Centuries of cyanobacteria

Aquatic blooms of algae or cyanobacteria (sometimes called blue-green algae, though they are a type of photosynthesizing bacteria, not algae) can be a nuisance – and they can also be dangerous.

“[B]looms of cyanobacteria pose a serious threat to drinking water sources worldwide because many taxa contain harmful hepato- and neurotoxins,” write the authors of a paper recently published in the journal Ecology Letters.

Scientists studying blooms of cyanobacteria or algae often narrow their focus to a single location and a short time-frame, sometimes just a single season or a few years. Those studies can be enlightening, and can help managers working to prevent future blooms (and I have written about a couple of them in the past), but large-scale studies emphasizing general trends across multiple centuries can also add to our understanding of algae or cyanobacteria blooms.

A team of researchers compiled data from 108 studies, each of which included a historical record, dating back about 200 years, of “paleolimnological pigment,” the residue that cyanobacteria and other organisms left behind in lake sediments. The researchers limited their study to temperate and sub-Arctic lakes, so most of the lakes they included in their analysis were located in North America and Europe.

The scientists found that cyanobacteria, more than other types of phytoplankton, have become more prevalent over the last 200 years, and especially so since about 1945. By including environmental conditions in their analysis, like lake depth, nutrient levels, and temperature, they were able to determine that, at least on the continent- and century-wide scale they studied, increasing nutrient fertilization was the factor most associated with increases in cyanobacteria.

The researchers also studied serial measurements of nutrients and cyanobacteria taken directly from the water column of 18 lakes over multiple years (rather than historical data from sediment cores). The lakes with decreasing nutrients over time also had fewer cyanobacteria, suggesting that restoring lakes by curtailing nutrient inputs may be an effective way to prevent future cyanobacteria blooms.

Cyanobacteria blooms can be problematic and hazardous – but by managing the human activities that impact lakes, it may be possible to avoid at least some of them.

Some species of anabaena, a type of filamentous cyanobacteria, can be highly toxic. 

(Image by Proyecto Agua via Flickr)

Manatee stressors

Last month, a herd of 19 manatees briefly made a splash on the national news circuit when they got stuck in (and were subsequently rescued from) a storm drain in Florida. The group swam into the drainpipe in an apparent attempt to find warmer water during a cold snap – manatees are sensitive to cold water, and temperatures below 68 degrees Fahrenheit can hurt or even kill them.

Florida manatees – marine mammals that are about 10 feet long and weigh 800 to 1,200 pounds – also face threats from other sources, including boat collisions, habitat loss, and red tides, or harmful algal blooms. Concentrations of the dinoflagellate Karenia brevis are the most common cause of red tides in the Gulf of Mexico; these microorganisms produce a suite of toxins, called brevetoxins, which are harmful to humans and other vertebrates, and can kill hundreds of manatees at a time. (The overall population of Florida manatees is estimated at 5,000 to 6,500 individuals, so hundreds of deaths during a single event is a big deal.).

Although many Florida manatees that encounter red tides succumb to the toxins the algae produce, some manage to survive (sometimes with the help of humans). A team of scientists working in Florida reported the results of a study they conducted on the adverse effects of red tide exposure on surviving manatees in a recent issue of the journal Aquatic Toxicology.

The researchers collected blood samples from 12 manatees that were rescued from a red tide, and from 11 free-ranging manatees from a different, red tide-free location. They measured several parameters that indicate immune response, as well as the concentration of brevetoxin in each manatee’s plasma.

Some immune system indicators were the same regardless of whether or not the manatees had been exposed to the red tide, but others, particularly lymphocyte proliferation (a measurement of the body’s ability to defend itself against pathogens), showed that manatees that endured a red tide displayed reduced immune system functioning. The scientists also found that the manatees with the highest concentrations of brevetoxin in their plasma tended to have the lowest lymphocyte proliferation scores. As the authors point out, the effect of red tides on manatee lymphocyte proliferation “has the potential to result in an immunosuppressed animal that could likely exhibit greater susceptibility to other stressors.”

Florida manatees encounter many hazards in their environment; according to this research, even threats that don’t prove immediately lethal may have lasting negative consequences.

Florida manatees at Crystal River National Wildlife Refuge, located on central Florida's gulf coast. 

(Image by U.S. Fish & Wildlife Service/David Hinkel via Flickr)

Winter fertilizer

By December, most stream ecologists in the northern U.S. have hung up their waders and retreated to their labs and offices, ready to spend the winter analyzing samples and writing reports after the end of another successful field season.

Most, but not all.

“I actually enjoyed going out to the streams in the winter, it was awesome seeing them change as the seasons changed,” Robert Mooney, a graduate student at University of Wisconsin La Crosse and lead author of a paper published this month in Freshwater Science, told me via email.

Mooney doesn’t mind the cold – he grew up in Wisconsin, where his interest in streams began with fishing and tying flies. Some of those flies would have been patterned after the adult forms of the aquatic macroinvertebrates that Mooney would go on to study in graduate school.

