Edible flowers

Flowers exist in most terrestrial ecosystems, and though humans have appropriated flowers for our own decorative and aromatic purposes, the plants that produce them use them for one thing – reproduction. When flowers are pollinated, they produce fertilized seeds that, given the right circumstances, develop into the next generation of the plant.

Though most Valentines Day bouquets are composed of terrestrial flowers, many aquatic plants produce flowers, too. These flowers typically grow at the tip of a long stem stretching to the surface of the water, so that pollination via the normal vectors (wind, insects, other animals) can occur. (Plants, including submerged vegetation, also have a few other options for reproduction, including fragmentation and root branching [pdf].)

In a study recently published in the journal Aquatic Botany, a team of Spanish scientists investigated the seasonal dynamics of waterfowl feeding on aquatic plants in a coastal lagoon in the northwestern Mediterranean Sea; they found that flowers appeared to be a particularly appealing meal for the birds.

The researchers suspected that waterfowl – ducks and coots – might consume more aquatic vegetation as a group during the autumn and winter because, due to their migratory patterns, they are much more abundant during those seasons than in the summer in the coastal lagoon the scientists studied. (During the year the study occurred, there were about five to six times as many individual birds present during the autumn and winter than in the summer.)

To test their idea, the scientists created “exclusion cages,” to protect aquatic plants from waterfowl, then compared vegetation height and mass between the exclusion plots and other plots where birds could feed freely. Contrary to their expectations, the scientists found that there were no differences in vegetation between the two types of plots during the autumn and winter months; the ducks and coots did not appear to be eating more vegetation during those seasons.

During the summer, however, the waterfowl did eat a significant amount of one species of aquatic plant, Ruppia cirrhosa, or spiral ditch grass (the plants were shorter, and their biomass smaller, in the plots were waterfowl were present). The birds also ate the flowers of the plant – there were approximately eight times fewer Ruppia cirrhosa flowers in the plots where ducks and coots were present and able to eat them than in the exclusion cages.

The scientists suggest that ducks and coots in the lagoon may have focused their feeding on other food resources, like algae, insects, and seeds, during the autumn and winter, when aquatic plants stopped growing. “[T]he strongest waterfowl impacts on the submerged vegetation within brackish Mediterranean lagoons do not occur when abundance of individuals is higher,” they write, “but in summer when plants and flowers are largely available.”

For plants, flowers are a practical way to reproduce; for humans, they’re a way to send a message of love or congratulations, or a fragrant way to decorate a counter; for waterfowl, they appear to be a convenient way to make a meal.

In the plots free of waterfowl, Ruppia cirrhosa produced about 10 times more flowers than Potamogeton pectinous (the plant shown here). 

(Image by Ruppia2000 via Wikimedia Commons)

Seeds, pits, and eggs

When I think of biological dispersal, the first few examples that come to mind all involve plants and seeds – the white puff of a dandelion head scattered by a gust of wind (based on the main photograph illustrating the Wikipedia page on dispersal, I’m not the only one who thinks of dandelions first); cherry pits spread far and wide by the lucky birds who found a tree laden with ripe fruit; even the squash plants sprouting from seeds tossed in a backyard compost pile.

But many organisms, animals as well as plants, disperse themselves, or are dispersed by the environment in which they find themselves: wind, or water, or humans move them around.

A team of Japanese researchers recently published a study in the journal Ecological Research detailing the dispersal of a particular type of coastal stick insect found in Japan and Taiwan, Megacrania tsudai, also known as Tsuda’s giant stick insect. Members of the genus Megacrania are large insects, usually between four and five-and-a-half inches long as adults. Only female Megacrania tsudai are found in the wild – they reproduce via parthenogenesis, an asexual process during which the young develop from unfertilized eggs. Megacrania tsudai eggs look like tiny, brown potatoes (pdf), the right size and shape for a dollhouse dinner plate, and adult females lay them often – the insects the scientists studied typically produced one egg per day.

The researchers were interested in whether or not Megacrania tsudai eggs, which are buoyant in seawater, can survive extended periods of time in the ocean – as a coastal species, they suspected that the insect might use ocean currents as a means of dispersal. They found that even after over a year spent floating in seawater, eggs hatched at the same rate as unexposed eggs (about 60% of the eggs eventually hatched, regardless of how long they had been in the water).

They also found that prolonged exposure to seawater delayed development – eggs not exposed to seawater began hatching after 120 days, while those floating in seawater for over a year didn’t begin hatching in substantial numbers until after 150 days, and some eggs were still in a pre-hatch development phase after 200 days.

In their paper, the scientists discuss the dangers Megacrania tsudai larvae and adults face as a terrestrial species living in coastal areas that regularly experience typhoons, strong winds, and floods. “However,” they write, “one or a few M. tsudai eggs are laid every day, and these eggs possess seawater tolerance and have a high variation in egg period duration. All of these characteristics are advantageous for an insect species living in a coastal forest habitat. Therefore, even if adults and larvae are completely lost due to natural disturbances, the eggs are an effective means of recovering and maintaining their population since they hatch normally after seawater exposure[.]”

