David J. S. Montagnes

Protists decrease in size linearly with temperature: ca. 2.5% degrees C(-1).

An inverse relationship between organism size and rearing temperature is widely observed in ectotherms (‘the temperature–size rule’, TSR). This has rarely been quantified for related taxa, and its applicability to protists also required testing. Here, we quantify the relationship between temperature and mean cell volume within the protists by a meta–analysis of published data covering marine, brackish water and freshwater autotrophs and heterotrophs. In each of 44 datasets, a linear relationship between temperature and size could not be rejected, and a negative trend was found in 32 cases (20 gave significant negative regressions, p < 0.05). By combining 65 datasets, we revealed, for each 1 °C increase, a cell–size reduction of 2.5% (95% CI of 1.7–3.3%) of the volume observed at 15 °C. The value did not differ across taxa (amoebae, ciliates, diatoms, dinoflagellates, flagellates), habitats, modes of nutrition or combinations of these. The data are consistent with two hypotheses that are capable of explaining the TSR in ectotherms generally: (i) resource, especially respiratory gas, limitation; and (ii) fitness gains from dividing earlier as population growth increases. Using the above relationship we show how changes in cell numbers with temperature can be estimated from changes in biomass and vice versa; ignoring this relationship would produce a systematic error.

The annual cycle of heterotrophic planktonic ciliates in the waters surrounding the Isles of Shoals, Gulf of Maine: an assessment of their trophic role

Ciliates in the waters surrounding the Isles of Shoals, Gulf of Maine were collected from May 1985 to August 1986 in sampling bottles, fixed in Bouins solution, and quantitatively protargol stained. Cell abundance and biomass were separated into four size classes. Large species were prevalent in the spring while smaller species dominated in the summer. Ciliate abundance ranged from 0.35 to 6×106 m-3 annually while biomass ranged from 2.7 to 240 J m-3. Production, estimated using a multiple regression equation which incorporated ambient temperature and cell volume, ranged from 2.5 to 105 J m-3d-1. A model was constructed to determine the relative importance of ciliates in the planktonic food web. Blooms could provide a brief but significant transfer of energy to upper trophic levels. However, at best, ciliates may contribute 12% to the copepod ration and 3% of their available food.

Taxonomic descriptions of some conspicuous species in the family Strombidiidae (Ciliophora: Oligotrichida) from the Isles of Shoals, Gulf of Maine

Ten species of marine strombidiid ciliates were identified after protargol staining plankton samples. The taxonomic redescriptions include a diagnosis for Tontonia gracillima Faure-Fremiet, 1924, Strombidium wulffi (Wulff, 1919) Kahl, 1932, Strombidium acutum Leegaard, 1915, Strombidium constrictum (Meunier, 1910) Wulff, 1919, Strombidium compressum (Leegaard, 1915) Kahl, 1932, and Strombidium sulcatum Claparede & Lachmann, 1858. Four new species, Strombidium dalum n.sp., Strombidium epidemum n.sp., Strombidium rhynchum n.sp., and Strombidium tressum n.sp., are defined based primarily on the characteristics of the anterior oral polykinetids, numbers of oral polykinetids, and presence of anterior protuberance.

The Effect of the Quantitative Protargol Stain and Lugol's and Bouin's Fixatives On Cell Size: A More Accurate Estimate of Ciliate Species Biomass

ABSTRACT. The quantitative protargol stain (QPS) is used to estimate ciliate biomass and species composition from mixed field samples. Length, width, breadth and volume of live Euplotes sp., Eutintinnus sp., Strobilidium spiralis, Strombidium acutum, and Gymnodinium sanguineum were compared with 0.6% acid Lugols fixed, 5% Bouins fixed, and QPS cells. Cells shrank due to treatments (ANOVA and Tukeys test, α= 0.05). Protistan post‐fixation cell volume (as a percentage of live volume) was 55%‐80% for acid Lugols fixed, 40%‐70% for Bouins fixed, and 30%‐65% for QPS. Each species shrank to a different extent; cytostructural elements apparently alter the effect of fixation. Egestion is likely not the main cause of shrinkage since the autotroph, G. sanguineum, shrank to the same extent as the heterotrophs when stained by QPS. If field studies do not consider fixation effects on cell size, biomass may be underestimated. We recommend, for studies on planktonic ciliates, either acid Lugols and QPS be used concurrently or QPS be used alone and biovolume values divided by 0.4 to correct for shrinkage. We stress that this is a rough estimate as this value ranges from 0.3 to 0.45 for planktonic protists.

Combined effects of ammonia and microcystin on survival, growth, antioxidant responses, and lipid peroxidation of bighead carp Hypophthalmythys nobilis larvae.

Hazardous materials, such as ammonia and microcystin, are released into lakes during cyanobacterial bloom degradation and may severely impact aquatic organisms. To assess the combined effects of ammonia and microcystin on survival, growth, and oxidative stress of larval fish, 14-day-old larvae of bighead carp Hypophthalmythys nobilis were exposed to solutions with different combined concentrations of ammonia (0, 0.06, 0.264mgL(-1)) and microcystin (0, 2, 10, 30μgL(-1)) for 10 days. Microcystin significantly decreased body length, while ammonia significantly increased body weight, specific growth rate, and condition factor, but there was no significant interaction between ammonia and microcystin on them. Superoxide dismutase, catalase, and malondialdehyde significantly changed with microcystin concentration, whereas glutathione was not affected by microcystin. Ammonia significantly affected the antioxidant system. There were significant interactions between ammonia and microcystin on superoxide dismutase and malondialdehyde. Our data clearly demonstrate that ammonia and microcystin adversely affect bighead carp larvae.

