M. Fitzpatrick

An overview of the impact of non-indigenous species on the food web integrity of North American Great Lakes: Lake Erie example

For the past several decades, the North American Great Lakes have suffered from eutrophication. The deteriorating state of the Great Lakes alarmed both the governments of Canada and the United States resulting in the Great Lakes Water Quality Agreement, which has brought about substantial improvements in water quality. While phosphorus abatement resulted in a significant decrease in nutrients, the sudden invasions of exotic species posed a serious threat to Great Lakes food webs. The zebra mussel (Dreissena polymorpha) and the quagga mussel (D. bugensis), followed by other exotic species, infested Lakes Erie and Ontario causing a drastic reduction in phytoplankton biomass and increasing water clarity. In Lake Erie, post-Dreissena declines in phytoplankton size structure and changes in community composition were observed in this study, along with significant declines in primary productivity in the west basin. At the other end of the food web, exotic species such as alewife (Alosa pseudoharengus), rainbow smelt (Osmerus mordax) and white perch (Morone americana) have become important to the Lake Erie commercial fishery, while other native fish species have declined. This paper presents an historical perspective and a general overview of the impact of nonindigenous species in the North American Great Lakes from the base of the food web to the fisheries. Lake Erie has been chosen as a case study to provide a detailed treatment. The expansion and growth of nonindigenous species has been responsible for significant modifications to the structural and functional characteristics of the food webs and fisheries of the Great Lakes. Our experience demonstrates the significance of the impact of exotics and the need to manage this serious problem on a global basis so that the integrity of food webs and fisheries throughout the world can be protected. This paper is dedicated to Dr. Jack Vallentyne for his contributions to Great Lakes research, especially for the implementation of the ‘ecosystem approach’. These contributions were in evidence in revisions to the Great Lakes Water Quality Agreement and more currently in the management of exotic species.

The relative importance of autotrophic and heterotrophic microbial communities in the planktonic food web of the Bay of Quinte, Lake Ontario 2000–2007

The structure and function of the microbial and planktonic communities of the Bay of Quinte, Lake Ontario were studied for 8 years from 2000 to 2007. The bay has a long history of eutrophication and has undergone remediation efforts which included reductions in phosphorus loadings and the implementation of a long term research and monitoring program (1972–present) conducted by Fisheries and Oceans Canada along with other federal and provincial agencies. Microbial loop research was added in 2000 to the ongoing monitoring program which included nutrients, phytoplankton, zooplankton, benthos and fish so that a comprehensive picture of food web linkages would emerge. The structure of the microbial-planktonic food web was determined based on microscopic analysis of bacteria, autotrophic picoplankton (APP), heterotrophic nanoflagellates (HNF), ciliates, phytoplankton and zooplankton and was compared to a traditional grazing food chain consisting of phytoplankton and zooplankton. On a seasonal weighted mean basis, HNF biomass (fresh weight) of 1.7–8.4 g m−3 at Belleville and 1.1–6.3 C m−3 at Conway exceeded that of zooplankton in virtually all observations and was often greater than the combination of phytoplankton and zooplankton. Furthermore, the results showed that HNF contributed upwards to 85% of the organic carbon pool on a seasonal weighted mean basis. Various parameters in the upper bay relating trophic status to autotrophic communities were measured including: point source phosphorus loadings (>10 kg d−1); primary production (>300 g C m−2 y−1); chlorophyll a (>12 μg l−1) and phytoplankton biomass (>3 g m−3) which indicated that the upper bay remained eutrophic. This was also confirmed by the “battery of tests” strategy of ecological indicators developed in our laboratory to assess trophic status, health, and potential Beneficial Use Impairments. Based on our observations spanning 8 years, it was concluded that the microbial food web was dominated by heterotrophic communities which are still widely ignored in Great Lakes research and monitoring efforts. Our data clearly demonstrates that future studies and management strategies should include the “microbial loop” to obtain a holistic picture of the structure, function and dynamics of the lower food web.

