M. Sswat - Academia.edu (original) (raw)

Papers by M. Sswat

Frontiers in Marine Science, 2021

The oceans’ uptake of anthropogenic carbon dioxide (CO2) decreases seawater pH and alters the ino... more The oceans’ uptake of anthropogenic carbon dioxide (CO2) decreases seawater pH and alters the inorganic carbon speciation – summarized in the term ocean acidification (OA). Already today, coastal regions experience episodic pH events during which surface layer pH drops below values projected for the surface ocean at the end of the century. Future OA is expected to further enhance the intensity of these coastal extreme pH events. To evaluate the influence of such episodic OA events in coastal regions, we deployed eight pelagic mesocosms for 53 days in Raunefjord, Norway, and enclosed 56–61 m3 of local seawater containing a natural plankton community under nutrient limited post-bloom conditions. Four mesocosms were enriched with CO2 to simulate extreme pCO2 levels of 1978 – 2069 μatm while the other four served as untreated controls. Here, we present results from multivariate analyses on OA-induced changes in the phyto-, micro-, and mesozooplankton community structure. Pronounced diff...

Nature Climate Change, 2018

Ocean acidification, the change in seawater carbonate chemistry due to the uptake of anthropogeni... more Ocean acidification, the change in seawater carbonate chemistry due to the uptake of anthropogenic CO 2 , affects the physiology of marine organisms in multiple ways 1. Diverse competitive and trophic interactions transform the metabolic responses to changes in community composition, seasonal succession and potentially geographical distribution of species. The health of ocean ecosystems depends on whether basic biotic functions are maintained, ecosystem engineers and keystone species are retained, and the spread of nuisance species is avoided 2. Here, we show in a field experiment that the toxic microalga Vicicitus globosus has a selective advantage under ocean acidification, increasing its abundance in natural plankton communities at CO 2 levels higher than 600 µatm and developing blooms above 800 µatm CO 2. The mass development of V. globosus has had a dramatic impact on the plankton community, preventing the development of the micro-and mesozooplankton communities, thereby disrupting trophic transfer of primary produced organic matter. This has prolonged the residence of particulate matter in the water column and caused a strong decline in export flux. Considering its wide geographical distribution and confirmed role in fish kills 3 , the proliferation of V. globosus under the IPCC 4 CO 2 emission representative concentration pathway (RCP4.5 to RCP8.5) scenarios may pose an emergent threat to coastal communities, aquaculture and fisheries. The ocean plays a key role in the climate system by taking up one quarter of anthropogenic CO 2 emissions 5. As CO 2 reacts with seawater to form carbonic acid, oceanic CO 2 uptake increases seawater acidity, a process termed ocean acidification. While elevated CO 2 can benefit carbon acquisition in photosynthetic organisms, increased acidity alters the transmembrane potential, which affects a range of cellular processes, including acid-base regulation, nutrient uptake and calcification 6,7. The sensitivity to acidification-induced changes in seawater conditions differs between phytoplankton groups and even between species of the same taxonomic group 8. By altering the competitive fitness of interacting species or the palatability for predators, this can shift the composition of phytoplankton communities. Basic ecosystem functions are generally maintained if the shifts occur among functionally redundant species. However, if the change in community composition involves the loss of a keystone

PLOS ONE, 2016

Every year, the oceans absorb about 30% of anthropogenic carbon dioxide (CO 2) leading to a re-eq... more Every year, the oceans absorb about 30% of anthropogenic carbon dioxide (CO 2) leading to a re-equilibration of the marine carbonate system and decreasing seawater pH. Today, there is increasing awareness that these changes-summarized by the term ocean acidification (OA)-could differentially affect the competitive ability of marine organisms, thereby provoking a restructuring of marine ecosystems and biogeochemical element cycles. In winter 2013, we deployed ten pelagic mesocosms in the Gullmar Fjord at the Swedish west coast in order to study the effect of OA on plankton ecology and biogeochemistry under close to natural conditions. Five of the ten mesocosms were left unperturbed and served as controls (~380 μatm pCO 2), whereas the others were enriched with CO 2-saturated water to simulate realistic end-of-the-century carbonate chemistry conditions (~760 μatm pCO 2). We ran the experiment for 113 days which allowed us to study the influence of high CO 2 on an entire winter-to-summer plankton succession and to investigate the potential of some plankton organisms for evolutionary adaptation to OA in their natural environment. This paper is the first in a PLOS collection and provides a detailed overview on the experimental design, important events, and the key complexities of such a "long-term mesocosm" approach. Furthermore, we analyzed whether simulated end-of-the-century carbonate chemistry PLOS ONE |

