Norman A. Andresen

Checklist of Diatoms from the Laurentian Great Lakes. II

An updated diatom (Bacillariophyta) checklist for the Great Lakes is provided. The present checklist supplants the preliminary checklist published in The Journal for Great Lakes Research in 1978 and effectively represents a 20-year update. A series of procedures were used in this update which included: a reexamination of taxa reported in the 1978 list, additions of taxa reported from the Great Lakes during the past 20 years, and a revision of taxonomy, commensurate with systematic and nomenclatural changes which have occurred primarily during the past 8 years. 1488 diatom species or subordinate taxa are considered to be correct reports from the Great Lakes out of the 2188 diatom entities reported in the list. Of the 124 genera reported 105 are considered to be names in current use. The number of diatom species reported represents a 16.5% increase and the number of genera reported represents a 78% increase over those reported in the 1978 checklist. 13% of the species reported and 32% of the genera reported are due solely to nomenclatural changes. Results indicate that Great Lakes diatoms are a biodiverse component of the ecosystem, commensurate with the wide range of habitats found in the system. The present checklist indicates that most of the newly added species are primarily benthic or periphytic in nature and these represent largely understudied habitats. These results suggest that the present checklist may only represent approximately 70% or less of the extant diatom flora of the Great Lakes system.

EFFECT OF GROWTH AND LIGHT/DARK CYCLES ON DIATOM LIPID CONTENT AND COMPOSITION1

Total extractable lipid (TEL) and lipid composition were studied throughout the growth cycle in three freshwater diatoms‐Cyclotella meneghiniana Kütz., Melosira varians C. A. Ag., and Stephanodiscus binderanus (Kütz.) Krieg under three light regimes (16:8 h LD, 20:4 h LD, and 12:12 h LD) at 20°C. Two of the diatoms demonstrated strong daylength preferences for growth; C. meneghiniana grew best under long‐day (20: 4‐h LD) conditions, whereas S. binderanus grew best under short‐day (12:12‐h LD) conditions. The lipid composition of the diatoms was similar throughout the growth cycle. Aged (2‐month‐old) cells were high in total lipid and triacylglycerols. Before the onset of active growth and during the early part of active growth, there was a reduction in total neutral lipids, primarily triacylglycerols, and an increase in all polar lipids, including chlorophyll a, acetone‐mobile polar lipids, and phospholipids. While cell numbers were still increasing, triacylglycerols increased and polar lipids decreased to levels near those found in aged cultures, Results suggest that increased triacylglycerol content of freshwater diatoms is not necessarily indicative of senescent populations.

Diatom succession in the recent sediments of Lake Okeechobee, Florida, U.S.A.

Diatoms and other siliceous microfossils were extracted from 1 cm samples of a 49 cm, 210Pb-dated core taken in 1988 from Lake Okeechobee, a large, shallow lake located in southern Florida (27° N Lat), U.S.A. Microfossil assemblages consisted mainly of sponge spicules and diatoms. Cysts or other chrysophyte remains were exceedingly rare. Although diatoms were present in low numbers and preservation was poor, trends in assemblage composition suggest that Lake Okeechobee has undergone substantial changes in hydrologic budget and trophic status during the period studied. The ratio of planktonic to benthic species was highest just prior to western settlement of the region and has been low and stable thereafter, probably indicating reduction in lake level. Taxa, particularly Actinocyclus, which are tolerant of eutrophication and salinization, increased after ca. 1940, indicating further modification of inputs to the lake.

Effect of lipid composition on the toxicity of trichlorobenzene isomers to diatoms. I. Short-term effects of 1,3,5-trichlorobenzene

Cultures ofCyclotella meneghiniana andMelosira varians were split into four flasks. Two flasks of each taxon were used for exposure experiments and two were used as controls. Exposure to 1,3,5-trichlorobenzene was initiated in one flask of each taxon in the 1 lth hour of the light period on a 16:8 h L/D regime. Another exposure was initiated four hours later in the same day (the 15th hour of the light period) in the second experimental flask of each taxon. These experiments were conducted at 15°C and 20°C for 2–4 days and were analyzed for lipid class composition.Cyclotella demonstrated some short-term changes in lipid class composition when exposures were initiated in the 11th hour of the light cycle at 20°C and in both exposures at 15°C. In contrast, short-term effects were only observed inMelosira when the exposure was initiated in the 11th hour of the light period at 20°C. Control cells demonstrated periodicities in lipid composition that appeared to be entrained with the light/dark cycle. The cultures that demonstrated toxicity effects were characterized by low triacylglycerol content, low neutral/polar lipid ratios, and a pattern of chlorophyll synthesis at the time of exposure. It is suggested that rapidly growing cells are more susceptible to short term effects of this trichlorobenzene isomer. Furthermore, timing of the initial exposure may alter toxicity results and this may be a consequence of lipid class composition at the time of exposure.

Siliceous microfossil succession in the recent history of Green Bay, Lake Michigan

Quantitative analysis of siliceous microfossils in a 210Pb dated core from Green Bay of Lake Michigan shows clear evidence of eutrophication, but a different pattern of population succession than observed in the main deposition basins of the Great Lakes. Sediments deposited prior to extensive European settlement (ca A.D. 1850) contain high relative abundance of chrysophyte cysts and benthic diatoms. Quantity and composition of microfossils deposited during the pre-settlement period represented in our core is quite uniform, except for the 30–32 cm interval which contains elevated microfossil abundance and particularly high levels of attached benthic species. Total microfossil abundance and the proportion of planktonic diatoms begins to increase ca 1860 and rises very rapidly beginning ca 1915. Maximum abundance occurs in sediments deposited during the 1970s, with a secondary peak in the late 1940s — early 1950s. Increased total abundance is accompanied by increased dominance of taxa tolerant of eutrophic conditions, however indigenous oligotrophic taxa, particularly those which are most abundant during the summer, are not eliminated from the flora, as in the lower Great Lakes. It appears that a combination of silica resupply from high riverine loadings and replacement of indigenous populations by periodic intrusions of Lake Michigan water allow sequential co-existence of species usually exclusively associated with either eutrophic or oligotrophic conditions.