Assessing ecosystem health impairments using a battery of ecological indicators: Bay of Quinte, Lake Ontario example

Large freshwater and marine ecosystems suffer from a variety of anthropogenic stressors which include eutrophication, chemical contamination, coastal degradation and overexploitation of fisheries to name only a few. Attempts at remediation are often confounded by the multitude of local, regional, national and international governments and agencies that exercise jurisdiction over smaller parts of these ecosystems. In the North American Great Lakes, there exists a (nearly) 40 year track record for international cooperation in managing anthropogenic stressors that emphasizes sound ecosystem based science. Among these efforts was the designation of 42 severely polluted coastal regions as Areas of Concern (AoCs) which were deemed to have at least 1 of 14 possible Beneficial Use Impairments. The Bay of Quinte, Lake Ontario, is one AoC with 10 listed impairments. We used a “battery of tests” strategy to assess the health of the bay with respect to the impairments of “eutrophication or undesirable algae” and “degradation of phytoplankton and zooplankton communities” in the bay. This strategy integrates structural, functional and chemical parameters into established ecosystem health models. The results of the battery of tests showed continued eutrophication of the bay and not coincidentally, continued degradation of the phytoplankton community. We also found that point sources of phosphorous do not account for all of the (pelagic) primary production observed in the bay and suggest that non-point sources of phosphorous contribute significantly to eutrophication. Our results further suggest that the battery of tests strategy is a sensitive science-based tool for assessing ecosystem health. These tests could also be applied to the evaluation of ecosystem health in other Great Lakes AoCs as well as large lakes and marine environments where cultural eutrophication is a problem.

The application of Vollenweider's eutrophication models for assessing ecosystem health: Hamilton Harbour (Lake Ontario) example

This note is motivated by the classical Vollenweider eutrophication models which were instrumental in the phosphorus abatement provisions of the Great Lakes Water Quality Agreement. The models were revisited as a tool for assessing the ecosystem health of Areas of Concern in terms of Beneficial Use Impairments and potential recovery. The models indicated that Hamilton Harbour is a hyper-eutrophic environment in spite of continued phosphorus abatement management efforts. The utility and potential of these models have been demonstrated and recommended for application not only in Areas of Concern, but also other stressed environments.

The phytoplankton community of Lake Ontario in 2008: Structure, biodiversity and long term changes

The phytoplankton community of Lake Ontario was assessed during April, July and September 2008 as part of the Cooperative Science and Monitoring Initiative (CSMI) framework. Results were also compared with historic surveys that began in 1970. A total of 320 unique species were identified during 2008, the vast majority being considered ‘rare’ or ‘less common’. The biomass was found to be, on average, 1.6 g m−3 in spring, 3.0 g m−3 in early summer and 2.4 g m−3 in late summer with rare and less common species accounting for 60–80% of the total. Analysis of the size structure of the phytoplankton community combined with size fractionated primary productivity experiments revealed that one picoplankton (<2 μm) species, Chroococcus dispersus var. minor, accounted for up to half of the observed primary productivity, despite contributing 1% or less to total biomass. Our results also showed that the lake was mesotrophic during the summer of 2008 (July and September) and that trophic state has fluctuated between hyper-eutrophic and ultra-oligotrophic since monitoring began in 1970. These findings demonstrate that the Lake Ontario ecosystem is continually changing and more frequent sampling is needed. A high level of taxonomic expertise is required for even the most basic assessments of the phytoplankton community structure and improved taxonomic training and implementation of standardized techniques are necessary.

