Lake

How Fit into Lake Webs

Ann St. Amand

WYSIWYG (What you see is the result of a whole bunch of algal ecology available and just a few of different processes going on at the same time!) my favorites are listed at the end of this article. elcome to the wild and wacky understand the system functionally, you world of algal population can’t effectively manage it. Growth Processes . . . dynamics! Many of you may Not only is the entire aquatic food Or What Grows Up . . . rememberW the term, WYSIWYG, coined web based on the algal composition at any So let’s start with the growth part in the ’80s as word processors became given time (okay, and maybe the bacteria, of the equation. It all initiates with more sophisticated and companies started too), but the ultimate community affects primary productivity, the process of advertising that what you actually saw how much carbon enters the lake system, adding carbon via photosynthesis. In on the computer screen was what you the trophic status, how much stress the order to photosynthesize, you have to were going to get when you printed. system is under from too much or too have pigment. The pigment common Programming that series of commands little algal biomass, the perceived water to all of the different algal groups is to make the text print in bold, indented, quality (which in turn affects property chlorophyll-a (as a reminder, algae are and capitalized is somewhat like the values), and ultimately how safe the an evolutionary trash can, so the only many processes that determine what algal water is for human and animal contact. thing they have in common is that they species or communities will dominate The question becomes: What population photosynthesize). Chlorophyll-a does under different environmental scenarios. dynamics are responsible for the taxa that not absorb green, instead it reflects We often observe what would appear are present? Amazingly, it’s all about the green, so that’s exactly what the most to be similar lakes with totally different relatively simple proportions of growing common algal color is, just like land dominant communities and our inclination versus dying. Many algal taxa have plants (Figure 2). Epi-fluorescence is a is to figure out why, so we can predict evolved very ingenious survival strategies special enhancement on a microscope that what might bloom in the next few to tip the scales toward growing. There allows us to shine a specific wavelength weeks or months (Figure 1). Unless you are some great references on general of light on the algae (excitation), and

Figure 1. (Left): Green algae dominated bloom (Cladophora); (right): Blue-green algae dominated bloom (Microcystis).

14 Summer 2011 / LAKELINE Figure 2. Examples of green algae. (Left): Ulothrix; (right): Pediastrum. it shines back a different wavelength heterocysts to fix nitrogen when it’s in have spines or extensions that increase of light (emission). A taxon like Chara short supply in the water column such their surface area and slow their sinking or stonewort has a lot of pigment, as Cylindrospermopsis (Figure 5). But (Stephanodiscus and Micratinium, Figure which is really obvious when you put beating the nutrient and temperature 9). it under blue light epi-fluorescence game is only part of the equation. Algae Staying near the light for (Figure 3). No matter what the pigment must maintain their position in the water photosynthesis may be a problem (there are also accessory pigments column so that they can be at optimum in winter, at depth or under intense called carotinoids, and phycobilins in light, be near the nutrients they need, and competition, so many algae have addition to other chlorophylls), primary hopefully avoid grazers (more about that evolved additional routes for nutrition. productivity potential will be modified below). On the spectrum of nutrition, there are by light and nutrient availability, There are some amazing adaptations pure where algae can only temperature (sometimes many weeks for staying where they need to be. photosynthesize, and then the facultative prior to a bloom), algal physiology, and Some algae have solved the problem , which can augment with or competition. with motility, like Pyramichlamys and completely switch to heterotrophy (clever Some algae do well under low Cryptomonas (Figure 6). Others have little cells!). Heterotrophy can take the light, low temperature conditions such developed buoyancy mechanisms by form of osmotrophy (uptake of organic as Plantothrix (Figure 4), forming pink either adding oils to their colonial compounds in the water) and phagotrophy blooms under the cracked ice or at depth structure (Botryococcocus, Figure 7) or (ingestion of organic material or even during the summer and fall. Others have air vesicles to their cells or filaments bacteria and other algae). Diatoms exhibit developed specialized structures called like Microcystis (Figure 8). Yet others classic osmotrophy (Nitzschia, Figure

Figure 3. Chara (stonewort). Chlorophyll-a Figure 4. Planktothrix from an under ice bloom. Figure 5. Cylindrospermopsi with terminal fluoresces red while the calcium carbonate heterocysts. glows green on the filament surface. Summer 2011 / LAKELINE 15 Figure 6. Examples of motile algae. (Left): Pyramychlamys; (right): Cryptomonas. Figure 7. Botryococcus with oil droplets.

Figure 8. Microcystis with clear air vesicles Figure 9. Examples of extensions. (Left): Stephanodiscus; (right): Micractinium. (arrows).

