Seal meals

Ecology is the study of how living organisms interact with their environment, and with each other. One of the most commonly studied interactions among different creatures is the flow of ingested energy – in other words, mealtimes.

An investigation into an animal’s eating habits might involve many questions – not just, ‘what does it eat?’ But also, ‘how often?’ And ‘where?’ And ‘at what time of day (or night)?’ And ‘under what conditions might it not eat at all?’

Direct observations can answer some of these questions, but the problem becomes more complicated if all the action occurs underwater – for instance, if you’re talking about harbor seals (or other marine mammals). Harbor seals can dive hundreds of meters underwater to catch the fish and other seafood that make up their diet.

Underwater video footage is one way to spy on harbor seals as they hunt for their meals, but, as a team of researchers who recently reported an alternate method in The Journal of Experimental Biology points out, the presence of the required light source may influence the very behaviors videographers attempt to witness and record during deep dives.

By strapping an accelerometer – a device that measures changes in speed – to the head of a harbor seal using a small neoprene headband, the scientists were able to record a characteristic jerk of the seal’s head each time it captured a fish. The researchers were working with a single harbor seal in a controlled environment for the purpose of testing the accelerometer; however, they say the method has the potential for use in months-long studies in the wild, partly because the battery demands of the accelerometer are so low.

“Such long records of foraging behavior will help us to understand how free-ranging aquatic predators search for and acquire energy from their dynamic environment in time and space,” the scientists write. By answering questions like, ‘when and where do seals find their meals?’ the researchers will be able to investigate the rest of the food web, too.

Harbor seal swimming in shallow water on the California coast.

(Original image by Tewy via Wikimedia Commons)

Under the waves

Last Saturday morning at 9 a.m., I plunged into Lake Pend Oreille with 668 other people and swam 1.76 miles, about half of it under the shadow of the long bridge that carries U.S. Highway 95 into Sandpoint, Idaho, for the 20th anniversary of the Long Bridge Swim.

Waves chopped at my face with every attempted breath – the wind was up – but I finished the swim in 72 minutes (the overall female winner, a woman in my age-group, swam the distance in just under 44 minutes). The sun-warmed water was the perfect temperature, and so was the post-race ice cream.

When I got home, I did some research on the lake. It’s one of the biggest lakes in Idaho, and the fifth deepest lake in the U.S., with a maximum depth of about 1,150 feet.

And the U.S. Navy operates a submarine-testing station there.

Evidently the combination of the depth of the lake and its relatively quiet location make it the optimum location for research on the acoustics of operating submarines. According to the official website of the Acoustic Research Detachment, “Lake Pend Oreille provides a deep (1150 ft), quiet body of water where a free-field ocean-like environment is available without the attendant problems and costs of open ocean operations.”

Recent research projects conducted at the site include the field-testing of a novel navigation system for autonomous underwater vehicles – basically underwater drones that are programmed to operate on their own once they’ve been launched – and the development of a new way to produce underwater sound waves for use in experiments and surveys that’s more environmentally friendly than other methods.

I didn’t see any model submarines or autonomous underwater vehicles during my swim (not surprising, since the Navy facility is located 26 miles south of Sandpoint in Bayview, Idaho), but I did see a lot of determined people, fighting the waves toward the finish line.

A swimmer's view of the lovely scenery. No submarines in sight.

(Image by Emily Benson)

Neurotoxin-producing diatoms

Amyotrophic lateral sclerosis, or ALS, commonly known as ‘Lou Gehrig’s disease,’ a neurodegenerative disease that destroys motor neurons and eventually leads to paralysis and death, currently affects about 30,000 people in the United States. (Before she passed away in 2009, my grandmother numbered among them.)

In recent years, scientists have discovered a link between ALS (and other neurodegenerative diseases) and a neurotoxin produced by cyanobacteria called β-N-methylamino-L-alanine, or BMAA. Cyanobacteria, along with other types of algae, form the base of the aquatic food web; as algae is consumed by zooplankton, and zooplankton are eaten by larger organisms in turn, the neurotoxin can accumulate in animals that may end up on the menu for humans, including oysters, mussels, crabs, and other seafood.

Earlier this year, a team of scientists reported the discovery of an additional source of BMAA in aquatic environments in the journal PLoS ONE. Diatoms, intricate single-celled photosynthetic organisms that are nearly ubiquitous in aquatic environments, and which are eaten by a variety of larger organisms – much like cyanobacteria – also produce BMAA.

The researchers found BMAA in each of the six species of diatoms they cultured in the lab. From samples of naturally occurring diatoms collected off the west coast of Sweden, they identified four dominant groups of diatoms, one of which contained BMAA.

The natural samples contained both diatoms and cyanobacteria. An experimental inhibition of diatom growth in the BMAA-producing samples (elicited by adding a compound which deters diatom growth but doesn’t affect cyanobacteria) resulted in BMAA levels that were one-third the amount detected in untreated samples, suggesting that two-thirds of the BMAA was produced by diatoms.

The production of BMAA by an additional group of aquatic organisms is cause for concern, according to the scientists. “Taken together, the data reported here give a clear answer supported by solid evidence that BMAA is not exclusively produced by cyanobacteria. As diatoms are a major bloom-forming phytoplankton in aquatic environments, the impact of this discovery suggests new bioaccumulation routes and that the risk of human exposure may have increased tremendously.”

Several species of diatoms magnified under a microscope. Rigid cell walls made of silica result in the intricate, crystalline structures characteristic of diatoms. 

(Original image by Wipeter via Wikimedia Commons)