Posts Tagged 'Baltic'

Climate change can cause complex responses in Baltic Sea macroalgae: A systematic review

Estuarine macroalgae are important primary producers in aquatic ecosystems, and often foundation species providing structurally complex habitat. Climate change alters many abiotic factors that affect their long-term persistence and distribution. Here, we review the existing scientific literature on the tolerance of key macroalgal species in the Baltic Sea, the world’s largest brackish water body. Elevated temperature is expected to intensify coastal eutrophication, further promoting growth of opportunistic, filamentous species, especially green algae, which are often species associated with intensive filamentous algal blooms. Declining salinities will push the distributions of marine species towards south, which may alter the Baltic Sea community compositions towards a more limnic state. Together with increasing eutrophication trends this may cause losses in marine-originating foundation species such as Fucus, causing severe biodiversity impacts. Experimental results on ocean acidification effects on macroalgae are mixed, with only few studies conducted in the Baltic Sea. We conclude that climate change can alter the structure and functioning of macroalgal ecosystems especially in the northern Baltic coastal areas, and can potentially act synergistically with eutrophication. We briefly discuss potential adaptation measures.

Continue reading ‘Climate change can cause complex responses in Baltic Sea macroalgae: A systematic review’

Changes in wintertime pH and hydrography of the Gulf of Finland (Baltic Sea) with focus on depth layers

We studied changes in sea water pH, temperature and salinity with focus on two depth layers, along the Gulf of Finland (the Baltic Sea) using long-term monitoring data from 1979 to 2015. Data from the most frequently sampled monitoring stations between western and eastern Gulf of Finland were used. The main result of the study reveals that pH has decreased both in surface and deep-water in the western Gulf of Finland with values ranging between −0.005 and −0.008 units year−1. We also demonstrate a rise in temperature (~2 °C) and decrease in salinity (~−0.7 g kg−1) at several stations over the last 36 years. In general, the changes are shown to be more pronounced in the western part of the gulf. This paper also stresses the importance of improving the sampling frequency and quality of monitoring measurements.

Continue reading ‘Changes in wintertime pH and hydrography of the Gulf of Finland (Baltic Sea) with focus on depth layers’

Climate change, zooplankton and fisheries

We summarize responses to and mechanisms by which zooplankton cope with climate change. Effects of ocean warming include altered phenology, body size reduction, decline of tropical zooplankton biomass, functional group shifts in Polar Regions, and poleward expansion of zooplankton distributions. Thermal specialists (zooplankton from tropical and Polar Regions) may already perform near their limits and will be more vulnerable to warming. Evolutionary adaptation may mitigate, but not always fully offset the adverse effects of warming; thus, dispersal may play a prevalent role in the future distribution of species. While direct negative effects of ocean acidification is largely confined to calcifying organisms, early life stages of noncalcifying species (e.g., copepods, fish larvae) are susceptible to sublethal effects, particularly in combination with increasing temperature. Evidence is emerging for a large adaptation potential to hypercapnia in zooplankton. Hypoxia negatively affects physiology and life history traits. Despite zooplankton physiological and behavioral adaptations to hypoxia, shoaling of hypoxic waters likely increases predation mortality. Combined effects of warming, hypercapnia and hypoxia are poorly characterized or understood, but will likely depress performance and narrow the thermal performance curve. Climate change could result in different kinds of mismatches between zooplankton and fish larvae, i.e., (i) temporal, (ii) spatial, (iii) bioenergetic, and (iv) evolutionary mistmatches that individually or in combination, would result in altered larval fish growth and survival. Linkages between climate, zooplankton and fisheries are explored using the Baltic Sea as a case study.

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Acidification and warming affect prominent bacteria in two seasonal phytoplankton bloom mesocosms

In contrast to clear stimulatory effects of rising temperature, recent studies of the effects of CO2 on planktonic bacteria have reported conflicting results. To better understand the potential impact of predicted climate scenarios on the development and performance of bacterial communities, we performed bifactorial mesocosm experiments (pCO2 and temperature) with Baltic Sea water, during a diatom dominated bloom in autumn and a mixed phytoplankton bloom in summer. The development of bacterial community composition (BCC) followed well-known algal bloom dynamics. A principal coordinate analysis (PCoA) of bacterial OTUs (operational taxonomic units) revealed that phytoplankton succession and temperature were the major variables structuring the bacterial community whereas the impact of pCO2 was weak. Prokaryotic abundance and carbon production, and organic matter concentration and composition were partly affected by temperature but not by increased pCO2. However, pCO2 did have significant and potentially direct effects on the relative abundance of several dominant OTUs; in some cases, these effects were accompanied by an antagonistic impact of temperature. Our results suggest the necessity of high-resolution BCC analyses and statistical analyses at the OTU level to detect the strong impact of CO2 on specific bacterial groups, which in turn might also influence specific organic matter degradation processes.

