“Because of the fast growth rates and short life spans of squid, they respond very quickly to environmental change.”

Squids are good model marine organisms. They grow fast, have short life spans, and have a metabolism geared to growth rather than storage. Squid therefore respond very quickly to environmental change. Furthermore, the fact that they can be aged from daily increments in their statoliths means that they keep a record of age and growth in these structures. We have known for some time that squid growth rates respond quickly to changes in temperature. A rise in temperature as little as 1 degree Celsius can produce marked differences in adult body size. However, it had been difficult to demonstrate the influence that food supply has on squid growth in the field. This paper was able to bring together biological information on growth and body size of squid along with important information on the physical and biological elements of the environment in which they live. The paper provided evidence of how squid responded to the dramatic environmental changes during the extraordinary El Niño/La Niña event of 1997/1998. Despite very warm temperatures during the El Niño, squid grew very slow and were relatively small. This was due to the lack of upwelling and the associated low level in productivity. In contrast, squid actually grew faster in the cooler La Niña temperatures when upwelling had re-commenced and there was ample food in the pelagic environment. The fact that this paper demonstrated a marked and rapid response by this squid species to an acute environmental change possibly accounts for the high rate of citations.

This paper uses the now standard practice of using daily increments in the statoliths of ageing squid. However, the combination of using the age and biological data of squid along with physical environmental data demonstrated that rapidly growing squid could act as useful ecosystem indicators. Enhanced body size and growth rates could be directly related to upwelling events which produce periods of greater food availability. There were questions on how such acute events affected squid populations, given that population declines were so dramatic during El Niño episodes. This paper helped to explain the biological response of squid to these acute events.

The squid statolith is essentially a small calcareous "bone" in the back of the squid head. These minute structures are extremely useful for the study of squid population dynamics as they grow incrementally by laying down a ring each day. When viewed under the microscope, increments within a statolith cross-section look just like tree rings in a stump. Thus, squids carry a calendar around in their head that informs us how old they are, how fast they grew, and when they hatched. When you age a number of individuals within a population you can collect important information with regard to population dynamics. Statolith research has shown that squid "grow fast and die young," with tropical species having life spans generally less than 200 days and most other species living less than a year. Because of the fast growth rates and short life spans of squid, they respond very quickly to environmental change. The California market squid has been noted for its dramatic changes in population numbers with the species almost disappearing during El Niño periods. Because this is a key species within the marine food web and forms the basis of a major fisheries industry off the coast of California, there was the need to better understand the interrelationship between this species and its environment. This paper used the statolith age, body size and growth rate data to reveal that the California market squid act as very useful "environmental indicators." By monitoring growth rates and body size of squid within the California Current, we can determine or infer the environmental conditions for the small pelagic organisms that live within this environment.

I have been involved with research on the development of statolith ageing techniques as well as age and growth studies of squid in Australia since 1986. My involvement with this project commenced as a result of an international meeting in 1997 where there was an expressed need to better understand the population dynamics of the California market squid Loligo opalescens. My collaboration with my coauthor Michael Domeier of the Pfleger Institute of Environmental Research in Oceanside, California, provided the opportunity to apply my skills to a squid species in one of the best-studied oceanographic regions in the world. This is an extremely important species in the California Current both in terms of the ecosystem dynamics and the fishery activity that takes place in these waters.