The Salient Features of Five Marine Ciliates in the Class Spirotrichea (Oligotrichia), with Notes on their Culturing and Behaviour

Descriptive information is provided for five ciliates collected from marine coastal British Columbian surface waters. In this paper we identify three new species, Strobilidium neptuni n. sp., Strobilidium veniliae n. sp., and Strombidinopsis multiauris n. sp.; provide a new name and description for one previously described species, Strombidium siculum nom. nov. and provide more taxonomic data for Strombidinopsis cheshiri Snyder and Ohman, 1991.

Do protozoa contribute significantly to the diet of larval fish in the Irish Sea

This study evaluates the role of protozoa in larval fish feeding by describing protozoa in larval fish diets and testing the hypothesis that, in the Irish Sea, larval fish feed on protozoan prey at rates that potentially sustain their food requirements. Gut contents of 11 taxonomic groups of larval fish were examined, and protist prey occurred in the diet of all of them. Protozoan prey were identified, which provided an insight into their trophic role. Most of the protozoan prey were autotrophic or mixotrophic. In general, larval fish diets were constant over the spring/summer period, regardless of prey availability in the field and the composition of larval fish assemblage (taxonomy and size). A laboratory experiment on ingestion rates of flounder larvae as a function of ciliates concentration was conducted. Combined laboratory and field data showed that, in the Irish Sea, it is unlikely that ciliates are often the primary food source of flounder larvae, and, by implication, other larval fish as well. However, ciliates and other protozoa could be a substantial component of the larval fish diet, and they may potentially prevent food limitation.

A Multidisciplinary Approach to Describe Protists: Redescriptions of Novistrombidium testaceum Anigstein 1914 and Strombidium inclinatum Montagnes, Taylor, and Lynn 1990 (Ciliophora, Oligotrichia)

Abstract We combined behavioral, morphological (live, stained, scanning and transmission electron-microscope), and molecular data to redescribe two common, intertidal oligotrich ciliates, Novistrombidium testaceum and Strombidium inclinatum. Both species were collected from a rocky shore near Leghorn, Ligurian Sea. A literature review revealed four morphotypes of Novistrombidium testaceum that differ in subtle ways, including oral morphology. These differences may be diagnostic, but we do not consider them sufficient to distinguish different taxa. Although other studies have synonymised Strombidium inclinatum and S. sulcatum, based on oral structures, size, and nuclear structure, there are morphological distinctions between them. In particular, the present study supports a lack of anterior protuberance in both live and preserved S. inclinatum, while S. sulcatum possesses a protuberance. The 18S rDNA molecular data, in accordance with morphological and ultrastructural observations, indicate that the Strombidiida (Oligotrichia) constitute a well-supported clade. The separation of the genera within this clade, even between Novistrombidium and Strombidium, remains unresolved, and the analysis of more species is required. Finally, we recommend that when possible, ecologists, morphological taxonomists, and molecular biologists combine their expertise to provide comprehensive taxonomic descriptions.

A Reassessment of the Genus Strombidinopsis (Ciliophora, Choreotrichida) with Descriptions of Four New Planktonic Species and Remarks in its Taxonomy and Phylogeny

Strombidinopsis species were collected from theGulf of Alaska, Gulf of Mexico, Caribbean Sea, Gulf of Maine, and Barents Sea. Six strains were conservatively placed in six species: Strombidinopsis chilorhax sp. nov.; Strombidinopsis batos sp. nov.; Strombidinopsis sphaira sp. nov.; Strombidinopsis cercionis sp. nov.; Strombidinopsis acuminatum Faure-Fremiet, 1924; and Strombidinopsis spiniferum (Leegaard, 1915) comb. nov. Based on the characters of these species, the diagnosis of the genus Strombidinopsis was revised.

The Protozooplankton-Ichthyoplankton Trophic Link: An Overlooked Aspect of Aquatic Food Webs

ABSTRACT. Since the introduction of the microbial loop concept, awareness of the role played by protozooplankton in marine food webs has grown. By consuming bacteria, and then being consumed by metazooplankton, protozoa form a trophic link that channels dissolved organic material into the “classic” marine food chain. Beyond enhancing energy transfer to higher trophic levels, protozoa play a key role in improving the food quality of metazooplankton. Here, we consider a third role played by protozoa, but one that has received comparatively little attention: that as prey items for ichthyoplankton. For >100 years it has been known that fish larvae consume protozoa. Despite this, fisheries scientists and biological oceanographers still largely ignore protozoa when assessing the foodweb dynamics that regulate the growth and survival of larval fish. We review evidence supporting the importance of the protozooplankton–ichthyoplankton link, including examples from the amateur aquarium trade, the commercial aquaculture industry, and contemporary studies of larval fish. We then consider why this potentially important link continues to receive very little attention. We conclude by offering suggestions for quantifying the importance of the protozooplankton–ichthyoplankton trophic link, using both existing methods and new technologies.