Arctic Plankton Communities Research Articles

Environmental control of Arctic marine zooplankton near a large archipelago during the summer season

In order to assess the impact of environmental conditions on marine zooplankton, we conducted a survey around Novaya Zemlya (NZ), a large archipelago located within the Arctic Ocean, during the summertime of 2022. Observations were made by employing net hauls that spanned the entire water column. Through the use of cluster analysis, we ascertained the existence of two unique assemblages inhabiting the Barents and Kara seas. The highest zooplankton abundance, biomass, and diversity were observed at the intersection of the warm Atlantic Water and the comparatively colder Barents Sea Water along the western coast of NZ. Copepods were the predominant species within the zooplankton population in both regions, registering similar numbers, while other groups were noticeably more numerous in the Barents Sea. The distribution of different plankton groups predominantly correlated with the current systems encircling NZ. The inshore waters proximate to the eastern segment of NZ were influenced by the presence of cold currents, while the western part was subjected to the effects of warmer currents. A strong association was observed between zooplankton and microbial variables, such as the abundance and biomass of prokaryoto- and virioplankton. Redundancy analysis indicated close interactions within the plankton ecosystems of the region. These findings may be valuable for assessing the potential impacts of recent climatic perturbations in the Arctic and establishing a baseline for studying Arctic plankton communities in coastal ecosystems.

A database of zooplankton abundance in the Atlantic sectors of the Southern and sub-Arctic Oceans

SummaryScientific sampling of zooplankton in the Atlantic sector of the Southern Ocean has been undertaken since the 1920s, but few analyzed datasets are available to the research community. We provide a database of standardized data derived from samples collected by Bongo nets in this sector between 1996 and 2013, amounting to almost 94,000 individual records. The study region contains some of the highest levels of pelagic biomass in the Southern Ocean and is also undergoing rapid ocean warming and changing seasonality in sea-ice distribution. Data from a single expedition to the sub-Arctic where the same sampling methodology was used are also included. Atlantic water is an increasing influence in that region, as is the prevalence of boreal plankton taxa within Arctic plankton communities. These data will be of value in supporting studies assessing the impacts of climate change on the structure and function of polar pelagic systems.

Parasite–copepod interactions in Svalbard: diversity, host specificity, and seasonal patterns

Copepods of the genera Calanus and Pseudocalanus are important components of Arctic marine ecosystems. Despite the key roles of these zooplankters, little is known about the organisms they interact with most intimately, their parasites and symbionts. We applied metabarcode sequencing to uncover eukaryotic parasites present within these two copepod genera from three areas around the high Arctic archipelago of Svalbard. Ten distinct parasite groups were observed: four different Apostome ciliates, four different dinoflagellates (Chytriodinium sp., Ellobiopsis sp., Thalassomyces sp., and Hematodinium sp.), a Paradinium sp., and a trematode. Apostome ciliates closely related to Pseudocollinia spp. were the most commonly observed parasite, with overall infection rates of 21.5% in Calanus and 12.5% in Pseudocalanus. Infection by these ciliates varied seasonally, with no infections observed in early winter, but infection rates exceeding 75% in spring. Host specificity varied between parasites, with significant differences in infection rate between the two host copepod genera for four parasites (two ciliates, Chytriodinium, and a trematode). The diverse assemblage of parasites observed in these copepods, and the frequency of infection, with over one in five copepod individuals infected, suggest parasites may be playing a greater role in Arctic plankton communities than generally acknowledged.

Warming and CO2 Enhance Arctic Heterotrophic Microbial Activity.

