Ecological Interactions Among Bangia, Cladophora, and Ulothrix Along the Lake Erie Shoreline

Bangia atropurpurea, a recent invader of Lake Erie, has altered the community structure of the littoral zone, which previously had been dominated by Cladophora or Ulothrix. Vertical and horizontal zonation patterns of these algae suggest that competition and differing physical tolerances may be involved. To determine the relative importance of these factors, seasonal changes in littoral algal distribution patterns and environmental conditions were monitored. Additionally, Bangia was examined in culture to relate growth and reproductive mechanisms to distribution patterns and competitive potential.Ulothrix established extensive cover immediately below mean water level (MWL) after thaw in mid-April along moderately exposed shores. By early May, Bangia colonized from +0.5–1.0 m to just below MWL coexisting with Ulothrix near MWL. As water temperature neared l5° C in late May, the distribution of Cladophora expanded from patches at ?0.5–1.0 m upward into the Ulothrix band. In early June, Ulothrix sporulated, the remaining empty filaments disintegrated, and the alga was not observed for the remainder of the summer. Cladophora continued upward colonization, eventually dominating the substrate to the +0.5–1.0 m level. Bangia was dominant above the Cladophora zone, up to +2.0 m. During periods of moderate wave wash, Cladophora dominated up to the +1.0 m level. Heavy wave wash resulted in the detachment of Cladophora, allowing domination by Bangia from +0.5 m to 2.0 m.Bangia shares substrate with Ulothrix in the limited areas where their distributions overlap, and perhaps through greater desiccation tolerance can persist in areas where Cladophora does not grow. This partial niche segregation provides Bangia with refugia in time as well as space. Coexistence between Bangia and the competitively dominant Cladophora occurs as a result of partial niche segregation as well as the impact of wave action in initiating the detachment of Cladophora.     

Residues of PCB in a Cladophora Community Along the Lake Huron Shoreline

PCB residues were measured in samples of Cladophora, Ulothrix, net plankton, water, and fish collected in the Harbor Beach area of Lake Huron. The average concentrations of total PCB in each of the sample groups were as follows: water - 0.154 ng/g; Cladophora - 92 ng/g; Ulothrix - 126 ng/g; net plankton - 1,651 ng/g; and fish - 40 to 4,400 ng/g. The PCB patterns in the samples were found to match a mixture of Aroclo6r 1242 and 1254. Aroclor 1242 represented about 60% of the mixture in all the samples except the fish, where Aroclor 1254 represented about 75% of the total PCB measured. The accumulation factors observed in the progression from Cladophora to net plankton to fish were 1:15:30; these were similar to the concentration factors (1:14:44) developed on these ecosystem compartments in Lake Ontario during the 1972 IFYGL program.     

Phosphorus Uptake Dynamics as Related to Mathematical Modeling of Cladophora at a Site on Lake Huron

Cladophora is a significant symptom of eutrophication in Lakes Erie and Ontario and is a local problem associated with nutrient perturbations in Lakes Huron, Michigan, and Superior. This paper presents results of measurements of phosphorus uptake rates as a function of internal phosphorus levels by Cladophora growing near Harbor Beach, Michigan. Cladophora collected near the Harbor Beach wastewater treatment plant had high levels of internal phosphorus and low (or even negative) phosphorus uptake rates. Cladophora distant from the wastewater treatment plant had low internal phosphorus levels and rapid phosphorus uptake rates. The experimental results are discussed in terms of quantitative kinetic formulations which may be incorporated into mathematical models useful for predicting the response of Cladophora to alternative management and control strategies. Preliminary model simulations of Cladophora biomass, internal phosphorus, and external phosphorus are qualitatively similar to observed field data.     

