Ted Ozersky

Dreissenid phosphorus excretion can sustain C. glomerata growth along a portion of Lake Ontario shoreline.

ABSTRACT One of the effects of the dreissenid invasion into the Laurentian Great Lakes appears to be a resurgence in the abundance of the nuisance alga Cladophora glomerata which experienced a marked decline following phosphorus abatement in the late 1970s and early 1980s. A subsidy of bioavailable phosphorus excreted by dreissenid mussels could be an important mechanism facilitating the growth of C. glomerata. To assess the importance of phosphorus released by mussels to C. glomerata growth in the nearshore, we conducted a survey of mussel distribution and abundance followed by in situ experiments designed to measure dreissenid phosphorus excretion rates. Average dreissenid mussel abundance in our study area was 3674 individuals/m2, with an average biomass of 52.2 g of shell free dry mass/m2. The mussels excreted bioavailable soluble reactive phosphorus at an average rate of 7.02 µg SRP/g shell free dry mass/hour, contributing about 11 t of soluble reactive phosphorus to our study area over the C. glomerata growing season. Dreissenids appear to be an important source of recycled bioavailable phosphorus to the nearshore, supplying more soluble reactive phosphorus to our study area than local watercourses and WWTPs, and more phosphorus than is required to sustain local C. glomerata growth.

The state of Lake Simcoe (Ontario, Canada): the effects of multiple stressors on phosphorus and oxygen dynamics

Abstract Lake Simcoe, the largest lake in southern Ontario outside of the Laurentian Great Lakes, is affected by numerous stressors including eutrophication resulting from total phosphorus (TP) loading, climate change, and invasions of exotic species. We synthesized the long-term responses of Lake Simcoe to these stressors by assessing trends in water quality and biological composition over multiple trophic levels. Evidence for climate change included increasing thermal stability of the lake and changes in subfossil diatom communities over time. Although the deep water dissolved oxygen (O2) minimum has increased significantly since TP load reductions, it is still below estimated historical values and the Lake Simcoe Protection Plan end-of-summer target level of 7 mg O2 L-1. Low deep water O2 concentrations corresponded with a decline in coldwater fish abundance. Since 1980, some nutrient concentrations have decreased (spring TP) while others have increased (silica), but many show no obvious changes (ice-free TP, nitrate, ammonium). Increases in water clarity, combined with declines in chlorophyll a and phytoplankton biovolumes in Cook’s Bay, were temporally consistent with declines in TP loading and the lake-wide establishment of dreissenid mussels as a major component of the Lake Simcoe ecosystem. Using an investigative tool, we identified 2 periods when abrupt shifts potentially occurred in multiple parameters: 1986 and 1995-1997. Additional ecosystem level changes such as declines in zooplankton, declines in offshore benthic invertebrate abundance, and increased nearshore invertebrate abundance likely reflect the effects of invasive species. The interaction of these multiple stressors have significantly altered the Lake Simcoe ecosystem.

Invasive Mussels Alter the Littoral Food Web of a Large Lake: Stable Isotopes Reveal Drastic Shifts in Sources and Flow of Energy

We investigated how establishment of invasive dreissenid mussels impacted the structure and energy sources of the littoral benthic food web of a large temperate lake. We combined information about pre- and postdreissenid abundance, biomass, and secondary production of the littoral benthos with results of carbon and nitrogen stable isotope analysis of archival (predreissenid) and recent (postdreissenid) samples of all common benthic taxa. This approach enabled us to determine the importance of benthic and sestonic carbon to the littoral food web before, and more than a decade after dreissenid establishment. Long term dreissenid presence was associated with a 32-fold increase in abundance, 6-fold increase in biomass, and 14-fold increase in secondary production of the littoral benthos. Dreissenids comprised a large portion of the post-invasion benthos, making up 13, 38, and 56% of total abundance, biomass, and secondary production, respectively. The predreissenid food web was supported primarily by benthic primary production, while sestonic material was relatively more important to the postdreissenid food web. The absolute importance of both sestonic material and benthic primary production to the littoral benthos increased considerably following dreissenid establishment. Our results show drastic alterations to food web structure and suggest that dreissenid mussels redirect energy and material from the water column to the littoral benthos both through biodeposition of sestonic material as well as stimulation of benthic primary production.

