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.     

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.     

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.     

A Comparison of Epiphytes On Bangia Atropurpurea (Rhodophyta) and Cladophora Glomerata (Chlorophyta) from Northern Lake Michigan

SEM studies have demonstrated the three-dimensional structure of the epiphyte community on Cladophora and mechanisms of epiphyte attachment. Common epiphytes on Cladophora in Grand Traverse Bay include the green alga Ulothrix sp. and the diatom species Cocconeis pediculus Ehr., Diatoma vulgare Bory, Gomphonema olivaceum (Lyngb.) Kütz., and Rhoicosphenia curvata (Kütz.) Grun. Thus, the tremendous area of substrate provided by Cladophora glomerata (L.) Kütz. may provide habitat for a community potentially important to the littoral area. In contrast, Bangia supported numerous bacteria, but 10³ fewer algal epiphytes were noted than occurred on Cladophora.Due to sloughing of the cell wall, Bangia does not provide a suitable attachment site for epiphytic algae which may be important in the food chain. This is of concern as Bangia continues to invade nearshore habitats.     

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.     

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.     

Phosphorus Nutrition of Two Potentially Competing Filamentous Algae, Cladophora Glomerata (L.) Kütz. and Stigeoclonium Tenue (Agardh) Kütz. from Lake Ontario

Cladophora glomerata and Stigeoclonium tenue were isolated from Lake Ontario. Batch culture growth experiments at 20° C and 175 μE/m²?sec continuous light show the maximum growth rate of Stigeoclonium (2.0 day^?1) to be about 2.5 times that of Cladophora (0.8 day^?1). The maximum phosphorus uptake rate for Stigeoclonium is 20 times greater than that for Cladophora and the half-saturation coefficient is larger by a factor of three. From growth experiments, the level of minimum cellular phosphorus of declining-phase cells is similar for both species but Stigeoclonium exhibits a greater luxury maximum level (in lag-phase cells) by a factor of over two. This, plus the fact that the growth rate of Stigeoclonium exceeds that of Cladophora at all levels of external and cellular phosphorus, allows Stigeoclonium to be more successful at phosphate-based competition. This is further confirmed by the facts that (compared to Stigeoclonium) the half-saturation growth constant is three times greater in Cladophora and the ratio of this constant to maximum growth rate is also eight times greater in Cladophora. It is hypothesized that the present-day dominance by Cladophora in the littoral region of the lower Great Lakes may not be determined by phosphate limitation but by certain competitive aspects of the life cycle, growth form, and physiology.     

Progress Toward the Rehabilitation of Lake Trout (Salvelinus namaycush) in South Bay,Lake Huron

Our objective was to evaluate the status of lake trout Salvelinus namaycush rehabilitation in South Bay, Lake Huron. Standardized surveys were conducted to quantify natural recruitment, annual mortality, and the contribution of wild-versus hatchery-origin lake trout. Some indicators suggest a high level of natural recruitment. The spawning population was comprised of multiple ages, and the mean age of spawners (8.4 years for females, 7.9 years for males) was at least 1 year older than the age at 50% maturity (5.8 years). Estimated annual total mortality rates (0.20–0.25) and sea-lamprey induced mortality rates (0.02) were less than maximum allowable values. The proportion of wild-origin fish captured was high among spawners but varied among sampling programs (42% in fall trap nets, 70% in fall gill nets, and 88% in summer gill nets). A strong year class (1997) could be tracked from 2001 to 2005. Few fish were captured from early (< 1996) or later (1999–2002) year classes. Possible explanations for low natural recruitment during these later years include declining spawning habitat quality caused by low water levels and/or invasion of non-native mussels (Dreissena spp.) and/or direct or indirect effects of alewife (Alosa pseudoharengus).     