Environmental Factors Controlling Physiological Changes in Cladophora in Lake Erie

Several physiological characteristics of Cladophora glomerata from eastern Lake Erie were monitored frequently during the summer of 1977. Soluble reactive phosphorus and nitrate-nitrogen in the lake water were also measured.Cladophora biomass generally increased throughout June, although there were periodic declines. In mid-July, biomass sharply decreased to a low level. Chlorophyll content tended to be high during periods of increasing biomass but was lower after each biomass decline. Changes in biomass did not correlate with changes in either phosphate-phosphorus or nitrate-nitrogen in the lake water. Cellular nitrogen levels fluctuated independent of lake water nitrate-nitrogen concentrations. Cellular nitrogen levels remained above the critical concentration, 1.1%-N. Luxury phosphorus levels were observed to increase following pulses of soluble orthophosphate in the lake water. Measurements of cellular total phosphorus indicate that levels remain well above the critical concentration of 0.06%-P. It is concluded that neither nitrogen nor phosphorus is limiting the growth of Cladophora at the sites sampled. The mid-summer die-off does not appear to be due to a simple nutrient deficiency.     

Fish Assemblages and Environmental Conditions in the Lower Reaches of Northeastern Lake Erie Tributaries

Lake Erie and its tributaries have experienced extensive changes in environmental conditions and community structure during recent decades. To assess the relative importance of environmental conditions in determining fish community composition, fish communities and their associated environmental conditions were sampled from the lower reaches and mouths of the tributaries flowing into the northeastern basin of Lake Erie. These data were used to assess relationships between habitat and fish community composition on spatial and temporal scales using correspondence analysis and canonical correspondence analysis. Multivariate analyses revealed that the fish assemblage was size structured and related to water chemistry but also showed influences due to temperature, sampling date and aquatic macrophytes. The community composition showed the effects of biotic interactions, predominantly negative predator-prey associations, but there were also assemblage differences specific to particular tributaries and sampling methodologies.     

Ecological Studies and Mathematical Modeling of Cladophora in Lake Huron: 2. Phosphorus Uptake Kinetics

Laboratory experiments were conducted with field populations of Cladophora glomerata to examine the phosphorus uptake process. Results from 35 experiments conducted over two field seasons emphasize the importance of two factors in regulating phosphorus uptake: dissolved phosphorus concentration and internal phosphorus pool size. The phosphorus uptake rate increases as dissolved phosphorus availability increases. Negative feedback on uptake rate by internal phosphorus pool size reduces the maximum phosphorus uptake rate as internal pools approach saturation. The absolute maximum phosphorus uptake rate for Cladophora was 4.5%P/day. Values for the half-saturation constant for uptake varied with internal phosphorus pool size and ranged between 30 and 250 μgP/L. The data were fit to published mathematical expressions which describe uptake as a function of internal and external phosphorus levels. The expressions may be used in mathematical models simulating the growth of Cladophora.     

Seasonal Abundance Patterns of Diatoms on Cladophora in Lake Huron

Rocks bearing Cladophora were collected from May to November 1979 at two locations near Harbor Beach, Michigan, in Lake Huron to document seasonal patterns of epiphytic diatom abundance and diatom proportion of the Cladophora-epiphyte assemblage biomass in an area receiving effluent from a municipal wastewater treatment plant. Data were examined for evidence of interactions between epiphytic diatoms and Cladophora.Cladophora first appeared in May at which time epiphytic diatoms comprised about 30% of the Cladophora-epiphytic assemblage biomass. Cladophora growth was greatest in June and July, accumulating much faster than diatoms. Peak Cladophora-epiphyte assemblage biomass was maintained from July to September. Cladophora biomass apparently decreased after August while diatom abundance increased to a September maximum. Diatoms were responsible for the sustained peak of Cladophora-epiphyte assemblage biomass as diatoms comprised over 60% of the assemblage biomass in September. The Cladophora-epiphyte assemblage collapsed by October.Low diversity of the epiphytic diatom taxocene and low diatom proportion of the Cladophora-epiphyte assemblage biomass indicated Cladophora may have outcompeted diatom epiphytes during the June-July Cladophora growth pulse. Subsequently epiphytic diatoms may have enhanced Cladophora sloughing by shading and successful nutrient competition.     