Dispersal is an important way for populations to endure in the face of challenging local conditions. Megacrania tsudai eggs, just like dandelion seeds and cherry pits, can survive voyages beyond the realm of possibility for their progenitors.

Adult Megacrania tsudai on screw pine leaves in Taiwan; screw pine leaves are a primary food source for the insect. 

(Image by Bettaman via Flickr)

Awareness of consumption

In a world where there’s no guarantee that rivers will reach the ocean, inland seas are drying up, and years-long droughts are causing faucets to spit out air instead of water, scientists, municipalities, and individual citizens are recognizing the importance of conserving water by reducing how much we use in the first place.

(Although reducing domestic water use is important, in-home water use is only a drop in the bucket – it represents only one percent of the total water used in the U.S. in 2010. Still, that one percent was a lot of water: 3.6 billion gallons per day.)

New research, conducted in Australia and recently published in the journal Water Resources Research, suggests that one way to get people to use less water is to simply show them how much they’re using, in real-time, by installing water meter display units in their homes.

Working in a suburb of Sydney, researchers compared water use in households that had display units installed in their homes for one year to households that did not. Prior to the installation, the two groups used equal amounts of water; afterward, the homes with display units used 6.8% less water than the homes without, and that difference was maintained even after the display units were removed from the homes.

As the scientists write, “[t]his behavioral change was motivated through the in-home displays and their capacity to raise occupants’ awareness of consumption associated with individual activities.” They also acknowledge that a “willingness to reduce consumption is required,” and it appears that participants in the study, who “initiated [their own] involvement in the trial,” may have been a self-selecting group of people who presumably may have had a greater willingness to save water than the general population.

Even so, technologies that help us reduce the amount of water we use are valuable. Something as simple as a unit that makes us aware of how much water we’re using when we jump in the shower or give the dog a bath can help us conserve the freshwater resources we have, and perhaps help keep our rivers flowing to the ocean.

The leading edge of the Colorado River in 2009, five miles short of the ocean. 

(Image by Pete McBride via U.S. Geological Survey)

Lake boundaries

“Historically, lake ecosystems were viewed as isolated ‘habitat islands in a sea of lands’ (Forbes 1887).”

So begins a paper recently published in the journal Oikos by a team of scientists working in northeast Germany. The paper they reference in their opening was written by Stephen Alfred Forbes, a prominent biologist from the 1870s until his death in 1930, and “the founder of the science of ecology in the United States,” according to L. O. Howard, writing for the National Academy of Sciences.

Though Forbes was one of the first scientists to investigate how species interact and influence one another, and emphasized the importance of studying a community rather than a single species in isolation, he did not recognize the ways in which the seemingly distinct habitats of lakes and land are interconnected. In his 1887 paper, he wrote:

“The animals of [a lake] are, as a whole, remarkably isolated – closely related among themselves in all their interests, but so far independent of the land about them that if every terrestrial animal were suddenly annihilated it would doubtless be long before the general multitude of the inhabitants of the lake would feel the effects of this event in any important way. … It forms a little world within itself.”

Recent research suggests that the boundaries of the ‘little world’ of a lake are not impermeable – energy and resources are exchanged between lakes and the terrestrial environments in which they are nestled. Sometimes, as in the study recently described in Oikos, the vector of that exchange is an insect with both aquatic and terrestrial life stages.

The researchers added corn leaves to part of two lakes (each lake was divided in half by a plastic curtain). Corn leaves have a different chemical signature than the other vegetation present in or near the lakes, allowing the researchers to trace the fate of the energy in the leaves as it made its way around the food web, from prey to predator.

In the sides of the lakes to which corn leaves had been added, the scientists found values consistent with the leaves in aquatic insect larvae that ate them, the adult forms of those insects, and the terrestrial spiders that ate the insects. In what they describe as a “boomerang flux,” they demonstrated the transfer of terrestrial carbon (in the form of corn leaves) first to aquatic organisms, and then back to a terrestrial setting.

Referring back to Forbes’ idea of lakes as distinct entities, separate from their surroundings, the scientists write: “a viewpoint of such isolation does not reflect the continued back-and-forth ‘boomerang’ cycling of organic matter (and probably nutrients) across the borders of terrestrial and aquatic systems.”

Forbes’ prescient insights into the importance of the relationships among species introduced the world to the concept of ecology and changed the way future scientists would think about and conduct their studies; with time, those future scientists would realize that the interconnectedness among species extends beyond the bounds of Forbes’ original idea of a lake, and beyond the shores of lakes themselves.

Many insects that spend their immature life stages underwater emerge to live in the terrestrial environment as adults. 

(Original image by Bj.schoenmakers via Wikimedia Commons)