Geology topics

Christopher Hotaling

Publications and source records attributed to Christopher Hotaling.

9 recordsLinked to original sources

USGS2023

Lake Ontario’s nearshore zooplankton: Community composition changes and comparisons to the offshore

In large lake systems the nearshore habitat is an intermediate zone between the shoreline and offshore, is an important nursery for larval fish, and is highlighted as an area in need of research in the Laurentian Great Lakes. In this study, we used two long-term monitoring programs to characterize the nearshore zooplankton community composition using seasonal data (May – October) and to compare the nearshore and offshore zooplankton community composition changes over time (1998 – 2019) to determine if the changes were synchronized. In the nearshore, we found the highest zooplankton biomass during the late summer/early fall (August 27th – Oct 6th), compared to mid-summer (July 1st – Aug 26th) and late spring (May 20th – June 30th). In the summer, the nearshore zooplankton community was dominated by cladocerans while copepods dominated the offshore community. From 1998 to 2019, both nearshore and offshore copepods shifted from a cyclopoid to a calanoid-dominated state, but the details of this change were different. For example, taxon-specific analysis revealed that despite reduced cyclopoids in both habitats, Mesocyclops edax increased in the nearshore. Additionally, taxon-specific analysis suggested the changes occurred an average of three years earlier in the nearshore. Using Analysis of Similarity, the nearshore and offshore summer zooplankton community compositions became increasingly distinct over time. Results from this study highlight the uniqueness of the nearshore in large lake systems, the importance of seasonal and long-term monitoring, and the potential of the nearshore as an early indicator of offshore changes.

Lake Ontario↗

USGS2021

2020 Status of the Lake Ontario lower trophic levels

Significant Findings for Year 2020: Note that due to covid-19 restrictions, offshore sampling was limited in 2020. 1) May – Oct total phosphorus (TP) in 2020 was 10.6 µg/L (offshore) and 7.7 µg/L (nearshore), higher than the long-term (1995-2019) average in the offshore (6.2 µg/L) and close to average in the nearshore (7.8 µg/L); mean TP values for the past decade (2010-2019) were 6.0 µg/L and 7.9 µg/L in the offshore and nearshore, respectively. In 2020, TP concentrations were significantly higher (p=0.03) in the offshore compared to the nearshore. Note that offshore duplicate samples had high relative percent difference (average 54%. 6-117%) making inferences for the offshore in 2020 uncertain. 2) May – Oct epilimnetic chlorophyll-a was similar at nearshore (1.9 µg/L) and offshore (2.1 µg/L) sites. These values were slightly higher than the average for 1995 – 2019 (1.7 µg/L, offshore; 1.5 µg/L, nearshore) and higher than for the last decade (1.4 µg/L, both offshore and nearshore). 3) May – Oct Secchi depth ranged from 3.5 m to 10.4 m (11 ft to 34 ft) at individual sites and was not significantly different between nearshore (6.3 m; 20.7 ft) and offshore (6.5 m; 21.3 ft) locations. Long-term (1995-2019) average was 7.2 m in the offshore and 6.4 m in the nearshore; means for the last decade were 7.8 m in the offshore and 6.2 m in the nearshore. 4) Despite higher TP values in 2020 than in recent years, TP, chlorophyll-a and Secchi depth are indicative of oligotrophic conditions in the offshore of Lake Ontario. 5) Nearshore summer zooplankton biomass was 10.5 µg/L, near the all-time low (9.4 µg/L, 2017) since monitoring began in 1995. Offshore epilimnetic summer zooplankton biomass was 11.7 µg/L. These values are similar to biomass in the last decade (2010-2019). 6) Peak (July) epilimnetic biomass of Cercopagis was 3.0 µg/L in the nearshore and represented 25% of the zooplankton community at that time; Cercopagis was absent from the July offshore epilimnetic samples in 2020 but was present in whole water column samples taken in August by other agencies. Epilimnetic biomass of Bythotrephes peaked in late-September in both the nearshore (1.0 µg/L) and offshore (1.8 µg/L) and represented 10% and 18% of the zooplankton community at those times, respectively. 7) Summer nearshore and offshore epilimnetic zooplankton density and biomass declined significantly 1995 – 2020. The declines were due mainly to reductions in cyclopoid copepods in both habitats.

Lake Ontario↗

USGS2020

2019 Status of the Lake Ontario Lower Trophic Levels

Spring total phosphorus (TP) in 2019 was 3.2 µg/L (offshore) and 4.7 µg/L (nearshore), both all-time lows; however, there is no significant time trend in our data series (1995-2019 for nearshore; 2002-2019 for offshore). Apr/May – Oct mean TP concentrations were low at both nearshore and offshore locations (range, 3.7 – 6.5 µg/L). TP and SRP concentrations were not significantly different between nearshore and offshore habitats. Chlorophyll- a and Secchi depth values are indicative of oligotrophic conditions in nearshore and offshore habitats. Offshore summer chlorophyll-a declined significantly 1995 – 2019. Nearshore chlorophyll- a increased 1995 – 2004 and then stabilized 2005 – 2019. In 2019, epilimnetic chlorophyll-a averaged between 1.3 and 2.9 μg/L across sites, and Apr/May – Oct concentrations were not significantly different between nearshore and offshore sites. Summer Secchi depth increased significantly in the offshore 1995 – 2019 from ~6 m to ~8 m. In the nearshore Secchi depth increased 1995 – 2004 but has remained around 6 m since 1999. Apr/May – Oct Secchi depth ranged from 3.8 m to 9.1 m (12 ft to 30 ft) at individual sites and was significantly higher offshore (7.6 m; 25 ft) than nearshore (5.7 m; 19 ft). In 2019, nearshore summer zooplankton biomass increased to 16.7 mg/m 3 after an all-time low (10.3 mg/m 3 ) in 2017. Offshore biomass (12.0 mg/m 3 ) was near the all-time low (8.1 mg/m 3 , 2006). Apr/May – Oct epilimnetic zooplankton density and biomass were not different between nearshore and offshore sites. However, zooplankton average size was significantly higher in the offshore (0.72 mm) than the nearshore (0.61 mm). Peak (July) epilimnetic biomass of Cercopagis was 2.4 mg/m 3 in the nearshore and 1.4 mg/m 3 in the offshore. Peak (September) epilimnetic biomass of Bythotrephes was 2.0 mg/m 3 in the nearshore and 2.9 mg/m 3 in the offshore. Summer nearshore zooplankton density and biomass declined significantly 1995 – 2004 and then remained stable 2005 – 2019. The decline was due mainly to reductions in cyclopoids copepods. Summer epilimnetic daytime offshore zooplankton density decreased significantly 1995 – 2004, but biomass did not. Density and biomass declined significantly 1995 – 2019. Density was 3885/m 3 in 2019, about one-fourth the level observed the previous year. Offshore summer epilimnetic zooplankton biomass in 2019 was 12 mg/m 3 —well below the mean from 2005 – 2018 (20 mg/m 3 ). Most offshore zooplankton biomass was found in the metalimnion in July and early-October, and in the hypolimnion in September. Limnocalanus dominated the metalimnion in July while daphnids comprised most of the biomass in October. In September, Limnocalanus dominated the hypolimnion.

New York, Ontario↗

USGS2019

2018 Status of the Lake Ontario lower trophic levels

Significant Findings for Year 2018: 1) Offshore spring total phosphorus (TP) in 2018 was 7.0 µg/L; values have remained stable since 2001. Offshore soluble reactive phosphorus (SRP) remained low (1.3 µg/L) in 2018; Apr/May – Oct mean values have been stable in nearshore and offshore habitats since 1998 (range, 0.4 – 3.3 µg/L). Apr/May – Oct mean TP concentrations were low at both nearshore and offshore locations (range, 3.9 – 7.8 µg/L). TP and SRP concentrations were not significantly different between nearshore and offshore habitats. 2) Chlorophyll-a and Secchi depth values are indicative of oligotrophic conditions in nearshore and offshore habitats. Offshore summer chlorophyll-a was stable 2000 – 2018. Nearshore chlorophyll-a increased 1995 - 2004 and then stabilized 2005 – 2018; values were below the long-term mean in 2018. In 2018, epilimnetic chlorophyll-a averaged between 0.9 and 1.8 μg/L across sites, and offshore and nearshore Apr/May – Oct concentrations were not significantly different. Summer Secchi depth increased significantly in the offshore 2000 – 2018 and in the nearshore 1995 – 2004. Apr/May – Oct Secchi depth ranged from 4.7 m to 13.5 m (15 ft to 44 ft) at individual sites and was not significantly different between offshore (8.6 m; 28 ft) and nearshore (6.3 m; 21 ft) locations. 3) In 2018, nearshore summer zooplankton biomass increased slightly to 10.7 mg/m3 after an all-time low (10.3 mg/m 3 ) in 2017. Apr/May – Oct epilimnetic zooplankton density was significantly higher in the offshore than the nearshore, but zooplankton size and biomass were not different. Cyclopoid copepods were primarily responsible for the higher density in the offshore. 4) Peak (July) epilimnetic biomass of Cercopagis was 1.3 mg/m 3 in the nearshore and 1.9 mg/m 3 in the offshore. Peak (September-October) epilimnetic biomass of Bythotrephes was 0.4 mg/m 3 in the nearshore and 0.6 mg/m3 in the offshore. Bythotrephes biomass has increased significantly in the nearshore, 1995 – 2018. 5) Summer nearshore zooplankton density and biomass declined significantly 1995 – 2004 and then remained stable 2005 – 2018. The decline was due mainly to reductions in cyclopoids copepods. 6) Summer epilimnetic daytime offshore zooplankton density and biomass decreased significantly 2000 – 2018, but density increased marginally since 2005. Density was 16000/m 3 in 2018, three times the levels seen 2015 – 2017. Offshore summer epilimnetic zooplankton biomass in 2018 was 11 mg/m 3 — well below the mean from 2005 – 2017 (20 mg/m 3 ). 7) Most offshore zooplankton biomass was found in the metalimnion in July and early-September, and in the hypolimnion in late-September and October. Cyclopoids dominated the metalimnion in July while daphnids and cyclopoids comprised most of the biomass in September. Daphnids dominated the October hypolimnion.

Lake Ontario↗

USGS2019

2017 Status of the Lake Ontario Lower Trophic Levels

Significant Findings for Year 2017: 1) Offshore spring total phosphorus (TP) in 2017 was 4.4 µg/L; values remained stable since 2001. Offshore soluble reactive phosphorus (SRP) remained low (1.1 µg/L) in 2017; Apr/May – Oct mean values have been stable in nearshore and offshore habitats since 1998 (range, 0.4 – 3.3 µg/L). Apr/May – Oct mean TP concentrations were low at both nearshore and offshore locations (range, 3.7 – 9.0 µg/L). TP and SRP concentrations were significantly higher in nearshore compared to offshore habitats (7.9 µg/L vs 5.3 µg/L, TP; 1.7 µg/L vs 1.0 µg/L, SRP). 2) Chlorophyll-a and Secchi depth values are indicative of oligotrophic conditions in nearshore and offshore habitats. Offshore summer chlorophyll-a was stable 2000 – 2017. Nearshore chlorophyll-a increased 1995 - 2004 but then declined 2005 – 2015; values were above the long-term mean for 2016 and 2017. In 2017, epilimnetic chlorophyll-a averaged between 1.2 and 2.6 μg/L across sites, and offshore and nearshore Apr/May – Oct concentrations were not significantly different. Summer Secchi depth increased significantly in the offshore 2005 – 2017 and in the nearshore 1995 – 2004. There was no trend in either habitat 1995 – 2017. Apr/May – Oct Secchi depth ranged from 4.4 m to 12.5 m at individual sites and was not significantly different between offshore (8.9 m) and nearshore (5.7 m) locations. 3) In 2017, nearshore summer zooplankton biomass was at an all-time low (10.3 mg/m3). Apr/May – Oct epilimnetic zooplankton density was not different between the offshore and the nearshore, but zooplankton size and biomass were significantly higher in the offshore. (0.7 mm vs 0.52 mm and 14.2 mg/m3 vs 7.7 mg/m3). Daphnid, calanoid copepod, and cyclopoid biomass were all higher in the offshore. 4) Peak (July) epilimnetic biomass of Cercopagis was 2.5 mg/m3 in the nearshore and 1.6 mg/m3 in the offshore. Peak (September/October) epilimnetic biomass of Bythotrephes was 0.9 mg/m3 in the nearshore and 0.5 mg/m3 in the offshore. Bythotrephes biomass has increased significantly in the nearshore, 1995 – 2017. 5) Summer nearshore zooplankton density and biomass declined significantly 1995 – 2004 and then remained stable 2005 – 2017. The decline was due mainly to reductions cyclopoids. 6) Summer epilimnetic offshore zooplankton density and biomass increased significantly 2005 – 2017, due mainly to increases in cyclopoids and daphnids. In 2017, offshore summer epilimnetic zooplankton biomass was 14 mg/m3—well below the mean from 2005 – 2016 (21 mg/m3). 7) Most offshore zooplankton biomass was found in the metalimnion in July and September, and in the hypolimnion in October. Limnocalanus and cyclopoids dominated the metalimnion in July while daphnids and cyclopoids comprised most of the biomass in September. Daphnids dominated the October hypolimnion. Whole water column samples show a declining zooplankton biomass 2015 – 2017. Bythotrephes biomass in whole water column tows is the highest it has been, 2010 – 2017.