10). There are also algae, like many euglenoids (, Figure 11), which has members who either uptake compounds or phagasotize. Then there are those that supplement nutrition only through phagotrophy (Cryptomonas and Dinobryon, Figure 12). In fact, Dinobryon cannot be cultured without bacteria present! That brings us to the coolest strategy of all: dinoflagellates. These ingenious algae, like Ceratium (Figure 13), exude something called a “pallium” that engulfs other algal colonies. The algal cell then swims around with the pallium attached, digesting the algae inside, and when they’re done sucking up the nutrients, Figure 10. Nitzschia, capable of absorbing Figure 11. Facultative – Euglena. the pallium is jettisoned and the organic compounds. dinoflagellate goes in search of another algal colony to digest. Continuing on our quest to add cells or biomass to the water column

16 Summer 2011 / LAKELINE Figure 12. Facultative heterotrophs. (Left): Cryptomona; (right): Dinobryon. Figure 13. Ceratium. is recruitment from the sediments. This one is tricky only because it’s both a loss and growth process depending on where you hit the cycle. There are really only two options at the end of the growing season: Either a small inoculum remains up in the water column so that next season the growth cycle can start again, or cysts or resting stages are produced that settle down to the bottom and wait for either the right conditions or turbulence to bring them up again. Many different groups of algae take advantage of cyst or resting cell formation. Chrysophytes, like Dinobryon, and dinoflagellates like Ceratium (Figure 14), produce cysts that float down to the bottom and wait Figure 14. Cyst forming algae. (Left): Dinobryon; (right): Ceratium. for the right environmental conditions (increasing light and nutrients, and increased turbulence at turnover) to bring water column. Many of these blue-greens them back up into the water column to are good at luxury uptake of phosphorus begin the life cycle again. Others, like as well, so that by the time they get to many members of the blue-green algae, the surface, nutrient availability is not produce either condensed filaments of a an issue and they can continue blooming few cells called hormogonia (Plectonema, with relatively low surface nutrient Figure 15) or resting cells called akinetes concentrations. (Aphanizomenon and Anabaena, Figure That brings us to the non-growing 16). Akinetes in particular are extremely part of the conversation, but still a process robust and can sit in the sediments for that adds cells to the water column, and decades (or even centuries!), waiting for a that is colonization. Although many of turnover event to bring them back up into us have to deal with invasive species the light. Additionally, akinetes often sit regularly, let’s ignore the human-induced on the sediment surface, waiting for the sources here like ballast water. That proper increases in light and temperature, leaves the few natural ways that algal Figure 15. Plectonema hormogonia. and then start growing on the bottom cells can be moved from system to without needing turbulence to re-suspend system. Although floods and drift from often under-quantified. We know that them. After a certain amount of growth, upstream are key mechanisms, and algal toxins and cells in lake spray and the colonies start to produce gas vesicles actually well documented, don’t forget updraft from lakes during wind and storm (remember buoyancy described above) the seemingly less obvious sources either. events can be measureable. The other and they rise on their own up through the Aerialization is one mechanism that is often overlooked and under-appreciated

Summer 2011 / LAKELINE 17 source is movement by wildlife, and This is very common in Asterionella and or resting cell formation (see above), or more specifically, waterfowl. We honestly other colonial diatoms (Figure 18). in an added twist, the ability to migrate can’t overlook the ubiquitous “duck feet When naked (cells back to the surface. This includes several and feathers” as a common source of with no particularly hardy outer cell motile genera of diatoms. Remember recruitment to new systems (Figure 17). wall or casing) like Cryptomonas or too, that physiological health greatly Chlamydomonas die, they are very labile affects sinking rates, so the healthier the Loss Processes . . . in the water column and often leave cell or colony is, the less likely it is to Or What Must Eventually Senesce . . . no lasting evidence. Other algae with sink. Hydraulic washout can be a factor, Loss processes are equally important more robust cell walls or tests (cases especially in reservoirs or during a flood and are often operating simultaneously that enclose the cell made of silica or (not much the algae can do about that with the growth processes (kind of like cellulose) often leave empty cells around one!). Desiccation can happen during photosynthesis and metabolism). The as evidence for several days to weeks normal hydrologic cycles or following most obvious is physiological mortality. (Dinobryon and Pediastrum, Figure large geologic events. The blue-green All cells have to die sometime, and 19). As discussed above, many of these algae handle desiccation the best, often whether they are single cells or colonial, algae will produce cysts (Peridinium and growing well after being dried for long often an entire population will senesce Cosmarium, Figure 20) or akinetes before time periods. within a week or two. Although limiting the end of the season as light, nutrients Grazing is perhaps the most resources or the inability to stay up in and temperature become limiting (see complicated loss process because the water column during stratification above). although it often results in death, are often the driving force behind Other loss processes that need to be sometimes it results in growth if you physiological death, infections and considered include sedimentation and/or happen to be one of the lucky ones parasites like chitrids are also important. burial. Strategies to survive include cyst that benefits from grazing, directly or

Figure 16. Examples of blue-green akinetes. (Left): Aphanizomenon; (right): Anabaena. Figure 17. Migratory waterfowl.

