Brad Seibel still recalls headlines from 20 years ago that sounded like they were taken from a B-rated science fiction film, such as "Invasion of the gigantic squid in Monterey Bay." At the time, he was a postdoctoral researcher at MBARI (Monterey Bay Aquarium Research Institute).
It was definitely not fiction. The voracious eaters, which typically inhabit more tropical latitudes, arrived off central California in record numbers and, to the dismay of local fishermen, filled their tummies with hake, rockfish, and other commercially significant species. Although the specifics were hazy, scientists believed that a combination of overfishing and climate change was to blame for their appearance.
Seibel, who is currently a professor and a specialist in marine physiology at the USF College of Marine Science, just released a research in Nature Climate Change that clarifies those old headlines. It ties all the data on animal metabolism that he has gathered over the course of 20 years and seven study voyages in the Gulf of California, Mexico, and opens a new chapter on how some creatures may adapt to the warming waters.
According to Seibel, "the fundamental story in recent years has been that as the ocean warms and loses oxygen, creatures would be driven from their natural home and move into cooler seas in more northern latitudes." But this is oversimplifying the situation.
Brad Seibel swimming among the giant squid (Dosidicus gigas). (These are scaled down.) You can hear one of the squid running into him on the dive if you turn up the volume. The squid is briefly startled before continuing to swim away. Credit goes to Open Boat Films and Stephani Gordon.
Different marine species will respond differently to shifting environmental factors.
Together with Matt Birk, a former graduate student and current professor at Saint Francis University in Pennsylvania, Seibel co-authored the book. The study is the first to delve deeply into the connection between oxygen, temperature, and the metabolic needs of vertical migrant marine organisms, which number in the billions and range in size from microscopic krill crustaceans to six-foot-long gigantic squid. Seibel and Birk used simulation to determine how the enormous squid and six kinds of krill would react metabolically to different conditions that approximate day and night environments.
According to Seibel, "vertical migrators defy the core narrative, which is mostly based on research of coastal species."
Squid and other vertical migrants living in tropical regions are likely to increase their habitat northward as ocean temperatures rise, although they may not necessarily abandon their native tropical regions.
According to Seibel, it is probably what occurred in Monterey twenty years ago. The shore saw temporarily warmer water due to an El Nino event. (Consider it a somewhat transient model of climate change.) Even while there was plenty of food back in the more tropical latitudes, the warmer water allowed the squid to extend their range northward where they took advantage of new food sources, severely affecting the local fisheries.
The link between oxygen, temperature, and the metabolic needs of vertical migrants, which range from krill to the gigantic squid, has never been thoroughly explored until now (shown here). Because of their metabolic needs, vertical migrants may see an expansion of their original habitat as a result of shifting ocean conditions. Credit goes to Open Boat Films and Stephani Gordon.
Many marine creatures, including fish and whales, depend heavily on the shrimp-like crustaceans known as krill for their sustenance. Credit goes to Open Boat Films and Stephani Gordon.
It's important to note a subtle distinction regarding their metabolic needs, according to Seibel: "It wasn't that they didn't have enough oxygen or that it was too hot for them down south; before the El Nino event it was too chilly for them up north.
The lives of vertical migrants are significantly different from those of coastal species, which have a steady supply of oxygen in seas that are well aerated. Migratory fish spend the daytime at depth, where it is cold, dark, and there is less oxygen, then at night, when it is safe to forage and there is more oxygen, they migrate hundreds of meters to the relatively warm ocean surface to eat.
The conclusions we frequently draw from well-researched—and simple to catch—organisms may not apply to the greater diversity of species and lifestyles found in the oceans, Birk said. "This study is a good example of this," he added.
It turns out that the metabolic rates of vertical migrants are 4-5 times more sensitive to temperature than are most coastal species. For instance, the squid are completely inactive at deep. Their metabolic rate soars as they migrate to shallower waters for a meal, according to Seibel.
Tropical vertical migrators' metabolically accessible habitat in the present and the future, projected schematically. Source: USF
By the end of the century, Seibel predicted, climate change will expand the habitat options for vertical migrants to the north and south by as much as 10-20 degrees of latitude. This prediction is based on modeling that takes into account the increased effects of temperature on the metabolic rate of vertical migrants.
Seibel stated, "We really need to delve into animal physiology to better comprehend how different species evolve and adapt to environmental conditions.
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