Fourteen years of dreissenid presence in the rocky littoral zone of a large lake: effects on macroinvertebrate abundance and diversity

Abstract Establishment of dreissenid mussels in aquatic systems is often accompanied by major changes in the abundance, diversity, and community composition of benthic invertebrates. However, few studies have been published that address the effects of long-term dreissenid presence on the littoral benthos inhabiting hard substrata in lakes. We present the results of a depth-stratified, quantitative survey of littoral benthos conducted at 4 sites in 1993, just before dreissenid invasion, and in 2008, 14 y after the establishment of dreissenids in Lake Simcoe, Ontario. Average densities of nondreissenid invertebrates were 45× greater in 2008 than in 1993. Amphipods, isopods, chironomids and oligochaetes underwent the largest increases in absolute abundance. The taxonomic diversity of the benthic invertebrate community (&agr; diversity) increased significantly. Community structure was more similar within and between depths and sites in 2008 than in 1993, a result implying lower &bgr; diversity of the postdreissenid littoral benthos. In addition, fewer differences were found in the densities of organisms between sampling locations in 2008 than in 1993. We suggest that dreissenids increase resource availability to benthic organisms and homogenize the littoral benthos by increasing the evenness of the distribution of food and physical-habitat resources across sites and depths. The transformation of the littoral benthic community of Lake Simcoe reflects a major change in the distribution of energy in the lake and is consistent with a dreissenid-mediated redirection of production from the pelagic to the littoral zone.

Invasive dreissenid mussels and round gobies: A benthic pathway for the trophic transfer of microcystin

In the present preliminary study, the authors identify 2 pathways through which invasive dreissenid mussels can transfer microcystin to higher trophic levels: either directly, through consumption by benthivorous fish such as the round goby; or indirectly, through their biodeposits, which are an important food source for benthic invertebrates. The results suggest that dreissenid mussels represent a potentially important benthic pathway for the food web transfer of microcystin.

Nearshore–offshore differences in planktonic chlorophyll and phytoplankton nutrient status after dreissenid establishment in a large shallow lake

Abstract In Lake Simcoe, a large lake in southern Ontario, Canada, with more than 50% of its surface area <15 m deep, dreissenid mussels are abundant in the extensive nearshore zone but not offshore. We hypothesized that mussel grazing would depress chlorophyll a (Chl-a) concentrations in the nearshore compared to the offshore while alleviating nearshore phosphorus (P) deficiency through nutrient regeneration. During both years of our study Chl-a concentration and other indicators of phytoplankton biomass, including particulate carbon (C), nitrogen, P, and silicon, were lower in the nearshore areas of Lake Simcoe where the exotic invader Dreissenia polymorpha was in contact with overlying epilimnetic water. In the first year of our study, grazing and associated nutrient regeneration activity seemed to reduce P deficiency in phytoplankton in the dreissenid-impacted shallow locations. In the second year, however, phytoplankton in the nearshore dreissenid-affected areas remained as strongly P deficient as phytoplankton in offshore waters physically separated from dreissenid grazing. Photoacclimation in the nearshore phytoplankton was evident in higher particulate C:Chl-a ratios and higher effective absorptive cross section of photosystem II (σPS II) throughout the stratified sampling season compared to offshore phytoplankton. A multiple linear regression utilizing the mean light intensity in the mixed layer as well as total P (TP) resulted in better predictions of Chl-a than TP alone. We conclude that, in shallow lakes where transparency is strongly impacted by dreissenid grazing, the comparison of Chl-a–TP relationships over time will require accounting for the effect of changing transparency.

