Sofia Ribeiro

Phytoplankton growth after a century of dormancy illuminates past resilience to catastrophic darkness

Photosynthesis evolved in the oceans more than 3 billion years ago and has persisted throughout all major extinction events in Earths history. The most recent of such events is linked to an abrupt collapse of primary production due to darkness following the Chicxulub asteroid impact 65.5 million years ago. Coastal phytoplankton groups (particularly dinoflagellates and diatoms) appear to have been resilient to this biotic crisis, but the reason for their high survival rates is still unknown. Here we show that the growth performance of dinoflagellate cells germinated from resting stages is unaffected by up to a century of dormancy. Our results clearly indicate that phytoplankton resting stages can endure periods of darkness far exceeding those estimated for the Cretaceous-Paleogene extinction and may effectively aid the rapid resurgence of primary production in coastal areas after events of prolonged photosynthesis shut-down.

Buried alive – germination of up to a century-old marine protist resting stages

Lundholm N., Ribeiro S., Andersen T.J., Koch T., Godhe A., Ekelund F. and Ellegaard M. 2011. Buried alive – germination of up to a century-old marine protist resting stages. Phycologia 50: 629–640. DOI: 10.2216/11-16.1 We report on the survival and germination of up to a century-old marine protist resting stages naturally preserved in sediments from Koljö Fjord on the west coast of Sweden. This work has focused on germination of dinoflagellate cysts, but diatom resting stages were also observed. We record the longest known survival of dormant dinoflagellate cells. We individually isolated more than 1200 cysts of the three most abundant dinoflagellate taxa: Pentapharsodinium dalei, Lingulodinium polyedrum and Scrippsiella spp. Germination success decreased with core depth, and all successful germinations took place within the first 2 wk of incubation. Pentapharsodinium dalei had the highest germination success rate, with a maximum of up to 80% in 28-yr-old sediment, and could successfully germinate from core sediments dated to 1920 ± 12. Scrippsiella spp. cysts with cell contents occurred down to c. 90-yr-old sediment and could germinate from down to ca. 40-yr-old sediments, with a maximum germination rate of 50–60% in recent sediments. Cysts of L. polyedrum germinated frequently down to 20 yr and rarely to c. 80 yr, with a maximum of 20–50% germination success in recent sediments. Cyst isolation under cooled conditions rather than at room temperature resulted in a significantly higher germination success in P. dalei, while no effect was observed for L. polyedrum. The time elapsed since slicing of the core affected survival of L. polyedrum cysts negatively, most likely due to the effect of oxygen. The long-term survival potential of benthic resting stages that we report here has important implications, as viable resting stages accumulated in bottom sediments can be transported back to the water column by, for example, bioturbation and human-mediated sediment dredging. Hence, the sediment may to a higher degree than previously considered play a role as seed bank. This is important in a changing climate and might have particularly severe impacts in the case of harmful species.

Protoperidinium minutum (Dinophyceae) from Portugal: cyst–theca relationship and phylogenetic position on the basis of single-cell SSU and LSU rDNA sequencing

Ribeiro S., Lundholm N., Amorim A. and Ellegaard M. 2010. Protoperidinium minutum (Dinophyceae) from Portugal: cyst–theca relationship and phylogenetic position on the basis of single-cell SSU and LSU rDNA sequencing. Phycologia 49: 48–63. DOI: 10.2216/09-11.1 Round brown spiny cysts are common elements of Recent and Quaternary dinoflagellate cyst records and are often used to infer past climate conditions. Echinidinium and Islandinium, two cyst-based genera composed of round brown spiny cysts, are believed to have affinities within the Protoperidiniaceae. However, their biological counterparts are still virtually unknown. In this study, we examined the cyst–theca relationship of an Echinidinium-like cyst isolated from recent sediments of the Portuguese coast. The cysts (25–34 µm) had an intercalary theropylic archeopyle and numerous processes (4–9 µm) with tapered stems and minutely expanded tips. Germinated cells were identified as Protoperidinium minutum on the basis of theca morphology and tabulation. This taxon has a complicated taxonomic history and most likely represents a complex of species with very similar thecae but different cyst morphologies. To provide a first step in elucidating the phylogeny of P. minutum and its evolutionary relationship among the Protoperidiniaceae, we undertook the first molecular study of this taxon on the basis of small-subunit (SSU) and large-subunit (LSU) ribosomal (r)DNA genetic sequences obtained through single-cell polymerase chain reaction. On the basis of SSU rDNA analysis, P. minutum formed a clade together with the Diplopsaloideae, not grouping together with the other Protoperidinium species. LSU rDNA-based phylogenies indicate P. minutum as early divergent within the Protoperidiniaceae. The evolutionary significance of round brown spiny cysts produced by P. minutum-like species and diplopsalids is discussed.

