ALGAL COMMUNITY COMPOSITION AND SUCCESSIONAL TRENDS

LONG LAKE, SHAWANO COUNTY, WISCONSINJUNE-NOVEMBER, 2004

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

University of Wisconsin-Stevens PointStevens Point, WI 54481

INTRODUCTIONAlgae are essentially microscopic plants and as such need the same things

as larger plants. All photosynthetic organisms 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 produces its own unique set of photosynthetic pigments and each group responds differently to changing environmental conditions. Individual taxa (like a genus) are then grouped in a phylum based on shared characteristics (pigments, genetics, cell type, 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, being photosynthetic, are considered the 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 like the protozoans) as well as many larger consumers (snails, planktivorous fishes) have a diet based largely on algae.

An often misunderstood aspect of aquatic biology is the concept of net growth rate. 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.

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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 driven 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 (feed by nutrients); 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. Most aquatic algal communities are limited by phosphorus and the timing and point of origin around phosphorus availability determines when and what algae will bloom.

MATERIALS AND METHODSLong Lake algae samples were collected five times during the 2004 growing

season (06/25, 08/06, 09/09, 10/06, and 11/03). 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 brown bottles and transported to UWSP on ice. All samples were collected, processed, and analyzed by Dr. Robert Bell, Department of Biology.

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.

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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).

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

and largely unremarkable. There were 48 algal genera from six algal divisions identified during the counting process in Long Lake (Table 1). Forty-five of the 48 taxa from Long Lake were from three phyla (15-Cyanobacteria, 15-Chlorophyta, and 15-Ochrophyta). These 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 and generally avoided by consumers like zooplankton and planktivorous fishes. There were 15 cyanobacterial taxa (Table 1) but only a few were common or dominant. Anabaena, Coelosphaerium, and Lyngbya were present in every sample and were the dominant organisms throughout the sampling period. These taxa are cosmopolitan and their abundance is generally associated with inorganically-enriched (especially phosphorus) waters. The dominance of Coelosphaerium at the end of the season indicates this organism is likely to be a persistent and increasingly dominant taxon in the future. These three dominant cyanobacteria are large enough (Anabaena and Lyngbya are filamentous, Coelosphaerium is colonial) that they are hard to ingest and their lipopolysaccharide cell walls and polysaccharide sheaths make them even harder to digest. As a group the Cyanobacteria generally increased in abundance across the sampling season rising from 19% to 55% 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. Lastly, there are no obvious toxin-producing organisms, a concern with this group.

Green algae (Chlorophyta) were represented by 15 genera (Table 1). Botryococcus, Cosmarium, and Scenedesmus were the most common and abundant taxa. 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 represented 39% of the initial cell counts and increased into the fall (43% in September) before declining

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significantly in abundance during the remaining sampling periods (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 15 genera of diatoms identified in the 2004 Long Lake samples. The most common taxa were Cocconeis, Melosira, Navicula, and Synedra. Diatoms (and other ochrophytes) generally start a little slow before rising in abundance early in the year and often showing a marked reduction in abundance in late summer and fall. This was not the case in Long Lake in 2004. The show start and summer rise was evident but numbers did not drop off during the late season as is often seen in similar situations. There is no immediate or obvious explanation for this pattern but given the typically beneficial aspects of diatoms in ecosystem function it is nothing to be concerned about. Generally the more diatoms the better.

The other three phyla (Dinophyta-dinoflagellates, Euglenophyta-euglenoids, and Cryptophyta-cryptophytes) were of very minor significance across the sampling period in 2004 (Table 1, Figure 2 and 3) and will not be discussed further.

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. It is likely that the onset, density, and extent of the cyanobacterial blooms of Coelosphaerium will continue to expand.

The causes of this slowly expanding cyanobacterial dominance were not the subject of this study and cannot easily or inexpensively be determined. However, through discussions of the watershed with Bob Holzbach and others; review of historic temperature, nutrient, and water chemistry data; and my personal experiences over 20+ years of algal ecology work I can make a few educated guesses. I suspect the inorganic enrichment in Long Lake is a combination of several sources – the 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).

