Flashing and flickering squid

“Humboldt squid can be very cannibalistic,” Stanford University graduate student and researcher Hannah Rosen told me via email, “and if they sense a weakness in another individual they will attack and eat it.”

I had asked her to speculate on the fate of one particular Humboldt squid. “Though I can’t say with any certainty what its fate was since the camera was ripped off, I’d say there is a good chance it was killed,” she replied.

Rosen and a team of researchers from Stanford University and National Geographic recently reported the results of a study in which they outfitted three Humboldt squid, large cephalopods that can grow up to four feet long (not including their arms and tentacles – scientists report squid sizes in terms of the length of the mantle, the torpedo-shaped part of the body above the head), with video cameras so they could spy on their underwater color-changing behavior without the interference of divers or submersible vehicles.

Two of the squid were lit only by natural light filtering down through the water; the recordings they gathered showed Humboldt squid exhibiting two types of dynamic color-changing behavior: ‘flashing,’ a whole-body, rhythmic and rapid change in color, and ‘flickering,’ a wave-like scattering of color across the skin that, the authors write, “mimic[s] reflections of down-welled light in the water column,” much like the play of light against the bottom of a pool. (Humboldt squid chromatophores, the small organs in their skin that they reveal to change their appearance, are a single, reddish-brown color; unlike some other species of squid which have chromatophores of many different colors, Humboldt squid are either white, when their chromatophores are hidden, or red, when they’re exposed.)

Flickering, the authors suggest, may be a form of camouflage for the squid, helping them to blend into their environment and perhaps avoid being eaten. Flashing occurred primarily when the squid were in groups, suggesting that it may be a form of communication; the video recordings captured a number of interactions between squid, including physical contact, possible mating attempts, and arm-splaying that appeared to be directed toward the squid wearing the camera.

One of the cameras also captured an aggressive episode of “numerous attacks” in which, the researchers write in their paper, “several other squid . . . tore the camera package off the camera-bearing squid shortly after it was released.”

That was the squid I asked Rosen about. The scientists had equipped that squid’s camera with a red LED light so they wouldn't have to rely on natural illumination, allowing them to observe nighttime behavior. The red light apparently had the unintended consequence of aggravating the surrounding squid, leading to the attacks. 

“We were hoping the red light would be out of their visual range,” Rosen said in an email, “but were obviously wrong.”

Rosen and her team didn’t give up there, though. Last year they tried infrared lighting, which did not lead to the same problems as the red LEDs; unfortunately, Rosen said, “it also didn’t provide enough light to really see anything that was happening around the squid.”

Moving forward, Rosen intends to continue studying Humboldt squid, their color-changing behavior, and how they control their chromatophores. In the meantime, she hopes that non-scientists embrace the importance of studying animals that experience the world in a completely different way than humans do.

“It’s easy to assume an animal is stupid just because of how it looks,” she said, “but just because an animal doesn’t act the same way we do, that doesn’t mean it isn’t smart, it might just have skills we can’t imagine because they aren’t something we would ever need.”

Researchers attached a video camera to a cloth sleeve slipped onto the mantle of each squid. The cameras were programmed to detach and float to the surface at a specified time. 

(Image by Joel Hollander)

Ocean acidification

Last week, there was a flurry of news reports on the effects of ocean acidification on shellfish stocks in the U.S. (in response to a paper on the subject published in Nature Climate Change), and the news wasn’t good – according to one report, “U.S. shellfish producers in the Northeast and the Gulf of Mexico will be most vulnerable to an acidification of the oceans.” Ocean acidification refers to the global phenomenon of decreasing pH in marine waters as a result of human-induced carbon dioxide emissions dissolving in the ocean, and it can have a big effect on marine organisms. Acidic ocean water holds less calcium carbonate – meaning it’s less available for the organisms that need it to build their exoskeletons and shells – and it can even dissolve already formed shells.

New research recently published in the journal Aquatic Toxicology suggests that the mechanisms behind the negative effects of ocean acidification are not always straightforward – ocean acidification can weaken organisms’ immune systems and make them more susceptible to other, more sporadic threats. 

A team of Swedish researchers exposed tanks of Norway lobsters (a small lobster native to northern Europe) to saltwater with a pH lowered to the level predicted to occur by 2100. They measured the lobsters’ immune response to an injection of a common marine bacteria, and the amount of bacteria that persisted in the lobsters for 24 hours after the injection – if the lobsters’ immune systems were unaffected by the experiment and working well, they expected to see fewer bacterial cells after 24 hours. 

In order to test the lobsters’ response to other stressors that might occur in the presence of acidic ocean water, the scientists also exposed some of the lobsters to low oxygen, or hypoxic, conditions and high levels of manganese, a heavy metal that can have toxic effects at high exposures. (Scientists predict increasingly frequent intermittent periods of hypoxia as well as increasing levels of bioavailable manganese in marine environments as the world’s climate continues to change.)

Based on counts of immune cells, acidic ocean water on its own did not appear to affect the immune response of Norway lobsters; however, when the lobsters were exposed to hypoxia or manganese as well as acidic conditions, they had fewer immune cells than lobsters that didn’t experience hypoxia or high manganese levels. (Lobsters that were exposed to manganese under current pH levels also had fewer immune cells.)

Bacterial counts, however, told a slightly different story – the lobsters in the acidic condition tanks that didn’t experience any additional stressors weren’t able to reduce their bacterial loads, suggesting that their immune cells, though not reduced in number, were not functioning properly. (The lobsters in the hypoxic and high manganese conditions also had high bacterial loads, as did the lobsters exposed to manganese but not acidic ocean water; only lobsters in water with current pH levels and either no additional stressors or low oxygen were able to reduce the amount of bacteria in their bodies.)