Ecological Studies and Mathematical Modeling of Cladophora in Lake Huron: 3. The Dependence of Growth Rates on Internal Phosphorus Pool Size

The relationship between growth rate and internal phosphorus pool size was examined using field populations of Cladophora glomerata from Lake Huron. Algal samples, representing a range of internal phosphorus concentrations, were harvested from the lake and used for laboratory measurements of growth. Rates of net photosynthesis and respiration were measured under controlled conditions of light and temperature using a dissolved oxygen (light/dark bottle) technique. The net specific growth rate and respiration rate were calculated from photosynthesis and respiration measurements using a fixed stoichiometric relationship and the measured carbon content of the algae. The maximum rates for net specific growth rate, gross specific growth rate, and specific respiration rate were 0.77, 1.08, and 0.44 day^?1, respectively. Management decisions may be importantly influenced by the relationships derived from these data. A non-linear response by growth to reductions in phosphorus loading is suggested from the results of these experiments. The internal nutrient status of algal populations (e.g. Cladophora) must be considered in predictions of the impact of phosphorus management strategies on aquatic systems.     

Growth Dynamics of Cladophora Glomerata in Western Lake Erie in Relation to Some Environmental Factors

Cladophora was monitored at two sites in western Lake Erie during 1979 and 1980 as part of a lake-wide Lake Erie Cladophora Surveillance Program. Two distinctive zones within the littoral region were colonized by the alga, the eulittoral (splash zone) and infralittoral (defined in the present study as the 0.5–4 m depth zone). Cladophora of the eulittoral zone became established in May and remained present until late fall. The infralittoral zone Cladophora exhibited a bimodal growth pattern related to the seasonal temperature regime, with growth occurring from April to July and again from September to November. The infralittoral zone supported the largest share of biomass, which resulted in nuisance accumulations upon the beaches in the island region. Peak biomass was observed from mid-June to early July, obtaining maximum values of 102 gDW/m² and 214 gDW/m² for the 1979 and 1980 seasons, respectively. The depth to which Cladophora colonized was limited by light availability; maximum depth of growth occurred between 2 and 4 m in western Lake Erie due to the turbid nature of the basin. Phosphorus and nitrogen were not limiting to Cladophora growth in western Lake Erie; tissue nutrients remained above the critical levels defined by Gerloffand Fitzgerald (1976) throughout the season.     

Spatiotemporal patterns of water quality in Lake Ontario and their implications for nuisance growth of Cladophora

This study, motivated by a resurgence in Cladophora, investigates changes in the nutrient environment in the littoral zone of Lake Ontario. We measured nutrient concentrations from 2004 to 2008 at two littoral zone (2–12 m) sites on the north shore of Lake Ontario where Cladophora has experienced a resurgence and compared concentrations with data collected in the late 1970s. Spring total phosphorus (TP) and soluble reactive P (SRP) concentrations have significantly declined at these two sites. Furthermore, P loading from the major tributaries to our study sites declined between 1964 and 2008. Upwelling events were not detectably associated with increases in P concentrations at our sites. We conclude that a recent upsurge in nuisance Cladophora, at least at these sites, cannot be explained by deteriorating littoral zone water quality in terms of P concentrations or by changes in catchment loading. For additional context, we also examined trends in coastal (14–20 m) and offshore (> 50 m) nutrients using Environment Canada epilimnetic surveillance data, 1975–2008. Significant declines in TP and SRP concentrations have occurred in north coast waters, concurrent with declines in the offshore. However, nutrient concentrations, notably spring SRP, have not decreased among south coast stations, potentially reflecting greater coastal entrapment of catchment-derived waters. We infer that EC-monitored north coast stations reflect integrated interannual water quality, while south coast stations are more strongly influenced by catchment loading. The effects of higher nutrient concentrations along the south coast, which co-occur with lower water transparency, on benthic algal growth have yet to be determined.     