Hundred Years of Environmental Change and Phytoplankton Ecophysiological Variability Archived in Coastal Sediments

Marine protist species have been used for several decades as environmental indicators under the assumption that their ecological requirements have remained more or less stable through time. However, a growing body of evidence suggests that marine protists, including several phytoplankton species, are in fact highly diverse and may quickly respond to changes in the environment. Predicting how future climate will impact phytoplankton populations is important, but this task has been challenged by a lack of time-series of ecophysiological parameters at time-scales relevant for climate studies (i.e. at least decadal). Here, we report on ecophysiological variability in a marine dinoflagellate over a 100-year period of well-documented environmental change, by using the sedimentary archive of living cysts from a Scandinavian fjord (Koljö Fjord, Sweden). During the past century, Koljö Fjord has experienced important changes in salinity linked to the North Atlantic Oscillation (NAO). We revived resting cysts of Pentapharsodinium dalei preserved in the fjord sediments and determined growth rates for 18 strains obtained from 3 sediment core layers at salinity 15 and 30, which represent extreme sea-surface conditions during periods of predominantly negative and positive NAO phases, respectively. Upper pH tolerance limits for growth were also tested. In general, P. dalei grew at a higher rate in salinity 30 than 15 for all layers, but there were significant differences among strains. When accounting for inter-strain variability, cyst age had no effect on growth performance or upper pH tolerance limits for this species, indicating a stable growth response over the 100-year period in spite of environmental fluctuations. Our findings give some support for the use of morphospecies in environmental studies, particularly at decadal to century scales. Furthermore, the high intra-specific variability found down to sediment layers dated as ca. 50 years-old indicates that cyst-beds of P. dalei are repositories of ecophysiological diversity.

Cyst-theca relationships and phylogenetic positions of Peridiniales (Dinophyceae) with two anterior intercalary plates, with description of Archaeperidinium bailongense sp. nov. and Protoperidinium fuzhouense sp. nov

Protoperidinium species with two anterior intercalary plates were originally classified by Jörgensen in the subgenus Archaeperidinium and assigned to the sections Excentrica, Avellana and Archaeperidinium by Taylor, on the basis of the relative size of anterior intercalary plates and the extent of cingulum displacement. Phylogenetic relationships among these three sections have not been fully explored. Recently, Archaeperidinium was reinstated as a genus, but several species fitting the emended description have not been transferred formally as molecular data were not available. In the present study we examined the cyst‐theca relationship of seven species with two anterior intercalary plates: four species assigned to Protoperidinium and three to Archaeperidinium, from the China Sea. Partial large subunit ribosomal DNA sequences were obtained from these seven species by single‐cell polymerase chain reaction, and for the cyst of Protoperidinium stellatum from France. Two new species, Archaeperidinium bailongense and Protoperidinium fuzhouense, were described based on both theca and cyst morphology, and the cyst‐theca relationships of A. constrictum and P. abei var. rotunda were established for the first time. Maximum‐likelihood and Bayesian inference analyses revealed that P. fuzhouense was nested within the Protoperidinium sensu stricto clade despite having only six postcingular plates, and sections Excentrica, Avellana and the genus Archaeperidinium were all monophyletic. Our results suggest that the presence/absence of a sulcal fin and antapical horns and the displacement of the cingulum are the most stable characteristics of the motile stages within the respective clades.

Sea ice and primary production proxies in surface sediments from a High Arctic Greenland fjord: Spatial distribution and implications for palaeoenvironmental studies

Abstract In order to establish a baseline for proxy-based reconstructions for the Young Sound–Tyrolerfjord system (Northeast Greenland), we analysed the spatial distribution of primary production and sea ice proxies in surface sediments from the fjord, against monitoring data from the Greenland Ecosystem Monitoring Programme. Clear spatial gradients in organic carbon and biogenic silica contents reflected marine influence, nutrient availability and river-induced turbidity, in good agreement with in situ measurements. The sea ice proxy IP25 was detected at all sites but at low concentrations, indicating that IP25 records from fjords need to be carefully considered and not directly compared to marine settings. The sea ice-associated biomarker HBI III revealed an open-water signature, with highest concentrations near the mid-July ice edge. This proxy evaluation is an important step towards reliable palaeoenvironmental reconstructions that will, ultimately, contribute to better predictions for this High Arctic ecosystem in a warming climate.