Biogeosciences Discussions, 2015

Ocean acidification is expected to influence plankton community structure and biogeochemical elem... more Ocean acidification is expected to influence plankton community structure and biogeochemical element cycles. To date, experiments with nutrient stimulated blooms have been primarily used to study the response of plankton communities to elevated CO 2. In this CO 2 manipulation study, we used large-volume (∼ 55 m 3) pelagic in situ mesocosms to enclose a natural, post spring-bloom plankton assemblage in the Baltic Sea to investigate the response of organic matter pools to ocean acidification. In the mesocosms, f CO 2 was manipulated yielding a range of average f CO 2 of 365 to ∼ 1231 µatm with no adjustment of naturally available nutrient concentrations. Plankton community development and key biogeochemical element pools were subsequently followed in this nitrogen-limited ecosystem over a period of seven weeks. We identified three distinct phases based on temperature fluctuations and plankton biomass: a warm, productive period with elevated chlorophyll a and particulate matter concentrations (Phase I), a decline in autotrophic biomass coinciding with cooler water temperatures associated with lower incoming photosynthetically active radiation (PAR) and higher zooplankton grazing pressure (Phase II), and a steady state phase with low net change in particulate and dissolved matter pools (Phase III). We observed higher sustained chlorophyll a and particulate matter concentrations (∼ 25 % higher) and lower inorganic phosphate concentrations in the water column in the highest f CO 2 treatment (1231 µatm) in Phase III. Size-fractionated phytoplankton pigment analyses indicated that these differences were driven by picophytoplankton (< 2 µm) and were already established early in the experiment during Phase I. However the influence of picophytoplankton on bulk organic matter pools was masked by high biomass of larger plankton until Phase III when the small size fraction (< 2 µm) contributed up to 90 % of chlorophyll a. Furthermore, CO 2-related differences in water column suspended matter concentrations were not reflected in sinking material flux. Our results from this study indicate that ocean acidification could have significant and sustained impacts on pelagic biogeochemical element pools in nitrogen-limited ecosystems.

Polar Biology, 2015

Benthic communities north of Svalbard are less investigated than in other Arctic shelf regions, a... more Benthic communities north of Svalbard are less investigated than in other Arctic shelf regions, as this area was covered by sea-ice during most of the year. Improving our knowledge on this region is timely, however, since climate change is strongly evident there, particularly with regard to the extent of sea-ice decline and its huge ecological impact on all marine biota, including the benthos. Moreover, longer ice-free periods will certainly lead to an increase in human activity levels in the area, including bottom trawling. In two adjacent shelf and slope regions off northern Svalbard, we studied the composition of epibenthic megafauna and seafloor habitat structures by analyzing seabed images taken with both still and video cameras. In addition, we also used an Agassiz trawl to catch epibenthic organisms for ground-truthing seabedimage information. A wide variety of mostly sessile organisms 141 epibenthic taxa were identified in the images. The brittle star Ophiura sarsii and the soft coral Gersemia rubiformis were the most common species. At all stations [300 m in depth, evidence of trawling activities was detected at the seabed. The distribution of the benthic fauna in the study area exhibited a clear depth zonation, mainly reflecting depth-related differences in seabed composition. We conclude that natural factors determining the composition of the seafloor mostly affect the distribution and composition of epibenthic assemblages. Anthropogenic impact indicated by the trawl scours found is likely also important at smaller spatial scales.

ABSTRACT This study investigated the effect of ocean acidification (OA) and warming on the surviv... more ABSTRACT This study investigated the effect of ocean acidification (OA) and warming on the survival of Western Baltic cod (Gadus morhua) larvae reared in the laboratory in 90 L tanks at ambient CO2 concentrations (400 ppm) and CO2 concentrations as predicted for the end of the century (1000 ppm). Temperature (7°C and 9°C) as an additional stressor was studied in a full-factorial design with CO2. Larvae were fed natural plankton at a low food density and mortality was measured daily by removing dead larvae from the tanks. Growth measurements including standard length, myotome height as well as otolith measurements were analysed. The results clearly show that an increased CO2 concentration had a significant negative effect on the survival of the larvae mostly during critical phases in larval development. An increase in temperature, however, did not further increase mortality. Growth and otolith measurements strongly suggest an increase in growth rate and size-selective mortality with selection for larger larvae occurring under increased CO2 conditions. The results will be compared and discussed in relation to other experimental results with respect to OA and cod larvae. The larval response to OA seems to be dependent on the developmental stage and their nutritional condition.

Biogeosciences, 2013

The effect of ocean acidification on the fatty acid composition of a natural plankton community i... more The effect of ocean acidification on the fatty acid composition of a natural plankton community in the Arctic was studied in a large-scale mesocosm experiment, carried out in Kongsfjorden (Svalbard, Norway) at 79°N. Nine mesocosms of ∼50 m 3 each were exposed to 8 different pCO 2 levels (from natural background conditions to ∼1420 µatm), yielding pH values (on the total scale) from ∼8.3 to 7.5. Inorganic nutrients were added on day 13. The phytoplankton development during this 30-day experiment passed three distinct phases: (1) prior to the addition of inorganic nutrients, (2) first bloom after nutrient addition, and (3) second bloom after nutrient addition. The fatty acid composition of the natural plankton community was analysed and showed, in general, high percentages of polyunsaturated fatty acids (PU-FAs): 44-60 % of total fatty acids. Positive correlations with pCO 2 were found for most PUFAs during phases 2 and/or 3, with the exception of 20:5n3 (eicosapentaenoic acid, EPA), an important diatom marker. These correlations are probably linked to changes in taxonomic composition in response to pCO 2. While diatoms (together with prasinophytes and haptophytes) increased during phase 3 mainly in the low and intermediate pCO 2 treatments, dinoflagellates were favoured by high CO 2 concentrations during the same time period. This is reflected in the development of group-specific fatty acid trophic markers. No indications were found for a generally detrimental effect of ocean acidification on the planktonic food quality in terms of essential fatty acids.