Eun Jin Yang

In the early 20th century, Alphonse Meunier described "Papulifères" as a group of enigmatic forms of unknown taxonomic affinity characterized by possessing a hyaline pimple, a "papula". In the early 1980's Papulifères were equated with cysts of tintinnid ciliates. The most conspicuous forms, the large Fusopsis, have been widely found, and are now known to resemble the cyst of a certain species of oligotrich ciliate (i.e., Cyrtostrombidium boreale). Thus today, Papulifère forms are often assumed to be cysts of oligotrich ciliates. Here we report on 26 Papulifère forms, of more or less distinct morphologies, found in the plankton of the Chukchi Sea. We found forms resembling some of those described by Meunier, and recorded here for the first time since Meunier's reports, and others that do not resemble any of Meunier's Papulifères. Here, we first review the literature on Papulifères, then we present the surprising variety of forms we found in Chukchi Sea, and for some, we provide for the first time data on morphological variability. With this report we have expanded the catalogue of observed Papulifère forms and documented variability in the dimensions of some morphotypes. However, we urge caution in assigning a ciliate species name to any given Papulifère form in the absence of corroborating data. There is a need for observational and/or sequence-based data to elucidate the identity of Papulifère forms.

We recently documented the existence of 26 different forms of Papulifères, presumptive ciliate cysts, from plankton net tow material of the Chukchi Sea gathered in 2015, 2021, and 2022. The forms appeared to be rare, found in only 7 of the 308 samples taken in annual August surveys from 2010 to 2022. Thus, we were surprised to find them relatively common and widespread in samples gathered in August of 2023. We found 18 different Papulifére forms, 8 of which appear to be new forms, in samples from 19 of the 36 stations sampled. They were found in localities ranging from 70.5°N to 80°N. Here we report on these Papulifére forms found in 2023, providing information on morphologies and geographical distributions. With this report we have expanded the catalogue of observed Papulifére, and photographed, forms of the Chukchi Sea to a grand total of 34 of morphologically distinct forms. However, we continue to urge caution in assigning a ciliate identity to any given Papulifére form in the absence of corroborating data.

The Chukchi Sea was sampled in August of 2011, a year of near-normal sea ice among recent years, and again in August 2012, a year of all time record low sea ice. We exploited this sampling to test the hypothesis that different sea ice conditions are associated with differences in abundances or species composition of microzooplankton through an examination of tintinnids and radiolarians. From 18 stations in 2011, and 19 stations in 2012, organisms were enumerated in plankton net tow material, and chlorophyll determinations made (total and ≤ 20 μm) from discrete depth samples. We found that the low sea ice conditions of 2012 were associated with higher chlorophyll concentrations (both total and the ≤ 20 μm size fraction), compared to 2011. However, tintinnid ciliates and radiolarians were much lower in concentration, by about an order of magnitude, compared to 2011. In both years the radiolarian assemblage was dominated by Amphiselma setosa. The species composition of the tintinnid ciliates was similar in the two years, but there were distinct differences in the relative abundances of certain species. The 2012, low sea ice assemblage, was dominated by small forms in contrast to 2011, when large species were the most abundant. We present these findings in detail and discuss possible explanations for the apparent differences in the microzooplankton communities associated with distinct sea ice conditions in the Chukchi Sea.

Here we summarize the results from 10 cruises in the Chukchi Sea, in August, each year from 2011 to 2020. Samples for the qualitative analysis of the microzooplankton were obtained from stations located across the Chukchi Sea using a 20μm plankton net. Conditions encountered, in terms of sea ice coverage and chlorophyll concentrations, varied widely from year to year without any obvious relationship with the composition of the microzooplankton assemblage. Examining a total of 242 samples gathered, we found a total of 44 tintinnid species (morphologically distinct forms). Plotting cumulative number of tintinnid species encountered vs cumulative number of samplings gave a typical species accumulation curve showing no sign of saturation suggesting that continued sampling in the Chukchi Sea will likely yield increases in the tintinnid species catalogue. The tintinnid species found ranged widely in lorica opening diameters (LOD) from about 11 μm to 80 μm in diameter. However, the median size of the LOD of the tintinnid assemblages varied little from year to year ranging only from about 30 μm to 40 μm. Most of the forms encountered were found in samples from only 1 or 2 cruises. Very few forms were found every year throughout the 10 years of sampling. These were 5 species of tintinnids (Acanthostomella norvegica, Leprotintinnus pellucidus, Pytchocylis obtusa, Salpingella acuminata, Salpingella faurei) and the nasselarian radiolarian Amphimelissa setosa. Examples of the morphological variability observed among individuals of Acanthostomella norvegica and Pytchocylis obtusa within single samples are shown with some individuals easily confused with forms described as other species are shown. To our knowledge, our data are the most extensive data set on Chukchi Sea microplankton. We provide all of the data recorded, which may serve as a baseline from which to assess changes projected in Arctic Sea systems, in a supplementary data file.