Phytoplankton, Zooplankton and Benthos Communities in Lake Superior M.L. Tuchman1 & R.P. Barbiero2 1USEPA GLNPO, Chicago, IL USA 2DynCorp I&ET, Chicago, IL USA

Great Lakes National Program Office USEPA Monitoring Began in 1983 Current Sampling Includes: Phytoplankton Zooplankton Benthos Physical/Chemical Parameters Biannual Sampling Spring mixed Summer stratified Monitoring of MI, HU ER began in 83; Ontario added in 86; SU added in 93 Program focuses on extensive spatial coverage Temporal coverage confined to two well-defined periods: Spring completely mixed Summer stable stratifies

1998 Summer Sampling Stations Plankton & Benthos Sites Benthos Only Sites Plankton Sites 90 sites overall; 72 plankton stations

TOPICS Focus on: Communities Examined: Offshore Waters Spring; Summer Communities Examined: Phytoplankton: biovolume; development Crustacean: composition, size structure Benthos: status of Diporeia Current Status - Results from 1999 Survey Sampling focuses on open water, two temporal periods Phytoplankton samples composited from ~ upper 20 m. Zooplankton - crustaceans enumerated from 100 m tows (153 um mesh); Here we’ll focus on: Phytoplankton biovolume, especially as compared to other lakes, and phyto community development Zooplankton biomass, compared to other lakes, and zooplankton size structure. Benthos, in particular the status of the main benthic organism Diporeia

This is the boat. It’s not always at dock This is the boat. It’s not always at dock. Sometimes it’s out on the water, doing very important work.

This is a technician (Ken Klubek) taking a zooplankton sample.

This is the crew taking a sample from a Canadian icecutter, since they’d foolishly leant their boat to someone else. This was spring, 99 – notice the ice. Question: how many EPAers does it take to fill a bottle with water? [answer: four, but only if they have four Canadians helping]

Locations of GLNPO Routine Monitoring Sites Plankton & Benthos Benthos Plankton 19 plankton sites distributed throughout open water 9 benthos sites

Major Types of Diatoms Centrics Pennates Cyclotella Aulacoseira First talk about phytoplankton. Most important type in Great Lakes: diatoms. Here are some examples: Aulacoseira prominent spring form; Cyclotella prominent summer form; pennates can be found any time (though usually in summer in Superior, if at all) Fragilaria Asterionella Tabellaria

Phytoplankton Biovolume, Spring 1998 SU MI HU ER ON Biovolume (106 mm3/ml) 1 2 3 4 2*106 mm3/ml 1*106 mm3/ml 5*105 mm3/ml Biomass in spring extremely low, even compared to other upper lakes. Biomass fairly consistent from site to site; no obvious spatial patterns. (in contrast, compare to ER where spatial heterogeneity very large)

Phytoplankton Biovolume, Spring 1999 SU MI HU ER ON 1 2 3 4 Biovolume (106 mm3/ml) 2*106 mm3/ml 1*106 mm3/ml 5*105 mm3/ml Same pattern in 99 as in 98.

Phytoplankton Biovolume, Summer 1998 SU MI HU ER ON Biovolume (106 mm3/ml) 1 2 3 4 2*106 mm3/ml 1*106 mm3/ml 5*105 mm3/ml Summer: biomass increases, while in other lakes decreases, so in summer biomass levels more similar to those in other lakes. Still notably lower than other upper lakes, but gap is narrowed. No discernable spatial patterns to biomass: appears to be pretty homogeneous. Note: same scale as spring graph

Phytoplankton Biovolume, Summer 1999 SU MI HU ER ON 1 2 3 4 Biovolume (106 mm3/ml) 2*106 mm3/ml 1*106 mm3/ml 5*105 mm3/ml Summer: biomass increases, while in other lakes decreases, so in summer biomass levels more similar to those in other lakes. In 1999, was about the same as in Huron, i.e. biovolume in Superior was higher in 99 than 98 at time of sampling. No discernable spatial patterns to biomass. Note: same scale as spring graph

Relative Composition of Phytoplankton Communities 1998 1999 SU MI HU ER ON 25 50 75 100 SU MI HU ER ON 25 50 75 100 Spring Percent Composition SU MI HU ER ON 25 50 75 100 100 75 Summer 50 Summer community: increase in chrysophyte biomass; diatoms about the same percent as spring, but decrease in other lakes, so SU has relatively higher diatom biomass. Again probably due to slower development, and consequent higher dissolved Si concentrations in summer compared to other lakes. Notice that in 1999, summer Huron more like Superior than Michigan. This probably normal case (I think 98 was an anomalous year). So to an extent Huron and Superior are more similar than Huron and Michigan when it comes to phytoplankton, probably due largely to historic P loads and subsequent Si losses in Michigan. 25 SU MI HU ER ON Diatoms Chlorophytes Cryptophytes Cyanophytes Dinoflagellates OTHER Chrysophytes