Phytoplankton ecology of a culturally eutrophic embayment: Hamilton Harbour, Lake Ontario

Hamilton Harbour is a chronically eutrophic embayment located at the western end of Lake Ontario that has experienced many decades of agricultural, industrial, and urban contamination. It has been identified as an Area of Concern under the terms of the Great Lakes Water Quality Agreement between Canada and the United States. This study examines the ecology of the phytoplankton communities at one centrally located station during the ice-free period (May–October) of three non-consecutive years: 2002, 2004 and 2006. This was the first comprehensive study to be conducted since the 1970s. It was found that the phytoplankton communities are diverse and fluctuate throughout the year, along with changing nutrient, physical and environmental conditions. No consistent patterns of seasonal succession were observed throughout the study. Phytoflagellates including Cryptophyceae and Dinophyceae had a tendency to outnumber and out-compete other phytoplankton since they are mobile and able to seek out optimal habitats within the water column. For a highly eutrophic water body, algal biomass (annual mean ≈ 2.0 g m−3) was lower than expected and more consistent with mesotrophic conditions–an observation first made by researchers in the 1970s and attributed to the highly variable physical environment. While our study supports these earlier results, we also conclude that zooplankton grazing likely has a significant role in limiting the size of the algal standing crop. Several algal bloom events were captured during our study. In addition to the somewhat predictable blooms of Diatomeae in the spring and Cyanophyta in the summer, we also observed blooms of Cryptophyceae and Dinophyceae. In one case we observed a bloom with no dominant taxon–it contained a diverse mixture of Cryptophyceae, Euglenophyta and Dinophyceae–challenging the commonly held notion that algal blooms are essentially monocultures. Our results show that such a variable and stressed ecosystem requires frequent sampling to capture the rapid changes that occur.

Microbial - Planktonic foodweb dynamics of a eutrophic Area of Concern: Hamilton Harbour

Hamilton Harbour, located on the western end of Lake Ontario, has a long history of cultural eutrophication as well as industrial contamination. We explored the structure and function of the microbial – planktonic foodweb during the growing seasons (May–October) of 2004 and 2006 in order to consider the flow of autochthonous production from lower to higher trophic levels. Our analyses included microscope based assessments of bacteria, heterotrophic nanoflagellates, ciliates, phytoplankton and zooplankton as well as radioisotope based measurements of primary productivity and bacterial growth. While routine measures of total phosphorus (avg: 25–33 µg l−1) and chlorophyll a (avg: 12–15 µg l−1) were indicative of eutrophy, mean phytoplankton biomass in 2004 (2.0 g m−3) and 2006 (2.2 g m−3) suggested mesotrophic conditions. However, the appearance of algal blooms in the summer of 2006 was an obvious indicator of cultural eutrophication. With respect to the microbial – planktonic foodweb, the organic carbon pool increased from a mean of 757.5 mg C m−3 in 2004 to 1160.3 mg C m−3 in 2006 and this increase was almost evenly split between autotrophs (198.7 mg C m−3) and heterotrophs (204.1 mg C m−3). The increased autotrophic carbon is readily attributable to the observed algal blooms driven by warmer temperatures and higher concentrations of soluble reactive phosphorus. However, the increase in heterotrophic carbon, primarily heterotrophic nanoflagellates, was apparent from the earliest observations in 2006 and remained consistently high throughout the year. We hypothesize that the increased heterotrophic carbon was the consequence of increased allochthonous carbon being shunted through the microbial foodweb; the energy generated was not likely transferred to zooplankton and passed on to higher trophic levels. More research into the dynamics of allochthonous and autochthonous carbon in eutrophic environments is called for.

Microbial foodweb comparison of the Laurentian Great Lakes during the summers of 2001–2004

A structural and functional assessment of the microbial foodweb of Lakes Superior, Huron, Erie and Ontario was undertaken during late summer (August) between 2001 and 2004. One lake was sampled in each year. Our analysis included microscopic enumerations of bacteria, autotrophic picoplankton, phytoplankton, heterotrophic nanoflagellates and ciliates coupled with radioisotope tracer measurements of primary productivity (14C) and bacterial growth (3H). Phytoplankton biomass was highest on average in Lake Erie (≈1.9 g m−3) and lowest in Lake Ontario (≈0.2 g m−3), whereas microbial loop biomass was highest in Lake Ontario (≈2.4 g m−3) and lowest in Lake Huron (≈0.1 g m−3). The organic carbon pool was found to be predominantly autotrophic (>80%) in Lakes Superior (≈280 mg C m−3), Huron (≈195 mg C m−3) and Erie (≈660 mg C m−3) and smaller picoplankton had the highest carbon turnover rates (≈0.4–1.5 d−1). However, in Lake Ontario (≈335 mg C m−3) the carbon pool was about 75% heterotrophic and larger net plankton had the highest carbon turnover rates (≈6.8 d−1). Despite differences in trophic state, the microbial foodwebs of Lakes Superior, Huron and Erie appeared to function in a similar and efficient manner. In contrast, the microbial foodweb of Lake Ontario appeared to be unhealthy with autochthonous production being sequestered by heterotrophic nanoflagellates. More detailed work is needed to understand the foodweb linkages both within the Great Lakes and among them.