Ocean acidification and warming are two main consequences of climate change that can directly affect biological and ecosystem processes in marine habitats. The Arctic Ocean is the region of the world experiencing climate change at the steepest rate compared with other latitudes. Since marine planktonic microorganisms play a key role in the biogeochemical cycles in the ocean it is crucial to simultaneously evaluate the effect of warming and increasing CO2 on marine microbial communities. In 20 L experimental microcosms filled with water from a high-Arctic fjord (Svalbard), we examined changes in phototrophic and heterotrophic microbial abundances and processes [bacterial production (BP) and mortality], and viral activity (lytic and lysogenic) in relation to warming and elevated CO2. The summer microbial plankton community living at 1.4°C in situ temperature, was exposed to increased CO2 concentrations (135–2,318 μatm) in three controlled temperature treatments (1, 6, and 10°C) at the UNIS installations in Longyearbyen (Svalbard), in summer 2010. Results showed that chlorophyll a concentration decreased at increasing temperatures, while BP significantly increased with pCO2 at 6 and 10°C. Lytic viral production was not affected by changes in pCO2 and temperature, while lysogeny increased significantly at increasing levels of pCO2, especially at 10°C (R2 = 0.858, p = 0.02). Moreover, protistan grazing rates showed a positive interaction between pCO2 and temperature. The averaged percentage of bacteria grazed per day was higher (19.56 ± 2.77% d-1) than the averaged percentage of lysed bacteria by virus (7.18 ± 1.50% d-1) for all treatments. Furthermore, the relationship among microbial abundances and processes showed that BP was significantly related to phototrophic pico/nanoflagellate abundance in the 1°C and the 6°C treatments, and BP triggered viral activity, mainly lysogeny at 6 and 10°C, while bacterial mortality rates was significantly related to bacterial abundances at 6°C. Consequently, our experimental results suggested that future increases in water temperature and pCO2 in Arctic waters will produce a decrease of phytoplankton biomass, enhancement of BP and changes in the carbon fluxes within the microbial food web. All these heterotrophic processes will contribute to weakening the CO2 sink capacity of the Arctic plankton community.

Episodic Arctic CO2 Limitation in the West Svalbard Shelf

The European Sector of the Arctic Ocean is characterized by low CO2 concentrations in seawater during spring and summer, largely due to strong biological uptake driven by extensive plankton blooms in spring. The spring plankton bloom is eventually terminated by nutrient depletion and grazing. However, low CO2 concentrations in seawater and low atmospheric resupply of CO2 can cause episodes during which the phytoplankton growth is limited by CO2. Here, we show that gross primary production (GPP) of Arctic plankton communities increases from 32 to 72 % on average with CO2 additions in spring. Enhanced GPP with CO2 additions occur during episodes of high productivity, low CO2 concentration and in the presence of dissolved inorganic nutrients. However, during summer the addition of CO2 supresses planktonic Arctic GPP. Events of CO2 limitation in spring may contribute to the termination of the Arctic spring plankton blooms. The stimulation of GPP by CO2 during the spring bloom provides a biotic feedback loop that might influence the global role played by the Arctic Ocean as a CO2 sink in the future.

Almost like a whale - first evidence of suction feeding in a seabird.

Little auks (Alle alle) are one of the most numerous seabird species in the world and feed primarily on copepods in arctic waters. Their high daily energy requirements leave them vulnerable to current changes in the arctic plankton community, where a smaller, less-profitable copepod species (Calanus finmarchicus) becomes increasingly abundant. Little auks have been estimated to require ∼60,000 copepods per day, necessitating prey capture rates of ∼6 copepods per second underwater. To achieve such performance, it has been suggested that little auks capture their prey by (non-visual) filter feeding. We tested this hypothesis by exposing little auks to varying copepod densities within a shallow experimental pool and filming their prey capture behaviour. At none of the copepod densities tested did birds filter feed. Instead, all birds captured copepods by what we identified as visually guided suction feeding, achieved through an extension of their sub-lingual pouch. Suction feeding is very common in fish and marine mammals, but to the best of our knowledge, this is the first time that it has been specifically identified in a seabird species. While presumably less efficient than filter feeding, this behaviour may allow little auks to foster higher resilience when facing the consequences of arctic climate change.

