| Summary: | ANOTACIJA Mezozooplanktona struktura un funkcionala loma Baltijas juras piekrastes ekosistema Solvita Strake Zooplanktonam ir „atslegas” loma pelagiskaja bariba kede nodrošinot organisko vielu apriti starp fotosintezejošu vienšunas algi un augstakajiem trofiskas kedes limeniem ka, piemeram, komercialajai zvejai svarigakajam pelagisko zivju sugam. Lai gan atseviškos Baltijas juras rajonos tiek veikti ilggadigi zooplanktona noverojumi un analizetas datu rindas, tradicionalie monitoringa noverojumi neatbild uz daudziem ar zooplanktona ekologiju saistitiem jautajumiem. Darba merkis ir noskaidrot maz petitus Baltijas juras mezozooplanktona ekologijas jautajumus, lai izprastu ta lomu ekosistemas funkcionešana. Petijuma dala par mezozooplanktona sugu sastavu, telpisko sadalijumu un sezonalo dinamiku Rigas lica litorala zona (1 m dziluma) tika noskaidrots, ka mezozooplanktona sugu sastavu Rigas lica sekludens zona veido saldudens un sajudens sugu kompleksi. Petijuma perioda laika ipaši izdalas rajons pret Salacgrivu, kur augstas skaita un biomasas vertibas sasniedz saldudens virpotaju sugas Brachionus calyciflorus, Brachionus quadridentatus, Euchlanis dilatata, Notholca acuminata, Notholca sp. un rajons pret Mersragu, kur atseviškos periodos mezozooplanktona cenoze domine saldudens sugu komplekss un sugu daudzveidiba ir lielaka ka parejos Rigas lica sekludens rajonos. Mezozooplanktona cenozes struktura vasaras sezona Rigas lica litorales zonas austrumdala ir laika un telpa neviendabigaka salidzinot ar rietumu dalu. Petijuma dala par invazivas mezozooplanktona sugas Cercopagis pengoi iegutie rezultati rada, ka Rigas lici tas veido stabilu populaciju ar skaita un biomasas maksimumiem vasaras sezona. Cercopagis pengoi populacijas struktura udens slani nav viendabiga – virseja siltaja udens slani lidz pat 92% no Cercopagis pengoi populacijas skaita veido juvenilie ipatni, bet palielinoties dzilumam populacija palielinas pieaugušo ipatnu proporcija. Augstakas skaita un biomasas vertibas Cercopagis pengoi sasniedz seklajos piekrastes udenos iespejams, ka rezultata radot butisku ietekmi uz baribas kedes strukturu. Eksperimentalais darbs ar toksisko cianobakteriju Microcystia aeruginosa un Nodularia spumigena ietekmi uz dominejošo Baltijas juras airkajvežu Eurytemora affinis un Acartia bifilosa olu produkciju un izdzivotibu rada, ka Eurytemora affinis un Acartia bifilosa spej producet olas un izdzivot toksisko cianobakteriju klatbutne, lai ari to izdzivotibas spejas ir mazakas ka apstaklos, kad bariba pieejams netoksisks fitoplanktons Lai izprastu mezozooplanktona lomu vielu biogeokimiskaja aprite Baltijas jura, tika veikts eksperimentals darbs lai noskaidrotu, ka dažadas baribas dietas ietekme airkajvežu fekalo kapsulu veidošanos, grimšanu un bakterialo degradaciju. Rezultati rada, ka barojoties ar nanoflagellatiem Rhodomonas salina un kramalgem Skeletonema costatum, tikai vienu trešo dalu airkajveža Acartia tonsa ekskrementu veido fekalas kapsulas, savukart atlikušo dalu veido amorfi izdalijumi. ANNOTATION Mesozooplankton structure and functional role in the Baltic Sea coastal ecosystem Solvita Strake Zooplankton occupies a key position in the pelagic food web as it transfers the organic energy unicellular algae produce by photosynthesis to higher trophic levels such as pelagic fish exploitable by man. Although long-term zooplankton monitoring programmes are carried out in several regions of the Baltic Sea, their results do not answer numerous questions connected to zooplankton ecology. This study therefore focuses on Baltic Sea mesozooplankton ecology to understand its functional role in the ecosystem. Analysis of mesozooplankton species composition, spatial distribution and seasonal dynamics in the Gulf of Riga littoral zone (1 m depth) shows that mesozooplankton species composition consists of freshwater and brackish water species. Especially in two of the coastal areas studied freshwater species are important. In Salacgriva the freshwater rotifer species Brachionus calyciflorus, Brachionus quadridentatus, Euchlanis dilatata, Notholca acuminata, and Notholca sp. reach high biomass and abundance, while in Mersrags, where freshwater species occasionally dominate the mesozooplankton community, species diversity is higher than in the adjacent shallow areas of the Gulf of Riga. Generally the summer mesozooplankton community structure is more homogenous in time and space at the Eastern coast of the Gulf than at the Western coast. Research on the invasive cladoceran species Cercopagis pengoi shows that it forms a permanent population in the Gulf of Riga with maximum abundance and biomass values in the summer season. The population structure of Cercopagis pengoi was not uniform throughout the water column – in the upper layer 92 % of the Cercopagis pengoi population consists of juveniles, while in the deeper part of the water column the proportion of adults became more significant. Highest values of abundance and biomass Cercopagis pengoi reaches in shallow coastal waters where it can significantly modify the food web structure. Experiments on the effect of the toxic cyanobacteria Microcytis aeruginosa and Nodularia spumigena on the survival and reproductive success of the dominant Baltic sea copepod species, Eurytemora affinis and Acartia bifilosa, demonstrate that copepods are able to survive and produce eggs in the presence of toxic cyanobacteria, although their survival rates are lower than with non-toxic phytoplankton available in the food. To understand the role of mesozooplankton for the biogeochemical cycle in the Baltic Sea laboratory experiments were performed to investigate, how different unialgal diets affect the egestion, degradation and sinking of copepod fecal material. Fecal pellets comprise only one third of the total feces loss when copepods feed on the nanoflagellate Rhodomonas salina and the diatom Skeletonema costatum. The pellets have approximately ten times higher sinking rates than amorphous fecal material.
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