Nutrient enrichment and water depth modify consumer control in rocky shore macroalgal communities

The objective of my thesis is to assess mechanisms of ecological community control in macroalgal communities in the Baltic Sea. In the top-down model, predatory fish feed on invertebrate mesograzers, releasing algae partly from grazing pressure. Such a reciprocal relationship is called trophic cascade. In the bottom-up model, nutrients increase biomass in the food chain. The nutrients are first assimilated by algae and, via food chain, increase also abundance of grazers and predators. Previous studies on oceanic shores have described these two regulative mechanisms in the grazer - alga link, but how they interact in the trophic cascades from fish to algae is still inadequately known. Because the top-down and bottom-up mechanisms are predicted to depend on environmental disturbances, such as wave stress and light, I have studied these models at two distinct water depths. There are five factorial field experiments behind the thesis, which were all conducted in the Finnish Archipelago Sea. In all the experiments, I studied macroalgal colonization - either density, filament length or biomass - on submerged colonization substrates. By excluding predatory fish and mesograzers from the algal communities, the studies compared the strength of the top-down control to natural algal communities. A part of the experimental units were, in addition, exposed to enriched nitrogen and phosphorus concentrations, which enabled testing of bottom-up control. These two models of community control were further investigated in shallow (<1 m) and deep (ca. 3 m) water. Moreover, the control mechanisms were also expected to depend on grazer species. Therefore different grazer species were enclosed into experimental units and their impacts on macroalgal communities were followed specifically. The community control in the Baltic rocky shores was found to follow theoretical predictions, which have not been confirmed by field studies before. Predatory fish limited grazing impact, which was seen as denser algal communities and longer algal filaments. Nutrient enrichment increased density and filament length of annual algae and, thus, changed the species composition of the algal community. The perennial alga Fucus vesiculosusA and the red alga Ceramium tenuicorne suffered from the increased nutrient availabilities. The enriched nutrient conditions led to denser grazer fauna, thereby causing strong top-down control over both the annual and perennial macroalgae. The strength of the top-down control seemed to depend on the density and diversity of grazers and predators as well as on the species composition of macroalgal assemblages. The nutrient enrichment led to, however, weaker limiting impact of predatory fish on grazer fauna, because fish stocks did not respond as quickly to enhanced resources in the environment as the invertebrate fauna. According to environmental stress model, environmental disturbances weaken the top-down control. For example, on a wave-exposed shore, wave stress causes more stress to animals close to the surface than deeper on the shore. Mesograzers were efficient consumers at both the depths, while predation by fish was weaker in shallow water. Thus, the results supported the environmental stress model, which predicts that environmental disturbance affects stronger the higher a species is in the food chain. This thesis assessed the mechanisms of community control in three-level food chains and did not take into account higher predators. Such predators in the Baltic Sea are, for example, cormorant, seals, white-tailed sea eagle, cod and salmon. All these predatory species were recently or are currently under intensive fishing, hunting and persecution, and their stocks have only recently increased in the region. Therefore, it is possible that future densities of top predators may yet alter the strengths of the controlling mechanisms in the Baltic littoral zone.Siirretty Doriast

Brackish-water benthic fauna under fluctuating environmental conditions : The role of eutrophication, hypoxia, and global change

We studied the spatio-temporal impacts of physical and chemical environmental variables (depth, sediment type, salinity, temperature, oxygen, total phosphorus, and total nitrogen) on soft-sediment zoobenthos in the open coastal Gulf of Finland during 2001–2015. The study included 55 sampling-stations covering the east-west gradient of the Finnish coastal zone. The chosen environmental variables significantly influenced the distribution of the species in space and over time. Some zoobenthic taxa formed assemblages with each other, occurring in similar environmental conditions, while Gammarus spp. and Chironomidae clearly differed from other taxa in regards to ecological requirements. We showed the critical influence of oxygen (normoxia, hypoxia, anoxia) on individual species, some better adapted to low oxygen conditions (e.g., Chironomidae) than others (e.g., Monoporeia affinis). The nutrient concentrations in the surface sediment also significantly affected the benthic assemblage patterns. The number of species in space and time increased with increasing oxygen concentrations. This study clearly shows that in order to maintain healthy marine communities, it is essential to counteract excess nutrient inputs and their indirect effects on sufficient O2 conditions for the benthic habitats

Physical oceanography sets the scene for the Marine Strategy Framework Directive implementation in the Baltic Sea

