Saltmarsh sparrows

The saltmarsh sparrow (“a secretive bird with skulking habits and a barely audible song,” according to the Cornell Lab of Ornithology) makes its home in salt marshes along North America’s Atlantic and Gulf coasts. It’s listed as “vulnerable” on the IUCN list of threatened species, which is not as bad as “endangered,” “critically endangered,” or “extinct in the wild,” but somewhat worse than “least concern,” and “near threatened.”

In other words, conservation-minded scientists and wildlife managers should be interested in mitigating the threats the bird faces in the wild, which revolve around habitat loss.

Salt marshes are complex ecosystems regularly inundated by tides in which tiny variations in elevation – sometimes just a few centimeters – can mean the difference between daily or twice-per-month flooding. As a result, completely different plant communities develop in low marsh and high marsh areas. Saltmarsh sparrows tend to build their nests in the high marsh areas, among plants that grow only at higher elevations. 

Humans have not always recognized the important services salt marshes provide (they help prevent coastal erosion, for example, and also provide food and shelter for fish and other aquatic species), and development, including water-control efforts and in-fill projects, have destroyed or degraded a lot of the salt marsh habitat that once lined much of the U.S. coast. Invasive species, particularly Phragmites australis, or common reed, and rising sea levels further threaten the marshes and saltmarsh sparrows that are left.

Salt marsh restoration projects typically involve elements designed to reestablish natural conditions, like removing or altering barriers to tidal flows or eliminating Phragmites stands. But, as a team of scientists from the University of Connecticut recently reported in the journal Restoration Ecology, even when managers are able to successfully alter a salt marsh plant community through restoration, that may not translate into increased habitat for saltmarsh sparrows.

The researchers, working in 18 different Connecticut marshes, compared remnant plots of healthy marsh to plots that had been restored, either through direct removal of Phragmites or renewed tidal flow. They found that tidal flow restoration appeared to control Phragmites growth and allow for the reestablishment of native low marsh plant communities, but not the plants typical of high marsh areas, where saltmarsh sparrows like to build their nests; consequently, there were fewer saltmarsh sparrows, and fewer nests, in the tidal flow restoration plots compared to the remnant marsh plots.

“[D]espite its successes,” the authors write, “saltmarsh tidal restoration is not providing conservation value for some of the most vulnerable species that use tidal marshes.” They go on to suggest that an emphasis on restoring high marsh areas, in addition to low marsh areas, is necessary to help species like the saltmarsh sparrow.

The saltmarsh sparrow may be a secretive, skulking bird, but it’s a fundamental part of salt marsh ecosystems. In order to fully rebuild salt marshes, future restoration efforts will have to target all elevations, even if they’re only a few centimeters apart.

Saltmarsh sparrows are four to five inches long, and weigh less than an ounce.

(Image by nebirdsplus via Flickr)

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)