Lake Ontario↗

USGS2017

Nutrients, phytoplankton, zooplankton, and macrobenthos

Lower trophic levels support the prey fish on which most sport fish depend. Therefore, understanding the production potential of lower trophic levels is integral to the management of Lake Ontario’s fishery resources. Lower trophic-level productivity differs among offshore and nearshore waters. In the offshore, there is concern about the ability of the lake to support Alewife (Table 1) production due to a perceived decline in productivity of phytoplankton and zooplankton whereas, in the nearshore, there is a concern about excessive attached algal production (e.g., Cladophora) associated with higher nutrient concentrations—the oligotrophication of the offshore and the eutrophication of the nearshore (Mills et al. 2003; Holeck et al. 2008; Dove 2009; Koops et al. 2015; Stewart et al. 2016). Even though the collapse of the Alewife population in Lake Huron in 2003 (and the associated decline in the Chinook Salmon fishery) may have been precipitated by a cold winter (Dunlop and Riley 2013), Alewife had not returned to high abundances in Lake Huron as of 2014 (Roseman et al. 2015). Failure of the Alewife population to recover from collapse has been attributed to declines in lower trophic-level production (Barbiero et al. 2011; Bunnell et al. 2014; but see He et al. 2015). In Lake Michigan, concerns of a similar Alewife collapse led to a decrease in the number of Chinook Salmon stocked. If lower trophic-level production declines in Lake Ontario, a similar management action could be considered. On the other hand, in Lake Erie, which supplies most of the water in Lake Ontario, eutrophication is increasing and so are harmful algal blooms. Thus, there is also a concern that nutrient levels and algal blooms could increase in Lake Ontario, especially in the nearshore. Solutions to the two processes of concern—eutrophication in the nearshore and oligotrophication in the offshore—may be mutually exclusive. In either circumstance, fisheries management needs information on the productivity of lower trophic levels in Lake Ontario. In this chapter, we review the status of lower trophic levels in Lake Ontario with special attention to the current (2008-2013) and previous (2003-2007) reporting periods. During the two reporting periods, three whole-lake surveys of lower trophic levels were conducted: the Lower Trophic Level Assessment (LOLA) in 2003 and 2008 (Makarewicz and Howell 2012; Munawar et al. 2015b) and the Cooperative Science and Management Initiative (CSMI) in 2013. Analyses of the CSMI data are ongoing. In addition to the three one-year sources of information on lower trophic levels, several multi-year sources of information are available, including data from the surveillance program conducted since 1965 by Environment Canada (EC) (Dove 2009), monitoring conducted since 1980 by the U.S. Environmental Protection Agency’s (EPA) Great Lakes National Program Office (GLNPO) (Barbiero et al. 2014; Reavie et al. 2014), sampling for a Bioindex Program at two stations, one offshore and one in the Eastern Basin, assessments of Mysis diluviana (formerly Mysis relicta) conducted since 1980 by Fisheries and Oceans Canada (Johannsson et al. 1998, 2011) and the Ontario Ministry of Natural Resources and Forestry (OMNRF), and monitoring conducted since 1995 by the Biomonitoring Program (BMP) on the New York side of the lake (Holeck et al. 2015b). The BMP is a collaboration of the New York State Department of Environmental Conservation (DEC), U.S. Fish and Wildlife Service, U.S. Geological Survey (USGS), and Cornell University.