Production of dissolved organic carbon by Arctic plankton communities: Responses to elevated carbon dioxide and the availability of light and nutrients

The extracellular release of dissolved organic carbon (DOC) by phytoplankton is a potentially important source of labile organic carbon for bacterioplankton in pelagic ecosystems. In the context of increasing seawater partial pressure of CO2 (pCO2), via the oceanic absorption of elevated atmospheric CO2 (ocean acidification), several previous studies have reported increases to the relative amount of carbon fixed into particulates, via primary production (PP), and dissolved phases (DOC). During the summer of 2012 we measured DOC production by phytoplankton communities in the Nordic seas of the Arctic Ocean (Greenland, Norwegian and Barents Sea) from both in situ sampling and during three bioassay experiments where pCO2 levels (targets ~550µatm, ~750µatm, ~1000µatm) were elevated relative to ambient conditions. Measurements of DOC production and PP came from 24h incubations and therefore represent net DOC production rates, where an unknown portion of the DOC released has potentially been utilised by heterotrophic organisms. Production of DOC (net pDOC) by in situ communities varied from 0.09 to 0.64mmolCm−3d−1 (average 0.25mmolCm−3d−1), with comparative rates in two of the experimental bioassays (0.04–1.23mmolCm−3d−1) and increasing dramatically in the third (up to 5.88mmolCm−3d−1). When expressed as a fraction of total carbon fixation (i.e., PP plus pDOC), percentage extracellular release (PER) was 14% on average (range 2–46%) for in situ measurements, with PER in the three bioassays having a very similar range (2–50%). A marked increase in pDOC (and PER) was only observed in one of the bioassays where nutrient levels (nitrate, silicic acid) dropped dramatically relative to starting (ambient) concentrations; no pCO2 treatment effect on pDOC (or PER) was evident across the three experiments. Examination of in situ net pDOC (and PER) found significant correlations with decreasing silicic acid and increasing euphotic zone depth, indicating that nutrient and light availability were strong drivers of the partitioning of primary production between particulate and dissolved phases. Furthermore, the third bioassay experiment had relatively high levels of diatom biomass as well as a strong response to nitrate and silicic acid depletion, and we suggest that nutrient starved or light limited diatom communities may be strong producers of DOC in Arctic ecosystems.

Experimental Assessment of Temperature Thresholds for Arctic Phytoplankton Communities

We examined the responses of two different natural arctic plankton communities to warming in an attempt to find temperature thresholds for abrupt changes in growth or biomass. We conducted two experiments in situ using two different plankton communities; incubation temperatures represented the annual variation in these Arctic waters plus 3–4 °C to account for the potential warming expected for the Arctic Ocean during the twenty-first century. We evaluated changes in nutrient and chlorophyll a concentrations, primary production, cell abundances, and growth rates as well as cell biovolume and percentage of living cells for the main groups found during our study. Phytoplankton communities were composed of diatoms, Phaeocystis sp., Micromonas, as well as other flagellates. Results indicate a decrease in chlorophyll a concentration and growth rate at the highest temperatures tested. We also found a differing effect on cell abundance and growth rates depending on the taxonomic group or cell size: diatom abundance decreased with warming while small-sized phytoplankton showed an increasing trend at the intermediate temperature treatments. Biovolume estimates also tended to decrease with increasing temperature. We find a perceptible change in trends at intermediate temperature treatments for most of the parameters which suggests a possible thermal threshold around 5–6 °C for the arctic plankton communities examined here.

