Regulation of phytoplankton dynamics in a Laurentian Great Lakes estuary

The composition and dynamics of phytoplankton populations were examined in Old Woman Creek estuary, Lake Erie (USA). The centric bacillariophytes,Cyclotella atomus Hust.,Cyclotella meneghiniana Kütz., andAulacoseira alpigena (Grun.) Krammer, and the cryptophytes,Cryptomonas erosa Ehren. andRhodomonas minuta var. nannoplanctonica Skuja, dominated the phytoplankton most of the year. Chlorophytes, euglenophytes, and cyanophytes were observed less frequently. Estuarine and Lake Erie phytoplankton were considered distinct populations; lake taxa were largely confined to the estuary mouth and present only in low biomass. Maxima and minima of estuarine phytoplankton coincided with meteorological and hydrological forcing in the form of rainfall and subsequent storm-water inflows, respectively. Distinct population dynamics between the upper and lower estuary following storm events were attributed to the presence/absence of refugia serving as a source for repopulation by opportunistic taxa, fluctuating light conditions in the water column resulting from influx of particulate matter and resuspension of bottom sediments, and nutrient inputs associated with surface runoff and sub-surface interflow. Additionally, agricultural herbicides introduced by storm-water inflows potentially may affect and/or control the growth and physiological responses of individual taxa.     

Late-summer phytoplankton in western Lake Erie (Laurentian Great Lakes): bloom distributions,toxicity, and environmental influences

Phytoplankton abundance and composition and the cyanotoxin, microcystin, were examined relative to environmental parameters in western Lake Erie during late-summer (2003–2005). Spatially explicit distributions of phytoplankton occurred on an annual basis, with the greatest chlorophyll (Chl) a concentrations occurring in waters impacted by Maumee River inflows and in Sandusky Bay. Chlorophytes, bacillariophytes, and cyanobacteria contributed the majority of phylogenetic-group Chl a basin-wide in 2003, 2004, and 2005, respectively. Water clarity, pH, and specific conductance delineated patterns of group Chl a, signifying that water mass movements and mixing were primary determinants of phytoplankton accumulations and distributions. Water temperature, irradiance, and phosphorus availability delineated patterns of cyanobacterial biovolumes, suggesting that biotic processes (most likely, resource-based competition) controlled cyanobacterial abundance and composition. Intracellular microcystin concentrations corresponded to Microcystis abundance and environmental parameters indicative of conditions coincident with biomass accumulations. It appears that environmental parameters regulate microcystin indirectly, via control of cyanobacterial abundance and distribution.     

Allozymic variation in tubificid oligochaetes from the Laurentian Great Lakes

Aquatic oligochaetes are an important component of the benthos in many freshwater habitats. Yet, virtually nothing is known about the population genetics of this group. Electrophoretic surveys of allozymic variation of selected members of the Family Tubificidae were conducted at six locations in the Laurentian Great Lakes of North America. Branchiura sowerbyi was the dominant member of the oligochaete fauna at two sites, and was found to be monomorphic at all enzyme loci that were examined. In contrast, members of the genus Limnodrilus, which included L. cervix, L. claparedianus, L. hoffmeisteri, L. maumeensis, and L. udekemianus showed considerable allozymic variation at several enzyme loci. L. udekemianus exhibited tri- and tetra-allelic heterozygous electromorph banding patterns at the monomeric Pgm locus, along with unbalanced heterozygous patterns at both Pgm and the dimeric Pgi locus.Genetic distance analyses suggest that L. cervix, L. claparedianus, and L. maumeensis are closely-related (genetic identifies ranged from 0.92–0.85), and may represent subspecies rather than distinct species. Breeding studies need to confirm this assertion. This survey represents the first attempt to characterize allozymic variation of aquatic oligochaetes in North America. Additional work should focus on elucidating taxonomic ambiguities within this group via both morphological and biochemical genetic studies.     

