples are taken monthly at different estuarine sampling stations (upper estuary at Doel (B) and lower estuary at Borssele (NL)). Catch per unit effort data, resulting from all the samples taken along the estuarine-inshore-offshore gradient, will be used to estimate stock size and the length-frequency structure of the population at the different sampling stations. Seasonal differences in number caught along the estuarine gradient will be used to infer fish movements\r\n\r\nOtoliths (earstones) are used to assess age from the daily concentric growth rings. They are metabolically inert and their building stones (Ca and trace elements) are derived from the ambient water. The concentration of trace elements (mainly Sr) changes along a freshwater-saltwater gradient. As a result, crossing the freshwater seawater boundary during the life history can be read individually from the otoliths. The Ca/Sr ratio is determined using microprobe technology and linked to age. fish caught in the estuary will be used for interpretation of the Sr signals. Migrations of gobies between the coastal spawning sites and the estuarine nursery can be quantified using stable isotopes because the food web isotopic signatures are substantially different between these two environments. Organisms moving between isotopically distinct food webs carry with them information about the location of previous feeding over a period of several months. At each sampling station in the estuary 15 gobies are randomly selected and analyzed for C and N isotope ratios in their muscular tissue, as well as in their stomach contents.","AbstractOtherLang":"Levende organimsen migreren tijdens hun leven tussen verschillende habitaten. Migraties tussen kraam-en kinderkamergebieden en overwinteringsgebieden vormen een goede strategie om de levensverwachting te verhogen. Bekende voorbeelden zijn trekvogels maar ook vissen verwisselen regelmatig van habitat tijdens hun levenscyclus. Mariene soorten zoals haring, grondel, schol en kabeljauw paaien in de diepere zones van de zee (paaigebieden). Tussen de lokale populaties (populaties die paaien op verschillende plaatsen) treden migraties en bijgevolg, uitwisseling van genetische informatie op. Deze verzameling van lokale populaties wordt ook omschreven als een metapopulatie. Na het paaien op de verschillende paaigronden drijven de eieren en de larven onder invloed van zeestromingen naar de ondiepe kustzones (de kinderkamer-gebieden) waar ze opgroeien. Een deel van deze juveniele vissen migreert echter naar estuaria, de brakke overgangszones tussen zoet landwater en zout zeewater. Vermoedelijk migreren deze jongen naar de estuaria na het maken van een compromis: de verhoogde fysiologische stress in een estuarium in vergelijking met de zee is nefast voor de groei, maar jonge vissen vinden in estuaria meer voedsel en minder predatoren. In dit voorstel wordt de functionele rol die estuaria vervullen voor jonge vissen uitgediept. Waarom zijn estuaria zo belangrijk voor mariene vissen tijdens de eerste maanden van hun levenscyclus? Wat is de impact van het korte estuariene verblijf op de metapopulatie-structuur van een soort. Daarom gaan we na in welke proportie een populatie van zandgrondels (Pomatoschistus minutus) bestaat uit individuen die enkele maanden tijdens hun leven in het brakke Schelde-estuarium door hebben gebracht en uit individuen die permanent in de ondiepe kustzones van het Belgisch Continentaal Plat hebben verbleven. Dit vertaalt zich concreet in twee wetenschappelijke vraagstellingen: (1) hoe is de (genetische) structuur van een metapopulatie van grondels opgebouwd en, (2) wat is de omvang van de migraties tussen de kustzone en het estuarium. Het antwoord op deze vragen wordt aangebracht via een multidisciplinaire aanpak. Stalen van grondels worden genomen op de paaigronden en kinderkamers langsheen de Belgische kust en langsheen een estuariene gradient van zoet naar zout in het Schelde estuarium.\r\nDe metapopulatiestructuur van grondels wordt bestudeerd aan de hand van genotypering en door het gebruik van biochemische spoorelementen die het habitatgebruik van een individu aantonen. We gaan na of er verschillen bestaan in het genetisch materiaal van verschillende lokale populaties voor de Belgische kust (genotypering van 60 vissen per staal op 8 polymorfe DNA microsatelieten loci. Daarnaast worden de otolieten van grondels (gehoorstenen) geanalyseerd op de aanwezigheid van spoorelementen. Otolieten worden opgebouwd door calcium en spoorelementen zoals strontium te onttrekken uit het water; dit resulteert in groeiringen. Omdat de proportie van spoorelementen in het water verandert over een gradiënt van zoet naar zout kan de microanalyse van de gehoorstenen uitsluitsel geven wanneer vissen welk habitat hebben gebruikt (bepaling van Sr/Ca in otolieten). Met beide technieken kunnen we de verschillende paaiplaatsen identificeren en het relatieve aandeel van estuariene migraten bepalen.\r\nDe dynamiek van de migraties tussen zee en estuarium wordt afgeleid uit de populatiedynamica (de seizoenale verandering van aantallen vissen en van de lengte-frequentie structuur) en uit de verhouding van stabiele koolstof- en stikstofisotopen in het spierweefsel van vissen. Natuurlijke verschillen van 13C/12C en 15N/14N langsheen de estuariene zoet-zoutgradiënt worden via het voedsel ingebouwd in het spierweefsel van vissen zodat hun recente habitatgebruik kan gereconstrueerd worden (massaspectroscopie van C and N). Trade-offs tussen voordelen en nadelen verbonden aan het estuarien verblijf worden geoptimaliseerd in een dynamische programmatieomgeving. De resultaten van de verschillende deelstudies worden geïntegreerd in een conceptueel metapopulatie-model voor grondels dat wordt aangewend bij het beoordelen van het beheer van visstocks en de menselijke ingrepen op deze natuurlijke rijkdommen.","DateLastModified":{"date":"2024-05-06 10:25:46.257000","timezone_type":1,"timezone":"+00:00"},"ParentProID":null,"BeginYear":2003,"EndYear":2008,"BMonth":1,"EMonth":2,"BeginMonth":"January","EndMonth":"February","OrigTitleLangCode":"nl","OrigTitleLangID":41,"OrigTitleLangNL":"Nederlands","OrigTitleLang":"Dutch","OtherAbstractLangCode":"nl","OtherAbstractLangID":41,"OtherAbstractLang":"Dutch","OtherAbstractLangNL":"Nederlands","Progress":"Completed","ProgressNL":"Afgelopen","PublicFlag":1,"CheckedFlag":1,"ND":"2006-03-13","UD":"2009-07-07","DMPFlag":0,"Budget":126892,"BudgetCurrency":"EUR"},"parent":null,"persons":null,"projects":null,"events":null,"datasets":null,"institutes":[{"instituterec":{"Acronym":null,"ProPartID":7147,"PublicFlag":1,"OrigNameLangCode":"en","OrigNameLangID":15,"FullOrigName":"Katholieke Universiteit Leuven; 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