Effects of physical disturbance and habitat-modifying species on sediment properties and benthic communities in the northern Baltic Sea
Date
2010-07-30
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Abstract
Häiringud on ebakorrapäraselt toimuvad sündmused, mis kutsuvad esile muutusi ökosüsteemi, koosluse või populatsioonide struktuuris ning loovad vaba ruumi uutele tulijatele. Häiringud on oluliseks looduslikke kooslusi kujundavaks teguriks põhjustades koosluste ruumilist ja ajalist muutlikkust. Elupaika kujundavad liigid muudavad keskkonnatingimusi ja toetavad suuremat liigirikkust. Doktoritöö eesmärgiks oli uurida füüsikaliste häiringute (põhjasette eemaldamine ja lisandumine, süvendustööd), häiringu toimumise aja ja elupaika kujundavate võtmeliikide (pikk merihein, söödav rannakarp jt) mõju põhjasette omadustele (orgaanilise materjali sisaldus, granulomeetriline koosseis, hapnikuvoog) ja põhjaelustiku kooslustele Läänemere põhjaosas. Pealmise settekihi eemaldamine vähendas põhjaelustiku liigirikkust ja asustustihedust, kuid ei mõjutanud orgaanilise materjali sisaldust põhjasettes. Häiringu mõju oli tugevam kevadel. Põhjaloomastiku domineerimisstruktuur taastus kiiremini kui liikide asustustihedused. Settekihi akumuleerumine ei põhjustanud olulisi muutusi põhjasette omadustes, küll aga langes meriheina eemaldamise tagajärjel liigirikkus ja põhjaorganismide asustustihedus. Meriheina eemaldamine vähendas peeneteralise fraktsiooni ja orgaanilise materjali hulka settes ja suurendas ajutiselt sette hapnikutarvet. Koloniseeriva põhjaloomastiku koosluse domineerimisstruktuur ei sõltunud koosluse esialgsest liigilisest koosseisust vaid avatusest lainetusele. Söödav rannakarp suurendas niitjate vetikate, herbivooride ja detrivooride hulka kuid vähendas mändvetikate biomassi. Rannakarbi mõju oli suurem lainetusele mõõdukalt avatud piirkonnas võrreldes lainetuse eest varjatud piirkonnaga. Ulatuslike süvendustööde mõju põhjaloomastikule oli nõrk ja koosluste taastumine oli kiire, mis näitab, et kõrge stressitaluvusega Läänemere põhjaloomastiku liigid elavad kergesti üle süvendustöödega seotud häiringud.
Disturbance is mainly described as discrete event in time that disrupts ecosystem, community, or population structure, and creates opportunities for new individuals to become established. Disturbance is a key factor regulating the structure and functioning of natural communities and causing spatial and temporal heterogeneity. Most habitats are generated by the presence of a single or a few habitat-modifying species that alter local environmental conditions and support species diversity. The aim of this thesis was to study the effects of physical disturbances (sediment removal and addition, dredging activities) and habitat-modifying species (e.g. Zostera marina, Mytilus trossulus) on sediment properties (organic matter content, granulometric composition, oxygen flux) and benthic communities in the northern Baltic Sea. The removal of the upper sediment layer decreased species diversity and species’ densities but did not influence the organic matter content of sediment. The impact of disturbance was stronger in spring than in summer. The dominance structure of zoobenthos recovered faster than the densities of zoobenthos species. The addition of sediment did not cause changes in sediment organic matter content and oxygen flux. The removal of Z. marina significantly decreased diversity and density of benthic organisms, content of fine particles and organic matter, and temporarily increased the sediment oxygen consumption. The dominance structure of the colonising invertebrates depended on the wave exposure rather than on the initial composition of the invertebrate community. M. trossulus enhanced the growth of filamentous algae, herbivores, and deposit feeders and decreased the biomass of charophytes. Stronger effects of M. trossulus emerged in the moderately exposed than in the sheltered area. Large-scale dredging had weak effects on benthic invertebrates and the recovery of the communities took place within a year.
Disturbance is mainly described as discrete event in time that disrupts ecosystem, community, or population structure, and creates opportunities for new individuals to become established. Disturbance is a key factor regulating the structure and functioning of natural communities and causing spatial and temporal heterogeneity. Most habitats are generated by the presence of a single or a few habitat-modifying species that alter local environmental conditions and support species diversity. The aim of this thesis was to study the effects of physical disturbances (sediment removal and addition, dredging activities) and habitat-modifying species (e.g. Zostera marina, Mytilus trossulus) on sediment properties (organic matter content, granulometric composition, oxygen flux) and benthic communities in the northern Baltic Sea. The removal of the upper sediment layer decreased species diversity and species’ densities but did not influence the organic matter content of sediment. The impact of disturbance was stronger in spring than in summer. The dominance structure of zoobenthos recovered faster than the densities of zoobenthos species. The addition of sediment did not cause changes in sediment organic matter content and oxygen flux. The removal of Z. marina significantly decreased diversity and density of benthic organisms, content of fine particles and organic matter, and temporarily increased the sediment oxygen consumption. The dominance structure of the colonising invertebrates depended on the wave exposure rather than on the initial composition of the invertebrate community. M. trossulus enhanced the growth of filamentous algae, herbivores, and deposit feeders and decreased the biomass of charophytes. Stronger effects of M. trossulus emerged in the moderately exposed than in the sheltered area. Large-scale dredging had weak effects on benthic invertebrates and the recovery of the communities took place within a year.
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Keywords
doktoritööd, vesikeskkond, häiringud, merepõhi, Läänemeri