As the acidity of the world’s oceans continues to increase, lobsters and other marine organisms may find themselves in an increasingly challenging environment in which they struggle to fight off infections, build their exoskeletons and shells, and survive.

Norway lobsters are typically about seven to eight inches long, including claws and tail. 

(Image by Hans Hillewaert via Wikimedia Commons)

Bioaccumulation

“Silent Spring,” writer and ecologist Rachel Carson’s most famous work, focuses on a discussion of the detrimental effects of chemical pesticides on the environment, and on humanity. The book was published in 1962, but the issue of contaminants reverberating throughout the ecosystem is still pertinent today; though Carson’s writing inspired reforms, the problems she exposed are far from solved.

The authors of a study recently published in the journal Ecological Applications consider Carson’s seminal work relevant enough to cite it in the opening of their paper, an investigation of the pathways that mercury can take as it moves through a food web spanning an ecosystem that includes both aquatic and terrestrial organisms. (‘Boundaries’ between aquatic and terrestrial areas are often permeable to a reciprocal flow of food and energy resources.)

Mercury, a toxic heavy metal, is produced by both natural and anthropogenic sources; in aquatic environments, it’s easily converted to a bioavailable form that humans and other organisms can absorb, methyl mercury. Methyl mercury can reach high levels in predators like large fish as it biomagnifies, or bioaccumulates, instead of dissolving or metabolizing – as organisms consume contaminated prey, methyl mercury builds up in their flesh.

The scientists measured the methyl mercury concentrations of several species of terrestrial spiders, insects, and mites (all types of arthropods) around two Icelandic lakes; because of bioaccumulation, they expected the organisms that fed predominantly on aquatic food sources, which contain elevated methyl mercury levels, to display higher contamination levels than organisms that consumed terrestrial foods.

What they found instead was the opposite – arthropods that had an aquatic-based diet had much lower concentrations of methyl mercury in their bodies than those that ate terrestrial foods. The arthropods collected within a few feet of the lake with a large population of midges – an aquatic insect that was a likely food source for the spiders, insects, and mites – contained, on average, less than half the amount of methyl mercury found in arthropods collected far from the lake (and therefore, presumably, far from an aquatic-based food source like the midges).

The researchers also found that arthropods with an aquatic diet were at the top of a shorter food web than those with a terrestrial diet; with fewer steps in the food web, the scientists hypothesize, there was less bioaccumulation of methyl mercury, creating what they termed a ‘trophic bypass.’ As they write in their paper, “direct consumption of aquatic inputs result[ed] in a trophic bypass that create[d] a shorter terrestrial food web and reduced biomagnification of [methyl mercury] across the food web.”

The findings of this study were unexpected, and contrary to other research that revealed higher levels of terrestrial contamination in areas adjacent to polluted streams; as the authors of the study write, “our research highlights the fact that we still know little about the potential implications of [aquatic-terrestrial] linkages for terrestrial food webs and ecosystems, particularly with regard to societally important applied issues such as contaminant bioaccumulation.”

Contaminants and pollutants in the environment are a perennial problem; a problem that, in some ways, is just as obscure as it was more than half a century ago, when Rachel Carson first brought it to the attention of the public with “Silent Spring.”

Rachel Carson and colleague Bob Hines collecting marine samples in Florida in 1952.

(Image by U.S. Fish & Wildlife Service via USFWS National Digital Library)

Branches, twigs, sticks and logs

Riparian vegetation, the plants that grow on the edges of streams (which I wrote about last week), serves many functions in aquatic ecosystems – plant roots stop riverbanks from eroding, grass and leaves shade the water and keep it cool, and limbs and trunks of trees fall into streams and create habitat and food for fish and insects.

Those limbs and trunks are collectively called ‘large woody debris’ by the scientists who study them. Two studies recently published in the Canadian Journal of Fisheries and Aquatic Sciences and the journal Water Resources Research examined the dynamics of how woody debris enters a stream, and how pieces of it move once they’re there.

A team of researchers from West Virginia University surveyed 25 headwater streams in West Virginia, both before and after Hurricane Sandy struck the eastern seaboard in Oct. 2012. They found that the effects of the storm were variable – in some streams, the level of woody debris didn’t change after Hurricane Sandy hit, but in others the scientists found almost three times as much wood after the storm. They also found that large wood inputs to some streams remained high for a year following the storm, perhaps because some trees or branches were weakened by the hurricane but didn’t immediately succumb to the effects of wind and snow.

A different team of scientists from the University of Southampton nailed an aluminum tag with a unique identification number onto each piece of large woody debris they found within five study reaches on the Highland Water, a river within the New Forest National Park in the U.K. They visited the study reaches several times over 32 months, and during that time 75 percent of the tagged pieces of wood moved; one log traveled three and a half miles from its original location.

The researchers found that logjams were a particularly important feature of the large woody debris dynamics in the river; where logs were already collected, more pieces of wood would tend to accumulate, often in the same locations during different seasons. Large logs seemed to anchor logjams, which smaller pieces of wood would cycle through, staying at one jam for a time before a flood would push them downstream to the next build-up.

In their paper, the scientists from the University of Southampton describe some of the many ways that wood and logjams influence streams and rivers: they can change water flow and sediment build-up patterns, alter the effects of floods by dissipating their energy, and create a variety of areas diverse in water depth, velocity, and gravel size, “which in turn provides habitat and refuges for a variety of aquatic and terrestrial organisms.”

Large woody debris can have large impacts on aquatic ecosystems; scientists are still sorting out the routes by which branches, twigs, sticks and logs make their way into streams, as well as their travels once they’re there.

Pieces of large woody debris were added to a stream in Bandon Marsh National Wildlife Refuge on the Oregon coast in an effort to improve fish habitat. 

(Image by U.S. Fish & Wildlife Service via Wikimedia Commons)