//
you're reading...

Ecology

The Blob: The movie monster attacking fish

von Biela, V. R., Arimitsu, M. L., Piatt, J. F., Heflin, B., Schoen, S. K., Trowbridge, J. L., & Clawson, C. M. (2019). Extreme reduction in nutritional value of a key forage fish during the Pacific marine heatwave of 2014-2016Marine Ecology Progress Series613, 171-182.

A Pacific sand lance nestled into the sediment. It’s slim body is why it is sometimes called a sand eel. Photo by Mandy Lindeberg and NOAA Photo Library.

Creeping, moving silently through the water, it stalked all before it, and nothing was left untouched. Throughout the Pacific, this menace loomed over the water for years, causing death and worry, warning of a future to come. What is this hideous sea monster? It is the Blob, the Pacific marine heatwave of 2013-2016, and a new study conducted by Dr. Vanessa von Biela and her colleagues in Alaska shows that one of the first things the Blob destroyed was the nutritional value of the humble Pacific sand lance, Ammodytes personatus.

What is a Marine Heat Wave?

A marine heat wave is a time of extreme ocean warming that severely impacts or impairs a marine ecosystem. The Pacific marine heatwave stretched from October 2013 through June 2016, starting in the Gulf of Alaska before spreading through the Pacific. The heat wave is believed to have developed due to a strong El Niño, a normal variation in ocean temperatures in the Pacific Ocean marked by a warm period, paired with a positive sea level pressure anomaly, meaning there was more pressure near the ocean’s surface, which prevented heat from the ocean from escaping into the atmosphere. If you are having a hard time imagining a pressure anomaly, you can think of how you might feel slightly different with the weather changing, or get a headache just before a rainstorm. It’s a change in barometric pressure as different atmospheric conditions move in; pressure isn’t the same everywhere, and when you are looking at anomaly, you can determine where pressure is higher or lower than the average. During the heat wave, there was more pressure over the Pacific than usual, trapping heat from the already warmer than average waters.

Ok, so it’s hot, but why do we care about the sand lance in particular?

Figure 2: An Atlantic Puffin with sand lances in it’s mouth. Photo by Steve Garvie.

The Pacific sand lance is a small, lipid-rich (or oily) fish that is one of the key species in the Gulf of Alaska. Over 100 different species rely on the sand lance as a source of food, including humpback whales, Steller sea lions, turfed puffins, and even fish we like to eat like Chinook and coho salmon. This thin little fish, sometimes referred to as a sand eel, is not a particularly picky eater; as long as the food, often plankton, is the right size, it will likely eat it. This means that a lot of energy from lower levels of the food chain get passed through the sand lance and into animals that eat the sand lance. There aren’t many other species filling this role in the Gulf of Alaska, so if sand lance disappeared, animals higher up on the food web would starve. During previous warm periods, it was the Pacific sand lance that provides food for species that would otherwise struggle to find enough food.

What’s the story?

In order to check on the health of this important species, researchers in Alaska measured the nutritional value of young-of-the-year (0 years old) and one-year-old sand lances. These fish were caught in the Prince William Sound in a number of ways, including purse seines, beach seines, herring jigs, cast nets, dip nets, and gill nets, although most of the samples came from purse seines and dip nets. All of the fish were caught for long-term monitoring efforts meant to look at the health of the Sound following the Exxon-Valdez Oil Spill of 1989 (one of the worst human-caused environmental disasters in US history where 10.8 million gallons of oil spilled into the sea).

Cleanup efforts after the Exxon-Valdez oil spill. An oil spill also bears a striking resemblance to the concept of the blob of movie lore. Photo from NOAA.

Researchers measured the length of each fish, then counted the annular rings in the otoliths (akin to ear bones, just made of calcium carbonate, the same material as egg shells) to determine its age—just like the rings on a stump indicate the age of a tree when it was felled. They then randomly selected 10 fish from each age class for each year (2012-2016) before drying, weighing, and calculating the amount of energy each fish’s body contained.

What they found spelled bad news for the sand lance. With warming waters, fish lengths were starting to change. The age-0 fish struggled, with the longest fish sampled during the coolest year (2012) before getting shorter in warmer years. But an even larger change was seen in 1-year-olds sampled. Age-1 sand lance were 38% shorter in 2015 and 2016 compared to 2012-2014, and in 2016, 1-year-olds were so much smaller that they resembled the age-0 fish. This meant that age-1 fish had 89% less consumable energy in 2016 compared to 2012-2014. That’s 89% less energy that a whale or salmon would get with each fish they consumed.

Why did this happen?

Alaska is one of the most northern points of the Pacific sand lance’s natural range, so waters in Alaska are generally cold enough for sand lance, even when they are unusually warm.  However, this time, they might have taken a punch to the gut – literally, the fish could well have been starving. These fish aren’t picky eaters, but they do rely on plankton for food. Von Biela’s team suggested that as waters warmed, the water column in the Sound stopped mixing, meaning nutrients settling in the sediment at the bottom of the water weren’t being churned up and pushed upwards. Without this mixing, phytoplankton (essentially tiny floating plants) didn’t have the food they needed to grow, and zooplankton (floating animals) didn’t have enough phytoplankton to eat. In fact, there were fewer diatoms (a phytoplankton) and zooplankton in 2014 and 2015, meaning less food for sand-lance. In a chain reaction, zooplankton, then sand lance, and potentially other higher predators faced a famine.

A shot of the trailer for the Blob. Photo from Wikimedia Commons.

It’s still early, so researchers aren’t certain how the sorry state of sand lance in 2015 and 2016 has impacted other species. Currently, the heat wave is thought to be responsible for declining catches of Pacific cod, lower abundances of benthic species caught in bottom trawls, and poor physical conditions and low birth rates of humpback whales. Humans have also been impacted: regulations changed, lowering the maximum cod limit by 80% in 2018, causing an economic squeeze for fishers. The Blob, as it came to be called, was a marine heat wave that in many ways lived up to its namesake: a horror movie monster with the tagline, “Indescribable, Indestructible, Nothing Can Stop It.” It is a scary reminder of what the future could look like under climate change. For now, the Blob is over, but marine heat waves will keep giving us the opportunity to study what the future may hold, and hopefully help us mitigate climate change and stop the horror. In the meantime, the best thing we can do to keep this monster from running amuck is to dedicate ourselves to finding a solution to climate change, whether that be marching with the students calling for a better future, choosing to make green energy a priority in political decisions, or cutting down our carbon emissions at home.

Discussion

No comments yet.

Talk to us!

%d bloggers like this: