ALGAL COMMUNITY COMPOSITION AND SUCCESSIONAL TRENDS

LONG LAKE, SHAWANO COUNTY, WISCONSINMAY-SEPTEMBER, 2006

All work and report by Robert Bell, Ph.D.Professor of Biology

University of Wisconsin-Stevens PointStevens Point, WI 54481

INTRODUCTIONAlgae need carbon dioxide, water, sunlight, and a variety of inorganic nutrients, all

in adequate amounts. The term algae is very general, this group of organisms encompasses both prokaryotic (like bacteria) and eukaryotic (like us) cell types. The algae range from single-celled to many meters long, some swim with flagella while others float or alter their buoyancy via physiological alterations. These organisms can be filamentous, colonial, tubular, sheet-like, and about every shape in between. They can be blue-green, green, yellow, black, brown, gold, pink, red, or orange.

There are 9 or more major groups or phyla of algae. Each group has a unique set of photosynthetic pigments and each group responds differently to changing environmental conditions. Individual taxa (like a genus) are grouped in a phylum based on shared characteristics such as pigments, cell type, and reproduction. Within that phylum groups are further subdivided based on more specialized shared and distinct characteristics relative to the other members of that division. These subgroups are called classes, orders, families, and genera. In this study I identified algae to genus and phylum. Algae within the same phylum (since they’re related to each other) typically respond in a similar manner to seasonal and nutrient changes. Seasonal changes in the composition of the algal communities in Long Lake were traced via changes in the relative abundance of algae at the genus and phylum level.

Algae are considered primary producers (see diagram on title page) in most aquatic food webs (along with macrophyte vegetation). They are responsible for capturing solar energy via their photosynthetic pigments and using that trapped energy to convert inorganic carbon dioxide into organic sugars. These sugars store some of the captured solar energy in their chemical bonds. The algae use the sugars to make other new organic matter (proteins, carbohydrates, nucleic acids, lipids) as they grow and divide. Consumers and decomposers also use these sugars for energy and recycle much of the other organic matter as well. Algae are critically important components of the aquatic food web as many zooplankters (microscopic animals) as well as many larger consumers (snails, planktivorous fishes) have a diet based largely on algae.

Net growth rates of algae are determined by the difference between growth (production of new algae via asexual and sexual reproduction) and death (consumption, parasitism, natural death). Algae differ in their digestibility (shape, size, production of sticky mucilage) and nutrient value (proteins, lipids, carbohydrates) to consumers and consequently some taxa are preferentially removed from the community by predation while others are largely ignored by consumers and continue to expand their biomass during the growing season. The algae present at any point in time are frequently based more on what hasn’t been eaten than what is growing the fastest. It’s often these “not eaten” algal taxa, especially the Cyanobacteria (or blue-green algae) that become persistence bloom formers in ever earlier and longer cycles.

The microbial decomposition loop (detritivorous) is fed largely by the algae. It is in the sediments that bacterial consumption of the dead algae can reduce oxygen content to anoxic levels setting the stage for fish kills. The seasonal pattern typical of lakes like Long Lake is one of spring and summer algal growth (fed by nutrients either input or resuspended from the sediments); summer and fall decomposition in the sediments

(converting organic matter to inorganic nutrients again); and resuspension of nutrients into the water column during spring and fall overturn. If there is a flux of nutrients in the fall it’s possible that more algae will overwinter beneath the ice. This can lead to increasing larger standing crops of undesirable algal taxa (see section above).

Different groups and taxa also respond differentially to seasonal fluxes in temperature, oxygen, and nutrients. The types of algae present, their relative abundance, and the dynamics of the algal community over time can provide insights into trophic status and might suggest possible remediation strategies or might provide evidence that watershed-level controls of nutrient inputs is having some effect. Most aquatic algal communities are limited by phosphorus and the timing and point of origin around phosphorus availability usually determines when and what algae will bloom.

MATERIALS AND METHODSLong Lake algae samples were collected five times during the 2006 growing season

(05/24, 06/20, 07/19, 08/14, 09/13). Collections were made with Mr. Bob Holzbach. Surface water samples were collected at the western end of the lake (Figure 1, site 1), off the small point on the southeastern-edge weed bed (site 2), and at eastern end near the inlet/outlet (site 3). Bottom (benthic) and attached (periphyton) samples were collected along the shore, dock, and shallows in front of W7917 Shady Lane (site 4 - Holzbach residence). Collections were made with a plankton net, dip bottles, and hand-grabs. The samples were transferred to 250-mL high-density polypropylene white bottles and transported to UWSP on ice. All samples were collected, processed, and analyzed by Dr. Robert Bell.

Algal samples were fractionated into fresh and iodine-preserved aliquots. Initial evaluations revealed general homogeneity between samples and consequently all samples were pooled for analysis. Fresh samples were surveyed immediately to provide the most accurate genus list. Preserved samples were stored, cold, until counting.

For analysis, 1ml aliquots of preserved material were placed into a Sedgewick-Rafter counting cell and allowed to settle for 1hr. Random fields were counted at 400X under an Olympus ZH20 Inverted Microscope with long working distance lenses. Colonial and filamentous organisms were counted as a single unit if intact. Counts were conducted until the sample total reached 300 per date. Generic identification was from standard freshwater reference texts including (but not limited to) “Freshwater Algae of the United States (G.M. Smith), Freshwater Algae of the Western Great Lakes Area (G. Prescott) and “Freshwater Algae of North America (R. Sheath, et al.).

RESULTSThe algal community in Long Lake was fairly typical of similar regional lakes and

largely unremarkable. There were 40 algal genera from six algal phyla identified during the counting process in Long Lake (Table 1). Thirty-four of the 40 taxa from Long Lake were from three phyla (10-Cyanobacteria, 13-Chlorophyta, and 11-Ochrophyta). These

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are the dominant groups in most temperate zone lakes, especially those with moderate eutrophication.

The Cyanobacteria (or Blue-Green Algae) are prokaryotic (bacteria-like) organisms with very wide metabolic and ecological tolerance. They are also largely unpalatable (the lipopolysaccharide cell walls and polysaccharide sheaths make them hard to digest) and generally avoided by consumers like zooplankton and planktivorous fishes. There were 10 cyanobacterial taxa (Table 1) but only a few were common or dominant. In past years there were more taxa (13 in 2004, 12 in 2005) but most taxa were rarely seen and infrequently occurring taxa could be missed by the enumeration procedure. Cyanobacterial taxa were in the top five taxa (according to cells counted) seven out of 25 possible times compared to nine times in the top five during the 2004 season and eight times in the top five during the 2005 season (Table 2). Spirulina and Microcystis were present in every sample, these taxa are cosmopolitan and their abundance is generally associated with inorganically-enriched (especially phosphorus) waters. In previous years Coelosphaerium (a spherical colony) was a dominant in four of five sample periods (2004) and five of five sample periods (2005) and was by far the most common taxon at the end of the season (29% of cells counted in 2004, 27% of cells counted in 2005). In 2006 this genus was present in four of five samples but did not rise to dominance until late in the season and to a lesser extent (12% of cells counted) than in past years. In the last sample of 2006 (09/13) Coelosphaerium was the second most abundant taxon. The dominance of this organism at the end of three consecutive seasons indicates that it is likely to be a persistent and increasingly dominant taxon in the future.

Microcystis, a colonial organism, was a dominant taxon in one of the 2004 samples, two of the 2005 samples, and one of the 2006 samples. The other common cyanobacterial taxa from 2004-2006 were filamentous genera (Lyngbya, Gloeotrichia, Anabaena, Spirulina) but none other than Anabaena and Spirulina ever rose to dominant positions. These variations of subdominant taxa are not uncommon and are indicative of the dynamic and variable conditions that exist in a lake from one year to the next. In 2006 the helical filaments of Spirulina were in the top five taxa (based on cells counted) in three of the five sampling periods but never higher than third on the list. The larger filaments of Anabaena were present in only three of five samples but in two of those three periods (08/14 and 09/13) it was one of the five dominant taxa although never higher than third. As in past years, the Cyanobacteria generally increased in abundance across the sampling season rising from 13% to 39% over the five months of collecting (Figure 2 and 3). This trend is typically caused by the combination of not being eaten, a fall surge in nutrients, and an extended temperature tolerance that allows them to survive deeper into the fall/winter than most of the eukaryotic algae. Microcystis is capable of “blooming” and in the bloom state it may produce toxins that can harm aquatic life, pets, and potentially humans. At this time in Long Lake it is not near bloom proportions and does not appear to be a toxin-producing threat but should be monitored in the future. Overall, the relative abundance of the cyanobacteria in the algal community at season’s end has declined over the three years of this study (55% in 2004, 49% in 2005, 39% in 2006). In the long-term this might be a statistical blip but it could also be interpreted as a sign that the water quality of Long Lake is improving.