Phytoplankton - Conclusions Biomass Low Relative to Other Lakes Lower in spring than summer Development Of Phytoplankton Community Delayed Diatoms Persist Further Into Season Summer Community Most Similar to Huron Important Points: Community development seems to lag behind other lakes, so less diatoms (and biomass) in spring, relatively more in summer. Other lakes biomass peaks in spring, in SU peaks in summer. Difference in biomass between SU and other upper lakes less in summer. Community probably most similar to Huron, at least in summer, in terms of both composition (at division level) and biomass. Note: community doesn’t seem to have changed since first records - Cyclotella and Dinobryon always seem to have been dominants. Stoermer would disagree; on the basis of cores he thinks lake has changed dramatically, starting with the dawn of civilization (1700’s). Whatever.

Cladocerans Daphnia retrocurva Bosmina longirostris Zooplankton: Crustaceans Two main types, cladocerans and copepods Two examples of cladocerans (neither of which found in SU to any great extent) Photo: SMSU Photo: Dr. Paul Hebert

Copepods Mesocyclops Diaptomus Two types of copepods: Cyclopoids and Calanoids Cyclopoids rounder, Calanoids more torpedo-like. Mesocyclops not found in Superior, but couldn’t get a picture of the cyclopoid that IS found in Su (Diacyclops thomasi) Photo: SMSU Photo: USGS

Biomass of Spring Crustaceans 1999 3 g/m2 1 g/m2 Biomass relatively uniform. Community made up of Calanoid copepods (blue slices), mostly Limnocalanus macrurus immatures and Diaptomus sicilis These are BIG critters, also very deep-living (hang out around 80 m or so), so I’m not sure what their availability to fish is. Also some Cyclops bicuspidatus thomasi (that’s the cyclopoid – brown pie slice) Cladocerans Calanoida Imm Calanoida Cyclopoida Imm Cyclopoida

Biomass of Summer Crustaceans 1999 3 g/m2 1 g/m2 Summer biomass higher. Some cladocerans, but not a lot. [cladocerans about equal parts D. galeata medotae and Holopedium gibberum – very characterisic of Superior] Typically more cladocerans and overall higher biomass nearshore. Dominant organisms still Limnocalanus macrurus and Diapotmus sicilis, and their immatures. As before, cyclopoid is Cyclops bicuspidatus thomasi. A few other critters show up, but those five make up the vast majority (> 95%) of individuals Cladocerans Calanoida Imm Calanoida Cyclopoida Imm Cyclopoida

Biomass of Spring Crustaceans 1999 SU MI HU W C E ON Percent Abundance 25 50 75 100 ER Calanoida Cladocerans Cyclopoida Imm Calanoida Imm Cyclopoida Comparing biomass across lakes, Superior relatively low in spring, but higher than Erie and northern Michigan. This was odd year for Michigan. Note high proportion of calanoids in Superior. Regarded as clean water indicators. In contrast, Ontario mostly cyclopoids. 2 g/m2 < 0.4 g/m2 1 g/m2

Biomass of Summer Crustaceans 1999 MI HU W C E ON Percent Abundance 25 50 75 100 ER Calanoida Cladocerans Cyclopoida Imm Calanoida Imm Cyclopoida Relatively low biomass in summer [this is different scale from spring graph] Note relative lack of cladocerans, dominance still by calanoids. [As an aside, this was a very unusual year for L. Michigan in that lots of cyclopoids and cladocerans were mostly Bosmina] 10 g/m2 < 1.5 g/m2 5 g/m2

Comparison of Crustacean Biomass in the Great Lakes, 1999 SU MI HU ER ON Biomass (g/m2) 5 10 15 Spring Summer Sprinig biomass low in Superior compared to other lakes. Note that in spring, Huron has highest areal biomass. Erie has next to nothing, but 1) we were out REALLY early in spring 99 [remember picture of boat on ice], and 2) areal biomass, and Erie very shallow Summer biomass a bit higher, but still very low. Comparable to Lake Erie! Other upper lakes substantially higher; Ontario highest.

