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  • 1.
    Donadi, Serena
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre. Swedish University of Agricultural Sciences (SLU), Sweden.
    Austin, Åsa N.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Bergström, U.
    Eriksson, B. K.
    Hansen, Joakim P.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Jacobson, P.
    Sundblad, G.
    van Regteren, M.
    Eklöf, Johan S.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    A cross-scale trophic cascade from large predatory fish to algae in coastal ecosystems2017In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 284, no 1859, article id 20170045Article in journal (Refereed)
    Abstract [en]

    Trophic cascades occur in many ecosystems, but the factors regulating them are still elusive. We suggest that an overlooked factor is that trophic interactions (TIs) are often scale-dependent and possibly interact across spatial scales. To explore the role of spatial scale for trophic cascades, and particularly the occurrence of cross-scale interactions (CSIs), we collected and analysed food-web data from 139 stations across 32 bays in the Baltic Sea. We found evidence of a four-level trophic cascade linking TIs across two spatial scales: at bay scale, piscivores (perch and pike) controlled mesopredators (three-spined stickleback), which in turn negatively affected epifaunal grazers. At station scale (within bays), grazers on average suppressed epiphytic algae, and indirectly benefitted habitat-forming vegetation. Moreover, the direction and strength of the grazer-algae relationship at station scale depended on the piscivore biomass at bay scale, indicating a cross-scale interaction effect, potentially caused by a shift in grazer assemblage composition. In summary, the trophic cascade from piscivores to algae appears to involve TIs that occur at, but also interact across, different spatial scales. Considering scale-dependence in general, and CSIs in particular, could therefore enhance our understanding of trophic cascades.

  • 2.
    Eklof, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Austin, Åsa
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Bergström, Ulf
    Donadi, Serena
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Eriksson, Britas D. H. K.
    Hansen, Joakim
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Sundblad, Göran
    Size matters: relationships between body size and body mass of common coastal, aquatic invertebrates in the Baltic Sea2017In: PeerJ, ISSN 2167-8359, E-ISSN 2167-8359, Vol. 5Article in journal (Refereed)
    Abstract [en]

    Background. Organism biomass is one of the most important variables in ecological studies, making biomass estimations one of the most common laboratory tasks. Biomass of small macroinvertebrates is usually estimated as dry mass or ash-free dry mass (hereafter `DM' vs. 'AFDM') per sample; a laborious and time consuming process, that often can be speeded up using easily measured and reliable proxy variables like body size or wet (fresh) mass. Another common way of estimating AFDM (one of the most accurate but also time-consuming estimates of biologically active tissue mass) is the use of AFDM/DM ratios as conversion factors. So far, however, these ratios typically ignore the possibility that the relative mass of biologically active vs. non-active support tissue (e.g., protective exoskeleton or shell)-and therefore, also AFDM/DM ratios-may change with body size, as previously shown for taxa like spiders, vertebrates and trees. Methods. We collected aquatic, epibenthic macroinvertebrates (>1 mm) in 32 shallow bays along a 360 km stretch of the Swedish coast along the Baltic Sea; one of the largest brackish water bodies on Earth. We then estimated statistical relationships between the body size (length or height in mm), body dry mass and ash-free dry mass for 14 of the most common taxa; five gastropods, three bivalves, three crustaceans and three insect larvae. Finally, we statistically estimated the potential influence of body size on the AFDM/DM ratio per taxon. Results. For most taxa, non-linear regression models describing the power relationship between body size and (i)DM and (ii) AFDM fit the data well (as indicated by low SE and high R-2). Moreover, for more than half of the taxa studied (including the vast majority of the shelled molluscs), body size had a negative influence on organism AFDM/DM ratios. Discussion. The good fit of the modelled power relationships suggests that the constants reported here can be used to quickly estimate organism dry-and ash-free dry mass based on body size, thereby freeing up considerable work resources. However, the considerable differences in constants between taxa emphasize the need for tax on specific relationships, and the potential dangers associated with ignoring body size. The negative influence of body size on the AFDM/DM ratio found in a majority of the molluscs could be caused by increasingly thicker shells with organism age, and/or spawning-induced loss of biologically active tissue in adults. Consequently, future studies utilizing AFDM/DM (and presumably also AFDM/wet mass) ratios should carefully assess the potential influence of body size to ensure more reliable estimates of organism body mass.