The development of ecosystem objectives for the Laurentian Great Lakes

Historically management of human use of ecosystems has been based around engineering and chemical approaches and through the construction of treatment facilities, effluent controls and setting chemical concentrations, both at end of pipe and in the aquatic environment. However, the general continued degradation of many ecosystems shows these approaches alone are insufficient. In the Laurentian Great Lakes the Great Lakes Water Quality Agreement was first signed in 1972 and ratified in 1978 and in 1987 tacitly acknowledged the problems with a chemical only approach by requiring the development of ecosystem objectives in the 1978 agreement. Furthermore, the agreement specifically identified numerical ecosystem objectives in the 1987 agreement. The evolution of ecosystem objectives in the Great Lakes has expanded from the strictly numerical objectives such as production of lake trout and abundance of the amphipod Pontoporeia hoyi. More recent developments in ecosystem objectives have been the inclusion of indicators for wildlife, habitat, human health and stewardship.Prepared as a discussion paper presented to the United Nations Economic Commission for Europe's seminar on an Ecosystems Approach to Water Management (May 27–31, 1991).     

Omega-3 Fatty Acids in Fish from the Laurentian Great Lakes Tribal Fisheries

Dietary fish must be assessed for benefits and risks to formulate risk management strategies. This article demonstrates that Laurentian Great Lakes (GL) freshwater species are good sources of omega-3 fatty acids using new data from a small sample (n = 7) of Lake Superior siscowet lake trout (Salvelinus namaycush siscowet) and five other GL fish species’ data. For Lake Superior (LS) siscowets, the saturates, mono-unsaturates, and poly-unsaturates composed 20.1, 40.7, and 39.1% of total lipid weight, respectively. Omega-3 poly-unsaturates (PUFAs) in these fish were more than twice the omega-6 (omega 3/6 ratio = 2.4). The LS lake trout data were combined with earlier LS data collected during the 1980s for eight other species and from five species of Lake Erie fish. All the GL freshwater species were compared with seven other published marine and freshwater fish studies from other global regions. PUFAs were compared based on latitude and marine versus freshwater origin. Differences between marine and freshwater species in omega-3 fatty acid were less at higher latitudes. GL freshwater fish species can be a good source of beneficial fats like marine fish and must be accounted in effective risk communications involving persistent bioaccumulative toxicants in dietary fish.     

A small population of planktonic Flavobacteria with disproportionally high growth during the spring phytoplankton bloom in a prealpine lake

Bacterioplankton growth in temperate Lake Zurich (Switzerland) was studied during the spring phytoplankton bloom by in situ techniques and short-term dilution bioassays. A peak of chlorophyll a (Chl a ) concentrations was followed by a rise of bacterial cell numbers and leucine assimilation rates, of the proportions of cells incorporating 5-bromo-2-deoxyuridine (BrdU), and of community net growth rates in dilution cultures. Incorporation of BrdU was low in Betaproteobacteria (2 ± 1%), indicating that these bacteria did not incorporate the tracer. Pronounced growth of Betaproteobacteria in the enrichments was only observed after the decline of the phytoplankton bloom. An initial peak in the proportions of BrdU-positive Actinobacteria (30%) preceded a distinct rise of their cell numbers during the period of the Chl a maximum. Cytophaga–Flavobacteria (CF) changed little in numbers, but featured high proportions of BrdU-positive cells (28 ± 12%). Moreover, CF represented > 90% of all newly formed cells in dilution cultures before and during the phytoplankton bloom. One phylogenetic lineage of cultivable Flavobacteria (FLAV2) represented a small (0.5–1%) but highly active population in lake plankton. The growth rates of FLAV2 in dilution cultures doubled during the period of the Chl a maximum, indicating stimulation by phytoplankton exudates. Thus, CF, and specifically Flavobacteria , appeared to be substantially more important for carbon transfer in Lake Zurich spring bacterioplankton than was suggested by their standing stocks. The high in situ growth potential of these bacteria might have been counterbalanced by top-down control.     