He and his co-authors investigated whether or not the excretions of Glossosoma intermedium – a caddisfly that builds a mobile, shell-like case for itself from tiny rocks and grains of sand that it finds on the streambed during its larval stage, when it lives underwater – could be supplying additional nutrients to the periphyton, or algae, that grows on the insects’ cases. In other words, they wondered if caddisfly poop could be fertilizing the periphyton.

Caddisfly larva in its case, balanced between two piles of sand grains. The red arrow is pointing to the head of the insect.

(Image by Robert Mooney)

They sampled streams in southwestern Wisconsin between November 2010 and February 2011, when densities of the caddisfly larvae were high, a period when average monthly air temperatures ranged from 14 to 37 degrees Fahrenheit in nearby La Crosse, Wis.

Mooney and his co-authors found that the larvae did seem to be fertilizing the periphyton on their cases in streams where the ratio of nitrogen to phosphorus was particularly high (a condition that suggests algae growth may be limited by a lack of phosphorus). In those streams, periphyton that grew on caddisfly cases was enriched relative to algae sampled from the streambed.

The nutrient-rich algae on their cases appeared to be an important food source for the caddisfly larvae – an analysis of their bodily nutrients matched the periphyton from the cases, but not the streambed, in the streams with the highest nitrogen to phosphorus ratios. (In the other stream, the periphyton from the cases and the streambed was too similar to distinguish which was the likely food source for the caddisflies.)

Other aquatic insects likely take part in the caddisfly case periphyton buffet, too. “I actually have observed other invertebrates living on the caddisfly cases,” Mooney said in an email, “and I would hypothesize that other invertebrates that feed on periphyton would utilize the case periphyton as a beneficial resource.”

Mooney stressed that this caddisfly, though only a single species, has an outsized effect on the ecosystem in which it lives. “Glossosoma intermedium is a keystone species in the streams [it] inhabit[s] and [is] sensitive to environmental changes. Possible declines in water quality could potentially reduce G. intermedium populations, removing the nutrient-rich periphyton resource.”

Sampling streams in the winter isn’t easy, but for Mooney and his colleagues, it was worth it to keep their waders out for a little bit longer as they explored the nutrient dynamics of Glossosoma intermedium, their poop, and the algae on their cases.

Periphyton growing on caddisfly cases may be an important food source for other macro invertebrates, too - here a different type of insect appears to graze on the algae on a caddisfly case. 

(Image by Robert Mooney)

Shetland's wind

The first thing I noticed about Shetland – a series of islands off the northern coast of mainland Scotland – was the lack of trees. The second thing was the water. Exquisite, turquoise seawater lapping at craggy cliffs, or, in some places, white sand beaches that looked like they’d been lifted straight from the latest ad campaign for some tropical resort, the only thing marring the picture the layers polar fleece and wool piled on the people there. In June.

A sandy shoreline on the coast of Shetland.

(Image by Emily Benson)

At roughly the same latitude as Anchorage, Alaska, mid-summer weather in Lerwick, the capital of Shetland, can be pretty chilly – typical temperatures barely hit 60°F on the hottest days of the year.

There are some trees in gardens and yards in and around Lerwick, but outside the town, the landscape is dominated by grass-covered hills. Trees once grew throughout the islands, but most were long ago cut down for firewood, and the ubiquitous presence of grazing sheep has kept the forests from growing back. I visited Shetland for three weeks in June almost 10 years ago (I was working on a project that had to do with modern interpretations of traditional folk art). If the wind came up when I was out walking in the hills, surrounded by nothing but open space, it felt as if the whole world was blowing by.

Rocky coastline in northern Shetland.

(Image by Emily Benson)

Recent research conducted by a team of scientists at the Scottish Marine Institute suggests that the same winds that I found overpowering on land might be changing the dynamics of algae blooms at sea. Seafood production, including catching or farming fish and shellfish, is a major component of Shetland’s economy; over the past few decades, blooms of Dinophysis, a dinoflagellate that produces toxins responsible for diarrhetic shellfish poisoning, have periodically threatened shellfish production and led to closures of shellfish harvesting areas. In order to predict when and where Dinophysis population booms might occur, these researchers turned to wind records.

I’ve written before about predicting algae blooms based on temperature; the blooms off the coast of Shetland appear to be increasing faster than Dinophysis can grow, suggesting that seawater containing Dinophysis cells is being blown in from other locations and that wind, rather than temperature, might be a good bloom predictor in this system.

The largest Dinophysis blooms the scientists studied occurred during the summers of 2006 and 2013; during those years, the prevailing summer winds were more westerly than in other years, when they tended to come from the south. The researchers suspect that the westerly winds blew in water full of Dinophysis, a supposition supported by their observation that water samples from sites on the eastern side of Shetland, protected from the westerly winds, contained fewer Dinophysis cells than samples from the western side of the islands.

“As the frequency of harmful algal blooms around the globe is perceived to be on the increase,” the scientists write, “and as the levels of investment in aquaculture rise, an understanding of their underlying causes . . . is more important than ever.”

When I recall standing on the stark cliffs and beaches of Shetland’s landscape, bundled in sweaters and a hat in June, it’s not hard to believe that wind may be exacerbating harmful algae blooms – in Shetland, wind seemed to be a driving force behind many things.

A storm blowing in on a windy day.

(Image by Emily Benson)