  • 3.
    Hansen, Joakim
    Stockholm University, Faculty of Science, Department of Botany.
    Distribution patterns of macroinvertebrates in vegetated shallow soft-bottom bays of the Baltic Sea2007Licentiate thesis, monograph (Other academic)
  • 4.
    Hansen, Joakim
    Stockholm University, Faculty of Science, Department of Botany.
    Effects of morphometric isolation and vegetation on the macroinvertebrate community in shallow Baltic Sea land-uplift bays2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Shallow sheltered Baltic Sea bays are ecologically important habitats that harbour a unique vegetation community and constitute vital reproduction areas for many coastal fish species. Knowledge about the invertebrate community in these bays is, however, limited. This thesis examines the macroinvertebrate community in shallow sheltered Baltic Sea bays and how it is affected by: (1) the natural morphometric isolation of bays from the sea due to post-glacial land uplift; and (2) differences in vegetation types. The invertebrate biomass and number of taxa was found to decrease with increased bay isolation. The taxon composition changed from dominance by bivalves and gastropods in open bays to a community composed of a larger proportion of insects in isolated bays. Stable isotope analysis indicated epiphytes and periphyton as the major energy resources for most of the examined consumers, but the relative importance of these in relation to larger plants decreased for some consumers with increased bay isolation. A comparison of invertebrate abundance between plants revealed a close relationship with morphological complexity of the plants. More complexly structured plants had higher invertebrate abundance than plants with simpler morphology. The results suggest that management of these coastal habitats should be dynamic and take into consideration the natural change in invertebrate community resulting from the slow bay isolation process. In addition, the results imply that changes in the aquatic vegetation due to anthropogenic influences could induce changes in the invertebrate community as the plant habitat structure is altered. A changed invertebrate community may in turn affect higher trophic levels since invertebrates are important food for many fish and waterfowl species.

  • 5.
    Hansen, Joakim
    Stockholm University, Faculty of Science, Department of Botany.
    The role of submersed angiosperms and charophytes for aquatic fauna communities2007Book (Other academic)
  • 6.
    Hansen, Joakim
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Uppföljning av bottenvegetation i grunda Östersjövikar: Varians- och precisionsanalyser av data insamlade med visuella metoder genom snorkling2016Report (Other academic)
    Abstract [sv]

    Syftet med den här studien var att analysera variation i bottenvegetation i tid och rum, samt precision i insamlandet av data för att ge rekommendationer för uppföljning av grunda vikar i Östersjön (habitatdirektivets naturtyp laguner 1150, med undergrupperna 1153 och 1154). I studien har variation analyserats avseende skillnader på olika geografisk skala (vik, län, havsområde) samt inventeringsår. Analysen utfördes på data som samlats in i den här miljön i lite mer än ett decennium (2001–2014), där stickprovsmetoder med visuell observation i 50×50-cm prov längs transekter eller slumpvist placerade stationer á 10 m diameter tillämpats. De responsvariabler som studerades var antal arter, antal typiska arter, täckningsgrad, två index baserade på indikatorarter, samt andelen långskottsvegetation. Variationen i de undersökta variablerna var störst inom vikar och mellan vikar, medan den var liten mellan län och havsområden. Det var även en viss variation mellan år, men den var inte samstämmig mellan vikar de olika åren. Vegetationens täckningsgrad varierade mest medan antalet arter och indexet beräknat på antalet indikatorarter varierade minst. Baserat på resultaten föreslås för samtliga havsområden att minst 100 små inventerings-rutor (0,25 m2) eller 30 större stationer (79 m2) bör inventeras per vik för att få en god precision* i medelvärdesskattning av antal arter och täckningsgraden av bottenvegetation per vik. Detta motsvarar ungefär 8 arbetstimmar med den första metoden, respektive 20 arbetstimmar med den andra metoden (fördelat på två personer). Med en lägre provtagningsinsats om 70 små inventeringsrutor (ca 6 h) eller 12 stationer (8 h) per vik nås en lägre men acceptabel precision**. Vid uppföljning av antal arter, typiska arter, täckningsgrad, indikatorartsindexen och andel långskottsvegetation på havsområdesnivå krävs att minst 16 vikar undersöks för att nå en god precision* i norra Egentliga Östersjön. För kumulativt artantal krävs att minst 8 vikar per naturtypsundergrupp provtas eftersom antalet arter och artsammansättningen skiljer mellan naturtypsundergrupperna i det här havsområdet. Då variationen mellan vikar var större i södra Egentliga Östersjön och Bottniska viken än i norra Egentliga Östersjön krävs en provtagning av 20 till 30 vikar per havsområde för att nå en god precision* i medelvärdesskattningar av de undersökta responsvariablerna i de två förstnämnda havsområdena. Med 16 vikar per havsområde når man dock en lägre, men acceptabel, precisionsnivå**. För god precision avseende mellanårsvariation föreslås en provtagning om sex år för de undersökta uppföljningsvariablerna. Resultaten som redovisas i den här studien kompletterar de undersökningar som gjorts av variation i fiskyngelförekomst i samma typ av Östersjövikar och tillsammans kan studierna utgöra en grund för att utforma uppföljningsprogram av grunda vikar i Östersjön.