The Laurentian Great Lakes in transition: A chronicle of research at the base of the foodweb

A unique science and management strategy has been developed for the Laurentian Great Lakes due to their enormous size, geographic-ecological diversity, political and economic importance. This article is a documentary of more than 40 years of research conducted at the base of the foodweb by Fisheries and Oceans Canada, which has contributed significantly to the management of the Great Lakes. In the 1960s, the governments of Canada and the United States responded to the threat of cultural eutrophication which eventually resulted in the signing of the binational Great Lakes Water Quality Agreement. Dr. R. A. Vollenweider and Dr. J. R. Vallentyne were instrumental in developing a phosphorus abatement program, as well as the adoption of the “ecosystem approach” resulting in an holistic and integrated protocol for managing multiple environmental stressors. By showcasing some selected examples (Lake Ontario, Bay of Quinte, current research activities), an attempt is made to chronicle the evolution of phytoplankton, primary productivity and microbial foodweb research in the Great Lakes. Some of the research programs, techniques, models, policies and international cooperation are highlighted, in addition to the strong European influences on Great Lakes research. The lessons learned from the long-term Great Lakes research experience could be extrapolated and applied to enhance understanding of the ecology and management of other large lake ecosystems throughout the world.

Autotrophic and heterotrophic indicators of ecological impairment in Toronto Harbour and coastal Lake Ontario

The Toronto and Region Area of Concern (also known as Toronto Harbour) includes 42 km of Lake Ontario coastline and 6 watersheds. Over 4 million people reside within its boundaries which includes the City of Toronto (Ontario, Canada). We sampled eleven sites along the Lake Ontario coastline approximately monthly with 6 cruises from May to early November. Our analyses included standard water quality indicators (total phosphorus, nitrate + nitrite, chlorophyll a) in addition to a robust suite of autotrophic and heterotrophic indicators of ecosystem health, specifically: primary productivity and bacterial growth assays, phytoplankton biomass assessments, and microbial loop assessments. The sites were compared using mean values from May – November. Results from the offshore waters of Lake Ontario, the Bay of Quinte and Hamilton Harbour have also been presented for comparative purposes. The highest mean values observed in Toronto Harbour for total phosphorus (26.5 µg l−1) and chlorophyll a (6.2 µg l−1) which were both in the inner harbour suggested mesotrophic conditions, although the majority of observations suggested oligotrophy. With respect to autotrophic indicators, primary productivity at the mouth of the Humber River as well as the inner harbour (averaging 15 – 20 mg C m−3 h−1) suggested mesotrophy whereas the remaining sites were more oligotrophic. Phytoplankton biomass (≈400 – 1000 mg m−3) suggested oligotrophy. There was a surprising amount of heterotrophic microbial activity at the Humber Bay and inner harbour sites which were influenced by the Humber and Don Rivers. This included elevated rates of bacterial production (≈2 – 3 mg C m−3 h−1) and a high biomass of heterotrophic nanoflagellates (≈1300 – 2600 mg m−3) which was not likely sustained by the autotrophic production. Our findings suggest that a significant amount of organic matter is being deposited by these two rivers and shunted to the microbial food web. Such findings are not obvious from standard indicators (e.g. total phosphorus, chlorophyll a). More work is needed to quantify the sources of organic carbon and assess its utility as ecological indicators.