A challenge of the EU's Marine Strategy Framework Directive (MSFD) is to ensure comparable status assessments for good environmental status (GES) in the European seas. To this end, the role of dynamic oceanographic features affecting GES must be understood. Natural variability is recognized in the MSFD, but only vague advice is available for scientists and managers about how to apply this in the marine strategies. In this paper it is illustrated how physical factors, and their pronounced natural variability, e.g., irregularity of Major Baltic Inflows (MBI), strong and persistent upwelling, and varying ice conditions, affect status indicators and possibly several of the 11 descriptors of GES in the Baltic Sea. It is recommended that these effects are better understood in all regional seas. They may lead to insights that promote adaption of environmental monitoring programmes, as well as re-definitions of GES and other elements of the marine strategy

Wave stress and biotic facilitation drive community composition in a marginal hard-bottom ecosystem

Abstract Ecological patterns are inherently scale-dependent and driven by the interplay of abiotic gradients and biotic processes. Despite the fundamental importance of such gradients, there are many gaps in our understanding of how abiotic stress gradients interplay with biotic processes and how these collectively affect species distributions. Using a hierarchical design, we sampled two communities separated by depth along wave exposure and salinity gradients to elucidate how these two gradients affect species composition in habitats formed by the foundation species Mytilus trossulus and Fucus vesiculosus. Specifically, we looked at the impacts of regional salinity and temperature, local wave exposure, and site-dependent facilitation effects on the associated community composition. Wave exposure was the best predictor for species assembly structure, which was also affected by Mytilus biomass and by salinity and water temperature. While the tested variables provided robust explanations for community structure and density, they did not provide conclusive explanations for variation in species richness or evenness. Mytilus biomass had a stronger effect on the associated community with increasing wave exposure at the deeper depth, but the patterns were less obvious at the shallower depth. The latter was also the case for Fucus. These findings comply partly with theoretical predictions suggesting stronger facilitation effects in physically harsh environments. Our results indicate that environmental drivers are the main structuring forces that affect species assembly structure, but also foundation species are important. Thus, predicting changes in species distributions and biodiversity requires the simultaneous consideration of environmental gradients, as well as the structure and composition of foundation species and the interplay between these factors. This work advances our understanding of the processes that modulate species distributions in a marginal marine area and broadens the knowledge of how biological and environmental factors interplay and have an influence on hard-bottom community structure in brackish water seas.peerReviewe

Reproductive rate of a top predator, the grey seal, as an indicator of the changes in the Baltic food web

Reproductive rate of grey seal (Halichoerus grypus) females has fluctuated during the 2000s, although reproductive disturbances, which occurred earlier, are rare at present. Here we aimed to study especially the food web factors possibly affecting the birth rate of Baltic grey seals and whether birth rate can be used as an indicator of the changes in the Baltic food web. Our results showed that the birth rate of grey seals was significantly related to herring (Clupea harengus membras) and sprat (Sprattus sprattus) quality (weight) which, in turn were influenced by sprat and cod (Gadus morhua) abundance, as well as zooplankton biomass and plankter size. This suggests strong trophic coupling over three trophic levels. We thus conclude that the birth rate of grey seals can be used as an indicator of the status of the Baltic food web. Based on this, we suggest a threshold value for good food web status for a stable, non-growing seal population. Highlights • Birth rate of grey seals was related to changes in the quality of clupeids. • The quality of clupeids reflected changes in the Baltic food web. • Birth rate can thus be used as an indicator of the status of the Baltic food web. • Different threshold values of birth rate for a growing and stable seal population should be determined

Exploring methods for predicting multiple pressures on ecosystem recovery: A case study on marine eutrophication and fisheries

AbstractEfforts to attain good environmental status in the marine realm require decisions which cannot be done without knowledge of effects of different management measures. Given the wide diversity of marine ecosystems, multitude of pressures affecting it and the still poor understanding on linkages between those, there are likely no models available to give all the required answers. Hence, several separate approaches can be used in parallel to give support for management measures. We tested three completely different methods – a spatial impact index, a food web model and a Bayesian expert method. We found that a large uncertainty existed regarding the ecosystem response to the management scenarios, and that the three different modelling approaches complemented each other. The models indicated that in order to reach an improved overall state of the ecosystem nutrient reductions are the more effective of the two management variables explored, and that cumulative effects of the management of nutrient inputs and fishing mortality are likely to exist

Integrated assessment of marine biodiversity status using a prototype indicator-based assessment tool

Integrated assessment of the status of marine biodiversity is and has been problematic compared to, for example, assessments of eutrophication and contamination status, mostly as a consequence of the fact that monitoring of marine habitats, communities and species is expensive, often collected at an incorrect spatial scale and/or poorly integrated with existing marine environmental monitoring efforts. The objective of this Method Paper is to introduce and describe a simple tool for integrated assessment of biodiversity status based on the HELCOM Biodiversity Assessment Tool (BEAT), where interim biodiversity indicators are grouped by themes: broad-scale habitats, communities, and species as well as supporting non-biodiversity indicators. Further, we report the application of an initial indicator-based assessment of biodiversity status of Danish marine waters where we have tentatively classified the biodiversity status of Danish marine waters. The biodiversity status was in no areas classified as “unaffected by human activities.” In all the 22 assessment areas, the status was classified as either “moderately affected by human activities” or “significantly affected by human activities.” Spatial variations in the biodiversity status were in general related to the eutrophication status as well as fishing pressure

