Cyanobacteria · Chapter 6
Cyanobacteria and Aquatic Food Webs
Learning objectives
After studying this chapter, you should be able to:
- Place cyanobacteria in a freshwater food web alongside green algae and diatoms.
- Explain why cyanobacteria are often poor food: nutrition, shape, toxins and digestive inhibitors.
- Describe evidence for naturally tolerant Daphnia populations and the role of gut microbiota.
In a healthy pond, green algae and diatoms are eaten by zooplankton such as rotifers, copepods and the water flea Daphnia, which are in turn eaten by fish; on stream rocks, snails and insect larvae graze the biofilm; and bacteria and fungi decompose what is not eaten. Cyanobacteria fit awkwardly into this web. Laboratory studies show that, as food, they generally support poorer zooplankton growth than small green algae and flagellates [1]. The reasons include a lack of key fatty acids and sterols, colonies and filaments too large or awkward to handle, toxins, and compounds that inhibit digestive enzymes [2, 3].
Yet blooms often coexist with abundant zooplankton in nature, and grazer responses are diverse and flexible [4]. Grazers adapt: Daphnia hatched from dated dormant eggs in Lake Constance showed that resistance to dietary cyanobacteria increased as the lake became eutrophic [5]; populations from lakes with toxic Microcystis tolerated it better than populations from lakes without [6]; and gut microbiota transplants showed that the microbiome can mediate tolerance [7].
Planned sections
6.1 Cyanobacteria, green algae and diatoms as food
Food quality differences among producers; edibility and size.
6.2 Rotifers, copepods and Daphnia
Different feeding modes and sensitivities; small-bodied grazers in bloom conditions [4, 8].
6.3 Aquatic snails and filter-feeding fish
Benthic grazers in streams; fish that filter plankton; effects on bloom dynamics.
6.4 Microbial decomposers
Bacterial breakdown of bloom biomass and the oxygen consequences (Chapter 5).
6.5 Why cyanobacteria are hard to eat
Nutritional quality, filaments and colonies, toxins, and digestive protease inhibitors that target trypsin and chymotrypsin in the Daphnia gut [9, 3, 1].
6.6 Naturally tolerant Daphnia
Rapid evolution, local adaptation and microbiome-associated tolerance [5, 6, 7].
6.7 Food webs on stream rocks
Grazing on biofilms and mats, and what is known about benthic cyanobacteria in stream food webs [10].
Connection to local research
Allen Branch is a stream, so its grazers are mostly benthic invertebrates rather than Daphnia; Daphnia work fits farm ponds and reservoir embayments better. Hypothesis Daphnia from ponds with frequent cyanobacteria will tolerate cyanobacterial food better than Daphnia from ponds without them — a contained laboratory comparison suited to undergraduates.
Related: native zooplankton, grazer interactions, Daphnia in the Atlas.
Key terms
- Zooplankton
- Small animals drifting in the water column.
- Grazer
- An animal that feeds on algae, cyanobacteria or biofilm.
- Food quality
- How well a food supports growth and reproduction.
- Protease inhibitor
- Compound that blocks digestive enzymes.
- Local adaptation
- Higher fitness of a population in its home environment.
References
- Wilson, A. E., Sarnelle, O., & Tillmanns, A. R. (2006). Effects of cyanobacterial toxicity and morphology on the population growth of freshwater zooplankton: Meta‐analyses of laboratory experiments. Limnology and Oceanography, 51(4), 1915-1924. https://doi.org/10.4319/lo.2006.51.4.1915 (external site, opens in a new tab)
- Ger, K. A., Hansson, L., & Lürling, M. (2014). Understanding cyanobacteria‐zooplankton interactions in a more eutrophic world. Freshwater Biology, 59(9), 1783-1798. https://doi.org/10.1111/fwb.12393 (external site, opens in a new tab)
- Schwarzenberger, A., Zitt, A., Kroth, P., Mueller, S., & Von Elert, E. (2010). Gene expression and activity of digestive proteases in Daphnia: effects of cyanobacterial protease inhibitors. BMC Physiology, 10(1), 6. https://doi.org/10.1186/1472-6793-10-6 (external site, opens in a new tab)
- Ger, K. A., Urrutia-Cordero, P., Frost, P. C., Hansson, L.-A., Sarnelle, O., Wilson, A. E., & Lürling, M. (2016). The interaction between cyanobacteria and zooplankton in a more eutrophic world. Harmful Algae, 54, 128-144. https://doi.org/10.1016/j.hal.2015.12.005 (external site, opens in a new tab)
- Hairston, N. G., Lampert, W., Cáceres, C. E., Holtmeier, C. L., Weider, L. J., Gaedke, U., Fischer, J. M., et al. (1999). Rapid evolution revealed by dormant eggs. Nature, 401(6752), 446-446. https://doi.org/10.1038/46731 (external site, opens in a new tab)
- Sarnelle, O., & Wilson, A. E. (2005). Local adaptation of Daphnia pulicaria to toxic cyanobacteria. Limnology and Oceanography, 50(5), 1565-1570. https://doi.org/10.4319/lo.2005.50.5.1565 (external site, opens in a new tab)
- Macke, E., Callens, M., De Meester, L., & Decaestecker, E. (2017). Host-genotype dependent gut microbiota drives zooplankton tolerance to toxic cyanobacteria. Nature Communications, 8(1), 1608. https://doi.org/10.1038/s41467-017-01714-x (external site, opens in a new tab)
- Tillmanns, A. R., Wilson, A. E., Pick, F. R., & Sarnelle, O. (2008). Meta-analysis of cyanobacterial effects on zooplankton population growth rate: species-specific responses. Fundamental and Applied Limnology, 171(4), 285-295. https://doi.org/10.1127/1863-9135/2008/0171-0285 (external site, opens in a new tab)
- von Elert, E., Agrawal, M. K., Gebauer, C., Jaensch, H., Bauer, U., & Zitt, A. (2004). Protease activity in gut of Daphnia magna: evidence for trypsin and chymotrypsin enzymes. Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology, 137(3), 287-296. https://doi.org/10.1016/j.cbpc.2003.11.008 (external site, opens in a new tab)
- Wood, S. A., Kelly, L. T., Bouma‐Gregson, K., Humbert, J., Laughinghouse, H. D., Lazorchak, J., McAllister, T. G., et al. (2020). Toxic benthic freshwater cyanobacterial proliferations: Challenges and solutions for enhancing knowledge and improving monitoring and mitigation. Freshwater Biology, 65(10), 1824-1842. https://doi.org/10.1111/fwb.13532 (external site, opens in a new tab)