Taxonomically and Functionally Distinct Ciliophora Assemblages Inhabiting Baltic Sea Ice

Ciliophora is a phylum of unicellular eukaryotes that are common and have pivotal roles in aquatic environments. Sea ice is a marine habitat, which is composed of a matrix of solid ice and pockets of saline water in which Ciliophora thrive. Here, we used phylogenetic placement to identify Ciliophora 18S ribosomal RNA reads obtained from wintertime water and sea ice, and assigned functions to the reads based on this taxonomic information. Based on our results, sea-ice Ciliophora assemblages are poorer in taxonomic and functional richness than under-ice water and water-column assemblages. Ciliophora diversity stayed stable throughout the ice-covered season both in sea ice and in water, although the assemblages changed during the course of our sampling. Under-ice water and the water column were distinctly predominated by planktonic orders Choreotrichida and Oligotrichida, which led to significantly lower taxonomic and functional evenness in water than in sea ice. In addition to planktonic Ciliophora, assemblages in sea ice included a set of moderately abundant surface-oriented species. Omnivory (feeding on bacteria and unicellular eukaryotes) was the most common feeding type but was not as predominant in sea ice as in water. Sea ice included cytotrophic (feeding on unicellular eukaryotes), bacterivorous and parasitic Ciliophora in addition to the predominant omnivorous Ciliophora. Potentially mixotrophic Ciliophora predominated the water column and heterotrophic Ciliophora sea ice. Our results highlight sea ice as an environment that creates a set of variable habitats, which may be threatened by the diminishing extent of sea ice due to changing climate.Peer reviewe