Special Publication↗

USGS2017

2016 status of the Lake Ontario Lower Trophic levels

Significant Findings for Year 2016: 1) Offshore spring total phosphorus (TP) in 2016 was 6.2 μg/L, higher than 2014 and 2015 (4.0 and 4.2 μg/L); there was no significant decline 2001 - 2016. Offshore soluble reactive phosphorus (SRP) was very low in 2016; Apr/May – Oct mean values were <1 μg/L. SRP has been stable in nearshore and offshore habitats since 1998 (range, 0.4 – 3.3 μg/L). Apr/May – Oct mean TP concentrations were low at both nearshore and offshore locations (range 5.2 – 9.9 μg/L). TP and SRP concentrations were significantly higher in nearshore compared to offshore habitats (7.6 μg/L vs 6.0 μg/L, TP; 1.4 μg/L vs 0.8 μg/L, SRP). 2) Chlorophyll-a and Secchi depth values are indicative of oligotrophic conditions in nearshore and offshore habitats. Offshore summer chlorophyll-a declined significantly 2000 - 2016. Nearshore chlorophyll-a increased 1995 - 2004 but then declined 2005 - 2016. Epilimnetic chlorophyll-a averaged between 1.4 and 2.5 μg/L across sites, and offshore and nearshore Apr/May – Oct concentrations were the same (1.9 μg/L). Summer Secchi depth increased significantly in the offshore 2000 - 2016 and showed no trend in the nearshore, 1995 – 2016. Apr/May – Oct Secchi depth ranged from 5.0 m to 13.0 m at individual sites and was significantly higher in the offshore (10.0 m) than nearshore (6.5 m). 3) In 2016, Apr/May – Oct epilimnetic zooplankton density and biomass were not different between the offshore and the nearshore, but calanoid copepod and Limnocalanus biomass were higher in the offshore (4.7 mg/m3 vs 2.6 mg/m3 and 0.7 mg/m3 vs 0.1 mg/m3), and bosminid biomass was higher in the nearshore (1.1 mg/m3 vs 0.3 mg/m3). Zooplankton size was significantly higher in the offshore than the nearshore (0.66 mm vs 0.49 mm). 4) Peak (July) epilimnetic biomass of Cercopagis was 1.0 mg/m3 in the nearshore and 1.4 mg/m3 in the offshore. Peak (October) epilimnetic biomass of Bythotrephes was 1.8 mg/m3 in the nearshore and 0.6 mg/m3 in the offshore. Bythotrephes biomass has increased significantly in the nearshore, 1995 – 2016. Bythotrephes was more abundant in 2016 than in the previous two years and the zooplankton community responded accordingly with a decrease in bosminds and cyclopoids. 5) Summer nearshore zooplankton density and biomass declined significantly 1995 – 2004 and then remained stable 2005 – 2016. The decline was due to reductions in bosminids and cyclopoids. 6) Summer epilimnetic offshore zooplankton density and biomass increased significantly 2005 – 2016. In 2016, offshore summer epilimnetic zooplankton biomass was 22 mg/m3--less than half that observed in 2015--but still slightly higher than the mean from 2005 – 2015 (21 mg/m3). 7) Most offshore zooplankton biomass was found in the metalimnion in July and September, and in the hypolimnion in October. Limnocalanus dominated the metalimnion in July while other calanoids and daphnids comprised most of the biomass in September. Limnocalanus and other calanoids dominated the October hypolimnion. Whole water column samples taken show a stable zooplankton biomass but changing community composition since 2010. Cyclopoids increased 2013 – 2015 and declined in 2016, while the calanoid pattern was the opposite. Daphnids declined 2014 – 2015 but rebounded in 2016.

