Sound pressure

In the autumn of 2001, ships employing compressed air guns were prospecting for gas and oil off the northwest coast of Spain. In the process of mapping the sea floor, they employed pulses of air that created explosively loud, high-intensity, low-frequency waves of sound. During September and October, five giant squid, cephalopods which can grow to be over 40 feet long, were found stranded along the coast, a much higher number than usual; and in 2003, amidst continued oil and gas exploration, four giant squid were found, dead or dying, on the coast or near the shore.

Examination of the animals and further scientific investigation suggested that the squid died as a result of physical damage to their statocysts, the structures they use to detect sound and orient their bodies in the water. (I read about these events here [pdf], here, and here.)

New research conducted on another cephalopod, the common cuttlefish, suggests that, in addition to being damaging at high intensities, lower intensity sound may be an important way that cephalopods sense the environment around them.

A team of scientists monitored the behavior of cuttlefish exposed to a series of sounds of different frequencies and intensities, each lasting for three seconds. The most extreme behaviors the researchers observed were “escape responses” – jetting quickly away, or inking. (Cuttlefish, like most cephalopods, can produce a cloud of ink that obscures them from a predator as they escape.) These behaviors were elicited by low-frequency, high-intensity tones, while lower intensity tones were associated with less extreme behaviors like body movements and changes in body coloring. (Cuttlefish are capable of altering both the color and the pattern of their body, in order to deter predators, attract mates, or blend into their surroundings.)

The researchers also assessed the extent to which cuttlefish become habituated to certain sounds – in other words, whether or not they will stop responding to a repeated tone. They found that “[a]fter several exposures and no imminent threat, the number of escape responses decreased, suggesting the cuttlefish were able to filter out the ‘irrelevant’ acoustic stimuli,” though the cuttlefish never completely stopped responding to the repeated sounds.

Sound may be an important indicator of their surroundings for cuttlefish – the scientists write that the “evasion responses suggest that the cuttlefish initially reacted to the [sound] stimulus as they would react to a predator or other form of danger, and that sound detection could be a mechanism for predator detection” in cuttlefish.

Sound can have disastrous effects on cephalopods – but in other circumstances, or at different intensities or durations, it may serve ecologically important functions like announcing the presence of a predator.

Common cuttlefish (Sepia officinalis) can grow to be up to two feet long. 

(Image by David Sim via Wikimedia Commons)

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)