A <sup>13</sup>C labelling study on carbon fluxes in Arctic plankton communities under elevated CO<sub>2</sub> levels

Abstract. The effect of CO2 on carbon fluxes (production, consumption, and export) in Arctic plankton communities was investigated during the 2010 EPOCA (European project on Ocean Acidification) mesocosm study off Ny Ålesund, Svalbard. 13C labelled bicarbonate was added to nine mesocosms with a range in pCO2 (185 to 1420 μatm) to follow the transfer of carbon from dissolved inorganic carbon (DIC) into phytoplankton, bacterial and zooplankton consumers, and export. A nutrient–phytoplankton–zooplankton–detritus model amended with 13C dynamics was constructed and fitted to the data to quantify uptake rates and carbon fluxes in the plankton community. The plankton community structure was characteristic for a post-bloom situation and retention food web and showed high bacterial production (∼31% of primary production), high abundance of mixotrophic phytoplankton, low mesozooplankton grazing (∼6% of primary production) and low export (∼7% of primary production). Zooplankton grazing and export of detritus were sensitive to CO2: grazing decreased and export increased with increasing pCO2. Nutrient addition halfway through the experiment increased the export, but not the production rates. Although mixotrophs showed initially higher production rates with increasing CO2, the overall production of POC (particulate organic carbon) after nutrient addition decreased with increasing CO2. Interestingly, and contrary to the low nutrient situation, much more material settled down in the sediment traps at low CO2. The observed CO2 related effects potentially alter future organic carbon flows and export, with possible consequences for the efficiency of the biological pump.

Experimentally determined temperature thresholds for Arctic plankton community metabolism

Abstract. Climate warming is especially severe in the Arctic, where the average temperature is increasing 0.4 °C per decade, two to three times higher than the global average rate. Furthermore, the Arctic has lost more than half of its summer ice extent since 1980 and predictions suggest that the Arctic will be ice free in the summer as early as 2050, which could increase the rate of warming. Predictions based on the metabolic theory of ecology assume that temperature increase will enhance metabolic rates and thus both the rate of primary production and respiration will increase. However, these predictions do not consider the specific metabolic balance of the communities. We tested, experimentally, the response of Arctic plankton communities to seawater temperature spanning from 1 °C to 10 °C. Two types of communities were tested, open-ocean Arctic communities from water collected in the Barents Sea and Atlantic influenced fjord communities from water collected in the Svalbard fjord system. Metabolic rates did indeed increase as suggested by metabolic theory, however these results suggest an experimental temperature threshold of 5 °C, beyond which the metabolism of plankton communities shifts from autotrophic to heterotrophic. This threshold is also validated by field measurements across a range of temperatures which suggested a temperature 5.4 °C beyond which Arctic plankton communities switch to heterotrophy. Barents Sea communities showed a much clearer threshold response to temperature manipulations than fjord communities.

Evaluation of fatty acids as biomarkers for a natural plankton community. A field study of a spring bloom and a post-bloom period off West Greenland

An investigation of the fatty acid composition of a natural arctic plankton community was carried out over two fishing banks located between 63°N and 65°N off the West Greenland coast. Samples for fatty acid analyses, species determination and biomass assessments of the plankton community were taken at the depth of fluorescence maximum. High biomass and diatom dominance during the spring bloom and low biomass and flagellate dominance in the post-bloom period were reflected by the fatty acid profiles. The total amount of fatty acid ranged from 55 to 132 µg l–1 during the spring bloom and from 1 to 5 µg l–1 during the post bloom. Analysis of the fatty acids showed that when the plankton was dominated by diatoms of the genera Thalassiosira and Chaetoceros, the proportions of C16:1(n-7) and C20:5(n-3) were correspondingly high. C18s, and particularly C18:1(n-9), were more abundant when the plankton was dominated by small autotrophic flagellates, primarily haptophytes. We found a good positive correlation between the common diatom marker, C16:1(n-7)/C16:0, and the biomass percentage of diatoms (r=0.742, P<0.001), as well as between the biomass percentage of flagellates and total C18 fatty acids (r=0.739, P<0.001). This supports the use of these specific fatty acids and fatty acid ratios as general biomarkers of the plankton community. However, the fatty acids are not specific enough to sufficiently characterise the composition of the plankton community, and microscopical support is needed to verify observed trends.