Biomass and Distribution of Cladophora Glomerata in Relation to Some Physical-Chemical Variables at Two Sites in Lake Erie

Cladophora was collected from 0.25-m² quadrats on alternate weeks at two sites located in Lake Erie near Hamburg, New York, and Walnut Creek near Erie, Pennsylvania, between June and November 1979. Cladophora biomass and internal nutrients (total Kjeldahl nitrogen and total phosphorus) were determined. Water samples were analyzed for total phosphorus, soluble reactive phosphorus, nitrate + nitrite nitrogen, total Kjeldahl nitrogen, and ammonia nitrogen. Temperature and Secchi disk transparency were also recorded.The peak standing crop for Cladophora was 211 gDW/m² (July) at the Hamburg site and 57 gDW/m² (July) at Walnut Creek. The depth distribution of Cladophora at the sample sites was influenced by wave activity and drifting sand. As a result of sand scouring at the shallower depths, Cladophora biomass generally was greatest at the 3-m depth.Reductions in Cladophora internal nutrients corresponded to decreased nutrients in the water. Cladophora detached from its substrate during periods when low internal nutrient levels were observed. Internal total phosphorus concentrations were low and approached the minimum cell quota (0.05–0.06% –P) most of the time. Soluble reactive phosphorus values were also low (1–4 μgP/L). Levels of soluble reactive phosphorus and internal total phosphorus were low and almost always limiting, and may be responsible for the low biomass values observed. In addition, internal total phosphorus levels showed a significant positive correlation with Cladophora biomass. Internal total nitrogen values were generally less than 1%-N at Walnut Creek and ammonia nitrogen measurements were near detection limits. Cladophora was nitrogen-limited at the Walnut Creek site during part of the study period. Nitrate + nitrite nitrogen showed a significant positive correlation with Cladophora biomass at that site.     

Ecological Studies and Mathematical Modeling of Cladophora in Lake Huron: 5. Model Development and Calibration

The development of a mathematical model for calculating the spatial distribution and temporal variation in Cladophora biomass and selected forms of phosphorus at a site on Lake Huron is described. The model is intended for use in evaluating the utility of various phosphorus management strategies in reducing the nuisance growth of Cladophora in the Great Lakes. The model is composed of a transport component which accounts for bulk transfer and exchange of phosphorus within the system and a kinetic component which describes chemical and biological reactions. The kinetic component includes the effects of light, temperature, and internal phosphorus levels on Cladophora growth rate, aspects of phosphorus uptake, and the impact of sloughing and self-shading on standing crop. The numerical value of coefficients associated with kinetic equations have been independently determined through laboratory studies.The model has been calibrated to a data set collected in the vicinity of the Harbor Beach, Michigan, wastewater treatment plant. A satisfactory fit was achieved for model calculations and observed levels of Cladophora biomass, internal phosphorus, and soluble reactive phosphorus. The model has few degrees of freedom because the coefficient values were fixed from field and laboratory measurements. A standing crop of Cladophora biomass of 300 gDW/m² with an internal phosphorus level of 0.35%P was characteristic of stations in the vicinity of the nutrient source. Soluble reactive phosphorus levels fluctuated widely due to mixing of the effluent plume with offshore waters, but averaged approximately 30 μgP/L. A distinct spatial trend was observed with Cladophora biomass, internal phosphorus, and soluble reactive phosphorus decreasing with distance from the point source of nutrients. The opportunity for model verification by perturbation through phosphorus removal is discussed.     

Occurrence of the Asiatic Clam Corbicula Fluminea in the Maumee River and Western Lake Erie

The Asiatic clam was found in only two locations along the southern shore of the western basin of Lake Erie: the thermal plume areas of two coal-fired power plants with once-through condenser cooling systems. Three sewage treatment plant outfalls were sampled, but Corbicula were found only in the sewage treatment plant outfall that was within the thermal plume of a power plant. No Corbicula were found in the vicinity of the nuclear power plant which has a closed-cycle natural draft cooling tower, and hence no significant thermal plume.From the age of some of the specimens, this clam has probably resided in the region since 1978. The Great Lakes are farther north than the natural range of this clam, and prolonged cold temperatures in this region may be responsible for the confinement of this clam to baseload power plants with continuous thermal plumes.     