Contaminant Trends in Freshwater Fish from the Laurentian Great Lakes: A 20-Year Analysis

Although dietary concerns of Laurentian Great Lakes (GL) fish focus on the risk from persistent bioaccumulative toxicant (PBT) contaminants, fish are also an important source of nutrients beneficial to human health such as polyunsaturated fatty acids (e.g., eicosapentanoic acid and docosahexanoic acid). This study presents PBT trend data from the GL tribal fisheries over the past 20 years. PBT contaminants (282 analytes) from fillet portions of lake trout and whitefish were analyzed for trending patterns from 1992 to 2011 and are reported on five of the ATSDR/USEPA Great Lakes biomonitoring legacy contaminants (Hg, ΣDDE, ΣDDT, HCB, mirex, and ΣPCBs), two of the optional biomonitoring PBTs (toxaphene and Σdioxins/furans) and PCB 153 as a specific congener marker. Similar to other recent reports our data indicate that most PBT contaminant concentrations in the GL biota have decreased, which may indicate progress in reducing environmental emissions. Our research confirms that all contaminants demonstrate significant declines except Hg and toxaphene. Both of those remained constant after correcting for known independent factors of age, lipid, and size. These results are potentially encouraging and may provide useful data for the long distance and perhaps global influences of PBTs on the safety of fish consumption.     

Growth and decline of a diatom spring bloom phytoplankton species composition, formation of marine snow and the role of heterotrophic dinoflagellates

During the spring of 1994, we determined the factors responsiblefor the decline of the seasonal diatom bloom in the Gullmarfjord, on the west coast of Sweden. Four species constituted>75% of the biomass—Detonula confervacea, Chaetocerosdiadema, Skeletonema costatum and Thalassiosira nordenskioeldii—reachingconcentrations of 4900, 350, 8200 and 270 cells ml^–1,respectively. Growth of phytoplankton was exponential (growthrate = 0.12 day^–1) from 3 to 21 March, after which a galewith winds >15 m s^–1 caused massive aggregation. Amaximum of 130 p.p.m. (v/v) of marine snow aggregates was observedby in situ video at the peak of the bloom. Critical concentrations(Jackson, Deep-Sea Res., 37, 1197–1211, 1990) were similarto observed showing that coagulation theory could explain thesudden decline of the bloom. The heterotrophic dinoflagellateGyrodinium cf. spirale increased exponentially after the peakof the bloom with maximum (temperature-adjusted) growth rates.After the rapid aggregation and sedimentation of the bloom,they were able to control any further growth of diatoms. Nitrateand silicate were never depleted, but phosphate may have beenlimiting by the end of the study period. We conclude that massaggregation during a gale marked the end of the bloom, and thatintense grazing by heterotrophic dinoflagellates prevented anysubsequent increase of diatoms.     

Further studies of a spring phytoplankton bloom in an enclosed experimental ecosystem

A detailed characterization is presented of the spring diatom bloom which occurred in the enclosed experimental ecosystem bags at Loch Ewe, Scotland, during March–April 1983. The nutrient condition and bacterial biomass of the water column, phytoplankton species distribution, gross biochemical composition and detailed lipid composition (lipid class, fatty acid and free sterol) of the phytoplankton are reported throughout the bloom period. The results are compared with results from previous years. The conclusions are that major changes take place in the biochemical composition of a rapidly growing diatom population which affect both the gross composition and also the more detailed lipid composition. Such changes can take place over a matter of days and appear to be very dependent upon available growth conditions. Both carbohydrate and lipids levels increase towards the end of the bloom as nitrate and silicate levels are depleted in the water. Neutral lipids are shown to be important lipid components of the phytoplankton populations and long-chain ω3 polyunsaturated fatty acids are found to be only minor components of the structural polar lipids. The fatty acid and sterol data are discussed in relation to present knowledge concerning phytoplankton lipid composition.     

Histology of herniations through the body wall and cuticle of zooplankton from the Laurentian Great Lakes

Zooplankton of the Laurentian Great Lakes developed hernial protrusions whose gross appearance matches those on zooplankton described elsewhere in the world. We have carried out a histologic and cytologic analysis of the protrusions and found that they are composed of apparently degenerating or necrotic tissue(s) that has been expressed from the organism through the process of herniation. At their base the protrusions are continuous with viable tissue(s) within the organism through a fissure in the exoskeleton. Our observations lead us to suspect that these hernial protrusions are lethal. The development of such protrusions in zooplankton may be a worldwide phenomenon, but the cause of the herniation remains a mystery.     