Size Frequency Distribution and Cumulative Biomass of Summer Crustaceans 1999 1 2 3 10 20 30 25 50 75 100 Relative Frequency Cumulative Biomass Size (mm) < 1 mm > 1 mm Bythotrephes 1 2 3 10 20 30 25 50 75 100 30 100 Frequency distribution bimodal: lots of individuals around 0.5 – 1.5 mm and 2.5 mm; very little between about 1.5 and 2.25 or so. Larger individuals deep living Diaptomids (Leptodiaptomus sicilis, Limnocalanus macrurus) so possible that predation pressure eliminating medium sized individuals. Because large individuals so big, substantial portion of biomass > 1 mm (light blue in pie charts), but unclear what fish it’s accessible to (larger zooplankton live around 80 m; don’t get up much). Interesting note: not much evidence of diurnal migration in Superior, suggesting low predation pressure. Also note: Bc pretty irrelevant in terms of biomass (1999 samples should be good estimate of Bc, since we counted whole samples for them) In graph: green line is cumulative biomass, corresponding to length categories; histograms are size frequencies. Pies percent of biomass contributed by critters < and > 1 mm. 75 20 50 1 2 3 10 20 30 25 50 75 100 10 25 1 2 3

Size Frequency Distribution and Cumulative Biomass of Summer Crustaceans 1998, 1999 1 2 3 10 20 25 50 75 100 1998 1999 1 2 3 10 20 25 50 75 100 Not much change between 1998 and 1999. Still see bimodal distribution of sizes and majority of biomass in individuals > 1 mm. 1 2 3 10 20 25 50 75 100

Amount of Biomass Contributed by Individuals < 1 mm and > 1 mm, Summer, 1998 % Biomass SU MI HU ER ON < 1 mm > 1 mm Bythotrephes Looking at all lakes, note: Biomass low in Superior; amount of biomass in individuals > 1mm high in upper lakes and central Erie; Bythotrephes only prominent in central Erie (this has always been the case) 10 g/m2 <1 g/m2 5 g/m2

Amount of Biomass Contributed by Individuals < 1 mm and > 1 mm, Summer, 1999 % Biomass SU MI HU ER ON < 1 mm > 1 mm Bythotrephes 1999 very different for other upper lakes: many more smaller individuals (and species shifts to Bosmina and cyclopoid copepods, makes lake look more like Ontario) Also N-S differentiation in Michigan. Superior still has most biomass in large (> 1mm) individuals. Impossible to tell with only two years of data whether Superior is inherently more stable in terms of zoop community size structure. SO: not much there, but what’s there is good eatin’! 10 g/m2 <1 g/m2 5 g/m2

Bythotrephes Areal Abundances 1999 1,000/m2 500/m2 100/m2 + absent Abundances of Bythotrephes across all lakes. Feels most at home in central and eastern basin of Lake Erie. [note: looks higher in eastern basin, but in preceding percent graphs seems higher in central basin – that’s because eastern basin deeper, so can fit more in on an areal basis] Shows up at most sites in Superior, but in pretty small numbers. Likely that it is present throughout open lake, but just very rare. Of upper lakes, Huron seems to support biggest populations. BTW, Cercopagis is MUCH more abundant in Lake Ontario than Bythotrephes is in any lake.

Zooplankton - Conclusions Community Makeup: Large, deep-living calanoid copepods dominate Cyclopoid copepods also abundant Percentage of cladocerans lowest of Great Lakes Biomass Low Relative to Other Lakes Most Biomass in Large Individuals ‘Medium’ Sized Individuals Largely Absent Key Points: Very few species Predominance of large, deep-water (glacial relic) calanoids Spp composition seems consistent with historic reports Biomass very low - very different from other upper lakes. Distinguished by paucity of cladocerans in the summer, and predominance of Holopedium (medium sized critter encased in big glob of goo)

Areal Abundances of Benthos in the Great Lakes, Summer 1999 MI HU ER ON Abundance/m2 2000 4000 6000 8000 10000 12000 14000 12,000/m2 8,000/m2 4,000/m2 Benthic abundances very low in Superior, due to great depth.

Throughout Great Lakes, 1999 Abundance of Diporeia Throughout Great Lakes, 1999 6,000 m-2 3,000 m-2 1,000 m-2 0 m-2 + Diporeia most important species, so we’ll focus on that. Abundances low compared to other lakes Let me know if you want a graph showing community composition. I figured you’d be pressed for time by now.

Changes in Diporeia Abundance, 1997-1999 No trends in Diporeia abundances from 97 – 99. Statistically significant declines at two sites (red minuses), increase at one site (green plus), and at fourth site abundances just not same in all three years (plus and minus). Otherwise, no interannual change (statistically significant at least) at other sites. + #/m2 1000 2000 +/-

Diporeia Abundance in Relation to SOLEC Criteria, 1999 Better Than SOLEC Criteria Worse Than SOLEC Criteria Meets SOLEC Criteria SOLEC Criteria: Depth < 100m: 220-320/m2 Depth > 100m: 30-160/m2 Meets or exceeds SOLEC criteria at all sites but one in Superior.

SHEMO IS HAPPY!!!! Meets Diporeia criterion, so SHEMO is Happy!!!