NEW NOMENCLATURAL COMBINATIONS REFERRING TO DIATOM TAXA WHICH OCCUR IN THE LAURENTIAN GREAT LAKES OF NORTH AMERICA

During a recent compilation of a Great Lakes Diatom species checklist (Stoermer et al. 1999) several new nomenclatural combinations, which to our knowledge have not yet been made in the literature, came to our attention. In order to more closely align literature on Great Lakes diatoms with current taxonomic understanding and practice, we propose the following new combinations. Names listed as synonyms are those used in the checklist list (Stoermer et al. 1999). When a synonym is not given the Great Lakes Diatom species checklist used the basionym. Brummitt & Powell (1992) have been used as a guide for orthographic consistency.

Paleolimnology of the Lake of the Woods southern basin: Continued water quality degradation despite lower nutrient influx

ABSTRACT Reavie ED, Edlund MB, Andresen NA, Engstrom DR, Leavitt PR, Schottler S, Cai M. 2017. Paleolimnology of the Lake of the Woods southern basin: continued water quality degradation despite lower nutrient influx. Lake Reserv Manage. 33:369–385. Despite decades of reduced nutrient inputs, Lake of the Woods, a large, shallow boreal lake on the US-Canadian border, shows little evidence of water quality improvements in the pelagic system. Here we analyzed sediments from 6 sites in the southern basin for diverse biogeochemical (loss-on-ignition, biogenic silica, pigments) and microfossil (diatoms, chrysophytes) remains to reconstruct the environmental history of the lake. Our objectives were to quantify the magnitude and direction of historical trophic change and evaluate reasons for an apparent lack of basin recovery following documented nutrient diversion. Evidence came from fossil indicator profiles and comparisons of these long-term trends with historical land use and monitoring data. Results indicate major changes in algal communities during and following peak nutrient loading in the mid-20th century as well as more recent increases in colonial cyanobacteria and high-nutrient diatom taxa. Combined, fossil indicators reflect an anthropogenically enriched system that has undergone substantial ecological change, particularly since ∼1980, due to multiple drivers. Physical changes in lake thermal regime resulting from climate warming may be exacerbating internal phosphorus release from sediments, thereby lowering nitrogen:phosphorus ratios and enhancing cyanobacterial abundance. These drivers of lake condition in the lake may apply to other large shallow lakes that exhibit only limited biological recovery from reduced external nutrient loading.

MORPHOLOGY OF OESTRUPIA ZACHARIASII AND ITS TRANSFER TO BIREMIS

Light and scanning electron microscopical studies of the rare freshwater taxon Oestrupia zachariasii from Lake Hovsgol, Mongolia, clearly indicate that this taxon does not have features characteristic of Oestrupia, but belongs within the genus Biremis as B. zachariasii (Reichelt) Edlund, Andresen & Soninkhishig comb. nov. Biremis has internal poroid cribral plates covering marginal chambered striae that open externally by two foramina, one on the valve face and one on the valve mantle. In contrast, Oestrupia is characterized by Pinnularia/Caloneis-type alveolate striae opening internally by large internal foramina and interrupted by longitudinal costae. Biremis zachariasii also has a longitudinal row of occluded areolae on each side of the axial area, similar to some specimens of B. ambigua. Oestrupia zachariasii var. undulata is separable from the nominate variety as a shape series and is similarly proposed for transfer to Biremis as B. undulata(Schulz) Andresen, Edlund & Soninkhishig comb, et stat. nov. As currently understood, Biremis includes both marine and freshwater taxa, whereas the removal of B. zachariasii and B. undulata leaves Oestrupia as a primarily marine/brackish genus.

Effect of diatom lipid composition on the toxicity of trichlorobenzene. II. Long-term effects of 1,2,3-trichlorobenzene

Exposures of four diatoms,Cyclotella meneghiniana, Melosira italica, Melosira varians, andSynedra filiformis to 0.3 ppm 1,2,3-trichlorobenzene were initiated at the 8th and 11th hours of the light period on a 16:8 h L/D cycle at 20°C. Cell counts, lipid content, and lipid class composition were monitored for 10 days.Melosira italica demonstrated the most long-term effects. Cell counts and chlorophylla were greatly reduced on the 10th day when exposure was initiated in the 11 th hour of the light period inS. filiformis and in the 8th hour of the light period inM. varians. The data demonstrate that more immediate effects occur when exposures are initiated during periods of high polar lipid content or when polar lipids are being synthesized. Long-term effects are observed when exposure initiation occurs during periods of high neutral lipid content and higher total extractable lipid. The results suggest that the response of diatoms to low levels of chlorinated benzenes is related to normal variation in diel lipid composition. These results are repeatable, they vary with species, and exposures initiated at different times of the day may produce quite different results.

A useful tool for image enhancement

Image enhancement provides a means to facilitate information transfer without altering the image information. A plug-in for the commonly used image capture and manipulation program Photoshop™ is discussed as one useful tool.