Warming of the ocean off the Pacific coast of California, could lead to changes in the typical range of jumbo squid

Jumbo squid appeared in Monterey Bay off the Californian coast around twenty years ago. Although it wasn’t unknown for the cephalopods to travel so far north, it was unusual for these voracious eaters to travel in such record numbers.

The sudden increase in numbers caused alarm amongst local fishermen as the squid consumed vast quantities of hake, rockfish and other commercially important species.

Brad Seibel was a postdoc student at the Monterey Bay Aquarium Research Institute (MBARI) at the time. Today he is a professor and marine physiology expert at the USF College of Marine Science and he recently published a paper that connects the dots pertaining to animal metabolism that he’s collected over 20 years and seven research cruises in the Gulf of California.

Seibel said: “The basic narrative in recent years has been that as the ocean warms and loses oxygen, animals in it will be chased out of their native habitat and move into cooler waters in more northern latitudes, but this is an oversimplification.”

The paper argues that ‘not all’ marine animals will react to changing conditions in the same way.

See also: Underwater ecosystem changes going undetected

six-foot long jumbo squid

Seibel co-authored the publication with his former graduate student, Matt Birk, now a professor at Saint Francis University in Pennsylvania.

The study is the first to drill down into the relationship between oxygen, temperature and the metabolic requirements of vertical migrators, which include billions of marine animals from tiny crustaceans called krill to the six-foot-long jumbo squid.

Seibel and Birk used modelling to understand how six species of krill and the jumbo squid would respond metabolically to the varying parameters approximating day and night habitats.

Seibel said: “Vertical migrators buck the basic narrative, which is based largely on studies of coastal animals.”

As the oceans warm squid and other vertical migrators living in tropical zones are likely to expand their habitat northward – but not necessarily leave their native tropical zones.

That’s what likely happened 20 years ago in Monterey; an El Nino event temporarily brought warmer water to the coast.

The warmer water allowed the squid to expand their range northward, where they took advantage of new food sources – heavily impacting the local fisheries – even though food was still plentiful in the more tropical latitudes.

Seibel explained: “It wasn’t that they didn’t have enough oxygen or that it was too hot for them further south; before the El Nino event it was too cold for them up north.”

expand the available habitat

Vertical migrators live very different lives than coastal species, which experience a fairly consistent supply of oxygen in waters well mixed with the atmosphere.

Migrators live at depth during the day, where it’s cold and dark and there’s less oxygen, and they travel hundreds of metres toward the relatively warm ocean surface at night to eat, where oxygen is plentiful and when it’s safer to forage.

Birk added: “This study is a good example of the fact that the conclusions we often draw from well-studied – and easy to catch – organisms may not hold true for the greater diversity of species and lifestyles found in the oceans.”

It turns out that the effect of temperature on the metabolic rates of vertical migrators is four to five times greater than for most coastal species.

When at depth, the squid, for example, don’t do much at all. When migrating to shallower waters for a meal, their metabolic rate ‘skyrockets’.

Seibel advised that modelling that incorporates the heightened effects of temperature on the metabolic rate of vertical migrators suggests that climate change will expand the available habitat for vertical migrators to the north and south by as much 10-20 degrees of latitude by the end of the century.

Seibel concluded: “We really need to drill down into animal physiology and better understand the ways that various species evolve and adapt to environmental conditions.”

The research is published in Nature Climate Change.

Image: The study is the culmination of 20 years of research by Brad Seibel on vertical migrators that has included scores of dives like this one. Credit: Stephani Gordon, Open Boat Films.