Botulism & Warming Waters
Updated: Dec 13, 2020
Climate Change: Impacts Near & Far
Photo by Karen Slote
Our world is interconnected. Everything exists in balance - and the way climate change tends to influence disease highlights this.
We all need water to survive. Some animals, like the Common loon (Gavia immer) spend nearly their entire lives on the water. That’s where they eat, sleep, interact, and raise their young. Aquatic ecosystems are among the most directly vulnerable to climate change impacts, as are the animals that inhabit them.
Loons are migratory birds. The ones we see locally likely spend their winters in either the Gulf or the Southern Atlantic, and pass through Western New York on their way to breeding lakes in Canada. If a loon takes a rest on Lake Erie on its migratory path, it will have to endure the lake’s conditions.
According to recent articles from Audubon and Frontiers in Microbiology, warmer lake temperatures - specifically over 20 degrees Celsius (68 degrees Fahrenheit) - may be associated with greater reporting incidences of Botulism. Essentially, climate change may impact ecosystems in a way that favors the proliferation of Botulism.
More specifically, increased temperatures in the Great Lakes can lead to increased algal growth. Algae flourishes in warm temperatures, and chokes out the lake by preventing light from getting through the water surface. This creates a stressful habitat with limited resources for fish populations, but creates good habitat for invasive species like zebra and quagga mussels that stow away in the ballast and on the surface of boats. A lack of oxygen - anoxia - can lead to a habitat with depleted resources for all of the animals that are supposed to help create balance in the environment.
This is important - zebra and quagga mussels are invasive to Western New York. Their presence in an altered ecosystem assists in creating conditions for Botulism to have the greatest impact on native bird species. Invasive mussels provide a food source for invasive round gobies. If gobies feed on mussels, then they become infected. If a loon then ingests an infected goby, it ingests the toxin - and will likely begin to show symptoms. We transport these invasive species in ships - specifically in ‘ballast water’. This is water that ships take in prior to departure from a port to help them balance on their journeys. It is later released after voyages, creating a clear invasion pathway.
Next, we need to understand Clostridium botulinum, the bacterium that causes Botulism in birds. This bacteria exists within the soil of aquatic environments, but becomes dangerous in high temperatures with anoxic conditions. While researchers are still investigating the exact mechanisms through which the disease works, it is understood that invertebrates and some fish consume the bacteria while feeding on sediment. Zebra mussels in particular may absorb the bacteria while filter feeding. Round gobies, an invasive fish in Lake Erie, feed on Zebra mussels and in turn, take in the toxin. Loons happen to eat these.
Graphic by Espelund & Klaveness, 2014: Botulism outbreaks in natural environments – an update, Frontiers in Microbiology. Read more at: doi: 10.3389/fmicb.2014.00287
In warm, anoxic waters, C. botulinum releases a neurotoxin - or a toxin that affects the Central Nervous System. If a loon eats a goby that has eaten a zebra or quagga mussel that has taken in the Clostridium bacteria, that loon is going to be in a lot of trouble.
If our loon becomes infected with botulism, it will suffer muscle paralysis, progressive weakness, and gradually lose its ability to fly. As it grows weaker over time, it will either lose its ability to hold its head above water and drown, or lose control of its respiratory muscles, and die of an inability to breathe. It will sink, and begin to decay, where the neurotoxin will be once again released into the environment.
If you walk along the beach and do find a live waterbird paralyzed by Botulism, it may appear conscious and alert despite its inability to move. It is important to get these birds help as soon as possible.
As far as we know, no living loon with botulism has been documented in Western New York. So far, they have all washed up on the shore dead.
Unfortunately, that means that many loons with botulism die in the lake. The animals that scavenge the body will likely suffer and die as well, and the problem will continue until the temperature in the lake decreases.
Botulism would be less of a problem for our avian friends in a world with stable temperatures; the most we can do to help is try to treat surviving birds swiftly; and remove not only dead bird carcasses, but dead fish and other carcasses at shorelines and within the water when we can. We can send samples to laboratories to confirm the presence of botulism - and doing this is important - if one animal tests positive in Lake Erie for botulism, we can almost certainly anticipate to see more. Some researchers suggest that raking algae and attempting to control lake temperatures may help - but these feats are difficult to accomplish.
Typically, diseases do not spread as a consequence of one disturbance or factor alone. Usually, there are multiple pathways - a number of things that play into creating the perfect set of circumstances for an epidemic to begin - or in other words, a perfect storm. In the case of Botulism, this involves the presence of invasive species, warm water temperatures, low water levels, pollution which favors the phenomenon of ‘eutrophication’ or excess nutrients in a lake leading to algal blooms and a lack of oxygen.
You can see the interconnections tie together - it’s not just a simple chain. The unknowing transport of invasive species also creates pollution. These emissions help create and enforce climate changes. The invasive species transported into our lakes help create lake conditions that, in conjunction with warmer temperatures, facilitate Botulism outbreaks.
Researchers anticipate that with increasing temperatures, we will continue to see increased Botulism outbreaks - though the exact mechanisms themselves are still being investigated, and researchers are still trying to determine the long-term impacts on population levels.
Some things are clear, however - lower lake temperatures and healthier ecosystems help end outbreaks.
Unless we work to reduce the impact of climate change and mitigate the effects of invasive species, this problem will only continue to grow.