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Green algae (Chlorophyta) were represented by 13 genera in 2006 cell counts (Table 1); previous years saw similar numbers of taxa (15 in 2004, 16 in 2005). Closterium, Oocystis, Staurastrum, Ankistrodesmus, and Scenedesmus were the most common and abundant genera. Staurastrum, Ankistrodesmus, and Scenedesmus were in the top five dominant taxa (Table 2) a total of five times (of a possible 25). In 2004 green algae taxa were in the top five taxa five times while they were in the top taxa eight times in 2005. Of these genera only Scenedesmus was dominant in more than one sample (most common taxon in May and July, fifth in August). The chlorophytes are quite variable in size (unicellular, filamentous, colonial) and habit (motile, floating, attached) but all are fairly digestible and are often eaten. The green algae were 27% of the season-opening cell count (05/24), dropped significantly in June (as in both previous years of the study as well) before rising to the dominant phylum in July (58%). In July three of the top five algal taxa were green algae (Scenedesmus, Staurastrum, and Ankistrodesmus). Green algal abundance dropped for the rest of the collecting season, represented only 15% of the final sample period of September (Figure 2 and 3). This pattern (strong early, peaking in middle, declining late) is very commonly encountered with the green algae. As with the Cyanobacteria, there were many green algal taxa that were of only minor importance or abundance and many were only seen in one or two of the five sampling periods. These organisms may have simply not been abundant or they may have been preferentially-selected food items for the zooplankton and planktivorous fishes. This level of analysis cannot distinguish between these two possibilities.

Diatoms are the most common and successful group of organisms within the phylum Ochrophyta. These unique organisms collect silica from the water and polymerize it into intricate glass cases called frustules that they use in place of a more traditional, organically-derived cell covering. These organisms are common food items and are easily ingested and digested. There were 11 genera of diatoms identified in the 2006 Long Lake samples compared to 13 genera counted in 2005 and 15 genera identified in 2004. The most common taxa were Asterionella, Fragilaria, and Melosira (= Aulacoseira) – together they were in the top five most abundant taxa ten times. Asterionella was in the top five taxa in every sample period, twice it was the most abundant taxon (06/20, 08/14), second, third, and fourth most common in the other sample periods (Table 2). Diatoms dominated the algal community early and late in the season. In the May samples, the three diatoms listed above were all in the top five taxa counted (39% of all cells counted). In June, Asterionella and Fragilaria were again in the top five taxa. Asterionella continued to be a dominant organism in all samples while Melosira reappeared in large numbers late in the season and ended the sampling period as the dominant genus (20% of all cells counted in September). A typical pattern for diatoms in temperate lakes is to start with low abundance in the early season before rising in abundance into the summer. Often there is a marked reduction in abundance in late summer due to silica depletion (required for cell walls). Fall turnover (resuspending silica) often leads to a late season diatom spike. This was not the case in Long Lake in 2004 or 2005. In both years diatoms started at around 20% of the community and held steady with small declines heading into the September or October samples. Diatoms represented 21-31% of the final sample in both years. In 2006 the diatoms started strong and ended strong with only a small decline in July. The diatom

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community, dominated by three taxa, was very steady across the entire sampling season of 2006. Percent algal community composition by diatoms dipped below 35% only once (July) and ended the season at 35%, the highest of the three study years with diatom abundance increasing at season-end each year. There is no immediate or obvious explanation for these patterns but given the typically beneficial aspects of diatoms in ecosystem function it is nothing to be concerned about. Generally the more diatoms the better.

As in the previous two years, the other three phyla (Dinophyta-dinoflagellates, Euglenophyta-euglenoids, and Cryptophyta-cryptophytes) were of varying but mostly minor significance across the 2006 sampling period (Table 1, Figure 2 and 3). The dinoflagellates never represented more than 4% of the community (September), and the cryptophytes appeared once in the top five taxa (5th, May). The euglenophyte genus Trachelomonas was abundant in June and July (2nd and 4th, respectively); comprising 10% of cells counted in those periods. By comparison, the dinoflagellate Peridinium and the euglenophyte Euglena were in the top five taxa once in 2004, both in the first sample period, no other taxa from these three phyla was common in any other sample. In 2005, taxa from these three phyla were in the top five taxa six times (2 from each phylum). Peridinium was common in May and September. A different euglenophyte genus, Phacus, and the cryptophyte Cryptomonas were both common in June and September with Cryptomonas being the most common taxa counted in September. Diversity is generally considered a good thing and the presence of these groups, especially the cryptophytes is a positive indication of a fairly healthy and balanced aquatic system.

