Successful germination

Invasive aquatic plants can cause real harm in lakes and ponds. They can spread between water bodies via many different pathways – they’ve been known to hitch rides on boat trailers, for instance, and can also spread via floods, wind, or even gardening.

Aquatic vegetation can also stow away on more mobile organisms – either when plant fragments cling to fur or feathers (a form of locomotion that crayfish may also take advantage of), or when animals or birds eat their seeds.

As a team of researchers recently reported in the journal Freshwater Biology, aquatic plant seeds eaten by waterfowl fare differently depending on what type of plant they come from. The scientists fed mallard ducks and greylag geese seeds from four different aquatic plants, two of which are invasive in Europe (where the scientists are based).

The researchers found that the seeds of one of the invasive species were particularly successful in making the trip through the gut of the birds intact – they recovered more than a third of the Ludwigia grandiflora (or water primrose) seeds from the birds’ waste, but less than a tenth of each of the other types of seeds they fed to the birds.

The scientists also attempted to grow the seeds they retrieved – after all, if seeds can’t develop once they’ve gone through digestion, it doesn’t matter if birds spread them around. They found that “[f]or mallards, 9.14% of the tested seeds germinated successfully, compared to 24.18% for the greylag geese.” Some of those seeds were retained in the birds’ guts for 72 or even 96 hours before they were excreted, though the seeds of one plant species, the other invasive, Spartina densiflora (or cordgrass), only sprouted if they spent eight hours or less inside the birds.

Ducks and geese can travel much farther than plants can on their own over three or four days. “Ducks and geese evidently have the potential for long-distance transport of alien and native plant seeds,” the authors write, “with maximal dispersal distances of well over 1,000 km,” or 620 miles, about 20 miles farther than the drive from Chicago to Chattanooga, Tenn. That’s a long way for an aquatic plant to hitch a ride.

Seeds from Ludwigia grandiflora, or water primrose, were better able to survive waterfowl digestion than the seeds of other aquatic plants. 

(Image by bathyporeia via Flickr)

Unplanned study

Five years and a few days ago, on April 20, 2010, BP’s Deepwater Horizon oil rig exploded in the Gulf of Mexico. Eleven workers were killed, several more were injured, and oil continued to spill from the burst well for the next three months.

NPR reported on the persistent effects of the oil spill earlier this week – despite immediate and on-going cleanup efforts, mangrove islands have disintegrated into tangles of dead roots and crab “traps have been coming up empty.” (Though as the author of that second NPR story points out, because scientists weren’t necessarily studying the area where the disaster occurred in detail before it happened, it’s difficult to trace the exact causes and effects in this situation.)

Among the tangled cascade of human and ecological responses to the oil spill, a team of researchers based in Louisiana selected one thread in particular on which to focus their studies. The scientists, who recently reported the results of their research in the journal Ecohydrology, took advantage of an “incidental test” of what happens to trees growing in coastal cypress swamps during a months-long inundation of fresh water.

In order to keep offshore oil from encroaching on coastal wetlands, water diversions in Louisiana (most of which were designed to control and direct the movement of water and sediment across the landscape) were allowed to release more water than usual following the oil spill, resulting in a freshwater pulse to the coastal swamps located downstream. The researchers focused on one particular diversion, the Davis Pond Diversion near Jean Lafitte National Historical Park and Preserve in coastal Louisiana, which was “operated at six times the normal discharge levels for almost four months.”

In the two years following the freshwater pulse, the dominant tree species in the coastal swamp downstream of the Davis Pond Diversion, baldcypress, produced about two-and-a-half to three times more leaf tissue than the average amount grown during each of the previous three years; reproductive tissues were also higher during the second year after the pulse compared to prior years. Root production decreased following the flood of fresh water, but rebounded the following year; the scientists speculate that the plants may have been preferentially allocating their resources toward leaf growth during the first year.

The Deepwater Horizon oil spill was a tragedy and a major environmental disaster. Amid the myriad negative consequences of the spill, the “unplanned study” these researchers were able to implement as a result of the subsequent response may at least have the small benefit of contributing to our understanding of coastal swamp ecology.

“Concerns are growing because of losses of coastal wetlands along the Gulf Coast,” the authors note. “Special attention should be given to our findings that freshwater release might reinvigorate the production of freshwater coastal vegetation.”

A baldcypress tree in October.

(Image by cm195902 via Flickr)

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)

Timing

Sometime in the next five or six weeks, the ice on the Tanana River in Nenana, Alaska, 55 miles southwest of Fairbanks, will break up. Every year since 1917, local residents have hosted a contest, called the Nenana Ice Classic: anyone who purchases a ticket can guess the exact date and time the ice will go out, and the closest guess wins the pot – in recent years, so many people have entered that multiple people have picked the right minute, and they’ve had to divide the prize money.

Last year’s winners split $363,627.

With that kind of cash on the line, it’s no surprise that the organizers of the Nenana Ice Classic have kept meticulous records. We know when, exactly, the ice on the Tanana broke up outside Nenana each year for almost the last hundred years – that’s the kind of archive that ecologists dream about, because it’s a long enough record to allow us to see changes over time.

 

The ice on the Tanana River in Nenana, Alaska, breaks up between mid-April and mid-May each spring. Since 1917, when the Nenana Ice Classic began, the average trend has been toward earlier ice-out dates. 

Sources: Data from the National Snow and Ice Data Center and the Nenana Ice Classic

(Figure by Emily Benson)

Environmental cues that organisms use to time their migrations or developmental milestones are changing as the world’s climate changes: plants are blooming earlier than ever before, frozen rivers are thawing sooner and sooner, and in some places, salmon are returning to freshwater to spawn weeks earlier or later than they have in the past.

That can be a problem for organisms that rely on the salmon, and their eggs, for food – if those animals don’t know when the salmon will be arriving, they might miss their chance to chow down. Enough mismatches in timing, and some species might face a serious threat to their survival.

A group of scientists working in a coastal Alaskan stream recently investigated the migration timing of Dolly Varden, a type of fish that often lives in the same streams as salmon, and which sometimes depends on salmon for food. As the authors write, “[w]here salmon remain at historical levels of abundance, Dolly Varden can acquire the majority of their annual energy intake by gorging on salmon eggs.”

The researchers recently reported their results in the journal Freshwater Biology. They compared the timing of Dolly Varden migrations to salmon migrations over ten years, and they also analyzed environmental conditions, like water temperature and precipitation, to see if Dolly Varden were responding to environmental cues (in which case they might be at risk of missing the salmon migration), or to the movement of salmon themselves.

They found that Dolly Varden seem to synchronize the timing of their migration with that of salmon. Dolly Varden migrations “appear to be cued directly by salmon migration rather than environmental conditions,” suggesting that Dolly Varden are less vulnerable to a timing mismatch than they might be otherwise.

Still, not all animals will be as lucky as Dolly Varden. The authors point out that Dolly Varden can likely see or smell salmon as they return to freshwater to spawn, alerting them to their presence; other migrating animals can’t be assured that the resources they depend on will await them at the end of their journey, and must rely on environmental cues as a proxy. Those organisms are the ones most vulnerable to a timing mismatch, and the ones most likely to suffer negative consequences as environmental indicators – like the date the ice goes out on the Tanana River – continue to shift in time.

Dolly Varden appear to base their migration timing on when salmon are migrating rather than on environmental cues. 

(Image by cinaflox via Flickr)