A systematic-ecological approach to Baltic Sea ice studies of algae and protists

The seasonal occurrence of sea ice that annually covers almost half the Baltic Sea area provides a unique habitat for halo- and cold temperature-tolerant extremophiles. Baltic Sea ice biology has more than 100 years of tradition that began with the floristic observation of species by the early pioneers using light microscopic techniques that were the only thing available at the time. Since the discovery of life within sea ice, more technologies have become available for taxonomy. Electron microscopy and genetic evidence have been used to identify sea ice biota revealing increased numbers of taxa. Meanwhile ecologists have used light microscopic cell enumeration in addition to the chemical and physical properties of sea ice in attempts to explain the food web structure of sea ice and its functions. Thus, during the Baltic winter, the sea ice hosts more abundant and diverse microbial communities than the water column beneath it. These communities are typically dominated by autotrophic diatoms together with a diverse assortment of dinoflagellates, auto- and heterotrophic flagellates, ciliates, metazoan rotifers and bacteria, which are mostly responsible for the recycling of nutrients. This thesis comprises ecological and systematic studies. In addition to the results of the previous studies carried out on landfast ice, the data presented here provide new insight into the spatial distribution of pelagial sea ice, which has remained largely unexplored. The studies reveal spatial heterogeneity in the pelagial sea ice of the Gulf of Bothnia. There were mismatches in chlorophyll-a concentrations and in photosynthetic efficiencies of the communities studied. The temporal succession was followed and experimental studies performed investigating the community responses towards increased or decreased light in landfast ice in the Gulf of Finland. The systematic studies carried out with established dinoflagellate cultures revealed a new resting cyst belonging to common sea ice dinoflagellate, Scrippsiella hangoei (Schiller) Larsen 1995. The cyst can be used to explain the overwintering of this species during prolonged periods of darkness. The dissimilarities and similarities in the material isolated from the sea ice called for description of a new subspecies Heterocapsa arctica ssp. frigida. The cells obtained in the cultured material were unlike those of the previously described species, necessitating description of ssp. frigida. As a result of its own unique habitus, the subspecies had been noted by Finnish taxonomists during the past three decades and thus its annual occurrence and geographical distribution in the Baltic Sea. This illustrates how combining ecology and systematics increases our understanding of organisms.Lähes joka vuosi Itämeren pinta-alasta n. puolet on merijään peitossa. Merijää toimii elinympäristönä laajoja lämpötila - ja suolaisuus eroja sietäville mikro-organismeille. Ensimmäiset jääbiologiset tutkimukset aloitettiin jo yli 100 vuotta sitten, jolloin jäätutkimuksen pioneerit raportoivat valomikroskooppisia havaintojaan merijäästä löytämistään lajeista. Sittemmin taksonominen tutkimus on teknisen kehityksen mm. elektronimikroskopian ja genetiikan yleistymisen myötävaikutuksella eriytynyt yhä edelleenkin uusia lajeja myöskin merijäästä identifioimalla. Toisaalla ekologinen tutkimus on jatkanut pieneerien alullepanemaan työtä selittääkseen merijään ravintoverkon rakennetta ja sen toimintaa, yhdistämällä valomikroskooppisin menetelmin tuotettuja eri lajien solulukumääriä merijään kemiallisiin ja fysikaalisiin ominaisuuksiin. Itämeren merijäässä esiintyy talvisin runsaslukuisempia ja monimuotoisempia mikrobieliöyhteisöjä kuin jään alapuolisessa talvisessa vesipatsaassa. Jääeliöyhteisöjen valtalajisto koostuu yleensä erilaisista yhteyttävistä piilevistä, jotka esiintyvät samanaikaisesti mitä erilaisimpien panssarisiimalevälajien, yhteyttävien ja toisenvaraisten siimaeliöiden, ripsi- ja rataseläimien sekä bakteerien kanssa. Bakteerien ollessa päävastuussa ravinteiden kierrätyksestä. Väitöskirjani perustuu osajulkaisuihin, joissa tutkitaan merijään ekologiaa ja systemaattisiin lajitutkimuksiin. Lisäyksenä aiemmin tehtyihin jääekologisiin tutkimuksiin, jotka ovat ilmesestikin logistisista käytännön syistä enimmäkseen keskittyneet yksinomaan biologisten kenttäasemien läheisyyteen muodostuvan kiintojäässä olevien mikrobiekologisten prosessien tutkimiseen, jättäen ulappa-alueelle muodostuvan ajojään lähes tutkimatta. Perämeren eri osista keräämäni aineiston perusteella ulappa-alueen jääeliöyhteisön lajistokoostumus vaihtelee maantieteellisesti ja lisäksi näiden eliöyhteisöjen yhteyttämistä varten tuottamansa klorofylli-a pigmentin määrä ja sen tehokkuus, eli kyky sitoa auringon valoenergiaa kasvien tarpeisiin eivät aina olleetkaan suhteessa toinen toisiinsa. Kokeellisin kenttätutkimuksia tekemällä tehtiin tutkimuksia jääeliöyhteisöjen ajallisista muutoksista Suomenlahdella. Sulatetusta merijäästä eristetyt puhdassoluviljelmiä tutkimalla löytyi uusi suvuton lepoitiö. Tämä jäässäkin yleisesti esiintyvä auringonvaloa tarvitsevan panssarisiimalevälaji Scrippsiella hangoei (Schiller) Larsen 1995, voisi mahdollisesti selviytyä sen avaulla pimeimmässäkin merijäässä. Merijäästä eristetyssä soluviljelmässä kasvavien panssarisiimalevä-soluissa havaituttujen samankaltaisuuksien ja erilaisuuksien perusteella päädyttiin kuvaamaan uusi ala-laji: Heterocapsa arctica subsp. frigida. Nämä solut erosivat ulkomuodoltaan muista aiemmin kuvatuista lajeista ollen geneettisesti samankaltaisia subsp actican kanssa, jolloin päättelimme että kyseessä on uusi ala-laji subsp. frigida. Kyse ei ole uustulokkaasta sillä ko. soluja on varmuudella havaittu ensimmäisen kerran jo 1970-luvulla (G. Hällfors), jonka jälkeen suomalaiset levätaksonomit ovat erottaneet sen muista lajeista ja näin ollen taksonomiaa ja ekologiaa yhdistämällä kyettiin ala-lajin kuvauksen lisäksi selvittämään ko. ala-lajin vuodenaikainen ja maantieteellinen levinneisyys Itämerellä

Mamiellophyceae shift in seasonal predominance in the Baltic Sea

The green algae Mamiellophyceae are a group of marine picoeukaryotes. We studied the succession of Mamiellophyceae in the Baltic Sea water column and ice from autumn to summer, using the hypervariable V4 region of the 18S ribosomal RNA (18S rRNA) gene. We show that species of Mamiellophyceae shift in seasonal predominance and that different species characterize sea ice, under-ice water, and the water column in the Baltic Sea.peerReviewe

Editorial : Sea Ice: Bridging Spatial-Temporal Scales and Disciplines

Non peer reviewe

Phases of microalgal succession in sea ice and the water column in the Baltic Sea from autumn to spring

The phytoplankton biomass in the Baltic Sea is low during the cold-water season (October to May) compared to the warm-water season(June to September). However, the sea ice is a habitat for diverse assemblages in polar and subpolar areas. These areas, including the Baltic Sea, are subject to changing environmental conditions due to global warming, and temporal and spatial studies are required to understand changes in the processes the organisms are involved in. We delineated microalgal succession in the northern Baltic Sea during the cold-water season using a weekly collected data set. Microscopy results together with molecular methods showed that 5 microbial groups could be distinguished: the sea-ice microalgal assemblage and 4 phytoplankton assemblages(fall, winter, under-ice water and spring). Based on cell enumeration, the microalgal biomass in the water column remained low until the end of the ice-covered season and was dominated by small flagellates and dinoflagellates. The young-ice assemblage in January resembled the water-column assemblage, but indicated a partly selective species-concentrating mechanism during ice formation due to lower species richness in ice than in the water column. Biomass of microalgae increased in the ice and water column during the March to May period, and the assemblage changed from flagellate-dominated to diatom-and dinoflagellate-dominated. The result that the spring phytoplankton, based on species and biomass, formed a separate as semblage indicates that sea-ice algae did not contribute to the spring bloom phytoplankton assemblage.Peer reviewe

Sea-ice eukaryotes of the Gulf of Finland, Baltic Sea, and evidence for herbivory on weakly shade-adapted ice algae

To determine community composition and physiological status of early spring sea-ice organisms, we collected sea-ice, slush and under-ice water samples from the Baltic Sea. We combined light microscopy, HPLC pigment analysis and pyrosequencing, and related the biomass and physiological status of sea-ice algae with the protistan community composition in a new way in the area. In terms of biomass, centric diatoms including a distinct Melosira arctica bloom in the upper intermediate section of the fast ice, dinoflagellates, euglenoids and the cyanobacterium Aphanizomenon sp. predominated in the sea-ice sections and unidentified flagellates in the slush. Based on pigment analyses, the ice-algal communities showed no adjusted photosynthetic pigment pools throughout the sea ice, and the bottom-ice communities were not shade-adapted. The sea ice included more characteristic phototrophic taxa (49%) than did slush (18%) and under-ice water (37%). Cercozoans and ciliates were the richest taxon groups, and the differences among the communities arose mainly from the various phagotrophic protistan taxa inhabiting the communities. The presence of pheophytin a coincided with an elevated ciliate biomass and read abundance in the drift ice and with a high Eurytemora affinis read abundance in the pack ice, indicating that ciliates and Eurytemora affinis were grazing on algae. (C) 2016 Elsevier GmbH. All rights reserved.Peer reviewe

On the phenology and seeding potential of sea-ice microalgal species

Sea ice is an important habitat for a wide variety of microalgal species. Depending on the species composition, sea ice can be a seeding source for pelagic phytoplankton blooms after ice melt in spring. Sea-ice algal communities were studied over 2 full winter seasons in 2014 and 2016 at Rothera Research Station, situated at the Western Antarctic Peninsula (WAP). Algal pigment patterns and microscopic observations were combined with photophysiological studies based on fluorescence analyses to monitor and explain the phenology of ice-algal species. Clear patterns in species succession were identified. Young sea ice contained a mixture of algal species including dinoflagellates, cryptophytes and diatoms like Chaetoceros spp. and Fragillariopsis spp. In winter, severe environmental conditions resulted in a decline in species diversity and selection towards heterotrophy. Pennate diatoms like Amphiprora kufferathii and Berkeleya adeliensis were the first to dominate the nutrient-enriched bottom-ice layers in early spring. The bottom communities exhibited a remarkably stable value for the photoadaptation parameter, E-k, of circa 25 mu mol photons m(-2) s(-1), Whereas pennate diatoms were most abundant in spring ice, the initial seeding event linked to ice melt was associated with flagellate species. Haptophyte species like Phaeocystis antarctica and prymnesiophytes like Pyramimonas spp. best sustained the transition from sea ice to seawater. Comparison with previous studies shows that the seeding patterns observed in Ryder Bay were characteristic over the wider sea-ice domain, Arctic and Antarctic. Over the course of this century, the WAP is predicted to experience continuing thinning and decline in sea-ice cover. For the near future, we expect that especially microalgal communities of haptophytes and chlorophytes will benefit from the changes, with yet unknown implications for carbon fluxes and higher trophic levels.Peer reviewe

Autumn to spring microbial community in the northern Baltic Sea : temporal variability in bacterial, viral and nanoflagellate abundance during the cold-water season

Marine microbial communities undergo drastic changes during the seasonal cycle in high latitude seas. Despite the dominance of microbial biomass in the oceans, comprehensive studies on the seasonal changes of microbial plankton during the complete winter period are lacking. To study the seasonal variation in abundance of the microbial community, water samples were collected weekly in the Northern Baltic Sea from October to May. During ice cover from mid-January to April, samples from the sea ice and the underlying water were taken in addition to the water column samples. Abundances of bacteria, virus-like particles, nanoflagellates, and chlorophyll a concentrations were measured from sea ice, under-ice water, and the water column, and examined in relation to environmental conditions. All studied organisms had clear seasonal changes in abundance, and the sea-ice microbial community had an independent wintertime development compared to the water column. Bacteria were observed to have a key role in the biotic interactions in both ice and the water column, and the dormant period during the cold-water months (October–May) was limited to before ice formation. Our results provide the first insights into the temporal dynamics of bacteria and viruses during the whole cold-water season (October–May) in coastal high latitude seas, and demonstrate that changes in the environmental conditions are likely to affect bacterial dynamics and have implications on trophic interactions