The relative abundance of all algal phyla over the sampling period is shown in Figure 2 and the dynamics of the three dominant phyla is shown in Figure 3. A selection of some of the commonly encountered algal taxa is shown in Figures 4 and 5. These data show a fairly typical season succession pattern and give no indication of any major problems with the lake. The data indicate a moderately enriched (eutrophic) lake. Over the three years of study the basic community structure has not changed significantly at either the phylum or genus levels but some positive trends can be drawn. A review of the season-ending algal community compositions shows a reduction in the numbers of cyanobacteria and an increase in the numbers of diatoms. These in turn may influence the following spring community compositions where there have been fewer cyanobacteria and more diatoms counted each year. These are good things but given the complex set of variables that influence lake chemistry and its biotic community they could change or they may be natural variation. Three years is a very brief snapshot of the life of a lake.

I suspect the inorganic enrichment that has pushed the algal community in Long Lake towards cyanobacteria is a combination of several sources –upstream agricultural inputs, local geological conditions (leaching of naturally occurring nutrients from the basal material), and local anthropomorphic inputs (fertilizing of lawns, septic systems, surface runoff). Once a body of nutrients is introduced to a lake system it is very difficult to manage or eliminate. These nutrients undergo a season change in location and form. The spring overturn of the lake resuspends available inorganic nutrients from the sediments. The algae assimilate these nutrients and consequently they are

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incorporated into organic molecules (DNA, protein) or are stored (“luxury storage”) in excess of their current need. As algae are eaten their organic and inorganic matter is echoed through the food web and becomes organic material within the various levels of consumers. Consumer waste, consumer death, and algal death all contribute abundant inorganic and organic matter to the sediments throughout the year but particularly in the fall/winter when most algae and aquatic plants die back. In the fall and winter the decomposing bacteria in the sediments metabolize these mostly organic forms of nitrogen and phosphorus back to inorganic forms that are once again available in the following spring during lake overturn.

In closing, Long Lake is a typical temperate zone lake with significant shoreline residential development and an agricultural watershed. The lake shows signs of moderate nutrient enrichment. If no actions are taken the problem of algal blooms and the potential of fish-killing oxygen depletion will continue to increase. The problems took a long time to develop and the solutions will be equally slow to take effect. Various nutrient abatement strategies are possible. They vary widely in effectiveness and cost. They include, in no particular order, but are not limited to:

Upstream diversion of water into the marshes to reduce sediment and nutrient load prior to water entering Long Lake.

Planting of vegetation buffer strips along the shoreline and the reduction/elimination of excessive fertilizer use in the residential landscapes around Long Lake.

Alum treatment of the sediments to seal off the resuspension of nutrients for several years.

Removal of sediments.

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Figure 1.

Figure 2: LONG LAKE ALGAE 2006

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Figure 3: LONG LAKE ALGAE 2006THREE DOMINANT PHYLA

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Microcystis Coelosphaerium

Figure 4. Selected algae of Long Lake – 2006 (part 1)Cyanobacteria: Microcystis, Coelosphaerium, Anabaena, and SpirulinaChlorophyta: Scenedesmus, Ankistrodesmus, and Staurastrum

Spirulina Anabaena

Scenedesmus Staurastrum Ankistrodesmus

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Figure 5.Selected algae of Long Lake – 2006 (part 2)Ochrophyta: Asterionella, Fragilaria, Melosira

Asterionella Fragilaria

Melosira

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TABLE 1.