  • 7.
    Hansen, Joakim
    et al.
    Stockholm University, Faculty of Science, Department of Botany. Avd. för växtekologi.
    Johansson, Gustav
    Johan.
    Grunda havsvikar längs Sveriges kust: Mellanårsvariationer i undervattensvegetation och fiskyngelförekomst2008Report (Other academic)
    Abstract [sv]

    Sammanfattning.

    I föreliggande studie undersöktes mellanårsvariationer i vattenvegetations- och fiskyngelsamhällen

    i grunda havsvikar längs den svenska östersjökusten. Syftet med studien var att ta fram

    riktlinjer för uppföljningsintervaller inom miljöövervakning av dessa miljöer. Variationer i

    vegetations- och fisksamhällena undersöktes även med hänsyn till faktorer som beskriver vikarnas

    geografiska läge, form och öppenhet mot havet. Inventeringar av vegetation och fiskyngel

    utfördes från slutet av juli till september i Västerbottens, Gävleborgs, Uppsala, Stockholms,

    Östergötlands, Kalmar, Blekinge och Skåne län. I denna studie analyserades 50 vikar

    med avseende på vegetation och 41 vikar med avseende på fiskyngel.

    Resultaten visade att täckningsgraden av stora vattenväxter och trådformiga alger varierade

    mycket mellan åren. Artsammansättningen av vegetation var relativt likartad i vikarna

    mellan åren, men i vissa vikar, främst inneslutna, varierade artsammansättningen mycket. Det

    förekom ingen samstämmig mellanårsvariation i växtartsammansättning i de grunda vikarna,

    d.v.s. förekomsten av arter var inte likartat hög eller låg i flera vikar samma år. En betydande

    del av skillnaderna i växtartsammansättning mellan vikarna kunde förklaras av skillnader i

    latitud och vikarnas öppenhet mot havet.

    Artsammansättningen av fiskyngel i vikarna varierade kraftigt mellan åren. Resultaten

    visade även en samstämmig mellanårsvariation av årsyngelsammansättningen, d.v.s. förekomsten

    av arter i vikarna var korrelerad till specifika år. Fiskyngelsammansättningen varierade

    även mycket med vikarnas öppenhet mot havet.

    Vi föreslår att inventeringsuppföljningar för naturtillståndsbedömning av grunda vikar

    görs med olika tidsintervaller för vegetation och fiskyngel samt för öppna och inneslutna vikar.

    Uppföljning av fiskyngelsamhället bör göras kontinuerligt och med korta tidsintervall,

    förslagsvis varje år, eftersom det är så stora mellanårsvariationer. Uppföljning av vegetationssamhället

    kan göras med längre tidsintervall i öppna vikar än i inneslutna vikar. Exempelvis

    kan vegetationen i öppna vikar inventeras enstaka år med påföljande tre till maximalt sex års

    intervall. För inneslutna vikar bör inventeringar ske vid tre på varandra följande år och därefter

    med exempelvis tre års intervall.

    Summary in English.