Long-Term and Ontogenetic Patterns of Heavy Metal Contamination in Lake Baikal Seals (Pusa sibirica)

Little is known about the history of heavy metal pollution of Russias Lake Baikal, one of the worlds largest lakes and a home to numerous endemic species, including the Baikal Seal, Pusa sibirica. We investigated the history of heavy metal (V, Cu, Zn, Cd, Hg, Tl, Pb, U) pollution in Lake Baikal seals over the past 8 decades. C and N stable isotope analysis (SIA) and laser-ablation ICP-MS of seal teeth were used to examine changes in feeding ecology, heavy metal levels associated with life history events and long-term variation in metal exposure. SIA did not suggest large changes in the feeding ecology of Baikal seals over the past 80 years. LA-ICP-MS analyses revealed element-specific ontogenetic variability in metal concentrations, likely related to maternal transfer, changes in food sources and starvation. Hg and Cd levels in seals varied significantly across the time series, with concentrations peaking in the 1960s - 1970s but then declining to contemporary levels similar to those observed in the 1930s and 1940s. Trends in atmospheric emissions of Hg suggest that local sources as well as emissions from eastern Russia and Europe may be important contributors of Hg to Lake Baikal and that, despite the size of Lake Baikal, its food web appears to respond rapidly to changing inputs of contaminants.

Nutrient limitation of benthic algae in Lake Baikal, Russia

Lake Baikal, one of the world’s largest and most biologically diverse lakes, has recently begun to experience uncharacteristic nuisance blooms of filamentous benthic algae. To contribute to understanding the causes of these blooms, we deployed nutrient-diffusing substrata (NDS) at 10 sites varying in shoreline land use in the southwestern portion of the lake. Our objectives were to assess the nature of nutrient limitation of benthic algae in Lake Baikal, the relationship between land use and limitation status, and the effect of enrichment on algal community composition. Algal biomass measured as chlorophyll a (Chl a) responded strongly to nutrient enrichment and showed serial limitation by N and P at all sites. Chl a levels were ~2 and 4× higher on N- and N+P-amended NDS, respectively, than on unenriched controls. Periphyton biomass varied significantly among sites, but differences in periphyton biomass and nutrient limitation status were not related to shoreline land use. The taxonomic composition of periphyton varied significantly among landuse categories, nutrient treatments, and sites. The filamentous green alga Stigeoclonium tenue, which has been associated with recently observed nuisance blooms in Lake Baikal, tended to be most abundant on N- and N+P-amended NDS. The results of our study demonstrate strong nutrient limitation of the periphyton in Lake Baikal and highlight the potential value of improved nutrient controls for addressing benthic algal blooms in the lake.

Past and present mercury accumulation in the Lake Baikal seal: Temporal trends, effects of life history, and toxicological implications

Despite global efforts to reduce anthropogenic mercury (Hg) emissions, the timescale and degree to which Hg concentrations in the environment and biota respond to decreased emissions remain challenging to assess or predict. In the present study we characterize long-term trends and life-history patterns in Hg accumulation and toxicological implications of Hg contamination for a freshwater seal from one of the worlds largest lakes (Lake Baikal, Siberia, Russia) using contemporary tissues and archival teeth. Stable isotope analysis and Hg analyses of soft tissues (muscle, liver, kidney, blood, brain, heart) and teeth from 22 contemporary seals revealed rapid changes in diet and Hg accumulation in the first year of life with a stable diet and increase in tissue Hg throughout the rest of life. Although maternal transfer of Hg was an important source of Hg to seal pups, reproduction and lactation by female seals did not appear to result in sex-related differences in Hg concentrations or age-related accumulation in adult seals. Based on Hg analysis of archival teeth (n = 114) and reconstructed values for soft tissues, we also assessed temporal trends in seal Hg between the years 1960 and 2013. Seal Hg concentrations in hard (teeth) and soft (e.g., muscle, liver) tissues were highest in the 1960s and 1970s, followed by a decrease. The decline in seal Hg concentrations in recent decades was most likely driven by a reduction in Hg inputs to the lake, suggesting that global and regional efforts to reduce Hg emissions have been successful at reducing ecosystem and human health risks posed by Hg in Lake Baikal. Environ Toxicol Chem 2018;37:1476-1486.