PHYLUM GENUS 2006: TOTAL CELLS COUNTED & PERCENTAGE OF TOTAL, COUNTS UNTIL N=300

05/24   06/20   07/19   08/14   09/13  Cyanobacteria Anabaena 0.0 2 0.7 0.0 19 6.3 27 9.0

Aphanizomenon 0.0 0.0 0.0 1 0.3 0.0Coelosphaerium 8 2.7 21 7.0 0.0 17 5.7 35 11.7Gloeotrichia 0.0 0.0 0.0 0.0 7 2.3Merismopedia 6 2.0 13 4.3 3 1.0 0.0 0.0Microcystis 3 1.0 11 3.7 21 7.0 14 4.7 15 5.0Oscillatoria 0.0 0.0 0.0 0.0 15 5.0Phormidium 0.0 5 1.7 0.0 8 2.7 0.0Snowella 0.0 0.0 4 1.3 9 3.0 3 1.0Spirulina 21 7.0 19 6.3 5 1.7 27 9.0 16 5.3

10 TOTAL 4 13 6 24 4 11 7 32 7 39         

Dinophyta Peridinium 10 3.3 8 2.7 3 1.0 2 0.7 13 4.31 TOTAL 1 3 1 3 1 1 1 1 1 4

         Chlorophyta Ankistrodesmus 0.0 0.0 27 9.0 3 1.0 6 2.0

Botryococcus 3 1.0 9 3.0 0.0 1 0.3 0.0Chlamydomonas 8 2.7 3 1.0 0.0 0.0 0.0Closterium 0.0 3 1.0 11 3.7 7 2.3 15 5.0Coelastrum 0.0 0.0 25 8.3 10 3.3 3 1.0Cosmarium 3 1.0 6 2.0 0.0 9 3.0 0.0Hydrodictyon 0.0 0.0 0.0 2 0.7 3 1.0Oedogonium 0.0 0.0 3 1.0 0.0 5 1.7Oocystis 18 6.0 12 4.0 24 8.0 13 4.3 0.0Pediastrum 0.0 1 0.3 0.0 5 1.7 0.0Scenedesmus 42 14.0 13 4.3 52 17.3 18 6.0 3 1.0Selenastrum 0.0 0.0 0.0 0.0 4 1.3Staurastrum 6 2.0 11 3.7 31 10.3 7 2.3 7 2.3

13 TOTAL 6 27 8 19 7 58 10 25 8 15         

Ochrophyta Asterionella 41 13.7 62 20.7 30 10.0 52 17.3 27 9.0Cocconeis 0.0 2 0.7 3 1.0 0.0 2 0.7Cymbella 0.0 0.0 0.0 9 3.0 0.0Diatoma 0.0 4 1.3 0.0 0.0 0.0Fragilaria 36 12.0 21 7.0 13 4.3 11 3.7 12 4.0Gomphonema 0.0 3 1.0 0.0 0.0 0.0Gyrosigma 2 0.7 2 0.7 0.0 0.0 0.0

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Melosira 41 13.7 10 3.3 5 1.7 37 12.3 61 20.3Navicula 1 0.3 0.0 0.0 0.0 2 0.7Pinnularia 0.0 0.0 0.0 5 1.7 0.0Synedra 3 1.0 13 4.3 0.0 0.0 0.0

11 TOTAL 6 41 8 39 4 17 5 38 5 35         

Euglenophyta Euglena 4 1.3 9 3.0 3 1.0 0.0 2 0.7Phacus 3 1.0 0.0 0.0 6 2.0 9 3.0Trachelomonas 14 4.7 30 10.0 30 10.0 4 1.3 0.0

3 TOTAL 3 7 2 13 2 11 2 3 2 4         

Cryptophyta Chroomonas 24 8.0 7 2.3 2 0.7 0.0 0.02 Cryptomonas 3 1.0 0.0 5 1.7 4 1.3 8 2.7

TOTAL 2 9 1 2 2 2 1 1 1 3         

300   300   300   300   300  300 100.0 300 100.0 300 100.0 300 100.0 300 100.0

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TABLE 2. Most Common Genera from Long Lake, Shawano County, WI, 2006

GENUS PHYLUM05/24

Scenedesmus ChlorophytaAsterionella OchrophytaMelosira OchrophytaFragilaria OchrophytaChroomonas Cryptophyta

06/20Asterionella OchrophytaTrachelomonas EuglenophytaFragilaria OchrophytaSpirulina CyanobacteriaMicrocystis Cyanobacteria

07/19Scendedesmus ChlorophytaStaurastrum ChlorophytaAsterionella OchrophytaTrachelomonas EuglenophytaAnkistrodesmus Chlorophyta

08/14Asterionella OchrophytaMelosira OchrophytaSpirulina CyanobacteriaAnabaena CyanobacteriaScenedesmus Chlorophyta

09/13Melosira OchrophytaCoelosphaerium CyanobacteriaAnabaena CyanobacteriaAsterionella OchrophytaSpirulina Cyanobacteria

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