April 1, 2021

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This article was originally published as a chapter in the book “Design and Catastrophe: 51 Scientists Explore Evidence in Nature"

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I started studying tropical squids in Australia back in the 1980s. I was using what was then a fairly new technique of looking at statolith growth increments to age squid. Statoliths are essentially small calcareous “bones” in the squid head used to provide balance for swimming.

What interested me were the amazing regular rings or increments within the microstructure of the statoliths. My research was able to demonstrate that these rings were laid down daily and could thus be used as a powerful aging tool. Each squid essentially had a calendar in its head to indicate its age at capture and its growth rate. By conducting a number of laboratory experiments and then applying the aging technique to field populations, I was able to start understanding how tropical squid grow.[1] To my surprise, I discovered that these tropical species were all completing their life cycle in just a few months. This contrasted with the understanding at the time that these marine creatures lived for approximately five years or so. Considerable research since then has reconfirmed how these organisms live “life in the fast lane.” Tropical species (including large reef squid) actually can complete their life span in less than 200 days, and it appears that many other temperate and cold-water species live for around a year.[2]

Squid show remarkable purpose in their complex biology. For example, they are designed to be able to dramatically adjust their rate of growth according to environmental conditions. Squid (especially tropical ones) are one of the fastest growing marine organisms, with incredibly rapid growth rates and short life spans. This raises the question as to how they achieve this. It turns out that they have a combination of unique features producing such fast growth rates. This includes rapid digestion and a protein-based metabolism, continual recruitment of new muscle fibers (hyperplasia), efficient oxygen utilization, and low levels of antioxidative defense.[3]

These features stand out in contrast to their fish competitors with which they share their ocean environment. Basically, a squid’s metabolism is in high gear, with energy being used for growth rather than storage (squids don’t seem to be able to use lipids as an energy store due to their protein-based metabolism). As a result, they grow rapidly and have short life spans. It is even possible that their efficient use of oxygen may be related to their mitochondria-rich fin musculature functioning independently of their circulatory system. This combination of design features means that squid display marked plasticity in growth. Simply being bigger doesn’t mean that an individual is older. It depends on the environmental conditions an individual encountered while growing, with their unique design features allowing individuals to respond quickly when the environment changes.

The application of the ability to age individual squids provides us with a valuable means of exploring squid growth and maturity in varying environmental conditions. The small loliginid squid Loligo opalescens is found off the coast of California and has a life span of less than 260 days. Our team was able to follow cohorts of individuals through one of the most dramatic El Niño and La Niña events experienced in 1997–1998.[4]

During the El Niño conditions squids matured with a very small body size and had much slower growth rates. However, cohorts later during the La Niña event were much larger (e.g., comparing the El Niño summer of 1998 to the La Niña summer of 1999, males were 31% longer and 173% heavier, while females were 19% longer and 65% heavier, respectively). This was despite the fact that there was no clear trend in the ages of the cohorts. Virtually all the individuals were mature and the dramatic differences in body size were due to differences in individual growth rates rather than differences in life spans. There was also a significant positive correlation between mean monthly body size (grouped by hatching month) and the upwelling index determined for Southern California. So, the more upwelling occurring when a squid hatched, the larger the body size that individual reached at maturity.

This ecological study of Loligo opalescens demonstrated that they have a finely tuned set of physiological and biological qualities designed to adapt to the changing environmental conditions off the California coast. Greater upwelling during the La Niña produced a burst in productivity and greater food supply, resulting in faster growing individuals that achieved a larger size at maturity. This contrasted with the El Niño period of warmer temperatures, reduced upwelling, lower food supply, slower growth rates, and a smaller body size at maturity. In this way, they are acting as “ecosystem recorders and productivity integrators over time and space and are useful organisms to tie oceanography to biology.”[5] This means that squid design includes a built-in ability to rapidly respond to favorable conditions, grow quickly, and reproduce in a very narrow window of time. This adaptability has resulted in an increase in squid and cephalopod populations generally as a result of overfishing of finfish.[6]

I personally see evidence of sophisticated design in the many complex facets of squid biology. Anatomy, metabolic, and physiological systems all work in concert to enable squid not only to survive but to thrive and adapt to rapidly changing oceanographic conditions. In reconciling these observations with my belief in a Creator God, I see this ability to respond and adjust as a manifestation of divine design.

NOTES

[1] GD Jackson, JH Choat. Growth in tropical cephalopods: an analysis based on statolith microstructures. Canadian Journal of Fisheries and Aquatic Sciences 1992; 49:218–228.

[2] GD Jackson. Application and future potential of statolith increment analysis in squids and sepioids. Canadian Journal of Fisheries and Aquatic Sciences 1994; 51:2612–2625.

[3] GD Jackson, RK O’Dor. Time, space and the ecophysiology of squid growth, life in the fast lane. Vie et Milieu 2001; 51:205–215.

[4] GD Jackson, ML Domeier. The effects of an extraordinary El Niño/La Niña event on the size and growth of the squid Loligo opalescens off Southern California. Marine Biology 2003; 142:925–935.

[5] Ibid., p. 925.

[6] ZA Doubleday, TAA Prowse, A Arkhipkin, GJ Pierce, J Semmens, M Steer, SC Leporati, S Lourenco, A Quetglas, W Sauer, et al. Global proliferation of cephalopods. Current Biology 2016; 26(10):R406–R407.

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George D. Jackson is a professor at the Department of Earth and Biological Sciences of Loma Linda University. He holds a PhD in Marine Biology from James Cook University. He has published over 90 scientific journal articles from research conducted in Australia, New Zealand, Thailand, Falkland Islands (Malvinas), the United States, Canada, and the Southern Ocean. He has held academic and research positions in five countries including serving as senior Scientist for the Pacific Ocean Shelf Tracking Project for the decade long Census of Marine Life.