    The present study investigated inter-annual variations in the aquatic vegetation and young-ofthe-

    year (Y-O-Y) fish communities in shallow bays of the Baltic Sea. The aim of the study

    was to provide a scientific background and suggestions for monitoring time intervals for these

    coastal environments. Additionally, variations in the aquatic vegetation and Y-O-Y fish

    communities were studied in relation to the geographic location and morphometry of the bays.

    The surveys of vegetation and Y-O-Y fish were conducted in late July to September in 8

    counties along the Swedish Baltic Sea coast. In total 50 bays were analysed with respect to

    vegetation and 41 bays with respect to Y-O-Y fish.

    We found large variations between years in the mean percentage cover of large

    macrophytes and the cover of filamentous algae. The species composition was rather

    consistent in the bays between years. Only a few bays showed a large variation in species

    composition between years. These were mainly bays which were enclosed and very isolated

    from the sea. We did not find any synchronized variations in the species composition between

    years, i.e. the cover of certain species was not similarly high or low in several bays the same

    years. The variation in species composition could to a large extent be explained by latitude

    and the degree of isolation of bays from the sea.

    The Y-O-Y fish community varied considerably between years. The fish community

    showed a synchronized variation between years, i.e. the density of Y-O-Y fish species were

    correlated with specific years. Furthermore, the Y-O-Y fish community varied with the degree

    of isolation of bays from the sea.

    We suggest that monitoring of shallow coastal bays in the Baltic Sea should be

    conducted with different time intervals for the vegetation and Y-O-Y fish communities. We

    also suggest different time intervals for monitoring of open and enclosed isolated bays.

    Monitoring of the Y-O-Y fish community should be conducted with regular and short time

    intervals; every year would be advantageous. Monitoring of the submerged vegetation

    community could be conducted with long time intervals in open bays, e.g. 3 to maximum 6

    years. Enclosed isolated bays should be monitored at least 3 years in a row to get reliable

    results, but periods of yearly monitoring could be alternated with e.g. 3 year intervals.

  • 8.
    Hansen, Joakim P.
    Stockholm University, Faculty of Science, Department of Botany.
    Benthic vegetation in shallow inlets of the Baltic Sea: Analysis of human influences and proposal of a method for assessment of ecological status2012Report (Refereed)
    Abstract [en]

    The European Union Water Framework Directive (WFD) has a general objective that all European waters should attain good ecological status by 2015. Shallow wave-protected inlets with soft-sediment bottoms are common environments along the Swedish and Finnish Baltic Sea coastlines. However, there is no suitable method for assessing the ecological status of this biotope. The current assessment methods based on macrovegetation for coastal waters in Sweden and Finland are mainly designed for hard-bottom biotopes and function poorly for shallow soft bottoms. The aim of this study was to analyse the effects of human activities on submerged macrovegetation in shallow inlets along the Swedish and Finnish Baltic Sea coasts, and to develop a method for assessment of environmental status for the inlets.

    The results of the study showed that the proportion of disturbance-sensitive species decreased with increasing total phosphorus concentration and boating activity. In addition, macrophyte cover was lower in inlets with high, as compared to low, boating pressure. Natural environmental factors were found to be very important for explaining variation in the macrophyte community. However, a large part of the variation was unexplained in the models tested, and should be examined further.

    Based on the results, an assessment method for classification of environmental status was developed. The method uses a macrophyte index based on a cover proportion of sensitive to tolerant species, as well as the mean cover of all species combined. The two macrophyte responses are expressed as ecological quality ratios relative to a reference condition. Specific threshold values were developed to classify the environmental status on a five-point scale, from high to good, moderate, poor, and bad status. The method suggested can be used as a complement to the existing methods that are applied to deeper areas. The method is applicable to individual inlets and may also be suitable to larger water areas according to divisions in the WFD. It does, however, need further development and independent testing before application.