Historical and recent biomass and food web relations of Limnocalanus in Lake Huron

Reported population biomass of Limnocalanus macrurus in Lake Huron has been underestimated by several-fold owing to application of an inappropriate length–weight regression model. During August and September the underestimates can exceed three-fold, suggesting that secondary production of the species in the lake is greater than previously thought. Increased representation of the species in the plankton community in recent years is associated with a decrease in its trophic level deduced through nitrogen stable isotope analysis of specimens from opportunistic samples obtained in 1993, 1995, and 2009. Limnocalanus¹⁵N enrichment relative to primary herbivores appears to have decreased by 1.5‰ over this time period. Similarly, Diaptomus¹⁵N enrichment relative to primary herbivores appeared to decrease by 1.1‰ from 1993 to 2009. Our data offer at least two possible explanations for this shift. (1) Limnocalanus has adopted a more herbivorous diet in response to the ecological changes in Lake Huron or (2) hypolimnetic Diaptomus have adopted a more herbivorous diet and Limnocalanus is relying in part on Diaptomus as a food source.     

Use of otolith chemistry to discriminate juvenile Chinook salmon (Oncorhynchus tshawytscha) from different wild populations and hatcheries in Lake Huron

Chinook salmon (Oncorhynchus tshawytscha) in Lake Huron consist of wild and hatchery-reared fish distributed among several populations. This study tested whether otolith chemistry can be used to identify the natal origin of Chinook salmon in this system. Concentrations of nine elements (Mg, K, Mn, Fe, Zn, Rb, Sr, Ba, and Pb) in the otoliths of Chinook salmon juveniles from 24 collection sites (17 streams and 7 hatcheries) around Lake Huron were analyzed using laser-ablation inductively-coupled mass spectrometry. Differences in otolith chemistry were found between rearing environments (wild and hatchery), among geological regions (Precambrian, Ordovician, Silurian, Devonian, and Carboniferous), and among collection sites. Discriminant function analysis showed high classification accuracies of juveniles to their rearing environment (wild versus hatchery, 82%), geological region (84%), and collection site (87%) of origin. With these values, there is excellent potential for otolith chemistry to be used to predict the natal origin of adults, and thus inform research and management of Chinook salmon in Lake Huron.     

Monitoring Cladophora Growth Conditions and the Effect of Phosphorus Additions at a Shoreline Site in Northeastern Lake Erie

A study to measure environmental conditions, Cladophora standing crop, internal nutrient levels, and the effect of the addition of phosphorus to Cladophora growth at a single location on the north shore in the eastern basin of Lake Erie is described. In 1979, the mean standing crop for depths 0.5–3 m was 431 gDW/m² as measured at the time of maximum standing crop in early July. Thereafter, the alga was sloughed and carried ashore causing a rapid decline in standing crop. These events coincided with the attainment of lake temperatures exceeding 20° C. Total phosphorus concentrations averaged about 18 μg P/L while soluble reactive phosphorus levels remained near the limit of detection. Stoichiometric ratios of nitrate nitrogen to soluble reactive phosphorus approximated 150:1, suggestive of phosphorus limited conditions. Internal phosphorus and nitrogen levels averaged about 0.06% and 1.80%, respectively. In 1980, phosphorus (0.34 kg/day) was discharged at the 0.5 m depth commencing July 19. No response was noted until the water temperature dropped below 20° C in September when a rapid regrowth occurred, apparently in response to the nutrient addition. It is concluded that Cladophora grows in response to available phosphorus in the eastern basin of Lake Erie and that limitation of this nutrient may be expected to reduce Cladophora growth.     

Abundance Patterns of Diatoms on Cladophora in Lake Huron with Respect to a Point Source of Wastewater Treatment Plant Effluent

Epiphytic diatoms on Cladophora were collected from July to September, 1979, at various distances from a point source of municipal wastewater treatment plant effluent to Lake Huron. Diatom accumulation rates were positively related to distance from the point source. Despite higher nutrient concentrations nearest the point source, low accumulation rates of Cladophora-epiphyte assemblage biomass and epiphytic diatoms indicated moderate growth inhibition by an undetermined factor. Evaluation of epiphytic diatom population abundance and ecology plus diatom taxocene species diversity supported our conclusions. A curvilinear relationship between diatom species diversity and impacts of growth inhibition is proposed and discussed. The diatom proportion of Cladophora-epiphyte assemblage biomass was positively related to distance from the point source of sewage effluent.     