Cladophora (green algae) and dreissenid mussels over a nutrient loading gradient on the north shore of Lake Ontario

Benthic algae, much of it the green alga Cladophora, blanket the nearshore lakebed of the north shore of Lake Ontario. Nearshore field studies in Toronto, Ajax, Oshawa and Cobourg in 2012 and 2013, and Toronto in 2015 examined the distribution of Cladophora over a nutrient gradient on the north shore of the lake. Concentrations of total phosphorus, dissolved phosphorus and total inorganic nitrogen in the water column decreased from west to east over the gradient corresponding with decreasing watershed development and size. However, high surface cover and nuisance levels of Cladophora biomass were found across the gradient, including the least developed study area where total phosphorus concentrations were similar to those in the open lake. The abundance of Dreissena, high in all areas, was measured concurrently with Cladophora biomass and correlated positively at depths of 6 to 10 m. External loading of phosphorus provides a basis for abatement of Cladophora; however, the influences of enrichment along the shoreline, internal loading at the lakebed and lake trophic status in sustaining growth remain obscure. Nuisance levels of Cladophora are not isolated to locations experiencing elevated external loading and should be viewed in the context of interacting area-specific and lake-wide nutrient supplies.     

Ecology and population status of Trout-perch (Percopsis omiscomaycus) in western Lake Erie

Trout-perch Percopsis omiscomaycus is among the most abundant benthic species in Lake Erie, but comparatively little is known about its ecology. Although others have conducted extensive studies on trout-perch ecology, those efforts predated invasions of white perch Morone americana, Dreissena spp., Bythotrephes longimanus and round goby Neogobius melanostomus, suggesting the need to revisit past work. Trout-perch were sampled with bottom trawls at 56 sites during June and September 2010. We examined diets, fecundity, average annual mortality, sex ratio, and long-term population trends at sites sampled since 1961. Trout-perch abundance fluctuated periodically, with distinct shorter- (4-year) and longer-term (over period of 50 years) fluctuations. Males had higher average annual mortality than females. Both sexes were equally abundant at age 0, but females outnumbered males 4:1 by age 2. Diets of trout-perch were dominated by macroinvertebrates, particularly chironomids and Hexagenia sp. Size distributions of trout-perch eggs varied widely and exhibited multiple modes indicative of protracted batch spawning. A review of the few other studies of trout-perch revealed periodic fluctuations in sex ratio of adults, which in light of our evidence of periodicity in abundance suggests the potential for sex-ratio-mediated intrinsic population regulation. Despite the introduction of numerous invasive species in Lake Erie, trout-perch remain one of the most abundant benthic invertivores and the population is relatively stable.     

Assessment of Microcystis growth rate potential and nutrient status across a trophic gradient in western Lake Erie

Plankton tow samples collected from 2002 through 2009 indicate that Microcystis biovolume in western Lake Erie is often most dense in transition zone (TZ) waters between Maumee Bay and the center of the western basin. TZ waters are generally high in nutrients and turbidity, and concentrations of each decrease with distance from Maumee Bay. High Microcystis biovolume in the TZ suggests the possibility that the conditions in these waters support a greater Microcystis growth rate relative to the open lake. To test this hypothesis, during the 2008 bloom, Microcystis was collected from western Lake Erie for measurements of total protein content (TPC) as an indicator of growth rate potential and cellular nutrient content to indicate nutrient deficiencies. TPC results indicate that Microcystis in the TZ had a higher potential growth rate compared to offshore waters. TPC values in Maumee Bay were intermediate but not significantly different from the TZ and offshore. Nitrogen content of Microcystis remained high over the summer at all sites, despite very low dissolved nitrate concentrations and low total nitrogen-to-total phosphorus ratio in late summer in the lake. Ammonium level in the lake was constant during the summer, and likely provided the nitrogen source for Microcystis. Cellular phosphorus content varied between site and sample date suggesting that Microcystis was moderately phosphorus deficient. Quotas of micronutrient indicated that Microcystis was not deficient of micronutrients. Results of this study suggest the waters in and adjacent to Maumee Bay provide more favorable growth conditions for Microcystis than offshore waters.