Climate Change and the Future of Marine Organisms

by Moises A. Bernal

Our great reliance on fossil fuels for energy is leading to unprecedented changes at a global scale. There is broad consensus among scientists that gases resulting from combustion and industrial processes (such as carbon dioxide, methane, sulfates, etc.) are accumulating in our atmosphere, acting as a blanket that traps heat in the atmosphere. Even when climatic changes have taken place in the past, there is no evidence that the changes seen today are associated with volcanic activity, changes in solar irradiance, changes in the earth’s orbit or tectonic movements. Further, changes seen today due to the greenhouse effect are unprecedented in the speed at which they are taking place. This increase in the concentrations of greenhouse gases is leading to fast paced changes in climatic conditions, which in turn can have detrimental effects for both terrestrial and marine organisms. 

The Bernal lab aims to understand the effects of environmental changes on marine fishes, with special emphasis on the effects of climate changes.

Humans are well equipped for adjusting their body temperature to slight changes in temperature, producing sweat at warm temperatures and shivering at cold temperatures, for example. However, many terrestrial species (such as lizards and turtles) and most marine species are unable to control their internal body temperatures as humans do. These species depend on the conditions of the environment for many natural processes, such as development and reproduction. Over the past decades, scientists have discovered that warming usually leads to an increase in energetic demands for these “thermal conformers”. In the event that the increased energetic demands are not met, there can be detrimental consequences to processes such as development, growth, locomotion and reproduction. These physiological challenges at the individual level are leading to broad scale changes in the oceans. Studies have shown that some species have reduced their population sizes, coral reef ecosystems are threatened by warming, species are changing their geographic ranges and reproductive seasons of many species are shifting. For example, in the shores of the Northern Gulf of Mexico (including Louisiana, Mississippi, Alabama and Florida) it is now possible to see species that were previously restricted to tropical Caribbean ecosystems. This is due to changes in water temperature, as winters are not as cold as they used to be, and tropical species are now able to expand and compete with local species. 

Given this complex scenario of climate changes, scientists are now interested in understanding how marine species react to fluctuations in coming decades. The Bernal Lab in the Department of Biological Sciences at Auburn focuses on the physiological and molecular responses of marine fishes to warming. They are currently developing studies on species of the Gulf of Mexico, with special focus on groups with high ecological relevance. One example is recent work conducted on the pinfish, a species that is key for food webs in the Gulf of Mexico, as it is consumed by larger species of fish (including snappers and groupers), dolphins and even marine birds. Despite their relevance, very few studies have evaluated the effects temperature has on the species. Work in the lab has shown that slight warming (3°C or 5.5°F) can lead to increase in the oxygen demand, and the activation of molecular stress responses in the liver and muscles. There are also effects on the immune system, as it is possible that the increased energy demands with warming make it challenging to invest resources into protection against diseases. In this study, juveniles were much more sensitive when compared to adults, which is relevant when we consider that younglings develop in shallow waters susceptible to environmental changes. Many more studies are needed to understand how different species in the gulf are responding to these changes, and the potential implications for humans that depend on fisheries of the region.

Despite the worrisome panorama presented by climate change, scientists are also interested in evaluating the potential for some species to acclimate and/or adapt to these changes. Studies have shown that for some species, certain populations can be more tolerant to the climatic conditions projected in coming decades. There is also the potential that species can quickly acclimate to warming by adjusting their physical conditioning throughout development (a process called plasticity). Still, it is important to remember that even with these mechanisms of protection, species have limits to the conditions they can tolerate. Thus, it is important to support initiatives to combat greenhouse gas emissions, as ameliorating temperature fluctuations in coming decades is essential for the conservation of marine systems.

Due to the effects of global warming, the Northern Gulf of Mexico now harbors tropical species from the Caribbean. These tropical groups can compete with local species, such as the spadefish. This school of spadefish was photographed in an oil rig in Dauphin Island, Alabama. 

Photo by: Moisés A. Bernal

Disclaimer: The views and opinions in this work are those of the author and do not necessarily reflect the views of Auburn University.