Henriette G. Horn

Universitetet i Agder | UIA · Centre for Coastal Research

Cold-water corals (CWCs) are important ecosystem engineers in the deep sea that provide habitat for numerous species and can form large coral mounds. These mounds influence surrounding currents and induce distinct hydrodynamic features, such as internal waves and episodic downwelling events that accelerate transport of organic matter towards the mo...

The Eastern Scheldt estuary in the Netherlands has been anthropogenically changed by the construction of a storm surge barrier about 30 years ago, affecting abiotic conditions as well as phytoplankton and zooplankton (ZP). As ZP communities have not been sampled in the last decades, it is unclear to what extent they have changed during the last 30...

## Full-text available: https://rdcu.be/b3Q7R ## Aquatic ecosystems face a multitude of environmental stressors, including warming and acidification. While warming is expected to have a pronounced effect on plankton communities, many components of the plankton seem fairly robust towards realistic end-of-century acidification conditions. However, in...

Ocean acidification, the change in seawater carbonate chemistry due to the uptake of anthropogenic CO2, affects the physiology of marine organisms in multiple ways. Diverse competitive and trophic interactions transform the metabolic responses to changes in community composition, seasonal succession and potentially geographical distribution of spec...

Ocean acidification (OA) is one of the most critical anthropogenic threats to marine ecosystems. While significant ecological responses of plankton communities to OA have been revealed mainly by small-scale laboratory approaches, the interactive effect of OA-related changes on zooplankton metabolism and their biogeochemical implications in the natu...

In the autumn of 2014, nine large mesocosms were deployed in the oligotrophic subtropical North-Atlantic coastal waters off Gran Canaria (Spain). Their deployment was designed to address the acidification effects of CO2 levels from 400 to 1,400 μatm, on a plankton community experiencing upwelling of nutrient-rich deep water. Among other parameters,...

Gravitational sinking of photosynthetically fixed particulate organic carbon (POC) constitutes a key component of the biological carbon pump. The fraction of POC leaving the surface ocean depends on POC sinking velocity (SV) and remineralization rate (Cremin), both of which depend on plankton community structure. However, the key drivers in plankto...

Ocean acidification (OA) is affecting marine ecosystems through changes in carbonate chemistry that may influence consumers of phytoplankton, often via trophic pathways. Using a mesocosm approach, we investigated OA effects on a subtropical zooplankton community during oligotrophic, bloom, and post-bloom phases under a range of different pCO2 level...

Ocean acidification (OA) is expected to alter plankton community structure in the future ocean. This, in turn, could change the composition of sinking organic matter and the efficiency of the biological carbon pump. So far, most OA experiments involving entire plankton communities have been conducted in meso- to eutrophic environments. However, rec...

The acidification of the oceans could potentially alter marine plankton communities with consequences for ecosystem functioning. While several studies have investigated effects of ocean acidification on communities using traditional methods, few have used genetic analyses. Here, we use community barcoding to assess the impact of ocean acidification...

Final OTU table based on the 18S gene region containing the HTS reads. Columns A—E contain information about the sampling day, sampling method, sampled mesocosms and CO2 treatment. Columns F—P contain information about environmental variables. Columns Q—ACB contain OTU information. This data was used for adonis, PCA (Fig 3), nMDS (Fig 2) and RDA (F...

Final OTU table based on the cox1 gene region containing the HTS reads. Columns A—E contain information about the sampling day, sampling method, sampled mesocosms and CO2 treatment. Columns F—AN contain OTU information. This data was used for adonis analysis. (TXT)

Steps of the bioinformatics pipeline. Including the programs used, decreasing sequence reads, and OTU numbers. (PDF)

Ocean acidification may affect zooplankton directly by decreasing in pH, as well as indirectly via trophic pathways, where changes in carbon availability or pH effects on primary producers may cascade up the food web thereby altering ecosystem functioning and community composition. Here, we present results from a mesocosm experiment carried out dur...

Oceanic uptake of anthropogenic carbon dioxide (CO2) causes pronounced shifts in marine carbonate chemistry and a decrease in seawater pH. Increasing evidence indicates that these changes—summarized by the term ocean acidification (OA)—can significantly affect marine food webs and biogeochemical cycles. However, current scientific knowledge is larg...