Mereiset avainluontotyypit ympäristöluvituksessa

Merialueiden käyttö kasvaa maailmanlaajuisesti. Kun yhä suurempaa osaa meri- ja ranta-alueista hyödynnetään taloudellisesti, lisääntyvät myös meriympäristöön kohdistuvat paineet, minkä seurauksena meriekosysteemin tila heikkenee. Meriekosysteemin toiminta ja meren meille tarjoamien ekosysteemipalveluiden määrä ja laatu voivat kasvavien paineiden myötä heikentyä. Tässä selvityksessä arvioidaan, miten mereiset luontoarvot on huomioitu Suomen rannikolla ja merialueilla tehdyssä ympäristölupaharkinnassa. Selvityksessä käytiin läpi ympäristö- ja vesilupia Suomen merialueella vuosilta 2014–2019, arvioitiin niihin sisällytettyjä meriympäristön rakennepiirteitä ja käytettyjä aineistoja, sekä vertailtiin luvituksen lopputuloksia. Tämän lisäksi selvitykseen koottiin mereisten avainluontotyyppien suojelua parantavia suosituksia. Aluehallintoviraston hallinnoimasta avoimesta Lupa-tietopalvelusta poimittiin yhteensä 77 hanketta liittyen ja/tai vaikuttaen mereen. Lupia anottiin eniten vuosina 2015 ja 2018. Lähes kaikki hakemukset koskivat uusia meri- ja rannikkoalueen käyttöön liittyviä hankkeita ja suurin osa kaikista hakemuksista myös hyväksyttiin. Lupahakemusten määrässä oli eroja myös merialueittain. Lupaprosesseihin liittyviä ympäristövaikutusten arvioita (YVA) edellytettiin harvoin; lähtökohtaisesti YVA:a edellytettiin hankkeilta, joilla arvioitiin mahdollisesti olevan merkittäviä vaikutuksia meriympäristölle. Hankkeissa arvioituja meriympäristöön liittyviä muuttujia arvioitiin vaihtelevasti; vesipuitedirektiiviin suoraan liittyviä vesimuodostumien ekologiseen laatuun liittyviä tekijöitä ja hankkeen vaikutuksia virkistyskäyttöön arvioitiin yleisimmin. Hankkeiden vaikutuksista meriympäristöön tehtiin asiantuntija-arvio, jossa ympäristöön kohdistuvat haittavaikutukset luokiteltiin kolmeen eri luokkaan. Ihmistoiminnan kumulatiivisia vaikutuksia oli arvioitu hyvin harvassa lupahakemuksessa. Kalastoon kohdistuvia taloudellisia kompensaatiotoimia edellytettiin 11 luparatkaisussa, mutta ekologisia tai ravinnekompensaatioita ei luparatkaisuissa määrätty. Koostettuun aineistoon perustuen, meriekosysteemin rakenteen ja toiminnan kannalta keskeiset avainluontotyypit on huomioitu Suomen rannikolla tehdyissä luvituspäätöksissä puutteellisesti. Raportin suositukset liittyvät tarpeeseen tarkentaa meriluonnon monimuotoisuutteen liittyvää sääntelyä ja luvituskäytäntöjä, aineistojen saatavuuden parantamiseen ja yhteisvaikutusten huomiointiin, jotta meri- ja rannikkoalueiden avainluontotyyppien suojelua voi parantaa

BEAT 3.0 – a Tool for Integrated Biodiversity Assessments

BEAT 3.0 is a multi-metric indicator-based tool for integrated assessments of marine biodiversity status implemented in R. It follows the structure and requirements of the EU Marine Strategy Framework Directive and allows for use of monotonic, unimodal, conditional, trend-based and qualitative indicators. The tool handles tabular data files (.txt format), in which the assessment structure and indicator results are specified. Integration of indicators is primarily based on weighted averaging, where both spatial assessment scale and ecosystem level are considered. Parallel to the biodiversity status assessment, a confidence assessment is also included. BEAT 3.0 uses HELCOM Assessment units and HELCOM core indicators as default but can be customized for use in any geographical region and any set of indicators. Funding Statement: BEAT 3.0 was developed in the HELCOM coordinated EU co-financed project ‘Baltic Sea project to boost regional coherence of marine strategies through improved data flow, assessments, and knowledge base for development of measures (BalticBOOST)’ EU grant number 11.0661/2015/712632/SUB/ENVC.2