Impact of Medieval Fjord Hydrography and Climate on the Western and Eastern Settlements in Norse Greenland

Abstract A comparison of the Medieval fjord hydrography and climate regime of the main Norse settlements in Greenland demonstrates important differences in the timing of sea-ice expansion and storminess when comparing the Western and Eastern Settlement regions. The Western Settlement, as well as the northern hunting grounds around Disko Bugt, had already experienced major climate deterioration in the first decades after AD 1200. This regime shift in West Greenland included an expansion of fjord and sea ice (“West Ice”) in coastal waters as well as a drastic atmospheric cooling and an increase in storminess, mainly in the summer season. In contrast, environmental conditions in the Eastern Settlement deteriorated notably later, i.e., around AD 1400. At that time, ice conditions became much more severe, whereas the previously prevailing strong wind activity decreased, which was coeval with a general decrease in aeolian activity in West Greenland, eastern Canada, and NW Iceland. Summer blockage of the fjord entrance by thick, multi-year sea ice (“Storisen”) is a specific feature of the Eastern Settlement area, whereas in the Western Settlement region, the West Ice would have threatened Norse sailing in late winter. We may thus conclude that by shortly after AD 1200 living conditions in the Western Settlement had already became less attractive due to adverse effects of the early, regional climate deterioration. Since then, the Western Settlement was probably increasingly dependent on supplies from the Eastern Settlement, where milder climate conditions continued to prevail for another century. Increased summer blockage of the Eastern Settlement fjords by the Storisen beginning around AD 1400 would have imposed serious limitations to sailing and pasture productivity in coastal areas and is suggested to have played a crucial role in the final demise of the Eastern Settlement a few decades later.

Microsatellite markers for the palaeo-temperature indicator Pentapharsodinium dalei (Dinophyceae)

Pentapharsodinium dalei is a widely distributed cold-water dinoflagellate, which is used in palaeoecology as an indicator of relatively warmer conditions in polar and sub-polar regions. This species has been proposed to be one of the first indicators of global warming at high latitudes. We developed the first microsatellite markers for P. dalei to facilitate the study of spatial and temporal population genetic changes. Single cysts were isolated from surface sediments in Koljö Fjord, Sweden. After cyst germination, single vegetative cells were isolated for establishing monoclonal cultures. Six dinucleotide polymorphic microsatellite markers were developed as multiplex polymerase chain reactions and were genotyped in 32 strains. The number of alleles per locus varied between 4 and 12, and the estimated gene diversity varied from 0.588 to 0.891. The haploid state of the vegetative cells was confirmed. The six selected microsatellites will be useful to explore population dynamics in P. dalei from contemporary planktonic and revived benthic samples to enable, for example, detailed studies into the evolutionary consequences of anthropogenic and climate-driven habitat changes.

The long-term persistence of phytoplankton resting stages in aquatic ‘seed banks’

In the past decade, research on long‐term persistence of phytoplankton resting stages has intensified. Simultaneously, insight into life‐cycle variability in the diverse groups of phytoplankton has also increased. Aquatic ‘seed banks’ have tremendous significance and show many interesting parallels to terrestrial seed beds of vascular plants, but are much less studied. It is therefore timely to review the phenomenon of long‐term persistence of aquatic resting stages in sediment seed banks. Herein we compare function, morphology and physiology of phytoplankton resting stages to factors central for persistence of terrestrial seeds. We review the types of resting stages found in different groups of phytoplankton and focus on the groups for which long‐term (multi‐decadal) persistence has been shown: dinoflagellates, diatoms, green algae and cyanobacteria. We discuss the metabolism of long‐term dormancy in phytoplankton resting stages and the ecological, evolutionary and management implications of this important trait. Phytoplankton resting stages exhibiting long‐term viability are characterized by thick, often multi‐layered walls and accumulation vesicles containing starch, lipids or other materials such as pigments, cyanophycin or unidentified granular materials. They are reported to play central roles in evolutionary resilience and survival of catastrophic events. Promising areas for future research include the role of hormones in mediating dormancy, elucidating the mechanisms behind metabolic shut‐down and testing bet‐hedging hypotheses.

A century-long genetic record reveals that protist effective population sizes are comparable to those of macroscopic species

Effective population size (Ne) determines the rate of genetic drift and the relative influence of selection over random genetic changes. While free-living protist populations characteristically consist of huge numbers of cells (N), the absence of any estimates of contemporary Ne raises the question whether protist effective population sizes are comparably large. Using microsatellite genotype data of strains derived from revived cysts of the marine dinoflagellate Pentapharsodinium dalei from sections of a sediment record that spanned some 100 years, we present the first estimates of contemporary Ne for a local population in a free-living protist. The estimates of Ne are relatively small, of the order of a few 100 individuals, and thus are similar in magnitude to values of Ne reported for multicellular animals: the implications are that Ne of P. dalei is of many orders of magnitude lower than the number of cells present (Ne/N ∼ 10−12) and that stochastic genetic processes may be more prevalent in protist populations than previously anticipated.