Figure 18. Asterionella infected with a Figure 19. Examples of remnants of dead cells. (Left): Dinobryon; (right): Pediastrum. parasite.

18 Summer 2011 / LAKELINE indirectly. Top down control (grazing) is small to be very effective grazers (0.4- in the water column, but they also make it always competing with bottom up control 0.5 mm, Figure 23), so although they hard to eat. It’s unclear whether the algal (resource availability like light and eat their fair share, they can only do so toxins produced by blue-green algae are nutrients). If algae avoid being grazed, it’s much damage to the algal community. a defense mechanism against grazing or very possible that they may benefit when Daphnia (0.5-3.5 mm), however, are secondary metabolites, but when they are competitors are grazed. Grazer size is one considered to be generalist grazers (pretty producing toxins in high concentrations, of the main determinants in how much much anything that can pass through the there tend to be fewer zooplankton in the grazing pressure the algal community feeding apparatus or up to about 30 µm, water column. Food preference goes as experiences. Copepods (Figure 21) can Figure 24). Any Daphnia above 1 mm follows: be predatory (cyclopoids) or herbivorous is considered to be an effective grazer (calanoids), but as a group are selective (kind of like teenage boys). Interestingly, Cryptomonads > Diatoms/Chrysophytes > and not very large (less than 1 mm for although very large colonies such as Greens > Blue-greens the most part, with a small threshold on the Aphanizomenon above and large food items). Rotifers are much smaller Anabaena colonies (Figure 25) are out Indirect effects within the grazer (grazers generally less than 0.3 mm), but of bounds, Daphnia have good success world can be significant as well. they can exert consistent grazing pressure grazing the periphery of Gloeotrichia Sphaerocystis is one of the algae on smaller algae, especially single cells colonies (Figure 26). They actually make (gulp) that can successfully travel the flagellates likePyramichlamys (Figure good use of picoplankton when present zooplankton gut, absorbing nutrients 22). as well (Figure 27). Cryptomonas avoids along the way (Figure 28). Other This brings us to the workhorses grazing by migrating down in the water algae benefit from differential grazing. of the grazer world, cladocerans. The column at night, away from the grazing Microcystis (Figure 29), for example, smaller cladocerans like Bosmina are too Daphnia. Micractinium spines keep it up is not a preferred food of zebra/quagga

Figure 20. Examples of encysting algae. (Left): Peridinium; (right): Cosmarium. Figure 21. Cyclopoid Copepod.

Figure 22. Brachionus (rotifer) grazing on Figure 23. Bosmina (Cladoceran). Figure 24. Daphnia (Cladoceran). Pyramichlamys.

Summer 2011 / LAKELINE 19 Figure 25. Anabaena colony. Figure 26. Gloeotrichia colony that has been Figure 27. Moina with picoplankton (the bright grazed by Daphnia. red rods and spheres are picoplankton in the 1-2 µm range) in the gut.

Figure 28. Moina with Sphaerocystis (green Figure 29. (Left): Dreissena before settling; (right): Microcystis colony. algae) in the gut. mussels, but benefits from the release Reynolds, C.S. 1984. The Ecology of 29,000 algal samples from competition that occurs when these Freshwater Phytoplankton. Cambridge in her career and has mussels filter everything else out of University Press. New York NY. 384 co-chaired a workshop the water column and then excrete in a pp. on Algal Identification nutrient ratio favorable to Microcystis. Sandgren, C.D. 1988. Growth and at the annual NALMS So the next time you are passing Reproductive Strategies of Freshwater symposium since 1991. by an interesting lake, before you Phytoplankton. Cambridge University She also serves on ask yourself how best to manage it, Press. New York, NY. 442 pp. several technical and perhaps you should ask yourself who’s Sommer, U. 1989. Plankton Ecology: educational committees physiologically healthy and who is eating Succession in Plankton Communities. at the local and national level, including the whom? Springer-Verlag. New York, NY. 369 pp. Indiana Blue-Green Algal Task Force and the Wehr, J.D. and Sheath, R.G. 2003. Plankton Sections of Standard Methods for References Freshwater Algae of North America. the Examination of Water and Wastewater. In American Water Works Association Academic Press, Boston. 918 pages. 2003, she became a NALMS Certified Lake (AWWA). 2010. Algae – Source to Professional. St. Amand has been a member Treatment – Manual of Water Supply Ann St. Amand, Ph.D., has been involved of NALMS since 1987 and has served Practices, M57 (1st Edition). Denver, in managing lakes across the United States NALMS in many positions. x CO. 439 pp. since 1990, as President of PhycoTech, Graham, L.E. and Wilcox, L.W. 2000. which specializes in aquatic sample Algae. Prentice-Hall, Englewood Cliffs, analysis, with an emphasis on algae and NJ., USA. 640 pp. zooplankton. St. Amand has processed over

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