The seasonality of phytoplankton in the North American Great Lakes,a comparative synthesis

The phytoplankton and productivity of the North American Great Lakes has been studied extensively by Fisheries and Oceans Canada during the past 15 years to monitor the impact of nutrient and contaminant loading on the plankton of the ecosystem. Lakewide cruises were conducted at monthly intervals mainly during the spring to fall period. This provided extensive biomass, species, size, productivity and nutrient concentration data for the Great Lakes. These data were collected using the Utermöhl inverted microscope technique together with standardized taxonomic, productivity and data-handling procedures. These standardized methodologies were applied to all the Great Lakes which resulted in a comprehensive phycological and ecological data base for the first time. These data form the basis for the evaluation of the complex phenomenon of seasonality.The eutrophic/mesotrophic Lower Great Lakes exhibited well-developed seasonal peaks of high biomass, with inshore-offshore differentiation and spring maxima most pronounced in the inshore region. However, the oligotrophic Upper Great Lakes had low biomass and generally lacked well-developed seasonal patterns. No marked seasonal trends were observed in the ultra-oligotrophic Lake Superior. The seasonality of biomass and various taxonomic groups of phytoplankton showed differentiation between individual lakes and is discussed in detail. The seasonal succession of species provided interesting comparisons between the Lower Great Lakes, which harbour eutrophic and mesotrophic species, and the Upper Great Lakes, which harbour oligotrophic species.Due to the voluminous nature of our data, a general overview has been given for all the Great Lakes with Lake Ontario treated in detail as a case study. The Lake Ontario case study provides the state-of-the-art status ranging from the lakewide surveys of 1970 to the current research with minute organisms such as ultraplankton and picoplankton.     

North Atlantic Oscillation and spring bloom phytoplankton composition in the English Channel

The spring phytoplankton composition has been investigated ata 50 m deep station off Plymouth in the English Channel for6 years (1993–1999). The percentage of diatoms duringthe spring bloom was significantly correlated with the NorthAtlantic Oscillation index. A similar relationship between phytoplanktonand North Atlantic Oscillation has also been found in a Swedishlake, suggesting a possible link between atmospheric forcingand phytoplankton composition.     

Climate change and the phytoplankton spring bloom: warming and overwintering zooplankton have similar effects on phytoplankton

Indoor mesocosms were used to study the combined effect of warming and of different densities of overwintering mesozooplankton (mainly copepods) on the spring development of phytoplankton in shallow, coastal waters. Similar to previous studies, warming accelerated the spring phytoplankton peak by ca. 1 day °C^?1 whereas zooplankton did not significantly influence timing. Phytoplankton biomass during the experimental period decreased with warming and with higher densities of overwintering zooplankton. Similarly, average cell size and average effective particle size (here: colony size) decreased both with zooplankton density and warming. A decrease in phytoplankton particle size is generally considered at typical footprint of copepod grazing. We conclude that warming induced changes in the magnitude and structure of the phytoplankton spring bloom cannot be understood without considering grazing by overwintering zooplankton.     

Microbial dynamics during the decline of a spring diatom bloom in the Northeast Atlantic

The microbial dynamics during a spring diatom bloom declinewas monitored in the Northeast Atlantic during a 5-day Lagrangianstudy (8–12 April 2002). Phytoplankton abundance, compositionand health status were related to viral and bacterial abundance,zooplankton abundance and grazing rates, as well as bacterialproduction. Phytoplankton reached maximum concentration on Day3 (Chl a >5 µg L^–1) and declined on Day 5 (Chla 2 µg L^–1) and was dominated (70% of Chl a) bydiatoms. Bacterial production increased substantially to >20µg C L^–1 day^–1 on Day 3 and concomitantlylarge viruses decreased in number by half to <10 x 10³ mL^–1.This was followed by a 5-fold increase in large viruses on Day5, indicating infection and subsequent lysis on Days 3 and 5,respectively. Micro- and mesozooplankton grazing were not theprincipal cause for the decline of the bloom and pheophorbide-ashowing little variation in concentration from Days 1–4(100 ng L^–1) although doubled on Day 5. The poor physiologicalstatus of the diatoms, indicated by the high chlorophyllide-aconcentrations (50–480 ng L^–1), likely promoteda series of closely interrelated events involving bacteria andviruses leading to the demise of the diatom bloom.     

