H. Niblock

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.

Is Lake Erie a resilient ecosystem

Lake Erie has a long history of natural and cultural perturbations ranging from glacial origins, arrival of Europeans, exploration-early colonization, degradation, exotic invasion, and phosphorus reduction to its recent recovery. Is Lake Erie a resilient ecosystem responding to phosphorus abatement and exotic invasion? It is believed that Erie was an oligotrophic system when glaciers receded followed by a long period of mesotrophic conditions. It has been classified from mesotrophic to eutrophic ecosystem during the past three decades. In the 1970s the Great Lakes Water Quality Agreement was signed between Canada and the United States and steps were taken to reduce the phosphorus loading to the Great Lakes including Lake Erie. Total phosphorus and chlorophyll a levels in the eutrophic west have dropped from 41 µg L -1 and 13.8 µg L -1 in the 1970s to <20 µg L -1 and 5.6 µg L -1 in the 1990s. Similarly a significant decrease in phytoplankton biomass was recorded from 1970 to 1992 in the western basin. During the same period Diatomeae decreased markedly from 55% to 10% whereas Chlorophyta increased from 8% to 55%. Similar trends were evident in the other biota. Primary production rates in the 1990s were dominated by small sized organisms (picoplankton and nanoplankton) similar to Lake Superior - a pristine oligotrophic ecosystem. Based on several criteria such as reduction of biomass and primary production, high species diversity, decrease of eutrophic and increase of mesotrophic-oligotrophic species and prevalence of picoplankton-nanoplankton, Lake Erie appears to be a rapidly changing and resilient ecosystem altering from eutrophic to meso-oligotrophic conditions. These observations are also supported by the response of other biota such as zooplankton and benthos. For example during 1993 the non-zebra mussel benthic biomass in the western basin had returned to a similar composition observed earlier in 1952 including the recovery of the mayfly. On the other hand eastern basin benthos has not shown the same extent of recovery as the west. Fish community trends are very complex, but the return of the walleye and whitefish in the western and eastern basins respectively are encouraging signs of recovery. The changes observed at various trophic levels are indicative of a meso-oligotrophic environment.

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.

Is sediment or pseudofaeces toxicity responsible for the decline of the amphipod Diporeia hoyi in Lakes Erie and Ontario

Abstract The deepwater amphipod Diporeia hoyi has disappeared from Lake Erie and much of Lake Ontario at depths < 80 m. This amphipod had supplied 20 percent of the fisheries energy budget in the Great Lakes. The exotic mussel Dreissena bugensis now forms most of the benthic biomass above 60 m depth, but Diporeia is absent over large areas where Dreissena are rare. The filamentous bacterium Thioploca ingrica is now common at many sites between 30 and 40 m where Diporeia has disappeared. Fisheries and Oceans, Canada, investigated the causes of the decline by examining the sediment chemistry, bacterial production and conducted sediment bioassays using Diporeia, Hyalella and Microtox® Microtox® showed no evidence of toxicity in sediments now devoid of Diporeia. Amphipod survival and growth was greatest in sediment that rapidly lost its Diporeia population in 1993. Presence of Thioploca had no effect on Diporeia survival. Hyalella was more sensitive than Diporeia to test sediments and to filtered water from mussel cultures. Sediment from sites with dense Dreissena populations had lower Diporeia survival. A diet of mussel pseudofaeces caused significantly lower survival in both Hyalella and Diporeia. The exact mechanism causing lower survival is currently unknown and may be related to a nutritional problem or associated waste metabolites.

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.

An Integrated Assessment of the Ecosystem Health of a Protected Area: Fathom Five National Marine Park, Lake Huron

An assessment of the aquatic ecosystem health of Fathom Five National Marine Park was carried out in an integrated fashion by applying a multi-trophic suite of structural and functional techniques to evaluate the food web (bacteria, heterotrophic nanoflagellates, ciliates, autotrophic picoplankton, phytoplankton, zooplankton and benthos). Extensive biotic assessment revealed the Fathom Five National Marine Park to be an oligotrophic healthy ecosystem similar to Lakes Huron and Superior. The multi-trophic and integrated food web assessment strategy applied previously in the Great Lakes was adopted for the evaluation of a protected area for the first time. Our approach is recommended for ecosystem health monitoring of other protected areas since it is sensitive, rapid, and holistic and includes the entire pelagic food web.

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.

Phytoplankton ecology in the Bay of Quinte, Lake Ontario: Spatial distribution, dynamics and heterogeneity

The Bay of Quinte, a large riverine embayment located on the northeastern shores of Lake Ontario, has a long history of cultural eutrophication. While the Bay has been the subject of an extensive research and monitoring program that began in 1972, phytoplankton assessments have been limited to 2–3 index stations with few exceptions. Our study consisted of three separate surveys conducted during the summer of 2010 (June, August, September) at 12 sites spread evenly throughout the Bay. Among the major findings were that conditions in the Bay ranged from oligo- to mesotrophic in June, but were primarily eutrophic in August and September with algal blooms observed at 50–75% of the sites; the spatial extent limited only by incursions of oligotrophic water from Lake Ontario. Furthermore, primary productivity in the Bay (e.g. 43.3–109.6 mg C m−3 h−1 in September) was among the highest reported in the Great Lakes, indicative of a phytoplankton community very well adapted to its environment. We also found that the Bay of Quinte supported a diverse algal flora containing 140 unique species in June, 209 in August and 169 in September which we attribute to the variable physical environment. Of the 35 phytoplankton samples assessed, Diatomeae were the most prevalent taxa in 16 of those assemblages followed by Cyanophyta (including many toxigenic species) in 12. The relative importance of diatoms are often overlooked in studies of eutrophication yet two species in particular, Aulacoseira granulata and A. ambigua, were major contributors to both the algal standing crop and the elevated rates of primary production. We recommend that future research be directed at understanding the ecology, physiology and dynamics of these filamentous diatoms as well as their associations with filamentous and colonial cyanobacteria.