Ocean acidification is considered as a crucial stressor for marine communities. In this study, we tested the effects of the IPCC RPC6.0 end-of-century acidification scenario on a natural plankton community in the Gullmar Fjord, Sweden, during a long-term mesocosm experiment from a spring bloom to a mid-summer situation. The focus of this study was...

Results from the dilution experiment. Mean values and standard error (Std.error) of the phytoplankton growth rate k, instantaneous (natural) phytoplankton growth rate μ0, phytoplankton mortality m and microzooplankton grazing rate g are shown for the different phytoplankton groups distinguished in the dilution experiment. (DOCX)

Results from the community grazing experiments. Mean values and standard error (Std.error) of the net growth rates calculated for the most abundant groups of phytoplankton, ciliates and dinoflagellates (dinos) in experiment (Exp.) 1 and 2. The four treatments used were low CO2 without grazer (Low -G), low CO2 with grazer (Low +G), high CO2 without...

Results from the analysis of the community grazing experiments. Results from the ANOVAs from the two community grazing experiments. Effects of CO2, grazer presence (Grazer), and the interaction of the two factors on growth rate of total phytoplankton and ciliates as well as the most common taxa of the two groups are shown. Transformations are indic...

Every year, the oceans absorb about 30% of anthropogenic carbon dioxide (CO2) 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, thereb...

Temperature profiles over the course of the study. Changes in temperature averaged over the entire water column are represented by the white line plots on top of the contours with the corresponding y-axes on the right side. The black lines at t37 mark the end of convective mixing (See also Fig 5). (DOCX)

Contributions intended to be published within the framework of the BIOACID II long-term mesocosm study. Note that two studies [16,32] have already been published before initiating the PLOS collection. (DOCX)

Abundance of individual plankton groups during peak chla concentrations in phase II. For the community-based analysis we generally included functional groups rather than species. For copepods, we only included Pseudocalanus sp. here since this species strongly dominated the copepod community both, numerically and in terms of biomass. (Note, however...

Abundance of individual plankton groups during the post bloom period in phase IV. For the community-based analysis we generally included functional groups rather than species. For copepods, we only included Pseudocalanus sp. here since this species strongly dominated the copepod community both, numerically and in terms of biomass. (Note, however, t...

Underwater photograph (~8 m depth) of a mesocosm at the end of the first (failed) experiment where we enclosed seawater with a considerably higher salinity than usually experienced in the fjord. The heavy water was accumulating at the bottom of the mesocosm and leaked out of the bags into the fjord through a weak point in the connection between the...

(A) Development of picoeukaryote abundance in the first experiment (12th February until the 3rd March). The two grey lines frame the period of CO2 addition. High CO2 mescosms (warm colors: M2, M4, M6, M7, M8) reached an average pCO2 of 1063 (±15) μatm on t-16. Ambient CO2 mesocosms (cold colors: M1, M3, M5, M9, M10) were left unperturbed with an av...

Abundance of individual plankton groups during peak chla concentrations in phase III. For the community-based analysis we generally included functional groups rather than species. For copepods, we only included Pseudocalanus sp. here since this species strongly dominated the copepod community both, numerically and in terms of biomass. (Note, howeve...

Ocean acidification has direct physiological effects on organisms, for example by dissolving the calcium carbonate structures of calcifying species. However, non-calcifiers may also be affected by changes in seawater chemistry. To disentangle the direct and indirect effects of ocean acidification on zooplankton growth, we undertook a study with two...

Among the environmental stressors affecting the oceans, warming and acidification have been identified as two of the most important ones. Currently, the understanding of the effects of the two stressors on plankton communities forming the base of the food web is still incomplete. Data availability for long-term effects, interactions effects of the...

Global warming and ocean acidification are among the most important stressors for aquatic ecosystems in the future. To investigate their direct and indirect effects on a near-natural plankton community, a multiple-stressor approach is needed. Hence, we set up mesocosms in a full-factorial design to study the effects of both warming and high CO2 on...