{"refrec":{"BRefID":12946,"RR":"<b>Seip, P.A.; Seip-Ottema, M.</b> (1981). De betekenis van predatie voor de dichtheidsafname van de calanoïde copepoden in juni/juli in de Zuidelijke Bocht van de Noordzee. <i>Interne verslagen Nederlands Instituut voor Onderzoek der Zee</i>, 1981(3). NIOZ: Texel. 66 pp.","BEntID":12946,"PublicFlag":1,"CheckedFlag":0,"wosflag":0,"vabbflag":0,"RefStringPartII":". <i>Interne verslagen Nederlands Instituut voor Onderzoek der Zee</i>, 1981(3). NIOZ: Texel.  66 pp.","DocTypID":13,"DocType":"Reports","MarineFlag":1,"FreshFlag":0,"BrackishFlag":0,"TerrestrialFlag":0,"Authorstring":"Seip, P.A.; Seip-Ottema, M.","OrigTitleTranslFlag":1,"Authorstringtrunc":"Seip, P.A.; Seip-Ottema, M.","Englishabstract":"Investigating zooplankton populations in the North Sea several times, a spring-peak density of herbivore copepod populations was observed in May/June, followed by a decline in June/July. This was for instance observed in 1973 in the Southern Bight (when a peak density of fish larvae coincided with that decline). The decline can be caused by lack of food (phytoplankton) and/or by heavy predation. The goal of this doctoral research was to assess the role of predation in the, in June/July expected, decline of herbivore copepod populations. We investigated the following possible predators: fish larvae, Hydromedusae, ctenophores and scyphomedusae. From June 14 to July 5 we sampled weekly in an coastal area and in a more offshore region along the Dutch coast. We determined the density and the length composition of the predator-species. Unfortunately we missed the decline of the herbivore copepod populations (in connection with the fixed sail-scheme). The development of the zooplankton may be retarded by the low (water) temperatures in the spring of 1977. This research cannot give an answer to the earlier stated problem. What we were able to do was to investigate if we could find a relationship between the amount of presence and production respectively mortality of the several predator-species on the one side and the copepods on the other hand. We found that the fish larvae can develop when the copepod densities are low. In that case they will presumably eat other animals. However when the densities of the copepods are high, as observed in the coastal area, the relative developmental rates are higher for both the hydromedusa <i>Phialidium hemisphaericum</i> and the ctenophore <i>Beroë gracilis</i> and the fish larvae. Compared with preceding research the development of the fish larvae was rather moderate (the density was as much as hundred times lower than in 1973 during the same period in the same area). A possible reason for that is the competition for food by for instance <i>Phialidium hemisphaericum</i>, that abounded in 1977. Another reason can be that <i>Phialidium hemisphaericum</i> as the Scyphomedusae <i>Aurelia aurita</i>, <i>Cyanea lamarckii</i> and <i>Chrysaora hyoscella</i> also can eat fish larvae, so that they may have caused by predation the low densities of the fish larvae.","AbstractOtherLang":"Bij het onderzoeken van zooplanktonpopulaties in de Noordzee werd een aantal malen (o.a. in 1973 in de Zuidelijke Bocht) een voorjaarspiek in mei/juni waargenomen in de dichtheden van het herbivore zooplankton, gevolgd door een sterke terugval daarvan in juni/juli. Deze terugval kan worden veroorzaakt door voedselgebrek en of door hoge predatiedruk. Het doel van ons doctoraalonderzoek was aan te geven welke rol predatie speelt bij de in juni/juli 1977 verwachte terugval van het herbivore zooplankton. Daarbij hebben wij als mogelijke predatoren onderzocht: de vislarven, de hydromedusen, de ctenophoren en de scyphomedusen. Van 14 juni tot 5 juli hebben wij wekelijks monsters genomen in het gebied langs de Nederlandse kust en in een meer uit de kust gelegen gebied. uit de monsters determineerden we de predator soorten en bepaalden de dichtheden en de lengte samenstelling. Helaas hebben wij (i.v.m. vastliggend vaarprogramma) de terugval van het herbivore zooplankton gemist. Vanwege de lage voorjaarstemperaturen kan een vertraging in de ontwikkeling van het zooplankton zijn opgetreden. Ons onderzoek kan dan ook geen antwoord geven op de eerder genoemde probleemstelling; wel hebben we kunnen kijken of we een verband konden vinden tussen de mate van voorkomen en produktie resp. mortaliteit van de verschillende predatoren en de copepoden. Er bleek dat de vislarven zich bij lage copepoden dichtheden kunnen ontwikkelen waarbij ze vermoedelijk ook op andere dieren predeerden. Echter bij hogere copepoden dichtheden, zoals waargenomen langs de Nederlandse kust, zijn de relatieve ontwikkelingssnelheden zowel bij de hydromeduse <i>Phialidium hemisphaericum</i> en de ctenophoor <i>Beroë gracilis</i> als bij de vislarven hoger. Vergeleken met eerder onderzoek hadden de vislarven zich dit jaar zeer matig ontwikkeld (100 maal zo lage dichtheid als in 1973 langs de Nederlandse kust werd gevonden) . Een mogelijke oorzaak daarvan is de concurrentie die de vislarven ondervonden van o.a. <i>Phialidium h.</i>, die dit jaar in grote getale aanwezig was. Daarbij komt dat <i>Phialidium h.</i> zich, evenals de scyphomedusen <i>Aurelia aurita</i>, <i>Cyanea lamarckii</i> en <i>Chrysaora hysoscella</i>, ook wel voedt met vislarven, zodat ook de predatiedruk een belangrijke oorzaak zou kunnen zijn van het in geringe mate voorkomen van de vislarven.","BibLvlCode":"MS","StandardTitle":"De betekenis van predatie voor de dichtheidsafname van de calanoïde copepoden in juni/juli in de Zuidelijke Bocht van de Noordzee","OrigTitleLangCode":"nl","OrigTitleLangCodeExtended":"dut","OrigTitleLangID":41,"DateLastModified":{"date":"2025-07-22 01:33:06.175990","timezone_type":1,"timezone":"+02:00"},"UserAccessRight":null,"UserAccID":null,"AuthorKeywords":null,"OtherDescriptors":null,"Notes":null,"AnaPub":null,"MonPub":1981,"DateUpdate":"2025-07-15","DateCreate":"2001-07-05","SecASFANote":null,"ConfID":null,"PeerRev":0,"VlizCoreFlag":1,"WoScode":null,"VABBcode":null,"OpenAcc":1},"refs":null,"anarec":null,"monrec":{"MonID":12946,"ISBN":null,"PubliDate":1981,"IssueDate":null,"Volume":"1981","Issue":"3","Pagination":"66","Place":"Texel","Edition":null,"BRefXtra":null,"BRefXtraRR":null,"SerID":5036,"SerRR":"Interne verslagen Nederlands Instituut voor Onderzoek der Zee. 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