Distribution and Abundance of Larval Fish in the Nearshore Waters of Western Lake Huron

Ichthyoplankton was collected at 17 nearshore (bottom depth ≥5 m but ≤10 m) sites in western Lake Huron during 1973–75 with a 0.5-m net of 351-micron mesh towed at 99 m/min. Larvae of rainbow smelt (Osmerus mordax) dominated late spring and early summer catches and larvae of alewives (Alosa pseudoharengus) the midsummer catches. Larval yellow perch (Perca flavescens) were caught in early summer but were rarely the dominant species. The time of spawning and hatching, and thus occurrence of larvae, differed between areas but was less variable for alewives than for yellow perch. The appearance of larvae in Saginaw Bay was followed successively by their appearance in southern, central, and northern Lake Huron. Rainbow smelt were most abundant in northern Lake Huron and yellow perch and alewives in inner Saginaw Bay. Densities of either rainbow smelt or alewives occasionally exceeded 1/m³, whereas those of yellow perch never exceeded 0.1/m³. Abundance of alewives was usually highest 1 to 3 m beneath the surface and that of rainbow smelt 2 to at least 6 m beneath the surface. Important nursery areas of rainbow smelt were in bays and off irregular coastlines and those of yellow perch were in bays. All nearshore waters seemed equally important as nursery areas of alewives.     

Fall diet and bathymetric distribution of deepwater sculpin (Myoxocephalus thompsonii) in Lake Huron

Deepwater sculpin Myoxocephalus thompsonii are an important component of Great Lake's offshore benthic food webs. Recent declines in deepwater sculpin abundance and changes in bathymetric distribution may be associated with changes in the deepwater food web of Lake Huron, particularly, decreased abundance of benthic invertebrates such as Diporeia. To assess how deepwater sculpins have responded to recent changes, we examined a fifteen-year time series of spatial and temporal patterns in abundance as well as the diets of fish collected in bottom trawls during fall of 2003, 2004, and 2005. During 1992–2007, deepwater sculpin abundance declined on a lake-wide scale but the decline in abundance at shallower depths and in the southern portion of Lake Huron was more pronounced. Of the 534 fish examined for diet analysis, 97% had food in the stomach. Mysis, Diporeia, and Chironomidae were consumed frequently, while sphaerid clams, ostracods, fish eggs, and small fish were found in only low numbers. We found an inverse relationship between prevalence of Mysis and Diporeia in diets that reflected geographic and temporal trends in abundance of these invertebrates in Lake Huron. Because deepwater sculpins are an important trophic link in offshore benthic food webs, declines in population abundance and changes in distribution may cascade throughout the food web and impede fish community restoration goals.     

Seasonal distribution of bloater (Coregonus hoyi) in the waters of Lake Huron surrounding the Bruce Peninsula

Information about bloater (Coregonus hoyi) habitat in Lake Huron was limited to correlations between commercial yield and fishing depth, despite available information from other Great Lakes. We identified seasonal patterns of bloater habitat use in hypolimnetic waters surrounding the Bruce Peninsula, Lake Huron. We applied a delta-lognormal model to fisheries-independent survey data to evaluate whether bloater catch-per-unit-effort was related to depth, temperature, and bathymetric slope. A Bayesian variable selection technique indicated that bloater distribution was most strongly related to bottom depth and water temperature. Our study also reconfirmed a previously-described pattern of seasonal inshore movement during warmer months followed by a return to deeper offshore waters during cooler months. By focusing our sampling within the hypolimnion, we characterized intra-annual patterns of bloater habitat use with respect to a temperature gradient near the minimum thermal requirements reported for this species. Bloater distribution under these thermal conditions has not been previously reported.     