Continue reading ‘Acidification and warming affect prominent bacteria in two seasonal phytoplankton bloom mesocosms’

The influence of CO2 enrichment on net photosynthesis of seagrass Zostera marina in a brackish water environment

Seagrasses are distributed across the globe and their communities may play key roles in the coastal ecosystems. Seagrass meadows are expected to benefit from the increased carbon availability which might be used in photosynthesis in a future high CO2 world. The main aim of this study was to examine the effect of elevated pCO2 on the net photosynthesis of seagrass Zostera marina in a brackish water environment. The short-term mesocosm experiments were conducted in Kõiguste Bay (northern part of Gulf of Riga, the Baltic Sea) in June–July 2013 and 2014. As the levels of pCO2 naturally range from ca. 150 μatm to well above 1000 μatm under summer conditions in Kõiguste Bay we chose to operate in mesocosms with the pCO2 levels of ca. 2000, ca. 1000, and ca. 200 μatm. Additionally, in 2014 the photosynthesis of Z. marina was measured outside of the mesocosm in the natural conditions. In the shallow coastal Baltic Sea seagrass Z. marina lives in a highly variable environment due to seasonality and rapid changes in meteorological conditions. This was demonstrated by the remarkable differences in water temperatures between experimental years of ca. 8°C. Thus, the current study also investigated the effect of elevated pCO2 in combination with short-term natural fluctuations of environmental factors, i.e., temperature and PAR on the photosynthesis of Z. marina. Our results show that elevated pCO2 alone did not enhance the photosynthesis of the seagrass. The photosynthetic response of Z. marina to CO2 enrichment was affected by changes in water temperature and light availability.

Continue reading ‘The influence of CO2 enrichment on net photosynthesis of seagrass Zostera marina in a brackish water environment’

Intra-population variability of ocean acidification impacts on the physiology of Baltic blue mussels (Mytilus edulis): integrating tissue and organism response

Increased maintenance costs at cellular, and consequently organism level, are thought to be involved in shaping the sensitivity of marine calcifiers to ocean acidification (OA). Yet, knowledge of the capacity of marine calcifiers to undergo metabolic adaptation is sparse. In Kiel Fjord, blue mussels thrive despite periodically high seawater PCO2, making this population interesting for studying metabolic adaptation under OA. Consequently, we conducted a multi-generation experiment and compared physiological responses of F1 mussels from ‘tolerant’ and ‘sensitive’ families exposed to OA for 1 year. Family classifications were based on larval survival; tolerant families settled at all PCO2 levels (700, 1120, 2400 µatm) while sensitive families did not settle at the highest PCO2 (≥99.8% mortality). We found similar filtration rates between family types at the control and intermediate PCO2 level. However, at 2400 µatm, filtration and metabolic scope of gill tissue decreased in tolerant families, indicating functional limitations at the tissue level. Routine metabolic rates (RMR) and summed tissue respiration (gill and outer mantle tissue) of tolerant families were increased at intermediate PCO2, indicating elevated cellular homeostatic costs in various tissues. By contrast, OA did not affect tissue and routine metabolism of sensitive families. However, tolerant mussels were characterised by lower RMR at control PCO2 than sensitive families, which had variable RMR. This might provide the energetic scope to cover increased energetic demands under OA, highlighting the importance of analysing intra-population variability. The mechanisms shaping such difference in RMR and scope, and thus species’ adaptation potential, remain to be identified.

Continue reading ‘Intra-population variability of ocean acidification impacts on the physiology of Baltic blue mussels (Mytilus edulis): integrating tissue and organism response’

Impact of environmental factors on bacterioplankton communities

Aquatic bacteria are main drivers of biogeochemical cycles and contribute predominantly to organic matter and nutrient recycling. As a high biodiversity is assumed to stabilize ecosystem functioning, it is necessary to understand the bacterial community dynamics and their structuring factors. It is known that different taxa are dominant across different habitats and seasons. This indicates an occurrence of species sorting by community structuring environmental factors. A first attempt for the understanding of bacterial distribution is to test for a correlation between microbial composition and measured environmental variables. In order to get further insights into the impact of environmental factors on bacterial communities, this thesis assessed the influence of major structuring drivers by using 16S rRNA gene amplicon sequencing, bacterial bulk parameters and interdisciplinary approaches in laboratory experiments and field studies.

In a field study in the Benguela upwelling system, the influence of different levels of primary production and the planktonic succession on bacterial community composition and its development was investigated. Community analysis revealed a clustering of different microbial assemblages along aging upwelled water. This zonation was mainly driven by phytoplankton composition and abundance and the spatial differences were comparable with a temporal succession that occurs during phytoplankton blooms in temperate coastal waters. A dominance of Bacteroidetes and Gammaproteobacteria was observed during algal blooming and high abundance of “Pelagibacterales” was found in regions with low algal abundance. Overall, this study highlightes the strong impact of quality and quantity of phytoplankton and nutrients on the bacterial communities.

A laboratory experiment with Baltic Sea water was performed to better understand the potential impact of rising temperature and CO2 on planktonic bacteria. The development of the bacterial community composition was followed in bifactorial mesocosm experiments during a diatom bloom in autumn and a phytoplankton bloom in summer. The results confirmed that phytoplankton succession and temperature were the major variables structuring the bacterial community. The impact of CO2 on the broad community was weak but high-resolution community analyses revealed a strong effect on specific bacterial groups, which might play important roles in specific organic matter degradation processes.

The response of bacterial communities to a disturbance by a saline intrusion could be investigated during a major Baltic inflow event. Community structuring factors were dominated by mixing of the inflow water with the former bottom water. Although the inflow had a selecting effect on the bacterial community, some immigrated taxa showed increased potential activity and seem to profit from changing environmental conditions. These results suggest a potential impact of inflow events on bacterial functions and therefore on biogeochemical processes.

Altogether, the results confirm the strong structuring effects of environmental conditions on bacterial community composition. Furthermore, high-resolution sequencing enabled an identification of specific affected taxa, which in turn give first clues for the impact of the investigated factors on specific bacterial functions.

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Ocean acidification in the IPCC AR5 WG II

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