  • 9.
    Hansen, Joakim P.
    et al.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Snickars, Martin
    Applying macrophyte community indicators to assess anthropogenic pressures on shallow soft bottoms2014In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 738, no 1, p. 171-189Article in journal (Refereed)
    Abstract [en]

    Vegetated soft bottoms are under pressure due to a number of anthropogenic stressors, such as coastal exploitation and eutrophication. The ecological value of these biotopes has gained recognition through international conventions and the EU directives, which request methods for assessment of the environmental status of coastal areas. However, currently there is no appropriate method for assessing the status of shallow vegetated soft bottoms in the northern Baltic Sea. Therefore, we developed a macrophyte community index and tested its response in relation to important pressures (eutrophication and boating activity) and natural gradients (topographic openness, depth and salinity) on shallow bays in the northern Baltic Sea. The macrophyte index, and hence the proportion of sensitive to tolerant species, decreased with increasing phosphorus concentration, turbidity and level of boating activity, while the cumulative cover of macrophytes only showed a negative trend in response to increasing turbidity. Juvenile fish abundance was positively related to the index, indicating importance of sensitive macrophyte species for ecosystem functioning. As the index was tested in a wide geographic area, and showed a uniform response across natural gradients, it is a promising tool for assessment of environmental status that may be applied also in other vegetated soft-bottom areas.

  • 10.
    Hansen, Joakim
    et al.
    Stockholm University, Faculty of Science, Department of Botany. Växtekologi.
    Robertson-Andersson, Deborah
    Troell, Max
    Department of Systems Ecology.
    Control of the herbivorous gastropod Fissurella mutabilis (Sow.) in a land-based integrated abalone-seaweed culture2006In: Aquaculture, Vol. 255, no 1-4, p. 384-388Article in journal (Refereed)
  • 11.
    Hansen, Joakim
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Sagerman, Josefin
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Sofia, Wikström
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Effects of plant morphology on small-scale distribution of invertebrates2010In: Marine Biology, ISSN 0025-3162, E-ISSN 1432-1793, Vol. 157, no 10, p. 2143-2155Article in journal (Refereed)
    Abstract [en]

    Habitat structure influences organism communities by mediating interactions between individuals and species, affecting abundance and species richness. We examined whether variations in the morphology of soft-bottom plants affect their function as habitat and whether complex structured plants support higher macroinvertebrate abundance and species richness. Three Baltic Sea plant species were studied, together with artificial plants resembling each species. In a field collection, we found higher invertebrate abundance on the morphologically more complex plants Myriophyllum spicatum and Chara baltica than on the structurally simpler plant Potamogeton perfoliatus. In a colonization experiment, we found the highest invertebrate abundance on artificial M. spicatum but found no difference between natural plants. Invertebrate taxon richness displayed no consistent relationship with plant structural complexity. The results imply that plant morphology influences small-scale invertebrate distribution, partly supporting the hypothesis that structurally complex plants harbour higher invertebrate abundance.

  • 12.
    Hansen, Joakim
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Wikström, Sofia
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Axemar, Hanna
    Stockholm University, Faculty of Science, Department of Botany.
    Kautsky, Lena
    Stockholm University, Faculty of Science, Department of Botany.
    Distribution differences and active habitat choices of invertebrates between macrophytes of different morphological complexity2011In: Aquatic Ecology, ISSN 1386-2588, E-ISSN 1573-5125, Vol. 45, no 1, p. 11-22Article in journal (Refereed)
    Abstract [en]

    This study explores: (1) whether the abundance of macroinvertebrates differs between macrophytes differing in both morphological complexity and tolerance to nutrient enrichment; (2) whether the distribution of invertebrates between macrophytes is due to active habitat choice; and (3) whether invertebrates prefer structurally complex to simple macrophytes. Macroinvertebrate abundance was compared between two common soft-bottom plants in the Baltic Sea that are tolerant to eutrophication, Myriophyllum spicatum and Potamogeton pectinatus, and one common plant that is sensitive to eutrophication, Chara baltica. Both field sampling and habitat choice experiments were conducted. We recorded higher total macroinvertebrate abundance on the structurally complex M. spicatum than on the more simply structured P. pectinatus and C. baltica, but found no difference in macroinvertebrate abundance between P. pectinatus and C. baltica. In accordance with the field results, our experiment indicated that the crustacean Gammarus oceanicus actively chose M. spicatum over the other macrophytes. Besides, we found that G. oceanicus actively preferred complex to simply structured artificial plants, indicating that the animal distribution was at least partly driven by differences in morphological complexity between plant species. In contrast, the gastropod Theodoxus fluviatilis did not make an active habitat choice between the plants. Our findings suggest that human-induced changes in vegetation composition can affect the faunal community. Increased abundance of structurally complex macrophytes, for example, M. spicatum, can result in increased abundance of macroinvertebrates, particularly mobile arthropods that may actively choose a more structurally complex macrophyte.