Dispelling common beliefs about angler opposition to lake trout (Salvelinus namaycush) rehabilitation efforts in Lake Huron

Rehabilitating native fish species in the Laurentian Great Lakes and elsewhere remains a challenge for fisheries managers. One factor that often makes rehabilitation a challenge is presumed opposition to rehabilitation programs. We examined the extent and variability in support and opposition for lake trout (Salvelinus namaycush) management and proposed rehabilitation activities for the Ontario waters of Lake Huron, principally amongst anglers. Specifically, we compared four common beliefs (hypotheses) that should affect angler opposition to lake trout rehabilitation. Through a questionnaire sent to a random sample of local licensed anglers, we found very high support for lake trout rehabilitation. As hypothesized, this support was lower among a sample of individuals who actively sought opportunities to complete the questionnaire (who were termed the convenience sample). However, even within this convenience sample, about an equal percentage of respondents supported and opposed lake trout rehabilitation. For the sample of local licensed anglers, we found little support for the remaining three hypotheses. Within this sample, very few differences in support for lake trout rehabilitation existed between respondents who did or did not fish Lake Huron, who were or were not participants in past public involvement opportunities for managing Lake Huron's fisheries, and who were and were not knowledgeable about the proposed rehabilitation plan. These results question common beliefs that anglers are unsupportive of lake trout rehabilitation in Lake Huron and that support for rehabilitation varies widely among anglers with different characteristics and experiences.     

Distribution of the Amphipod Diporeia in Lake Superior: The Ring of Fire

Diporeia, formerly the dominant benthic macroinvertebrate in the Great Lakes, remains a keystone species in Lake Superior. Little is known, however, about fine scale amphipod distributions, especially as influenced by the production, transport and transformation of energy resources. Here, we document the distribution and abundance of Diporeia along 19 transects around the lake's perimeter. Regions of elevated density, averaging 958 ± 408 Diporeia/m² (mean ± S.D.) were observed along all transects, typically within slope habitat (depth of 30–125 m). Waters shoreward (shelf habitat, < 30 m) and lakeward (profundal habitat, > 125 m) of these regions supported significantly lower densities, averaging 239 ± 178/m² and 106 ± 59/m², respectively. Amphipods within regions of elevated density, termed here the Ring of Fire, account for two-thirds of the lakewide population while occupying only one-quarter of the benthic habitat. The Ring of Fire, observed lakewide as a band averaging 14.2 ± 9.4 km in width, is characterized as a region of transitional sediment deposition with gentle slope, proximate to nearshore locations of elevated primary production. Within the Ring of Fire exceptionally high densities are found in the south central region, where the Keweenaw Current and slope bathymetries serve to funnel production from adjoining regions of high production. Density measurements for the 173 stations sampled here are used to estimate lakewide Diporeia standing stock (22.5–37.7 trillion individuals, 4.4–7.4 Gg dry weight, 2.1–3.5 Gg C), individual and biomass density (274–460/m², 0.05–0.09 g DW/m², 0.03–0.04 gC/m²) and areal (0.02–0.03 g C/m²/yr) and total (1.6–2.6 Gg C/yr) production.     

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.     

In Situ Determination of the Annual Thermal Habitat Use by Lake Trout (Salvelinus namaycush) in Lake Huron

Records of the temperatures occupied by 33 lake trout (Salvelinus namaycush) at large in Lake Huron were obtained for up to 14 months per fish, at 75-minute intervals, from surgically implanted archival temperature tags. The dataset covered nearly three years, from October 1998 to June 2001, and included 160,000 observations. The objectives of the tagging were to obtain temperature data to refine bioenergetics models of sea lamprey (Petromyzon marinus) predation on lake trout, and compare the temperatures occupied by strains of lake trout stocked in Lake Huron. The seasonal, thermal-use profiles of lake trout followed the general warming and cooling pattern of Lake Huron. During periods when the zone of surface water mixing extended below the depth range occupied by lake trout, variability among individual fish and strains was low and followed surface temperature. However, during the period of summer stratification, the average temperatures occupied varied substantially among individual fish and strains. Strains originating from the upper Great Lakes (Lake Superior and Lewis Lake, WY) occupied similar temperatures. Between June and mid August, upper Great Lakes lake trout typically occupied water several degrees warmer than that occupied by lake trout of Finger Lakes, New York origin. Most of the lake trout occupied summer temperatures lower than the preferred temperatures suggested by laboratory studies. In October, all strains occupied water as warm or warmer than that occupied in summer, which may partially explain the higher lethality of sea lamprey attacks during October.     

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.