Pelagic zonation of water quality and phytoplankton in the Great Lakes

Analysis of aquatic ecosystem data collected from large water bodies must consider spatial variations. A suite of pelagic survey stations exists for the Laurentian Great Lakes, but little is known about their redundancy. We present a strategy to delineate the lakes into zones based on water quality and phytoplankton biovolume. Water samples were collected from 72 sites in two seasons (spring and summer) from 2007 to 2010 in all five lakes. Integrated samples were analyzed for phytoplankton biovolume and nine water quality parameters. We conducted cluster analysis, principal components analysis and non-metric multidimensional scaling methods for water quality and phytoplankton taxon-specific biovolume for the Great Lakes basin and for each lake separately. There were significant lake-to-lake differences, and based on lake-specific analyses, Lake Superior, Lake Michigan and Lake Erie were each divided into three zones; Lake Huron and Lake Ontario were each grouped into two zones. The zones identified by water quality and phytoplankton provide an understanding of spatial distributions for evaluating monitoring data.     

Distribution and habitat of Nitellopsis obtusa (Characeae) in the Laurentian Great Lakes

Nitellopsis obtusa, a macroalga (Characeae) native to Europe and Asia, was found in U.S. waters of the St. Clair-Detroit River system in 1983, thus extending the range of this taxon into the Laurentian Great Lakes about 850 km from the St. Lawrence River where it was first discovered in North America in 1978. Its occurrence only in water frequented by commercial shipping vessels suggests that it is distributed via this mechanism. In the St. Clair-Detroit River system, N. obtusa was collected with a Ponar grab at four locations, and with a grapnel at one additional location. It was the ninth most frequently found macrophyte and it was most abundant at Belle Isle in the Detroit River, where the mean dry-weight biomass in Ponar samples was 0 g m^-2 in June, 37 g m^-2 in August, and 32 g m⁻² in September. Maximum biomass of this taxon in one Ponar grab at this location was 289 g m^-2 in September. The alga occurred primarily in water of relatively low current velocity (11.3 cm s⁻¹) and in association with Vallisneria americana, Myriophyllum spicatum, Potamogeton richardsonii, Najas flexilis, and Elodea canadensis. Contribution 654, Great Lakes Fishery Laboratory, Ann Arbor, MI 48105, USA Contribution 654, Great Lakes Fishery Laboratory, Ann Arbor, MI 48105, USA     

Comparison of phosphorus deficiency indices during a spring phytoplankton bloom in a eutrophic reservoir

1. Phosphorus limitation was studied along the eutrophic, canyon-type ?ímov reservoir (Czech Republic) during a spring phytoplankton bloom. Concentration of soluble reactive phosphorus (SRP), C:P molar ratio in seston, extracellular alkaline phosphatase activity (APA), and P limitation (bioassay) were used as indices for phosphorus deficiency in the phytoplankton. 2. SRP, C:P, APA, and P limitation indicated a moderate P deficiency in the downstream, but not upper, part of the reservoir. 3. Significant correlations between these parameters were found in the downstream part. Chlorophyll a concentration correlated with APA and P limitation in the upper part. 4. APA was significantly enhanced in the phosphorus-deficient phytoplankton. However, APA was apparently not related to total biomass or species composition of the phytoplankton. 5. Generally, APA was closely correlated with pH in the reservoir. However, extracellular alkaline phosphatases, with a pH optimum above 9.0, were induced and active only during the phytoplankton bloom, whereas low background activity of extracellular phosphatases was found at low chlorophyll a concentrations (winter, clear-water phase).