How will climate change affect the life cycles of fish?

by Asta Mail, RJD Intern

In a coffee shop the other day, I overheard two teens discussing technology and how it affected their lives. “How did anyone ever grow up without cell phones?” they wondered aloud. “How did they know when and where to meet up?”

Hearing this, I began to consider the ways people navigate the world, and how differently we do so now than we did in the past. Today’s youth has quickly learned and adapted to a very different social climate than that the previous generation. Growing up in an age of rapid development, they are accustomed to regular advances in communication, travel, and social interaction. Young people encounter very different obstacles through the stages of their development than their parents once did.

As a species, humans can adapt quickly to changes happening around us; but will fish be able to do the same as the ocean environment changes?

Cod, via wikimedia commons

This question piqued the interest of a European research team, headed by Pierre Petitgas. In their recently published paper, “Impacts of Climate Change on the Complex life Cycles of Fish”, Petitgas et al. (2012) developed a frame work for understanding how changes in the marine environment caused by global climate change will affect the life cycles of commercially valuable fish.

Fish have complex life cycles, the stages of which usually occur in several different marine environments. Often, a successful journey from egg, to larvae, to juvenile, to spawning adult fish, involves several migrations from one environment to another. Successful reproduction relies on the fishes’ ability to connect with the right environment for each stage of its development. As ocean temperatures, currents, tidal fluctuations, and water levels change, so may the success of fish to reach the appropriate environment for their own growth and reproduction. By developing a life cycle framework, this particular study shows researchers “how climate variability and change may impact marine fish populations” (Petitgas et al. 2012).

Petitgas et al.’s research is unique in the field of marine adaptation to climate change. Unlike previous research, which focused more on effects of climate change on the individual, population, or even the ecosystem as a whole, this study aimed to determine how much climate change will affect individual stages of fish development.

Petitgas et al. chose to focus their study on four commercially valuable species of fish. Each species was chosen to represent a unique life history type. The researchers chose the European Anchovy (Engraulis encrasicolus), Atlantic Herring (Clupea harengus), European Plaice (Engraulis encrasicolus) and Atlantic Cod (Pleuronectes platessa). These fish are all found at approximately the same latitude, throughout the Atlantic, Norwegian, North and Barents seas.

To create a framework for assessing the impacts of climate change on the individual life cycle stages of the fish, researchers first assessed the habitat requirements of each species at each stage of their development. Then, they assessed the availability of different habitats for each life stage, and examined the connectivity of the required habitats for a complete life cycle. Their next step was to assess the “likely impact of climate variability and climate change on each of the factors.” (Petitgas et al. 2012).

For each individual stage of life, the research team developed qualitative categorizations to describe how the stage might be affected by environmental changes. These categorizations were then analyzed and compared between species.
To predict which stages of the life cycle would be most sensitive to climate change, Petitgas et al. also created a quantitative characterization of the individual life cycles. They examined the temperature and food availability of each environment, as well as the spatial extent of the required environments, and the distance travelled between each important habitat. The selected species’ tolerance to temperature change was assessed at each life stage to show how vulnerable they would be if ocean temperature rose significantly.

Using both qualitative and quantitative categorizations, Petitgas et al. could identify phases of the life cycle that were particularly sensitive to climate change. Their analyses revealed “bottle necks” -particularly important stages that were limited by their size, their quality, or their relative distance from other important environments.

Petitgas et al. discovered several distinct differences in the sensitivities of the species chosen. The Biscay Anchovy, having the most broad habitat requirements and a high level of connectivity between life cycle habitats appeared to be the best suited species for adaptation to climate change. The habitat requirements of the Herring and North Sea Plaice displayed strong bottlenecks in their early developmental stage. They therefore appeared to be more sensitive to change. The Plaice fish was deemed to be least resilient to “climate driven changes, due to its strict connectivity between spawning and nursing [habitats]” (Petitgas et al 2012).

In their 2012 paper, Petitgas et al. note that it is difficult to foresee the physical changes that the ocean will undergo. Their analysis does not examine how changes in the food chain between predator and prey species will affect the outcome of a species’ survival. Their paper also only briefly touched upon how overfishing and other oceanic changes could affect the chosen species.

Petitgas et al. concluded that life cycle analysis is an adequate and encompassing tool that can be used for drawing better conclusions about the role of climate change in fish population dynamics. The research team succeeded in developing a framework that can be applied to many other different fish species in order to more accurately predict the oceans’ fish populations for the future.

Though the future of these important fish species is uncertain, adaptation has always been a key trait to survival. Just as the current generation of humans has conformed to changes in their world, fish species will likely have to adapt and mold their life histories to new conditions if they are to survive in the changing ocean

REFERENCES

Petitgas P, Rijnsdorp A, Dickey-Collas M, Engelhard G, Peck M, Pinnegar J, Drinkwater K, Huret M, and Nash R. 2012. “Impacts of Climate Change on the Complex life cycles of fish.” Fish Oceanogr. Blackwell Publishing Ltd.