  • 13.
    Hansen, Joakim
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Wikström, Sofia
    Kautsky, Lena
    Stockholm University, Faculty of Science, Department of Botany.
    Effects of water exchange and vegetation on the macroinvertebrate fauna composition of shallow land-uplift bays in the Baltic Sea2008In: Estuarine, Coastal and Shelf Science, ISSN 0272-7714, E-ISSN 1096-0015, Vol. 77, no 3, p. 535-547Article in journal (Refereed)
    Abstract [en]

    Shallow bays with soft sediment bottoms are common habitats along the Swedish and Finnish Baltic Sea coastline. These bays undergo a process of geomorphometric evolution with the natural isostatic land-uplift process, whereby open bays and sounds decrease in depth and are gradually isolated from the sea, forming bays with narrow openings. This study tested the relationship between the morphometric isolation of the bays from the sea and the macroinvertebrate fauna community of these bays. Additionally, we tested the specific role of the submerged vegetation as an indicator of the macroinvertebrate fauna community. We chose two environmental factors for the analyses, water exchange of the bays and the taxon richness of the macroflora in the bays. We found a hierarchical relationship between water exchange, flora taxon richness, and fauna biomass and taxon richness using structural equation modelling: decreased biomass and taxon richness of fauna were related to decreased flora taxon richness, which in turn was related to decreased water exchange. Using multivariate redundancy analysis, the two environmental factors included in the model were found to explain 47.7% of the variation in the fauna taxon composition and 57.5% of the variation in the functional feeding groups of the fauna. Along the morphometric isolation gradient of the bays, the fauna assemblages changed from a community dominated by gastropods, bivalves, and crustaceans, to a community mainly consisting of a few insect taxa. Moreover, the proportion of predators, gathering collectors, and shredders increased while that of filtering collectors and scrapers decreased. Our results indicate that the density and taxon richness of macroinvertebrate fauna are higher in less morphometrically isolated bays than in more isolated bays in the Baltic Sea. Furthermore, we suggest that the taxon richness of macroflora can serve as an indicator of the fauna community.

  • 14.
    Hansen, Joakim
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Wikström, Sofia
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Kautsky, Lena
    Stockholm University, Faculty of Science, Department of Botany.
    Taxon composition and food-web structure in a morphometric gradient of Baltic Sea land-uplift bays2012In: Boreal environment research, ISSN 1239-6095, E-ISSN 1797-2469, Vol. 17, no 1, p. 1-20Article in journal (Refereed)
    Abstract [en]

    Shallow Baltic Sea bays undergo a process of morphometric isolation from the sea due to post-glacial land uplift. Recent studies have documented that both flora and fauna communities change along this gradient. Changes in taxon composition may in turn alter feeding ecology and trophic relationships. In addition, the relative importance of carbon from terrestrial sources may increase with bay isolation. In accordance with previous studies, we found a change in the community composition of both flora and fauna with bay isolation. Results of stable isotope analysis (δ13C, δ15N) suggested that epiphytes and periphyton are the major carbon sources for most benthic primary consumers, but that their importance in relation to angiosperms and charophytes decreased with bay isolation. The results also indicated that filter feeders utilize terrestrially derived carbon, but its importance could not be critically related to bay isolation. Trophic positions of the consumers were similar across the bay isolation gradient.

  • 15.
    Joakim, Hansen
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Undervattensvegetation på mjukbottnar i Blekinge läns kustvatten: En sammanställning och analys av inventeringar utförda 2001–20082010Report (Other academic)
    Abstract [sv]