Lake Ontario↗

USGS2016

2015 status of the Lake Ontario lower trophic levels

Offshore spring total phosphorus (TP) in 2015 was 4.2 μ g/L, the same as in 2014; this is lower than 2001 - 2013, but there is no significant time trend 2001 - 2015. Offshore soluble reactive phosphorus (SRP) was very low in 2015; Apr/May - Oct mean values were <1 μ g/L at most sites. SRP has been stable in nearshore and offshore habitats since 1998 (range, 0.4 – 3.3 μ g/L). TP concentrations were low at both nearshore and offshore locations (range 4.2 - 8.1 μ g/L), and TP and SRP concentrations were significantly higher in the nearshore as compared to the offshore (6.8 μ g/L vs 4.8 μ g/L, TP; 1.1 μ g/L vs 0.7 μ g/L, SRP). Chlorophyll- a and Secchi depth values are indicative of oligotrophic conditions in nearshore and offshore habitats. Offshore summer chlorophyll- a declined significantly 2000 - 2015. Nearshore chlorophyll- a increased 1995 - 2004 but then declined 2005 - 2015. Epilimnetic chlorophyll- a averaged between 0.9 and 1.9 1 μg/L across sites, and offshore concentrations (1.4 1 μg/L) were significantly higher than nearshore (1.1 μg/L). Summer Secchi depth increased significantly in the offshore 2000 -2015 and showed no trend in the nearshore, 1995 - 2015. Apr/May - Oct Secchi depth ranged from 5.0 m to 13.0 m at individual sites and was higher in the offshore (9.5 m) than nearshore (6.2 m). In 2015, Apr/May - Oct epilimnetic zooplankton density, size, and biomass were not different between the offshore and the nearshore, but cyclopoid biomass was higher in the offshore (8.3 mg/m 3 vs 2.0 mg/m 3 ) and Bythotrephes biomass was higher in the nearshore (0.17 mg/m 3 vs 0.04 mg/m 3 ). Zooplankton density and biomass peaked in September, an atypical pattern. This coincided with peaks in calanoid copepod, daphnid, and Holopedium Holopedium biomass in the nearshore has increased significantly since 1995. The predatory cladoceran Cercopagis continued to be abundant in summer in the nearshore (3.4 μ g/L) but not in the offshore (0.8 μ g/L). Bythotrephes biomass was very low (<0.3 μ g/L) in both nearshore and offshore habitats. Combined biomass of these predatory cladocerans in the offshore was the lowest recorded since 2001. Summer nearshore zooplankton density and biomass declined significantly 1995 - 2004 and then increased significantly 2005 – 2015. The decline was due to reductions in bosminids and cyclopoids and the increase was due mostly to a rebound in bosminids. Summer offshore zooplankton density and biomass increased significantly 2005 - 2015. The increase was due to an increase in bosminids and cyclopoids. In 2015, offshore summer epilimnetic zooplankton biomass was 52 mg/m 3 (2005 - 2014 mean=18 mg/m 3 ). Most zooplankton biomass was found in the metalimnion in July and in the hypolimnion in September. Cyclopoids and Limnocalanus dominated the metalimnion and Limnocalanus dominated the hypolimnion. Whole water column samples taken show a stable zooplankton biomass but changing community composition since 2010. Cyclopoids increased 2013 - 2015 and daphnids declined 2014 - 2015.

Lake Ontario↗

USGS2015

2014 status of the Lake Ontario lower trophic levels

Soluble reactive phosphorus (SRP) concentrations have been stable in nearshore and offshore habitats since 1998 (0.4 – 3.3 μg/L). SRP concentrations were low in 2014; Apr/May – Oct mean values were <1 μg/L at most sites. Spring TP concentrations at individual sites exceeded 10 μg/L on occasion, but spring means were below the 10 μg/L target set by the Great Lakes Water Quality Agreement of 1978 for offshore waters of Lake Ontario. TP concentrations were low at both nearshore and offshore locations; Apr/May – Oct mean values from individual sites ranged from 4.6 – 9.1 μg/L. Spring TP has declined significantly in the longer data series (since 1981), but not since 1995 indicating stable nutrient loading into Lake Ontario for nearly two decades. It averaged 7.8 μg/L in the nearshore and 5.6 μg/L in the offshore in 2014. Chlorophyll-a and secchi depth values are indicative of oligotrophic conditions in nearshore and offshore habitats. Offshore summer chlorophyll-a declined significantly in both the short- (2000-2014) and long-term (1981-2014) time series at a rate of 4-6% per year. Nearshore chlorophyll-a increased after 2003 but then declined again after 2009. Epilimnetic chlorophyll-a averaged between 0.6 and 1.6 μg/L across sites with no difference between nearshore and offshore habitats. Apr/May – Oct Secchi depth ranged from 4.0 m to 10.8 m at individual sites and was higher in the offshore (average 9.1 m) than nearshore (5.9 m). In 2014, Apr/May – Oct epilimnetic zooplankton density, size, and biomass were not different between the offshore and the nearshore, and there were no differences in epilimnetic biomass between offshore and nearshore areas for any of the zooplankton groups. Zooplankton density and biomass peaked in September, an atypical pattern. This coincided with peaks in calanoid copepod, daphnid, and Holopedium biomass. Holopedium biomass in the nearshore increased significantly since 1995. The predatory cladoceran Cercopagis continued to be abundant in the summer, peaking at ~10 mg/m3in the offshore. Bythotrephes biomass was at its lowest level since 2005 in both offshore and nearshore habitats. Summer nearshore zooplankton density and biomass have declined significantly since 1995 at rates of 9-10% per year but have remained stable since 2005. However, bosminids and daphnids increased in 2013 and 2014. Summer offshore zooplankton density and biomass declined significantly in the long-term (since 1981), but remained at a lower stable level 2000 – 2014. A positive change point in 2013 is due to increases in bosminids, cyclopoid copepods, and daphnids. The observed decline in zooplankton biomass may be due in part to redistribution of zooplankton throughout the water column. Most of the zooplankton biomass was in the metalimnion and hypolimnion during the stratified period in 2014. By October, the bulk of the biomass was in the epilimnion.

Lake Ontario↗