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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 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 and 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 not nearly as bad as many lakes I’ve seen. This is, however, hollow praise and likely not terribly reassuring to the residents of Long Lake. 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 2004

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Figure 3: LONG LAKE ALGAE 2004THREE DOMINANT PHYLA

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TABLE 1. Algae from Long Lake, Shawano County, WI, 2004

PHYLUM GENUS2004: TOTAL CELLS COUNTED & PERCENTAGE OF TOTAL, COUNTS UNTIL N=30006/25 08/06 09/09 10/06 11/03

Cyanobacteria Anabaena 6 2.0 12 4.0 19 6.3 8 2.7 6 2.0Anacystis 2 0.7 0.0 0.0 0.0 0.0Aphanizomenon 0.0 0.0 0.0 0.0 3 1.0Aphanocapsa 3 1.0 0.0 0.0 0.0 0.0Coelosphaerium 18 6.0 49 16.3 26 8.7 38 12.7 88 29.3Eucapsis 1 0.3 0.0 0.0 0.0 2 0.7Gloeotrichia 0.0 0.0 0.0 0.0 3 1.0Lyngbya 9 3.0 20 6.7 11 3.7 42 14.0 41 13.7Merismopedia 0.0 3 1.0 0.0 0.0 2 0.7Microcystis 1 0.3 0.0 0.0 31 10.3 0.0Oscillatoria 0.0 0.0 2 0.7 6 2.0 0.0Phormidium 2 0.7 2 0.7 0.0 0.0 0.0Plectonema 0.0 0.0 0.0 0.0 21 7.0Snowella 16 5.3 5 1.7 2 0.7 29 9.7 0.0

15 Spirulina 0.0 0.0 5 1.7 0.0 0.0TOTAL 9 19 6 30 6 22 6 51 8 55

Dinophyta Peridinium 32 10.7 10 3.3 3 1.0 0.0 2 0.7TOTAL 1 11 1 3 1 1 0 0 1 1

Chlorophyta Botryococcus 41 13.7 33 11.0 8 2.7 15 5.0 22 7.3Chlamydomonas 0.0 0.0 0.0 1 0.3 3 1.0Chlorococcum 8 2.7 4 1.3 0.0 4 1.3 0.0Cladophora 0.0 0.0 36 12.0 0.0 14 4.7Coelastrum 10 3.3 0.0 8 2.7 0.0 2 0.7Cosmarium 2 0.7 6 2.0 0.0 6 2.0 3 1.0Eudorina 6 2.0 0.0 0.0 2 0.7 0.0Hydrodictyon 7 2.3 2 0.7 0.0 0.0 0.0Oedogonium 0.0 0.0 37 12.3 0.0 4 1.3Oocystis 0.0 0.0 6 2.0 14 4.7 4 1.3Pandorina 2 0.7 0.0 0.0 0.0 0.0Pediastrum 0.0 0.0 5 1.7 3 1.0 1 0.3Scenedesmus 30 10.0 52 17.3 6 2.0 7 2.3 6 2.0Selenastrum 0.0 24 8.0 2 0.7 0.0 0.0

15 Staurastrum 12 4.0 0.0 20 6.7 6 2.0 0.0TOTAL 9 39 6 40 9 43 9 19 9 20

Ochrophyta Asterionella 0.0 13 4.3 22 7.3 0.0 0.0Cocconeis 3 1.0 23 7.7 38 12.7 21 7.0 0.0Cosinodiscus 0.0 0.0 0.0 0.0 2 0.7Cymbella 0.0 0.0 7 2.3 26 8.7 0.0Diatoma 0.0 7 2.3 0.0 3 1.0 0.0Epithemia 0.0 0.0 0.0 1 0.3 0.0Fragilaria 5 1.7 0.0 4 1.3 0.0 0.0Gomphonema 0.0 2 0.7 1 0.3 0.0 0.0Gyrosigma 0.0 3 1.0 0.0 3 1.0 0.0Melosira 0.0 7 2.3 1 0.3 0.0 18 6.0Navicula 32 10.7 0.0 3 1.0 26 8.7 0.0Pinnularia 0.0 0.0 0.0 0.0 3 1.0

Stephanodiscus 0.0 0.0 0.0 0.0 9 3.0Synedra 14 4.7 8 2.7 15 5.0 0.0 17 5.7

15 Tabellaria 0.0 2 0.7 0.0 0.0 14 4.7TOTAL 4 18 8 22 8 30 6 27 6 21

Euglenophyta Euglena 27 9.0 11 3.7 13 4.3 8 2.7 3 1.0TOTAL 1 9 1 4 1 4 1 3 1 1

Cryptophyta Cryptomonas 11 3.7 2 0.7 0.0 0.0 7 2.3TOTAL 1 4 1 1 0 0 0 0 1 2

300 300 300 300 30048 300 100.0 300 100.0 300 100.0 300 100.0 300 100.0

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