    I den här studien sammanställdes inventeringar av vattenväxter utförda mellan år 2001 – 2008 i 25 vattenförekomster i Blekinge skärgård. Syftet med studien var att analysera rumsliga variationer i växtartsammansättning på mjukbotten, samt undersöka vilka arter som är representativa respektive unika för en viss typ av miljö. Vidare syftade projektet till att undersöka hur väl variationen i artsammansättning kan förklaras av skillnader i vågexponering, djup och närsaltsbelastning. Resultaten visade att artsammansättningen på mjukbotten i Blekinge skärgård är relativt lika mellan flertalet vattenförekomster. Endast några få vattenförekomster hade en artsammansättning markant skild från de övriga. De vanligaste arterna i det sammanställda datamaterialet var borstnate Potamogeton pectinatus, lösliggande blåstång Fucus vesiculosus, natingar Ruppia spp., ålgräs Zostera marina, axslinga Myriophyllum spicatum samt trådformiga alger. Dessa arter påträffades i flertalet av vattenförekomsterna. Ovanliga arter var rödsträfse Chara tomentosa, murkelalg Leathesia difformis, hjulmöja Ranunculus circinatus, slangalger Vaucheriaceae, korsandmat Lemna trisulca och havsrufse Tolypella nidifica. Dessa arter påträffades endast i enstaka vattenförekomster. Artsammansättningen i vågexponerade djupa miljöer skilde sig signifikant från artsammansättningen i vågexponerade grunda och i skyddade grunda miljöer. Vidare skilde artsammansättningen signifikant mellan vattenförekomster med hög närsaltsbelastning och vattenförekomster med lägre närsaltbelastning. Vattenförekomster med hög närsaltbelastning hade högre täckningsgrad av trådformiga alger, natingar Ruppia spp., ålnate Potamogeton perfoliatus och havsnajas Najas marina än vattenförekomster med lägre närsaltsbelastning. Omvänt hade vattenförekomster med lägre närsaltsbelastning högre täckningsgrad av blåstång Fucus vesiculosus, ålgräs Zostera marina, borstnate Potamogeton pectinatus och sudare Chorda filum. Skillnader i koncentration av totalfosfor och totalkväve kunde förklara en förhållandevis stor del av variationen i artsammansättning mellan vattenförekomsterna. Skillnader i närsaltsbelastning samvarierade med skärgårdsgradienten, exempelvis fanns entydlig samvariation mellan koncentrationen totalkväve och salthalt. Detta gör det svårt att urskilja effekter av enskilda miljöfaktorer på artsammansättningen.

  • 16.
    Joakim P., Hansen
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Effects of shore-level displacement on the ecology of Baltic Sea bays2013Report (Other academic)
    Abstract [en]

    This report presents the up to date understanding of changes in ecological structure of small Baltic Sea bays following shore-level displacement and isolation of bays from the sea. It was producedas a part of the biosphere research programme, which has a strong emphasis on the characterization of properties and processes affecting the fate of potentially released radionuclides from the suggested repository of nuclear waste in the bedrock of the Forsmark area. The report has a focus on ecology and gives a description of input data, methodology and results on changes in flora and fauna communities, as well as some abiotic factors, with topographic isolation of bays from the sea. It is intended to describe the properties and conditions at the Forsmark site and to give information essential for demonstrating site specific understanding of processes and properties linked to a sea-to-lake succession. Long-term landscape development in the Forsmark area is dependent on two main and partly interdependent factors; shore-level displacement and climate variations. These two factors in combination strongly affect a number of processes, which in turn influence the development of ecosystems. Some examples of such processes are erosion and sedimentation, primary production and decomposition of organic matter. In this work focus has been to report changes in the structure and biomass of flora and fauna communities, which affect primary production, and influence the processes of decomposition of organic matter and sedimentation. A section of the study also deals with the biological processes of primary production, autotrophic carbon uptake and influence of allochtonous energy. The study is part of a description of the Forsmark ecosystem succession during a glacial cycle, which is one of the main objectives of the biosphere modelling at the Swedish Nuclear Fuel and Waste Management Company (SKB). The biomass of macrofauna was found to decrease with increasing isolation of bays. The changes in the macrofauna community also reflected the animals ability to re-colonize an unstable habitat, where slow colonizers with passively dispersed larvae were almost absent from the most isolated bays. Fast colonizers – particularly the ones with flying adults (insects) – were however found inhigher proportions in isolated bays. Contrary to the macrofauna and flora, the zooplankton and juvenile fish increased in biomass with increasing bay isolation. This study describes a significant change in ecological properties of Baltic Sea bays with shore-level displacement. This change affects ecosystem processes which may be of importance for the fate of potentially released radionuclides to the biosphere.

  • 17.
    Nilsson Austin, Åsa
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hansen, Joakim P.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Donadi, Serena
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Eklöf, Johan S.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Relationships between aquatic vegetation and water turbidity: A field survey across seasons and spatial scales2017In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 12, no 8, article id e0181419Article in journal (Refereed)
    Abstract [en]

    Field surveys often show that high water turbidity limits cover of aquatic vegetation, while many small-scale experiments show that vegetation can reduce turbidity by decreasing water flow, stabilizing sediments, and competing with phytoplankton for nutrients. Here we bridged these two views by exploring the direction and strength of causal relationships between aquatic vegetation and turbidity across seasons (spring and late summer) and spatial scales (local and regional), using causal modeling based on data from a field survey along the central Swedish Baltic Sea coast. The two best-fitting regional-scale models both suggested that in spring, high cover of vegetation reduces water turbidity. In summer, the relationships differed between the two models; in the first model high vegetation cover reduced turbidity; while in the second model reduction of summer turbidity by high vegetation cover in spring had a positive effect on summer vegetation which suggests a positive feedback of vegetation on itself. Nitrogen load had a positive effect on turbidity in both seasons, which was comparable in strength to the effect of vegetation on turbidity. To assess whether the effect of vegetation was primarily caused by sediment stabilization or a reduction of phytoplankton, we also tested models where turbidity was replaced by phytoplankton fluorescence or sediment-driven turbidity. The best-fitting regional-scale models suggested that high sediment-driven turbidity in spring reduces vegetation cover in summer, which in turn has a negative effect on sediment-driven turbidity in summer, indicating a potential positive feedback of sediment-driven turbidity on itself. Using data at the local scale, few relationships were significant, likely due to the influence of unmeasured variables and/or spatial heterogeneity. In summary, causal modeling based on data from a large-scale field survey suggested that aquatic vegetation can reduce turbidity at regional scales, and that high vegetation cover vs. high sediment-driven turbidity may represent two self-enhancing, alternative states of shallow bay ecosystems.

  • 18. Robertson-Andersson, Deborah V.
    et al.
    Potgieter, Michelle
    Hansen, Joakim
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Bolton, John J.
    Troell, Max
    Stockholm University, Faculty of Science, Department of Systems Ecology. Stockholm University, Stockholm Resilience Centre.
    Anderson, Robert J.
    Halling, Christina
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Probyn, Trevor
    Integrated seaweed cultivation on an abalone farm in South Africa2008In: Journal of Applied Phycology, ISSN 0921-8971, E-ISSN 1573-5176, Vol. 20, no 5, p. 579-595Article in journal (Refereed)
    Abstract [en]

    Land-based abalone aquaculture in South Africa, based on the local species Haliotis midae, started in the early 1990s and has grown rapidly in the last decade, with 13 commercial farms now producing over 850 t per annum. Over 6,000 t per annum of kelp Ecklonia maxima are now harvested for this purpose, and some kelp beds are reaching maximum sustainable limits. Research into seaweed aquacultureas feed (Ulva and some Gracilaria) for abalone started in the late 1990s on the southeast coast (where thereare no kelp beds) using abalone waste water. A growing body of evidence suggests that a mixed diet of kelp plus other seaweeds can give growth rates at least as good ascompound feed, and can improve abalone quality and reduce parasite loads. A pilot scale Ulva lactuca and abalone integrated recirculation unit using 25% recirculation was designed and built on the south west coast of South Africa using one 12,000-L abalone tank containing 13,200 15±2.5 g abalone, connected to two 3,000-L seaweed tanks containing an initial starting biomass of 10 kg of seaweed, replicated 3 times. In an 18-month period, there were no significant differences in abalone health or growth rates, sediment build up and composition, mobile macro fauna densities and species between the recirculation or the flowthroug hunits. Transfer of oxygen generated by the seaweeds to the abalone tanks was poor, resulting in the recirculated abalone tanks having lower (33%) dissolved oxygen concentrations than a comparable flow-through abalone unit. Seaweed nutrient content and specific growth rates in the units were comparable to seaweeds cultivated in fertilized effluent (SGR=3.2±3.4%.day−1; Yield=0.2±0.19 kg.m2.day−1). Indications were that at this low recirculation ratio the seaweeds in the units were nutrient limited and that there were no negative effects to the abalone being cultivated insuch a recirculation unit at this recirculation ratio.

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